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High-tension power transmission.
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HIGH-TENSION
POWER TRANSMISSION
A Series of Papers and Discussions
Presented at the Meetings of the
American Institute of Electrical Engi-
neers, under the Auspices of the Com-
mittee on High-Tension Transmission
REPUBLISHED BY THE
McGRAW PUBLISHING COMPANY
NEW YORK
By Special Arrangement with the
American Institute of Electrical Engmeers
1905
Copyrighted, 1905
BY THE
American Institute of Electrical Engineers
New York
HIGH-TENSION TRANSMISSION COMMITTEE
1902- 1903
Raiph D. Mershon, Chairman
F. O. Blackwell
C. C. Chesney
P. M. Lincoln
C. L. Cory
1903-1904
Ralph D. Mershon, Chairman
F. O. Blackwell
C. C. Chesney
P. M. Lincoln
A. M. Hunt.
PREFACE
At a meeting of the Board of Directors of the American Insti-
tute of Electrical Engineers, held September 26, 1902, the follow-
ing resolution was passed :
" Resolved, That a Committee on High-Tension Transmission,
consisting of five members, may be appointed for the purpose of
collecting data respecting present practise in electric transmission
at high voltage, and of presenting a report which will indicate the
successful methods which are now in operation in such form as to
be of immediate value to electrical engineers. It is within the scope
of the Committee to secure data upon Hne construction, insulators,
insulator-pins, and the Uke, and the conditions of operation at
different voltages and under different climatic conditions; to
investigate methods of testing insulators, and to indicate the
method or methods which in its judgment are superior. Also to
ascertain the methods employed for voltage regulation, the condi-
tions attendant upon the switching of high-tension circuits, and to
collect data respecting Ughtning and static disturbances and the
use of grounded protective wires."
The Transmission Committee, appointed in accordance with this
resolution, decided to adopt two methods of procedure. One of
these was to send out printed lists of questions, relative to high-ten-
sion transmission, to the various transmission plants in the United
States, with a request that answers to the questions be filled in and
the fists returned.
The other was that of instituting discussions on chosen topics
which would bring forth from the engineers taking part in these
discussions information in regard to the work in question, which
could not otherwise be obtained. These discussions took place on
regular meeting evenings of the Institute, the particular meeting for
which they were arranged being directly under the auspices of the
Transmission Committee.
Previous to the discussion on each of the several subjects chosen
for the evening, there was read an "introduction" prepared by
PREFACE.
some member of the Institute prominent in transmission work.
These "introductions" were not intended to be foimal or com-
plete "papers," but merely to serve as a basis or frame- work for
discussion on the subjects with which they dealt. As it was desired
that as many as possible of the members of the Institute should
take part in these discussions, the "introductions" were sent out
sufficiently ahead of the meeting, so that those who were not able
to be present could take part in the discussion by sending in a
written ' ' contribution. ' '
In the matter of the following pages is comprised the work ac-
comphshed by the Transmission Committee along the hues laid
down above. It includes the "introductions," with the discussions
which took place upon them, and the results obtained from the
Usts of questions sent out.
The matter is here collected in book-form by special permission
of the Institute, and as it here appears has been taken directly
from the Transactions of the Institute, with such minor changes as
were necessary for co-ordinating the different parts.
As the work of the Transmission Committee brought out much
valuable information, which is available only by searching through
the pages of the Institute Transactions, it is beUeved that the
collection of this information, in compact and convenient form
for reference, will constitute a valuable addition to engineering
Hterature.
CONTENTS.
PAGE
Mechanical Specifications of a Proposed Standard Insulator Pin, . i
Testing of Insulators, 6
Transposition and Relative Location of Power and Telephone
Wires, ii
Burning of Wooden Pins on High-tension Transmission Lines, . i8
Discussion of the Foregoing Chapters, 26
Methods of Bringing High-tension Conductors into Buildings, . 79
The Grounded Wire as a Protection Against Lightning, . . 96
The Testing of Electrical Apparatus for Dielectric Strength, . 116
Choice of Frequency for very Long Lines, 136
Y or Delta Connection of Transformers, 148
Electric Cables for High- voltage Service, 180
The Operation and Maintenance of High-tension Underground
Systems, 184
The Use of Automatic Means for Disconnecting Disabled Appa-
ratus, 188
The Relative Fire Risk of Oil and Air-blast Transformers, . . 207
The Use of Group Switches in Large Power Plants, . . . 233
Oil Switches for High Pressures, 248
Terminals and Bushings for High-pressure Transformers, . .258
The Protection of Cables from Arcs due to the Failure of Adjacent
Cables, 282
Synchronous Motors for the Regulation of Power Factor and Line
Pressure, 291
Long Spans for Transmission Lines, 309
Conditions for Continuous Service Over Lines Operated in Parallel, 343
The Use of Ground Shields in Transformers, . . . .347
The Protection of High-pressure Transmission Lines from Static
Discharges, 35^
Report of Committee on High-tension Transmission, . . .366
General Discussion, 404
The Maximum Distance to which Power can be Economically
Transmitted, 410
A paper read at the I74th Meeting of the American
Institutt of Electrical Engineers, New York,
March 27, 1903.
MECHANICAL SPECIFICATIONS OF A PROPOSED
STANDARD INSULATOR PIN.
BY RALPH D. MERSHON.
A mathematical consideration of the fibre
stresses in wooden insulator pins and a recom-
mendation as regards standard dimensions
and methods of construction.
At present no general standard exists in the matter of Insulator
Pins. As a result, there is often confusion and dissatisfaction in
ordering and obtaining pins. This discussion of a proposed
standard pin is intended to lead up to a general specification
covering wooden pins, and, so far as it may, metal ones.
Theory. — The expression for the extreme fibre stress at any
point of a beam of circular section fixed at one end and loaded at
the other, as in Fig. 1 is
FIG, 1.
Px
s =
. 0982 (P
1
(1)
2 HIGH-TENSION TRANSMISSION.
where (assuming inches and pounds as our units) P is the pull or
weight in pounds ; x is the distance in inches from the point of
application of P to any point a of the beam ; d is the diameter in
inches at the point a; s is the extreme fibre stress in pounds per
square inch, i.e., s is the stress on the extreme fibres at che top
and bottom of the beam at the point a.
This equation shows that for a given pull P the fibre stress at
any point a at a distance x from the point of application of P
varies directly as x and inverselv as the cube of d. It is possible,
therefore, to design a beam of circular section whose diameter in
passing from the point of appUcation of P to the point of support
shall vary in such a way that ^ will have the same value all the
way along the beam. Such a beam will be of uniform strength
throughout its length. The value which, in such a beam, d must
have at any point distant x from the outer end may be found by
assuming s and P constant in Equation (1) and solving for d in
terms of x. This gives
(p \i i. 1
where K is a constant whose value must be determined from the
extreme fibre stress allowable with a given pull P. Equation (2)
shows that in order to have the beam of uniform strength through-
out its length, its diameter must vary as the cube root of the
distance from the point of application of its load.
An insulator pin is the case of a beam of circular section fixed
at one end and with a load (any side pull which may come upon
it) applied at or near the other end. There is no object in having
an insulator pin any stronger at any one point than at another.
It should, therefore, in its capacity as a beam, be tapered as
nearly as practicable in such a way that 5 will be constant
throughout; that is, so that equation (2) will apply to it.
The point where pins usually break, their weakest point, is
just at the cross-arm. The wooden pin most generally in use is
one having a diameter of about 1 J inches in the cross-arrn and a
length such that the wire is from 5 to 6 inches from the cross-arm.
Let us obtain the value of K in (2) on the assumption oi d = ly
.^nd x = 5". This gives the value of K as .877, so that, substi-
tuting, (2) becomes
d = 877 3^ (3)
PROPOSED STANDARD INSULATOR PIN. 3
From (3) we may find the diameter required at any point in
any length of pin, the pin to be of uniform strength throughout.
Substituting various value of x we have the following:
X (inches)
d (inches)
1
.877
2
1.106
3
1.263
4
1.395
5
1.5
6
1.592
7
1.678
8
1.754
9
1.825
10
1.888
11
1.95
13
2.06
15
2.17
17
2.25
19
2.34
21
2.42
This table shows that for a pin having upon it a pull one inch
above the cross arm, the diameter at the cross-arm must be .877
inches ; that one having a pull upon it 10 inches above the cross-
arm must have a diameter at the cross-arm of 1.88 inches, etc.
I
li«^-
-21-
FIG. 2.
Fig. 2 is a sketch of such a theoretical pin drawn by platting the
above values to a scale one-quarter of full size. Fig. 2 repre-
sents all sizes of pins up to and including one the pull upon
which is applied 21 inches above the cross-arm. That is, if we
want a theoretical 6 inch pin we must cut 6 inches off the end of
Fig. 2 and use that; for a 10 inch pin we must cut off 10 inches,
etc.
4 HIGH-TENSION TRANSMISSION.
The practical pin must be a modification of the theoretical pin.
The end must be square and a portion of the small end must be.
threaded. The pin must also have a shoulder just above the
cross-arm. It will be noticed that, except near the end, the sides
of the theoretical pin are practically straight. It will suffice,
therefore, if in designing a pin we fix the diameter at the lower
end of the thread portion and the diameter just above the
cross-arm and make the contour between these points a straight
line.
Threaded End. — It is proposed to make the diameter of the
small end of the pin 1 inch; the length of the threaded portion
2i inches; and the diameter at the lower end of the threaded
portion 1.25 inches.so that the threaded portion will taper from
1.25 inches to 1 inch in a length of 2^ inches. The threaded
portion of the insulator should have the same dimensions and
taper as that of the pin.
Shoulder. — It is proposed to make the shoulder 3/16 inch on
all pins. That is, the diameter of the pin just above the cross-
arm will be f inch greater than the nominal diameter of that
portion of the pin in the cross-arm; it is proposed to carry this
diameter J inch above the cross-arm before tapering the pin.
Dimensions in Cross-Arm. — It is proposed to make the diame-
ter of that portion of the pin in the cross-arm, just below the
shoulder, 1/32 inch less than the diameter of the hole in the cross-
arm and at the lower end of the pin 1/16 less than the diameter
of the hole in the cross-arm. It is proposed, also, to designate
this portion of the pin as having a nominal diameter equal to that
of the hole in the cross-arm into which the pin fits. Therefore,
that portion of a pin which is to fit a 1^ inch hole in a cross-arm
will have a nominal diameter of IJ inch but will have an actual
diameter just below the shoulder of 1-15/32 inch, and at the
lower end of the pin of 1-7/16 inch.
FIG. 3.
Thread. — It is proposed to use on all pins a thread having a
pitch of i inch or 4 threads to the inch, the form of thread to be
that shown in Fig. 3 (scale three times full size). As there shown.
PROPOSED STANDARD INSULATOR PIN. 5
the angle between the faces of the thread is 90° and the top of the
thread is flattened by cutting off, from the form the thread
would have if not flattened, one-fourth its unflattened depth.
The form of the thread in the insulator should be the same as
that on the pin. If this is done it will insure the bearing surface
being always on the sides of the threads and never on the edges.
Designation. — It is proposed to designate that portion of the
pin above the cross-arm as the " stem " of the pin. That por-
tion in the cross-arm as the " shank " of the pin. It is proposed
to designate a pin by the length of its stem, i.e., a pin whose stem
is 5 inches long will be designated as a " 5 " inch pin, one 6
inches long as a " 6 " inch pin, etc.
Dimensions of Standard Pins. — In accordance with the above
the following table has been prepared, giving a number of sizes
of pins, and their dimensions, which it is proposed to make
standard. The diameter of the shank has in each case been fixed
by making it approximately equal to (slightly larger than) the
diameter of the theoretical pin corresponding to the length of the
stem of the pin in question. The headings of the columns of the
table refer to the lettering of Fig. 4.
Fia 4.
Size of
Pin.
A
B
c
Nom-
inal.
c
Act-
ual,
D
E
P
G
H
I
5"
if
4}"
U"
144"
l^"
li"
1"
J"
H"
2i"
7
f|
n
m
m
CO
C3
n
(A
a
»
Si
n
m
Hi
p.
o
o
c
2i
o
11
101
3
m
HI
'm
.2
2f
'tCi
18
12f
f*
iJA
V^
'3
'*
'«
2i
'5
IS
14i
i!i
^sV
2tV
«lH
21
17
161
r a
'-i
m
2A
a
s
24
1
19
181
5f
n
24i
2^
24
.4 paper read at the 17 4th Meeting of the American
Institute of Electrical Engineers, New York,
March 27, 1903.
THE TESTING OF INSULATORS.
BY F. 0. BLACKWELL.
A statement of the requirements for satis-
factory insulators and recommendations as
to apparatus and methods of carrying on in-
sulator tests.
An electric power transmission cannot be successful unless it
is able to deliver uninterrupted power.
Continuous operation, so far as the transmission line is con-
cerned, depends largely upon the effectiveness of the insulator
which is employed. Insulators must, therefore, be obtained
which will not fail in service and this can only be assured by the
thorough testing of each one that goes on the electric lines.
The potential that can be employed safely for the transmission
of power is now limited by the pressure the insulators will bear, as
transformers that are reliable and not excessive in cost can
be built for twice the voltage that any line yet constructed will
withstand.
As the distance over which power can be transmitted with a
fixed cost of conductor varies with the potential, the length of
transmission lines is to a great extent limited by the insulator.
The design of new and improved types of insulators is, there-
fore, most important, and these can only be developed by experi-
ment with adequate testing facilities. In order to ascertain the
value of such insulators, no method of testing can equal a practi-
cal trial tmder conditions of actual service. Placing newi insu-
lators on power transmission lines in commercial operation is
impracticable in most cases and should only be permitted} after
they have successfully withstood tests to demonstrate' their
6
TESTING OF INSULATORS. 7
ability to stand operating conditions. These tests should dupli-
cate as nearly as possible the electrical and mechanical strains
set up in the insulators under the most severe conditions that
would ever be met with on a transniission line.
There are certain facts which must be considered if correct
deductions are to be made from insulator tests. For instance,
we cannot test each insulator with a given number of volts con-
tinuously as it would be in service. As is well known, all insulat-
ing materials are most apt to break down on long applied electric
stress. The prepared cloth wrappings used on the windings of
electrical machinery will stand instantaneously two or three
times the potential that they will carry continuously. Glass and
porcelain are not affected by time to the same extent as organic
materials , but we know that both kinds of insulators have been
pimctured by long continued applications of lower pressures
than those which they have withstood in tests of short duration.
The shape of the potential wave also has a pronounced effect
in breaking down insulation. A wave may be either flat topped
or peaked, so that the maximum instantaneous potential is much
less or greater than that of a sine wave of the same square root of
the mean square potential. We might have for the same poten-
tial as read by the voltmeter, maximum instantaneous potentials
which differ as much as two to one.
In air, the maximum point of the wave determines the distance
which the current will jump. Different generators or even the
same generator under different conditions of load will show
widely varying arcing distances for the same potential.
Insulating materials being more affected by time than air,
show in their ability to resist puncture that the average potential
of the wave is more important than the maximum.
It is not safe to assume the potential either by the voltmeter or
air gap as the true potential for determining the insulating
value, as it is somewhere between the two. Moisture in the atmos-
phere also effects the arcing distance. In steam, a given potential
will jump twice as far and in a fog 25 per cent, farther than under
ordinary conditions. Of course, if the altitude is high and the
air more rarified, the arc will also jump a greater distance.
I would like to call attention to the characteristics of the
apparatus reqtiired for testing insulators.
The alternators generally used for long-distance transmission
plants give very nearly a sine wave and therefore the testing gen-
erator should be one which will give a sine wave under all
8 HIGH-TENSION TRANSMISSION.
conditions. It is not sufficient to do so at full potential and no
load, as tests are made with all degrees of excitation and with
both leading and lagging currents.
The armature reaction should be as small as possible, which
means that the generator should be much larger than would
ordinarily be thought necessary. It is also desirable to have a
high reluctance in the magnetic circuit to secure stability when
running with weak fields and permit of control with a reasonable
amount of field resistance.
There should be but one transformer used to step up to the
highest potential required and its reactance should be as low as
possible. A number of transformers in series is particularly
bad, as it gives poor regulation and leads to great uncertainty
as to the actual potential to which an insulator is being subjected.
I have known testing sets with transformers in series and a
generator of poor regulation to vary widely in the relation of
the generator volts and the length of the spark gap due to change
of wave form with different magnetic saturations of the appar-
atus and different numbers of insulators and consequently
various capacities on the testing circuit. The only certain way to
determine the real potential is to have a step-down instrument
transformer on the high potential circuit.
Assuming that insulators are to be passed upon for a specific
transmission plant, they should first be inspected to see that they
are free from cracks, bubbles or pits that will impair their strength
or in which moisture can lodge. If of porcelain, the glaze should
cover all the outer surfaces. The glaze is of no insulating value
in itself, but dirt sticks to unglazed surfaces.
Experience has shown that porcelain insulators which are not
absolutely non-absorbent are worthless. The best porcelain
shows a polished fracture like glass. If there is any doubt about
the quality of the porcelain in this respect, it should be broken
into small pieces, kept in a hot dry place for some time, weighed,
and immersed in water for a day. When taken out of the water
the weight should be the same as at first. A puncture test should
be made by setting the insulator in a cup of salt water, filling the
pin-hole also with water and slowly increasing the potential
between the top and bottom until the desired test potential is
reached or the insulator either punctures or arcs over the sur-
face.
If an insulator is built up of several parts, each part should be
able to withstand a pressure greater than it will have to sustain
TESTING OF INSULATORS. 9
when the complete insulator is tested. If it is to be tested for
100,000 volts and is made in two parts, each part might, for in
stance, be tested with 70,000 volts. The object of this is to have
the weak parts rejected before they are assembled. A fair punc-
ture test for an insulator is twice the potential for which it is to
be employed, applied between the head and the interior for one
minute. For example, the insulators for a 50,000 volt line
should each stand 100,000 volts. As the potential from any wire
to ground on a 5000 volt three-phase system would only be about
30,000 volts, a 100,000 volt test gives a factor of safety of nearly
three and one-half to one. If one branch were grounded, as
sometimes occurs in practice, the factor of safety would be but
two to one. A one-minute test is not so severe as a continuous
application of an equal potential, but insulators that have
passed this test stand up well in service.
New types of insulators should be moimted on iron pins and
tested both wet and dry, to determine the potentials which will
arc over them. The dry test is of little value, as the potential
at which the arc jumps from the head to the pin can be pre-
determined by measuring the shortest distance between them and
referring to a curve of arcing distances in air. In a wet arcing
test, a stream of water from a sprinkler-nozzle under a pressure
of at least 50 poionds to the inch should be played on the insula-
tor at an angle of say 30 degrees from the horizontal. This will
be similar to the condition which exists in a rain and wind
storm. The insulator should not arc over from the wire to the
pin at less than the potential which will exist in service between
any two conductors.
In no case should wooden pins be relied on for insulation, as
their value is only temporary. All wooden pins in time become
dirty, absorb moisture and eventually burn off unless the
insulator is good enough to be used with an iron pin. If an
insulator is going to fail, it is better to have it do so at the
start and not interrupt the service bv breaking down perhaps
years afterwards.
In addition to the electrical tests, it is well (if the insulator is of
a type that seems to require it), to try samples for mechanical
strength. When mounted on pins the instdator should stand a
side strain of at least ten times the pressure exerted by the air
on the conductor with a wind velocity of, say, 100 miles an hour.
It should also be able to slip the conductor through the tie-wire
should the former break.
10 HIGH-TENSION TRANSMISSION.
These tests are particularly desirable with btiilt-up insulators
in order to be certain that the parts will not separate. With
such insulators, it would also be well to test them in tension
along the axis of the pin, as in transmission lines crossing de-
pressions such an upward pull is not infrequently exerted on
the insulator.
The above notes and suggestions are the result of the writer's
tests of insulators, and observations of high potential lines.
There are many members of the Institute whose experience
has been wider and who have doubtless given the matter much
thought.
It is the purpose of this paper only to touch briefly upon an
important subject in order to open a discussion which it is hoped
will bring out much valuable information.
A paper read at the n4th Meeting of the American
Institute of Electrical Engineers, New York.
March 27, 1903.
TRANSPOSITION AND RELATIVE LOCATION OF POWER
AND TELEPHONE WIRES.
BY P. M. LINCOLN.
A consideration of the causes of elec-
trical disturbances in telephone lines
which parallel high-tension lines, and
of means for reducing these disturb-
(1) The extraordinary sensitiveness of the telephone receiver
makes this instrument peculiarly susceptible to electrical dis-
turbances. One authority states that the energy used in a six-
teen candle power incandescent lamp is sufficient to produce an
audible sound in thirty billion receivers. The methods, therefore
of shielding telephone wires from the inductive effects of neigh-
boring wires become important. Particularly is this true in the
case of a telephone line paralleling a high-tension transmission
line, where the inductive disturbances are apt to be large, and
uninterrupted service on the telephone line important.
(2) The remarks and discussion in this " Introduction to Dis-
cussion " apply particularly to telephone lines paralleling high-
tension lines, but comments hereon need not be restricted to such
cases.
(3) There are three ways in which disturbing current in tele-
phone circuits may be caused by the high-tension circuit.
(1) Electromagnetic induction.
(2) Electrostatic induction.
(3) Leakage.
It is the first two causes of disturbances which will claim par-
ticular attention in the following discussion.
11
12
HIGH-TENSION TRANSMISSION.
(4) Electromagnetic induction may be briefly described as a
transformer action. In Fig. 1 let a. b and c be the conductors of
a three-phase line, and m and n the two wires of a paralleling
telephone circuit, a and h may then be regarded as the primary
and m and n as the secondary of a transformer. The e.m.f. in
circuit mn will depend, among other things, upon the amount and
frequency of the current in the inducing circuit. By transposing
m and w in the well-known manner, the e.m.f. 's set up in one part
of the telephone circuit will be neutraUzed by equal and opposite
e.m.f.'s set up in other parts. Thus, the electromagnetic
effects between m and n may be entirely neutralized by trans-
A
j:
a
m
c
n
U
rig.1
posing the telephone wires only, regardless of whether the trans-
mission wires are transposed or not. It may be well to note,
however, that while the e.m.f. between the two telephone wires
may be reduced to zero by properly transposing the telephone
wires only, the e.m.f. between the two telephone conductors con-
sidered as one side of a circuit and the earth as the other, can be
reduced to zero only by transposing the power wires. This point
is of little importance, however, as any electromagnetic e.m.f.
betv.^een the telephone wires and ground is entirely overshadowed
by the electrostatic which will be considered later.
(5) Electrostatic effects will also take place in m, n, due to
transmission circuit a, b, c. If conductor a has a minus charge
TRANSPOSITION OF WIRES. 13
for instance, it will induce a certain plus charge on m and a
smaller plus charge on n, on account of w'i greater distance from
a. If now the minus charge be removed from a, current will flow
from mton, proportional to the difference in the amounts of these
charges. The electrostatic influence of b, being oppoite a in
sign, will reinforce the action of a. Transposition of the tele-
phone wires will have the effect of neutralizing this tendency of
setting up electrostatic currents between m and n. It is impor-
tant to note that a system of transpositions designed to correct
electromagnetic induction between the wires will also be correct
for electrostatic induction.
(6) Considering the comparative electromagnetic and electro-
static disturbances in a section of untransposed telephone line, it
may be interesting to observe that the first is in the nature of a
constant potential effect and the second of a constant current
effect. It is evident that induced electromagnetic e.m.f. is
constant as long as the inducing current is constant. As for the
electrostatic effect, it is evident that the amounts of the induced
charges on m and n, and therefore the electrostatically induced
current between them, will not become appreciably reduced until
the current flowing between m and n makes a difference of poten-
tial between them appreciable, compared with the inducing differ-
ence of potential. With telephone receivers of varying resist-
anc«, therefore, the ampere-turns in the receiver due to electro-
magnetic induction are practically constant, while those due to
electrostatic induction increase with number of turns and there-
fore the resistance of receiver. The electrostatic and electro-
magnetic effect become roughly equal with an arrangement
shown in Pig. 1, when a, b,c is a line carrying 50 amperes at 20,000
volts, and the telephone circuit contains a total resistance of
1,000 ohms, including receivers.
__
w
v-
■*■
X
B
b
+
V
c
>
(7) The bridged telephone has almost universally taken the
place of the series instrument for all telephone work. The series
telephone is particularly objectionable for use on a circuit in
which static induction takes place to any great extent. The
reason for this is seen by an inspection of Fig. 2. The telephone
14 HIGH-TENSION TRANSMISSION.
wire m has between A and B a plus charge induced and between
B and C a minus charge. _ There is, therefore, at the transposition
point B a flow of current from one section of m to the other. If
now a series telephone be placed in series with m at B,it not only
gets the benefit of this charging current between the two sections
of m, but it also creates a difference of potential and, therefore,
disturbing currents in telephones at A and C as well.
(8) Although a proper system of transposition will prevent the
establishment of an induced e.m.f. between the two telephone
wires, it does not necessarily prevent the two wires from assum-
ing a potential which differs from that of the earth. In a prop-
erly transposed system, each telephone wire is the same average
distance from each power wire. The potential, therefore, which
the telephone system tends to assume from the static induction
of the power wires is that of the neutral point of the power sys-
tem. By neutral point is meant that point between which and
each of the power wires the average e.m.f. is the same. Under
normal conditions this neutral point is at ground potential. If,
however, leakage takes place from one of the power conductors
to ground, this neutral point will differ in potential from the
ground and the amount of this difference becomes greater as the
resistance of the leak becomes less. In a three-phase system,
when the resistance of this leak becomes zero, the maximum
difference of potential between the neutral point and ground
occurs, and is 58 per cent, of the power circuit voltage. In a
20,000 volt system, for instance, there may exist a potiential of
nearly 12 000 volts between the neutral point and ground. When
the neutral point of the power line differs in potential from the
ground, an electrostatic difference of potential tends to exist
between the telephone wires and earth, and will exist if the insu-
lation of the telephone circuit is perfect.
(9) The amount of this electrostatic potential between the
telephone circuit and the earth will depend upon the relative
capacities between power and telephone lines on one hand and
between telephone line and earth on the other. The power and
telephone lines may be considered as opposite plates of one con-
denser and the telephone line and ground as opposite plates of
another condenser. These two condensers being in series, they
will distribute the total e.m.f. in inverse ratio to their capacities.
With usual construction, the capacity between telephone line and
ground will not be less than that between telephone and power
wires, so that the potential of the telephone wires above ground
TRANSPOSITION OF WIRES. 15
will be equal to at least one-half the potential of the power line
neutral point above ground. A grounded power line may thus
cause a potential between the telephone wires and ground which
will reach well into thousands of volts and even a bad insulator
may cause such an e.m.f. measured by hunderds of volts. In
this connection it is significant to note that in the great majority
of cases the telephones become inoperative when a ground occurs
on the power lines. Is it any wonder? How many telephone
lines are btiilt to stand up under a strain of even 1,000 volts, let
alone 5,000 or 10,000 volts to ground? It is hardly necessary to
point out the path of the disturbing currents. The first voltage
strain comes not between telephone wires, but between the two
wires and ground. A break down of its insulation, either partial
or complete, occurs at some point, and the wire to which the
break occurs discharges to ground either partially or completely
and the other wire must discharge through the telephones to
ground.
(10) The points, therefore, which deserve careful consideration
in the installation and operation of a telephone line when it is to
be operated in proximity to a high-tension transmission line are
the following:
(1) Insulation.
(2) Transpositions.
(3) Use of bridge telephones instead of series telephones.
(4) Making static capacity of telephone wires to ground
as great as possible, and capacity to power wires as
small as possible.
(1) Insulation.
(11) Insulation is put first as being the point of first import-
ance. A ground on the transmission line is going to cause either
volts or trouble on the telephone line. There is no reason why
the telephone wires will not transmit speech properly, even if it
does differ in potential from the ground. But to obtain this
result, disturbing currents from the line to earth must be pre-
vented by perfect insulation. When it is realized that the poten-
tial between the telephone line and ground may be as high as 30
per cent, of the potential between power wires, the importance of
insulation is better understood. By insulation, too, is meant the
insulation throughout the entire line. There is little use in pro-
viding glass insulators for pole supports capable of standing a
voltage of 15,000 or 20,000 and then, inside buildings, attaching
the telephone wires directly to woodwork which may be damp, or
13 HIGH-TENSION TRANSMISSION.
to an instrument mounted on a damp brick wall. Above all,
there is no use in putting up a line which may be able to stand a
test of 15,000 or 20,000 volts, and then attach to this same line
a lightning arrester which will break down at 300 volts, as the
standard telephone lightning arrester is expected to do.
(12) When providing high tension insulation for the telephone
line, the insulation of the man using it should not be forgotten.
This insulation of the telephone user is advisable, not only to
protect him from the induced voltage but also to protect him
in case of a cross with the power line. The induced voltage
is not so dangerous as its amount would indicate because the
current is limited to that of a condenser consisting of power
line as one plate and the telephone line as the other. It may be
noted that the telephone insulation is subjected to high strains
only when the power line is grounded or heavily unbalanced
statically. This is just the time, however, that uninterrupted
service of the telephone line is apt to be of the utmost importance.
(2) Transpositions.
(13) The necessity of transposing the telephone line is almost
so apparent as not to need comment. Otherwise continuous
disturbances will exist, due both to electromagnetic and electro-
static effects. So far as the telephone line is concerned, transpo-
sition of the power wires is not so important. An untransposed
power line cannot induce either electrostatic or electromagnetic
effects between two transposed telephone wires, but only between
these two wires and ground. The amount the statically balanced
untransposed power line can elevate the telephone wires above
the ground potential is small compared to the effect of the power
line when statically unbalanced, whether transposed or untrans-
posed. If the telephone line is insulated to meet the worst con-
ditions, it will be ample to meet the normal condition of an
untransposed power line.
(3) Use of Bridge Instead of Series Telephones.
(14) This point is one which need only be mentioned. The ad-
vantages of the bridged over the series telephone are so well
known that the reason before mentioned for using a bridged
instead of a series instrument is simply throwing another shovel-
ful of earth on the grave of the series instrument.
(4) Making Capacity of Telephone Wires to Earth as Great as
Possible, and Telephone Wires to Power Wires as Small as
Possible.
(15) In Montana there is a line in operation at 50,000 volts.
TRANSPOSITION OF WIRES. 17
Uther lines are projected as high as 60,000 to 80,000 volts, and
there is a possibility of going higher. When one realizes that with
the usual construction as shown in Fig. 1, there may be in such
cases an elevation in the potential of the telephone wires of 20,000
to 25,000 volts above ground he begins to cast about for some
method of reducing this potential. The total voltage between
the neutral point of the power -wires and ground may be con-
sidered as taken up across two condensers, one consisting of the
power and telephone wires, and the other the telephone wires and
earth. To decrease the possible potential of the telephone wires
to ground, therefore, one must either decrease the capacity of the
power wire — ^telephone wire condenser, or increase the capacity
of the telephone wire — earth condenser, or both. This may be
accomplished by increasing the distance between power and
telephone wires, and decreasing the distance between telephone
wires and earth. If the same supporting structure be used, there
is a limit to which this can be carried, at which the possible
voltage between telephone wires and earth may be still prohibi-
tive. The capacity of the telephone wire-earth condenser,
may be still further increased by bringing the earth to the tele-
phone wires, instead of the telephone wires to earth. That is, one
or more ground wires may be run in close proximity to the tele-
phone wires, thereby increasing the capacity of the telephone
wire-earth condenser, to almost any desired limit. By this
means the possible potential between telephone wires and earth
may be brought within limits where it may be taken care of with
safety.
(16) In conclusion, the writer asks for the freest comments on
the foregoing remarks, particularly from those who have had ex-
perience in operating a telephone line paralleling high-tension
wires. If such can agree with the writer in his remarks, he will
be pleased to know it. If they cannot agree, he will be still more
pleased to find out wherein he is wrong.
A fiaper read at the f74th Meeting oj the
American Institute of Electrical En-
gineers^ New York, March 21tk^
iqo3.
BURNING OF WOODEN PINS ON HIGH-TENSION
TRANSMISSION LINES.
BY C. C. CHESNEY.
Facts concerning a number of examples of
the burning of wooden insulators pins and a
recommendation as to the use of iron pins.
In this country it has been almost the uniform practice in
high-tension pole line construction to use wooden pins. The
reason for their use has been the belief that because they were
made of wood they strengthened the entire insulation of the pole
line system, and were in consequence additional safeguards.
These pins have generally been made of locust, oak or eucaliptus ;
and in order that the insulation might not deteriorate from the
action of the weather, they have usually been treated carefully
with hot asphaltum, parafhne or linseed oil. The temperature
and character of the treating liquid have depended more or less
upon the whim of the constructing or designing engineer. Al-
though there has been no uniform method followed and although
the materials used in the treatment have differed greatly, the
results have been universally the same. Wood pins when used
with glass or well vitrified porcelain insulators, have given very
good service on potentials as high as 25,000 or 30,000 volts.
There have been no unusual pin troubles at these voltages which
could not readily be explained by porous or cracked insulators
or by some peculiar climatic conditions. In my opinion, the
success secured in the operation of the great majority of these
lines is due to good insulation of the insulator, and the insulation
of the pin has in reality contributed very little to that success.
For 40,000 volts and for higher potentials, the insulators offered
by all manufacturers do not have the same factors of safety as
18
BURNING OF PINS.
19
tho insulators for lower voltages offered by the same manu-
facturers. The difference is not so much in the thickness or
in the quality of the glass or porcelain used ; it is more particularly
in the general shape of the insulator and in the dimensions of the
insulating surfaces and petticoats. For this reason, even under
severe local surroundings, the 10,000, 15,000, 20,000 or 30,000
volt insulators have shown very little surface leakage and in
consequence there has been comparatively little pin burning at
these voltages. It is true that in localities of salt storms, of
Fig. 1.
heavy sea fogs or chemical factories, there has been more or less
pin burning without regard to the type of insulator used, or to
the potential of the system. The writer has been informed that a
certain plant using only 440 volts has at times great trouble from
the burning of pins, although 10,000 volt insulators are used.
This trouble is due entirely to the deposit on the insulators from
a neighboring chemical factory, and as might be expected their
period of no-burning is during the rainy season. These instances
20
HIGH-TENSION TRANSMISSION.
however, are rare, and when the cause is apparent, the remedy is
usually at hand. The pin burning on 40,000 and 50,000 volt
lines is somewhat different. Eliminating all causes due to
broken or defective insulators, the actual flow of current over the
surfaces ana through the body of the pin is probably very small.
On the lines from which the writer has secured burned pins two
used 11-inch Locke insulators, as shown in Figs. 1 and 2; the
third used the Redlands type, Fig. 3. The first two lines were
operated at a potential between 45,000 and 50,000 volts, and the
Fig. 2.
third at about 33,000 volts. The pins shown were taken from
perfect insulators and in some cases the insulators were immedi-
ately put back on the line. Pins shown in Figs. 1 and 2 were
made of eucaliptus and boiled in linseed oil. The line using pin
shown in Fig. 2 also used a porcelain sleeve covering the base of
the pin. Fig. 3 shows the well-known Locke iron-pin with porce-
lain base and oak thread. Fig. 4 and Fig. 5 show three pins all of
the type shown in Fig. 1. These pins were taken from the same
BURNING OF PINS.
21
pole and occupied the relative positions as shown in the cuts. The
burned sides stood towards the damp winds from the ocean. Fig.
6 shows a burned pin of the type shown in Fig. 2. Fig. 7 is the
Locke iron-pin with porcelain base (Fig. 3) taken from a 33,000
volt line. The striking fieature is the burning of the wooden
thread to the iron pin. The writer has been informed by the
general superintendent of this plant that every pin that has been
examined on this line is burned in exactly the same way, yet
Fig. 3.
there has been comparatively few punctured insulators and no
cross-arms burned from the current leaking over the surface of
the insulators. Fig. 8 shows the pin taken from the same 50,000
volt line as those shown in Fig. 4. This pin is shown sawed in
sections in Fig. 9. The noticeable feature is that the burned
section is entirely in the upper part of the pin about If" below
the thread. The outside surface and the centre of the pin below
this point shows no charring. It would appear that at least in
this instance the burned section was the point of highest resist-
ance of the pin, and that the lower part of the pin was a good
22
HIGH-TENSION TRA NSMISSION.
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r-7,!-. ^J'/t.^' CC.
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Fig. 5.
BURNING OF rLW^.
23
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does not bear well, as shown in sketch, Fig. No. 1, and the sharp
corner at the point of greatest strain, introduces an element of
weakness. In Fig. No. 2, a form of shoulder is shown which has
been used by the writer with considerable success. This shoulder
tapers at an angle of 60°, and fits into a counter-bore in the top
of the cross-arm. With this design the pins may be driven to a
5]
t
Pole-Top Pin
^
FIG. 5
firm bearing at the top of the cross-arm, which has the effect of
steadying them and increasing the strength of the construction
at this point.
In lieu of the form of thread proposed by Mr Mershon, the
writer suggests that shown by sketch. Fig. No 3. In this design
28
JJIGJI-TKX.SIOX TRAXSMISSIOX.
the square top of the thread is r:s wide as the groove, resulting
in increased area of wood to withstand shearing strains. The
threads of the insulators are always stronger than those of the
pins, and for this reason the form of thread as proposed has con-
siderable advantage. This form of thread may also be easily
cut, in either seasoned or unseasoned wood, and the depth not
being so great the pin is stronger at the bottom of the thread.
Fig. G
Figs. Xo. 4 and Xo. 5 are drawings of the high-tension pins now
used b}' the Alissouri River Power Company. They show the
form of the thread and of the shoulder as described above, and
also give the general dimensions of the p)ins. The upper shoulder
as shown by the drawings is for the support of a glass sleeve,
which is used to protect the pin from the weather. Fig. No. 6 is
from a photograph of the 50,000 volt line insulate? assembled on
one of the pins.
STANDARD INSULATOR PIN. 29
Mr. Mershon: — The next written contribution is by Mr.
William R. C. Corson, Electrical Engineer, of Hartford, Conn.
Mr. William R. C. Corson : — I believe I am only concurring
with the general feeling in expressing my pleasure that our
Committee on High-Tension Transmission has seen fit to com-
mence its work by an effort to standardize an essential element
oi construction, and in hoping that this line of effort may be con-
tinued and result in recognized and approved standards for all
other items capable of a general determination.
Mr. Mershon's method of developing the table of dimensions of
the proposed pin is so rational that criticism of it is difficult.
Briefly stated, of course, this method assumes the pin in general
use as a basis, and mathematically determines the diameters of
pins of differing length, which shall be capable of sustaining the
same tension at their extremity as will this pin. In other words,
the safe load that may be applied at the top of the proposed pins
is of constant value in all. This value is not discussed in the
" Introduction," and feeling that its determination would be of
interest to me, and might prove of value, I have made a series of
tests in a Sellers' machine to ascertain the value of 5 in
equation (1,) for the ordinary locust pins, under the actual
conditions of support suggested.
Six standard locust wood pins were selected at random from a
supply at hand. The larger diameter of the shank varied from
1 7/16 inches to 1^ inches, while the smaller diameter was uni-
formly 1 11/32 inches. These were supported in a 1^ inch hole in
a hard wood block, and the measured tension applied about 4J
inches from the block, the exact distance of the point of applica-
tion being measured.
The load was very gradually applied in increments of a few
pounds, and the amount noted when the first separation of the
fibre appeared. Most of the specimens showed distress at from
700 to 750 lbs., with maximum strength of about 10 per cent,
above this. One specimen, however, showed a crack at 600
lbs., and an ultimate strength of 1083 lbs. The average value of
.s determined from the tension at which the first fibre separation
appeared was 11,130 lbs. per sq. inch, and the average value
calculated from the maximum loads sustained was 13,623. The
value of s, calculated for the specimen crackling at 600 lbs., was
9,280. While this is somewhat below the average due to an
apparent defect in the wood, it is probably best to assume that
for a maximum load, s should not be greater than 9,000. Assum-
ing this value, the maximum load that may be applied to the
proposed pins at a distance from the cross-arm equal to the
designation of size, would be as follows:
Size of Pin. Value of P. Size of Pin. Value of P.
5 in. 557 13 in. 621
7 " 639 15 " 694
9 " 615 17 " 670
11 " 610 19 " 700
30 HIGH-TENSION TRANSMISSION.
Of course these values of P would be identical but for the
difference between the actual diameter selected and that of the
theoretical pin. The average value is 636 lbs., which may be
considered the maximum load that the standard pins will sus-
tain at the point designated.
Even with very generous factors of safety, it would appear that
the pins suggested would prove of ample strength to withstand
the side strains to which they may be subjected. For heavy
work and for end poles, an insulator carrying the wire at some
distance below the top of the pin would, of course, increase the
strength of the construction. A table of standard insulators
could perhaps with advantage be prepared so proportioned
between groove and bottom of threaded bore as to maintain the
stress on the pin within the allowable safe values for the various
tensions applied.
I would call attention to one seeming error in the table of the
dimensions of the proposed pins. In the paragraph headed
" Designation," the following appears: " It is proposed to desig-
nate that portion of the pin above the cross-arm as the ' stem '
of the pin," and further, " It is proposed to designate a pin by
the length of its stem." From this definition the stem of the
pin would have a length equal to the sum of the dimensions A
and G of the table.. For the five-inch pin shown in the table
this would be 5|- inches, and thus is not equal to the designation.
Mr. Mershon : — Another written contribution to this discus-
sion is by Mr. C. L. Cory, of San Francisco.
Mr. C. L. Cory: — The mechanical strength of insulator pins for
use on long distance transmission lines has been given much con-
sideration by electrical engineers in California during the past
six years. For the most part the insulator pins in use are wood.
On the 33,000 volt, 83 mile, double circuit, three-phase trans-
mission line of the Edison Electric Co., from their Santa Ana
power house to the city of Los Angeles, iron pins with porcelain
sleeves are used. This transmission is the most notable system
in California at the present time using insulator pins other than
wood.
Eucalyptus has been found to be perhaps the best wood to use
for insulator pins. After being turned up and threaded, they are
usually treated with hot linseed oil. This treatment is desirable
more on account of the protection which such treatment gives
the pin against weather than on account of the insulating quali-
ties of the oil or oil treatment.
It should be understood in this connection that an insulator
pin should be depended upon only to support the insulator. The
insulator in turn should be depended upon to provide the neces-
sary insulation for the line wires. No pin after being in use for a
few years on a pole line can maintain to any marked degree the
insulating qualities originally existing, due to such oil or paraffin
treatment.
The tests outlined below were made in the electrical laboratory
of the University of California, for the purpose of determining
STANDARD INSULATOR PIN.
31
how near the pins generally in use in California conform to the
proposed standard pins suggested by Mr. Mershon. In the test
twenty-two pins were broken. These were not selected particu-
larly for the test, but were taken at random from a large lot of
such pins which were to be used in construction work. Of these,
twelve were of the size generally in use on transmission lines
where the voltage does not exceed 30,000 volts. These pins are
Hi inches long, including shank and stem, the latter being 6|
inches in length. The other ten pins tested were of the size used
on the lines of what has been known as the Bay Counties Power
Co., now the California Gas & Electric Corporation, and the
Standard Electric Co. The line voltage in each of these trans-
mission systems is from 40,000 to 60,000 volts. These pins are
FIG.1
15} inches long, including shank and stem, the latter being 10^
inches long. All of the dimensions of the pins tested are given in
Figs. 1 and 2.
These pins do not exactly conform in size or length of stem
with any of the proposed standard pins. Below, however, is
given the comparative dimensions of the two samples of pins
tested and the nearest sizes of the corresponding proposed pins.
For sake of comparison, a 7-inch pin, as proposed, is contrasted
with the 6|- inch tested pin, and the 11 inch proposed pin is con-
trasted with the 10|- inch tested pin. The above dimensions
refer to the length of the stem of the pin, as suggested by. Mr
Mershon.
COMPARISON OF PROPOSED PIN AND PINS TESTED.
Size
of
Pin.
r
A
7"
B
C
Nom-
ioal
c
Act-
ual
D
E
F
1"
G
H
2i
I
Proposed Pin.
aj
Pin Tested.
61
6i
41
n
n
n
If
11
—
3"
3
Proposed Pin.
11
11
4f
3
m
m
n
1"
i
3J
^
Pin Tested
lOi
m
51
2A
2i
SxV
31
n
i
2i
H
In general, it will be seen that the dimensions of the proposed
and tested pin agree fairly well. The most marked difference is
in the diameter of the portion of the pin which is threaded to
32
HIGH-TENSION TRANSMISSION.
receive the insulator. It seems evident that one inch is not a
sufficient diameter for the thread of the pin for all sizes. If
there is any burning of the pin just below the insulator, the
inevitable result will be breaking at the bottom portion of the
thread. Such a break will usually leave the pin, except the ,
threaded portion, standing in the cross-arm, while the insulator
with the threaded portion of the pin inside, will hang suspended
on the line wire. This sort of break has often been observed
on high-voltage transmission lines.
The method of testing the pins is clearly shown in the accom-
panying photograph. It was impossible to mount the cross-arm
in the testing machine so that the strain on the pin would be at
right angles to its axis. The variation from a right angle, how-
ever, is small and to a certain degree conforms with the direction
of the strain on the pin, due to the sag in the line wire. The
" breaking load," as given in the tables below, refers to the strain
in the direction of the cable, while the " real breaking load " is
the component of this strain at right angles to the axis of the
pin.
Real
Real
Breaking
Breaking
Breaking
Breaking
No.
Load.
Load,
No.
Load.
Load.
1
1010
950
1
2250
2120
2
1090
1035
2
3140
2960
3
1450
1360
3
2380
2240
4
1360
1280
4
2010
1890
6
920
865
6
2780
2620
6
1220
1150
7
2280
2140
7
1350
1270
8
1570
1475
8
940
875
9
2390
2250
9
1360
1280
10
3390
3190
10
1360
1280
Average.
2465
2310
11
750
705
12
1060
1010
Average.
1155
1085
The average results, referring to the " real breaking load,"
of the tests of the two pins are respectively, 1085 pounds for the
6J inch pin and 2310 pounds for the 10^ inch pin. The character
STANDARD IXSULATOR PIN.
■.i?,
of break in the two pins, however, is not the same. Ahnost
without exception, the 6-j inch pins were broken approximately
square off at the cross-arm. The larger pins, however, split in
the stem, the beginning of the split being just at the bottom of
the thread. An inspection of the photographs clearly shows the
difference in the character of break in the two pins.
Method of Mounting Cross-Arms, Pins and Insulators in Testing Machine.
It seems from the tests that the shank is the weakest part in
the 6| inch pins, while the stem, and particularly the upper
Dortion of the stem, or thread, is the weakest part of the 10-^ inch
pins
34 HIGH-TENSION TRANSMISSION.
The variation of the " real breaking load " for the different
6| inch pins tested is from 705 pounds minimum to 1360 pounds
maximum. For the 10^ inch pins, this variation is from 1475
pounds minimum to 3190 pounds maximum.
During the progress of the test, it was observed that the
" allowable breaking load " was least when the pin was turned in
the cross-arm, so that the strain was across the grain of the pin,
while the greatest allowable ' 'breaking load' ' corresponded with the
position of the pin in the cross-arm, so that the strain was parallel
to the grain of the pin'. In the tests made, no particular care
was taken to turn the pins in any fixed position relative to the
grain of the pin and the direction of the strain applied.
For good construction on lines using 30,000 to 60,000 volts
the larger pin must be used. It does not seem, however, that any
good reason exists for a great number of different sizes of pins, as
it would seem probable that the two sizes tested might be used
to fulfil almost every requirement for transmission work where
wooden pins are at all allowable.
In many respects an iron pin is better than one of wood. In
the first place, to secure sufficient strength in the shank, the
wooden pin must be of such a large diameter that the size of the
cross-arm is necessarily increased. In addition, using an iron
pin, the insulator can be held down on poles or~supports where
the tendency of the line wire is to raise or pull the pin out of the
cross-arm. In using wooden pins, this is usually prevented by
driving a nail through the cross-arm into the shank of the pin.
An iron insulator pin, possessing many desirable features, has
been designed for use on the extensive transmission lines
of the Vancouver Power Co., of Vancouver, British Columbia,
the design being due to Mr. Wynn Meredith, of San Francisco.
In general, the pin consists of a steel bolt approximately 12
inches long. A cast iron sleeve 4^ inches long, and fitting closely
to the cross-arm, fills the space between the thread, and corres-
ponds to the stem of the ordinary wooden pin. The thread of the
pin is made of lead, this lead thread being cast upon the end of
the steel bolt, the steel bolt being first chopped or made ragged,
so that the lead is held firmly to the steel bolt after being cast.
The tests upon this form of pin have not as yet been com-
pleted, but as soon as possible the results will be presented to the
Institute.
Mr. Mershon : — The fourth and last written contribution to
this part of the subject is by Mr. D. L. Huntifigton, electrical
engineer of the Washington Power Company, Spokane, Wash.
Mr. D. L. Huntington: — Wooden pins are subject to so
many uncertainties when used in connection with very high
voltages, especially where the atmosphere contains salt, smoke
or dust, that it seems desirable to abandon their use for such
purposes wherever possible, and to substitute a metallic pin.
The construction of a long distance line for 60,000 volts, led the
writer to make some investigation as to what could be done in
this direction, without excessive cost.
STANDARD INSULATOR PIN.
35
It was decided that a drop-forged or a turned steel pin would
be so expensive as to exclude it, even if the time at our dis-
posal would have permitted us to wait for its delivery.
Experiments were made with a cast-iron pin almost identical
in dimensions to that shown in Fig. 2 of Mr. Chesney's paper,
except that it was cored out internally so as to make its weight
about 10 pounds. The diameter of the shank was 2| inches.
This pin, before fracturing, sustained a load slightly in excess of
3,000 pounds, suspended from near the end of the threaded
portion.
Fear was felt, however, as to what might occur under the sud-
den strain of a line parting in winter time, with the possibility
I-. .■'
r'Dia.
Cut Eccentric In BoPb
Cutter
1 'sDia.
Mild Steel
Composite Pin
for
High Tension Insulator
Fig. 1.
of the fracture of several pins at a time due to the sudden shock.
To avoid this, several designs were made of pins cut from
round steel bars of 1 inch and 1^ inch diameter. The difficulty
in obtaining a satisfactory shoulder for the pin at the cross-arm
proved serious. Furthermore, it was feared that with a pin of
that small diameter, the cross-arm would be likely to burn out at
the pin-hole, as the interior surface of the hole would be com-
paratively small for distributing the leakage currents to the
cross-arm. Moreover, actual experience with wooden pins has
shown more or less conclusively that with a shank diameter of
36 HIGH-TENSION TRANSMISSION.
two inches or greater, there is Httle or nothing to fear from this
trouble.
As a result of these several difficulties we have designed and
adopted a pin (see Fig. 1) eighteen inches long, made of IJ inch
round mild steel bar, and having a shoulder and shank cast upon
it as shown. This pin we find will begin to bend when loaded
with about 1,000 pounds at the upper end, the shank being
rigidly supported. This is much lower than the results obtained
by the cast iron pin referred to above, but it is believed that it is
more reliable and that it is sufficient for nearly all ordinary work.
In addition, the steel bar will not snap off under sudden shock,
but will support the insulator and line safely even when badly
bent. We were unable, in the time at our disposal, to investi-
gate what could be done in the way of malleable castings of a
design somewhat similar to the cast-iron pin mentioned above,
but it is the writer's opinion that it would prove a fruitful line of
investigation.
High freight rates of the west and a higher initial cost will
doubtless make some of those in charge of the construction of such
lines hesitate at the extra expenditure (in our case it was about
double the cost of euralyptus pins), but it is in the line of safe
and conservative engineering and certainly strengthens the
weakest link in our high-voltage chain, our lines.
Mr. W. N. Smith : — It seems to me that the dimensions given are
all very well for a pin carrying a certain weight of wire, but it does
not seem to me that a single standard table of dimensions could
be laid down to cover anything like all the conditions of various
power transmission lines, all the way from a line of 5,000 or 6,000
volts, with, say. No. 4 wire, up to one like the Niagara Falls
power transmission line, which is of 300,000 cm. cable. The
scheme of the tabulation should be enlarged and gone over care-
fully, so as to have a separate tabulation for a reasonably small
range of weights of copper wire to cable; that is, one table for
sizes from No. 6 to No. 3, another No. 3 to No. 0, another from
No. to No. 0000, and another from No. 0000 up. In this way
the design of a standard pin would more nearly meet the varying
conditions of transmission line construction. I remember read-
ing Mr. Stillwell's paper a year or more ago on the Niagara Falls
transmission plant, in which, if I remember correctly, he stated
that the principal trouble with pins was their breaking at the
root of the thread. I do not see that this point has been covered
in Mr. Mershon's discussion, although it was referred to in Mr.
Gerry's contribution. I should think it a matter of considerable
importance in the design of the pin. I further agree with Mr.
Gerry in his opinion that the top of the pin is rather small, cer-
tainly, for the very heavy insulators that would be required for a
transmission above 30,000 volts.
Mr. p. H. Thomas,: — It would be a great gain to those who
hope to get information from the report of the committee, if the
characteristics of the different types of wood commonly used
STANDARD INSULATOR PIN. 37
could be discussed, e.g., oak, eucalyptus and locust. It is to be
hoped that in the local sections this question will be very fully
discussed. Also, something should be said about the method of
treating pins, which is one of the most important questions in
the insulation of the line. The treating of pins to make them
waterproof, without injuring the mechanical strength, is a difficult
matter.
In putting up an insulator, where the pin comes to a bearing
on its end inside of the insulatoi , expansion of the pin or contrac-
tion of the insulator may crack off the top of the insulator,
especially with glass. To amend this difficulty, a shoulder might
be arranged so that the pin would not touch the top of the insu-
lator.
Mr. Mershon: — As to the question of the size of the pin, it
may be desirable to have a pin larger at the top, perhaps, but I
do not think the reason which has been given for this holds very
well. In the first place, an insulator properly designed will not
tip. If the insulator is designed so that the side pull of the line
on it is transmitted directly to the pin, instead of being all the
way from an inch and a half to two inches above the top of the
pin, as in the case of most insulators, it will not tip. If it does,
that is a fault in the design of the insulator and not in the dimen-
sions of the pin. Mr. Gerry has criticized the shearing strength
of the thread. I doubt if the thread of the pin proposed by Mr.
Gerry will have a greater shearing strength than the thread of
the pin referred to in the paper. The question of the shearing
strength is not so important. A well-designed line will not have
much up-strain. A line with much up-strain is not laid out as
it should be. You cannot prevent some up-strain on some
insulators, but it may be made so light that the shearing
strength of the thread will not be of much importance.
Vice-President Sheldon : — If there is no further discussion,
we will proceed to the next paper. Do you care to make any
closing remarks, Mr. Mershon?
Mr. Mershon: — There was a further remark made by Mr.
Gerry to the effect that it is too early to adopt a standard pin. I
think if we adopted a standard and changed it from year to year,
we should not be any worse off than we are now, when we have
no standard. There are as many standards as there are manu-
facturers of pins and designers of pole lines. The only way now
to get a pin to fit an insulator is to send the insulator to the pin
manufacturer and in that way have the pins made so that they will
fit. If you buy a pin from one manufacturer and the insulator
from another, they may fit, or they may not fit.
Vice-President Sheldcw : — We will now proceed to the dis-
cussion of the paper by Mr. F. O. Blackwell on " The Testing of
Insulators." As Mr. Blackwell is not present and has not dele-
gated any one to present his paper, I will call upon Mr. Mershon
to present the introduction.
Mr. Mershon: — If there is no objection, I will pursue the
same course in regard to Mr. Blackwell's introduction as with
38 HIGH-TENSION TRANSMISSION.
my own. I will omit reading Tiis introduction*and read tlie con-
tributions to it. I think they take up most of the main points
and will serve as a basis for the discussion this evening. The
first contribution is by Mr. M. H. Gerry, Jr. It is as follows:
Mr. M. H. Gerry, Jr. — Mr. Blackwell has ably discussed a
number of important matters in connection with the testing of
high-voltage insulators. There are, however, a number of addi-
tional points which have not been touched upon.
Insulators are tested for two purposes: first, to determine the
design, shape, material and dimensions best suited for a given
voltage and set of conditions; secondly, insulators are tested as
a matter of routine, to determine whether manufacturers have
complied with specifications regarding material and workman-
ship.
There can be no complete set of tests to cover the first purpose,
as it is not only a matter of experiment, but of skill and judg-
ment in properly interpreting the results of many tests, in rela-
tion to service conditions. The testing of insulators for the
second purpose is comparatively simple. For glass insulators it
is usually sufficient to inspect them for physical defects, such as
cracks, bubbles and incorrect dimensions. A certain percentage
of the insulators should also be tested for proper annealing, and
for mechanical strength. A chemical analysis of the glass of a
few of the insulators is also desirable. Electrical tests of glass
insulators are unnecessary, as the physical inspection will reveal
everything that can be found by an electrical test. Porcelain
insulators are more difficult to test than are glass insulators, on
account of many defects being covered by the glaze. For very
high voltages, porcelain insulators should be tested electrically,
and should also be carefully inspected during the process of manu-
facture, and before the glaze is applied. This is especially
desirable with insulators built up of several parts and cemented
together by glaze or other material. Defects in insulators of
this type are difficult to detect, even by electrical tests, unless
they are pronounced.
Mr. Blackwell has indicated the proper method of making
electrical tests of insulators. The puncture test mentioned by
him, of twice the potential between wires, is usually sufficient,
but a higher test is desirable where the insulators are to be
exposed to severe lightning strains.
Mr. Mershon : — I would like to speak in regard to the follow-
ing sentence in the contribution of Mr. Gerry, which has just
been read. " The puncture test mentioned by him (Mr. Black-
well), of twice the potential between wires, is usually sufficient,
but a higher test is desirable where the insulators are to be
exposed to severe lightning strains." I have never personally
known or heard of a case of insulators having been punctured
where the puiicture could be laid to lightning. It seems to me
the lightning would flash around most insvdators rather than
puncture them.
* See page 6.
TESTING OF INSULATORS. 39
Then as to the question of the chemical analysis of glass
insulators. I have never had any reason to think that the
chemical composition of the glass madr any difference in the
behavior of glass insulators. I have made tests for difference in
behavior due to composition on both insulators and tubes of
glass, but never succeeded in finding any.
Vice-President Sheldon: — The subject is open for general
discussion.
Mr. p. M. Lincoln: — I would take issue with Mr. Gerry,
who made a statement that glass insulators did not need testing
beyond visual inspection. I know of a certain line, the insulators
of which were not given a voltage test, but were simply tapped
with a mallet in order to eliminate, if possible, any which had
undue internal strains. After the insulators were up and the
normal voltage applied, quite a number of them broke down in
actual service, which probably would not have occurred if they
had been tested with voltage before being erected.
Another point, in regard to lightning, which Mr. Mershon
speaks of — it is a fact that rain usually accompanies lightning
storms, and that, of course, will give you a wet surface on the
insulator. This wet surface is a very good conductor of the
sudden surges which occur in lightning storms, so that lightning
strains will be very apt to go over the surface rather than through
the insulator. I do not think there is much danger of breaking
iown of an insulator from lightning strains, after a test of double
normal potential has been applied.
Vice-President Sheldon: — Is there any more discussion?
Mr. W. N. Smith: — While the subject is before the Insti-
tute, I think it would be quite interesting if any members
present would state their preferences between porcelain and
glass for high-tension insulators. It is a question that comes
up every now and then, and no doubt there are members present
who may have a very strong leaning toward one or the other
material for high-tension transmission.
Mr. Mershon: — As between glass and porcelain, it seems to
me about the only advantage, other things being equal, that
porcelain has over glass for transmission work is that of mechani-
cal strength. Sometimes it has that advantage and sometimes
it has not. It is a fact, however, that in some forms of insulator
— in some complex forms — it is possible to get the porcelain
insulator cheaper than the glass one. I have found this true, to
my surprise, in one or two cases. ■ When the insulator is large, so
that it takes the form of a very heavy central portion of glass,
with long, thin petticoats, it seems to be almost impossible to
make it of glass and have it symmetrical. The thinner portions
cool first, and when the insulator is taken from the mold the
weight of the outer portions distort the inner portion of the
insulator, which is still hot. An advantage has also been
claimed for porcelain over glass because of the lesser hygroscopic
effeats, but I think in most power transmissions the small amount
of power necessary to dry up whatever moisture will get on the
40 HIGH-TENSION TRANSMISSION.
surface ot the insulator in that way would not be serious. As a
matter of fact, in any mea-^'irement I have ever made, no differ'
ence could be detected between porcelain and glass in the matter
of losses over their surfaces at high voltages.
Mr. T. W. Shock: — I had the pleasure of building a line this
last year in the State of Pennsylvania, in which I used an insu-
lator which tested for 75,000 volts. The ordinary pressure will
be 24,000 volts — that gives a factor of safety of over two. I
think I agree with Mr. Blackwell, that in testing insulators for
a line of high pressure the testing pressure should be at least two
and possibly three times the ordmar}? line pressure. My idea in
adopting that style of insulator is due to the fact that it was built
for a line on the Pacific coast, for 40,000 volts, and I adopted it
to give me an extra factor of safety. I made the test at a pres-
sure of 7.5,000 volts. I think the insulator will give us very
good satisfaction.
Mr. F. N. W.\term.a.n: — Mr. Blackwell's reference to test-
ing a double insulator — an insulator primarily of two parts —
Broken lOJ" pins (Stem,) Total Length, 15|-" Showing How Pins Split.
requiring that each part should be separately tested, seems
to me practically to bar out double insulators and does not
seem to be logically founded. He says, " if it is to be tested for
100,000 volts and is made in two parts, each part might, for
instance, be tested with 70,000 volts. The object of this is to
have the weak parts rejected before they are assembled." The
objection to that, from a practical standpoint of course, is evi-
dent; but there is a further objection, not so evident, and that
is, as I understand the porcelain people, in tne baking or
vitrifying of the two parts it is not desirable to take the entire
shrinkage out on the first heat. Consequently, if the insulators
are to be tested before being filled with glaze and re-vitrified,
they are not tested at all in their final condition. Furthermore,
I think it is illogical for the reason that it is a well-known fact
that if we get porcelain in thin parts, we have a very much more
than equal chance of getting sound porcelain. That is, if the
same insulators were made in one part they would only have our
final test, while the double insulator with much greater initial
TESTING OF INSULATORS. 41
chance of being sound is required to be tested twice. The test
peculiarly required by the double insulator is the mechanical
test, and as far as my observation goes — I have tested a good
many of them — if they are substantially free from large air
spaces, they will stand up under the final electrical test. It
seems to me that the requirement of a double test is unfair and
unnecessary.
Mr. Thom.\s; — Mr. Gerry, Mr. Lincoln and Mr. Mershon have
referred to one point in the testing of glass insulators that de-
serves a good deal more consideration, and that is the initial
strains left in the manufacture and annealing of the glass. The
breakage of glass insulators on the line during service may more
often be due to too much sun on one side of a poorly annealed
insulator than to electrical strain. I do not know of any test
which has been suggested to determine whether glass has been
properly annealed or not, but I do not doubt that some test could
be gotten up, and I make the suggestion to the committee that
the}^ consider this point carefully. A successful test would save
a great deal of trouble in high-tension lines after the insulators
Iron-Pin Insulator.
are installed. There is one rather old point which should be
mentioned in the testing of porcelain insulators — not only should
they be tested with salt water, but the regulator should soak
a certain definite time; the Standardization Committee might
determine how long.
Mr. C. C. Chesney: — A glass insulator, if it is not properly
and uniformly annealed, has unequal strains in the different parts
of the glass. I have known a number of such insulators after a
cool night to break when the sun struck them in the morning.
The side towards the sun cracks off. Aside from this feature,
I believe a glass insulator will give as good satisfaction as a
porcelain one.
Mr. Mershon: — I cannot entirely agree with the author in
regard to the use of one transformer for testing purposes. A
series of transformers need not have a bad regulation or seriously
distort the wave form, and such a testing set has a very great
advantage that a transformer breakdown is much less senous
than in the case of a single testing transformer. The knowledge
42 HIGH-TENSION TRANSMISSION.
of this fact gives one more confidence in testing, especially in
experimental testing. For very accurate results in any case a
step-dovvn voltmeter transformer is desirable.
Neither can I agree that insulators should necessarily be tested
on iron pins. As I have stated before, an iron pin is likely to be
the means of putting upon the insulator a mechanical stress all
out of proportion to any which it would meet in practice if
installed upon a wooden pin. For instance, if the insulator be
screwed down tight upon a metal pin there will result stresses
in the head tending to force the top of it off either at one of
the threads or at the bottom of the pin-hole, or tending to
burst the head. In either case there is a resulting mechani-
cal strain in the substance of the insulator inviting puncture
perpendicular to the lines of stress. An insulator that will
stand up well under a salt water test, will often break down
quickly when tested on a metal pin. While I do not believe in
depending upon the wooden pin for insulation, I see no good
reason for condemning it in general where there will be no
Parts of Iron-Pin Insulator.
trouble from burning. The author says that wooden pins burn
off eventually unless the insulator be good enough to be used
with an iron pin If the insulator be good enough to prevent
burning of the wooden pin, why not use the wooden pin unless
there be some mechanical requirement which it cannot meet.
I agree thoroughly that any new type of insulator should be
given a rain test; that is, a voltage test while water is being
sprayed upon the insulator in imitation of rain. If a wooden pm
is used in this test, it should be covered with tin-foil from a point
inside the petticoat nearest the pin to a point two or three inches
below. The voltage should be applied between the foil and a
wire around the neck of the insulator, or, preferably, between the
foil and a piece of wire representing the line wire and tied to
the insulator as it will be in practice. The recommendations
of the Introduction as regards the angle at which water should be
sprayed, is all right, if this angle be uniformly adopted in testing ;
but some definite angle should be adopted, as the angle makes
considerable difference in the voltage at which the current will
arc from the line wire to the pin. The recommendations in
TESTING OF INSULATORS. 43
regard to the spray are not, however, so specific as could be
desired. The amount of water sprayed, as well as the angle,
makes a difference in the arcing voltage. Some time ago I
endeavored to obtain from the United States Weather Bureau
information as to the most violent precipitation on record in this
country. The record sent me showed the most violent down-
pour as being about .8 of an inch in five minutes.
The maximum rate of downpours during that time may, of
course, have been greater than this. It has been my practice
to endeavor to adjust the spray for a precipitation of one inch in
five minutes. This can be most conveniently done by placing
under the insulator a suitable pan and collecting in it the water
for five minutes. Care must be taken that in placing the pan it
does not receive water from any part of the cross-arm other than
that just over it. The question of the method of obtaining the
spray is one which it is well to consider. It is no easy thing
properly to adjust the spray from an ordinary garden spray-nozzle
or rose-spray and it is no wonder that uniform results are not
Parts of Iron-Pin Insulator.
easily obtainable. It is desirable, if possible, to have some
special form of spray-nozzle which will give a uniformly dis-
tributed spray. This might perhaps be in the form of a very
large rose-spray of a foot or more in diameter.
It is desirable that if possible we arrive at some definite decision
this evening on the points mentioned in regard to the methods of
testing insulators, so that recommendations can be made on this
subject to the Standardization Committee.
Vice-President Sheldon: — There is a written contribution on
this subject from Mr. W. L. Waters, of Milwaukee, Wis.
Mr. W. L. Waters: — The form of potential wave given by
modem alternators differs very little from a sine wave. The
worst case commonly met with is that of a three-phase alternator
wound for high voltages. These machines have usually three
slots per pole, and the wave form shows pronounced harmonics
of five and seven times the fundamental frequency, but the
effect of this distortion on breakdown voltage of an insulator is
inappreciable. The only commercial machines that have wave
44
IIIGII-TEXSIOX TRA .WSMISSIUN.
forms which would affect the accuracy of the results to any extent
are the old single-phase revolving armature machines with pro-
jecting poles on the armature, which show a pronounced third
harmonic. But these machines are seldom met with now. The
charging current in a test on insulators or an overhead line
generally conforms more or less to the potential wave form of the
alternator, and whether the current is lagging or leading the
distorting effect on the wave form is slight, and with all ordinary
excitation and loads on the alternator the effect on the insulator
test will be inappreciable.
Generally speaking, an insulator will stand momentarily a volt-
age strain which, if continued long enough, will break it down;
1. Pin Split in Shank and Broken 2. Pm Broken at Upper Part oi
at Cross-Arm. Shank at Cross-Arm.
3. Pm Broken at Upper Part of 4, Pin Broken at Upper Part ci
Shank at Cross-Arm. Shank at Cross-Arm.
and this time effect is most marked in solid insulators. A
gas such as air does not show this. When air is going to break
down under a given strain, it will do so almost as soon as it is
applied, except where the insulation of the air is subsequently
weakened by a violent brush discharge. Solids show this effect
to the greatest extent, and liquids such as oil to a lesser extent.
And I have found that in insulating materials where this effect
is most marked, differences in wave form have little effect upon
the breakdown voltage; it seems to be the mean voltage or
possibly the r.m.s. voltage which decides the breakdown. In
air the wave form has quite an appreciable effect, and the differ-
ence between a peaked wave and a flat wave may be as much a.
TRANSPOSITION OF WIRES. 45
20 per cent, of the sparking distance. Porcelain insulators show
very markedly this time effect; they will stand a much higher
potential if applied instantaneously than they will if applied
continuously, and as far as can be seen from the experiments I
have made, they appear to conform with the rule mentioned
above, and are practically unaffected by wave form. The
sparking distance in air, on the other hand, being considerably
affected by wave form, shows at once the unsuitableness of using
a spark gap as a voltmeter if there is any doubt about the wave
form. And I have found that unless it was in the hands of a very
careful and experienced man, a spark gap was not of very much
use in accurate work. Using needles as electrodes, the voltage
seems to vary so much with the condition of the points, the state
of the atmosphere, the proximity of other high tension conductors
etc., that consistent results cannot be obtained in ordinary work.
Using amalgamated brass balls, one inch in diameter, gave better
results, but they are far from satisfactory. I think there is only
one really satisfactory way of measuring high voltages, and
that is by means of a voltmeter transformer connected straight
across the insulator being tested. This method is accurate and
is direct reading, and there is no chance of mistake and no con-
tinual trouble fixing and adjusting your spark gap. Reliable
voltmeter transformers can be made for all ordinary voltages for
a few hundred dollars, and the use of one would save its cost in
worry and hard work in a very short time.
The above remarks are, strictly, only applicable to voltages up
to 50,000, as I have had no experience with higher voltages. But
I think that with slight changes thev will apply to the highest
voltages at present in use.
Vice-President Sheldon: — ^We will now take up the paper
by Mr. P. M. Lincoln, entitled, " Transposition and Relative
Location of Power and Telephone Wires."
Mr. Lincoln read his introduction (see page 11), and the fol-
lowing contribution by Mr. M. H. Gerry, Jr.
Mr. M. H. Gerry, Jr.: — Mr. Lincoln has discussed the most
important requirements of telephone construction in connection
with high-tension transmission lines. There is no especial diffi-
culty in instalHng a successful telephone circuit which will give
satisfactory service and reasonable safety in operation on a pole
line carrying from 50,000 to 60,000 volts.
Mr. Lincoln has mentioned the principal requisites of successful
design, which-are a proper adjustment of the capacity, a mainte-
nance of high insulation from ground, and a complete transposi-
tion of the telephone wires in reference to each other, to the power
circuit and to the ground. In addition, might be added the use
of certain safety devices, which reduce the danger in handling
telephones connected with circuits on high tension pole lines.
In regard to transpositions: Mr. Lincoln advocates the trans-
position of the telephone wires only, but it is desirable also to
transpose the main power circuits, m order to reduce to a mini-
46 HIGH-TENSION TRANSMISSION.
mum the voltage to ground on the telephone circuits. But few
transpositions of the power circuit are required, and the service
as a rule is materially improved thereby. Where there is con-
siderable lightning, arresters should be installed on the telephone
circuits of a design similar to those used on lighting circuits.
The ordinary telephone lightning arrester is an undesirable and
unsafe piece of apparatus for this purpose. Fig. No. 7 is a
sketch of a telephone arrangement devised by the writer, which
will give excellent results in service. Especial attention is called
to the short gaps across the line, to the location of the lightning
p LIGHTNINQ N^j/^ >y/
FIQJ
arresters, and to the repeating-coils, which should be insulated
for at least 5,000 volts, and may be immersed in small glass jars
containing transformer oil.
The Missouri River Power Company, with which the writer is
connected, regularly maintains a very satisfactory telephone
service on its 50,000 volt transmission lines between Canyon
Ferry and Butte, a distance of sixty-four miles, and this service
is rarely interrupted, even during the most severe lightning
disturbances. Under normal conditions, there is no potential
on this telephone line, and only the slightest hum can be detected.
Mr. Lincoln: — There is one point upon which possibly my
discussion is not quite clear, and that is in regard to the trans-
position of the power circuits. I have stated that it is not of
very great importance. My reason possibly is not very clear in
the paper, and it is this — a telephone line ought to be so made
that it will at all times operate, even if one leg of the power line
is dead grounded. If it is made to operate under these conditions
it will operate under the normal conditions of an untransposed
power line, because the normal static potential induced in the
telephone line by an untransposed power line is vastly less than
that which will be induced in the telephone line by grounding
the power line; so that if the telephone line is installed so as to
run under grounded conditi'^ns, that is, with the power line
grounded, it will certainly run with an untransposed power line.
Vice-President Sheldon: — The subject is now open for
general discussion.
Mr. Ralph D. Mershon; — The truth of the observations of
paragraph (6) is not clearly evident to me. The relation between
the telephone circuit and the power -ircuit is, as stated in para-
graph (4) such that in their electromagnetic relations they con-
TRANSPOSITION OF WIRES. 47
stitute a transformer — an air-core transformer and one having
very poor regulation. This transformer has in its primary — the
power wires — a current unaffected in value by any current in the
telephone wires and which may therefore for any given condition
of power load be considered as a constant current. If the tele-
phones took any appreciable amount of current, an amount
comparable to the power current, we should have a tendency
toward constant current in the telephones. If, as is the case, the
telephones take a current very much less than the power current,
we will have a tendency for constant voltage.
Electrostatically, each telephone wire is a plate of a condenser,
the power wires being the other plate. These two condensers
are in series through the telephones and have impressed upon
them a constant e.m.f . The condition here is similar to that for
the electromagnetic action, in that if the current in the tele-
phones be such as will convey a charge approximating that which
the impressed e.m.f. can impose upon the condensers, there will
be a tendency toward constant current; if not, as seems to me is
usually the case, there will be a tendency towards constant volt-
age. In short, it seems to me that the conditions are about the
same in the case of the electromagnetic and electrostatic dis-
turbances. This is on the assumption that the reactance of the
telephone is low relative to its resistance. If this is not *-he
case, and the reactance is comparable to the condensance con-
cerned in the telephone circuit, then the current conditions may
be almost anything, depending upon the relations between these
two quantities Further, if by telephones of various resistances
it is meant to designate telephones of various numbers of turns
in the transmitter, then it seems to me the statement in regard
to the disturbing ampere-turns is incorrect. The resistance of a
coil varies as the square of the number of turns (assuming the
same space available in each case for copper). The ampere-tunis
on constant e.m.f. vary, therefore, inversely as the square root Of
the resistance. It would seem, therefore, that if, as stated above,
the electromagnetic and electrostatic effects are constant poten -
tial in their nature, telephones should be wound for as high resist-
ance as possible. This seems reasonable, as it is equivalent to
saying that the telephonic e.m.f. should be kept as high as possi-
ble, which in turn is equivalent to saying that the disturbing
e.m.f. should be as small a percentage of the telephonic e.m.f. as
possible. In order to solve some of these questions, it is neces-
sary to know the current and e.m.f. of telephones. I have no
such data and have not been able so far to obtain them.
(7) It does not seem as though the objection given for the use
of the series telephone were a valid one, since one ought not to
introduce a telephone at b. Fig. 2, any more than one would
connect a bridging telephone at this point. In other words,
telephones, whether series or shunt instruments, should be con-
nected at even transpositions in order to obtain the best results.
(14) It is not quite clear to me why the series telephone should
48 HIGH-TENSION TRANSMISSION.
not be a satisfactory instrument. As has already been stated,
the reason mentioned in (7) seems hardly a valid one for con-
demning it.
(15) There is another method of accomplishing this desired
end of having the telephone lines as nearly as possible at the
same potential as the earth, which seems preferable for the use
of a grounded wire ; first, on the score of simplicity, and secondly,
because it may also be a means of protection against loss of life
or fire. This method is that of using autotransformers con-
nected across the telephone line at a number of points, preferably
at each of the telephone stations, each having its middle point
connected to ground. Each transformer should be designed so
as to take a very small amount of the telephonic current, but
should have wires sufficiently heavy to enable it to take, in case
of a cross with a high voltage wire, a current heavy enough to
operate the circuit-opening devices in the power station or else
to blow a suitable fuse in the telephone circuit itself. Such a
device would protect the users of the telephones from disagreable
or dangerous shocks, whether due to crosses, leakage or
electrostatic induction, and would also help to minimize disturb-
ances due to grounds, etc.
Mr. p. H. Thomas: — I think that the subject of tele-
phones on long distance power transmission lines is perhaps
the most important subject we have to-night. Mr. Lincoln has
given a very good statement of the fundamental principles
underlying the difficulties that have been found in many cases.
By exchanging experiences and making suggestions, we can
probably base on these fundamental principles improved methods
by which the present service can be very much benefitted. As
Mr. Lincoln concludes, I think there is no doubt that the trouble
is chiefly due to the electrostatic induction from the normal
voltage which tends to raise both telephone wires above the
earth, either positively or negatively. There will also be a
momentary disturbance whenever we have a charge of a light-
ning arrester, or any static discharge, in the neighborhood, but
that will not give much trouble as regards clearness of commu-
nication, because it is over quickly. The transposition of the
transmission line is, I think, an important point practically in
high-voltage transmission. As Mr. Lincoln states, a telephone
circuit should be built to work under all conditions ; for instance,
when one line is dead grounded. But if it is impossible to make
it work at such times, and if you can make it work smoothly
when not grounded by transposing the power line, you had better
transpose it, and that is the actual condition of practice.
Assuming both telephone wires are going to reach high poten-
tial above the earth, there is only one thing to do to get service
at all times, and that is to eliminate the baneful effects of the high
potential.
I will make a suggestion for accomplishing this purpose, which
may not have much practical value, but should be worth trying.
TRANSPOSITION OF WIRES. 49
I hope that some of the engineers who have opportunities for
experimenting at hand will try it for their own and the general
good. For instance, it is possible we may be able to insulate the
telephone wires, perhaps for 30,000 or 40,000 volts in an extreme
case, and at the end of the line put the primary of a transformer
and connect the telephone to the secondary, thus making very
high insulation between the prijnary and secondary. By this
means it would be possible to protect the operator, and since
static disturbances do not induce potential between the two
wires, it should not disturb the speech. The same result may
possibly be accomplished with condensers, by connecting two
condensers in series between the two pair of wires and putting the
telephone in between the condensers, not connected with the
line. In this case it will probably be necessary to put a choke-
coil between the condensers and ground its middle point. The
charging current of the condensers will be neutralized by going
through the two halves of the coil in opposite directions and a
telephone winding could be taken from the same core.
Mr. Lincoln suggested carrying ground wires in close proximity
to the telephone wires. This should help much and would be a
good method to try, but it would probably be necessary to use
insulated wire for the telephone circuit, otherwise there would be
trouble from repeated grounding. One method, which would be
effective, but perhaps not practicable, would be to use for each
side of the telephone wire a twisted pair ; one wire of the pair for
the telephone circuit and the other of the pair grounded. This
method would make a large capacity between the telephone wire
and ground, but would not actually ground the telephone wire
itself.
There is another interesting possibility for those who like to
speculate. Can we not use the power transmission wires them-
selves for sending signals? If not for telephoning, at least for
general signaling. For instance, as a suggestion, we might con-
nect a high resistance between each wire and a common point,
and connect this point to ground, and similarly at the other end;
then put a high frequency generator between the ground and the
common connection at one end of the line, and some kind of
receiving apparatus in the other. The high frequency would
prevent the transformers from taking too much current, and
you might be able to signal when power was on the lines. The
same thing might be done with condensers or choke-coils. The
advantage of using all the wires in parallel for sig^naling is that if
you have three or four wires burnt off, there might yet be one
wire you could signal through.
Another point is, it would be possible to make temporary
arrangements for signaling in times of shut-down, until the
power comes. That is, when voltages go off, it would be possible
to use the dead wires to make arrangements to start up again.
Things are in a critical state when the power is off, and the tele-
phone lines down, and such a system of signaling might easily be
arranged..
50 HIGH-TENSION TRANSMISSION.
Another thing is very important, and that is the protection of
the man using the telephone. One or two fatal accidents have
recently occurred to operators on the telephone circuits. They
should either be msulated in a booth, or the circuits should be
dead grounded, or protected through an air-gap small enough to
be safe for the operators.
In regard to Mr. Lincoln's statement that telephone wires may
reach as high a voltage as 20,000 volts. It occurs to me that as
perhaps his statement is based on theoretical considerations, I
can emphasize it by stating that I have seen this voltage in fact,
in Mr. Gerry's plant. I have seen sparks from telephone line
to grotmd which were something like half an inch long, indicating
perhaps 20,000 volts, perhaps higher than that. The possibility
which Mr. Lincoln describes is not at all imaginary; it is very
real.
Mr. C. E. Skinner: — I wish to emphasize the last point
made by Mr. Thomas, that is, the protection of the work-
man. The insulation of the instruments in the building
has been mentioned by Mr. Lincoln. The insulation of the
workman is even more important, and it is not difficult to make
arrangements so that he will be well enough insulated, so that even
a cross between a high potential line and a telephone line will not
do serious harm. It is usually painful to receive a shock of this
character, but not particularly dangerous. It has been my
observation that men handling telephones on high-tension trans-
mission lines, soon learn to be very cautious and are usually
compelled to watch the surrounding material, walls, etc., when
telephoning. This could be easily avoided by proper arrange-
ments, so that the man need not touch anything which would
connect him to the ground.
Mr. C. O. Mailloux: — I would like to mention a phe-
nomenon in connection with the charging of lines which,
while not exactly within the scope of this paper, is still interest-
ing, especially as it is a phenomenon which has puzzled me and
which has puzzled others to whom I have mentioned it. I have
observed the fact that the transmission line will become spon-
taneously charged electrostatically without being connected to
any generating machinery. About a year ago, in Arizona, we
repeatedly observed that the three wires of a 25 or 26 mile line
would become charged spontaneously to a considerable potential
under various atmospheric conditions. In Phoenix, Ariz, at
this time of the year, the weather is very much the same as it
would be here in June of July, except that there is no rain. The
weather is usually very pleasant, quite warm in the day time —
one can wear summer clothes — and it cools but very little in the
evening. There are occasionally slight winds, especially over the
deserts, over a portion of which the line runs. I have repeatedly
observed, but during the day time only, or until early evening,
that the three lines became charged electrostatically. They
could be discharged by making a connection to earth, but if left
TRANSPOSITION OF WIRES. 51
alone they would soon charge again (in 10 to 15 seconds). The
three wires would always charge at approximately the same
potential with respect to earth, but this potential varied, as
might be expected. It depended on the weather apparently,
and varied, of course, with the length of time allowed for re-
charging. On one occasion, v/hen there was a heavy wind pre-
ceding a rain, the potential was so high that we got sparks an inch
and a half between the lines and the ground, through spark gaps,
I have repeatedly observed cases where the spark was 1/16 to |
of an inch between sparking points. There were no indications
of lightning or storm. There have been cases where the phe-
nomenon was observed when it was raining, (at the distant
end, which is near the mountains, where it rains occa-
sionally), or shortly after it had rained; but the phenomenon
was never so marked at such times; it was repeatedly observed
when there was no indication of rain whatsoever, the sun shining
brightly, but there was then always some wind or slight breeze
somewhere along the line. My own theory was that the charge
was either caused or translated by the wind, and taken up by the
wire surfaces acting as condensers. I have mentioned the matter
to several physicists, but my theory was rejected, as moisture in
the air is considered indispensable, and it was lacking in this case.
I have not succeeded in getting any satisfactory explanation.
I hope there is someone here this evening who may be- able to
give it.
Another interesting phenomenon which I have observed in the
same climate is the fact that the lightning arrester, which is
located at each end of the line, has generally a tendency to frying
discharge, which is more pronounced between the lightning
arrester gap of one line than of the others. It was not always
the same line, but changed from one line to another. I could not
determine with the facilities we had what that was due to, but I
was tempted to ascribe it to some sort of electrostatic action.
The three line wires were systematically transposed in building
this line, so as to bring an equal length of each of the three wires
in the same relation with the surface of the ground.
Mr. Lincoln: — The point has been brought up about the use
of series telephone versus the bridge telephone. I know by
bitter experience that the series telephone does not give very
good satisfaction. I once had charge of a line on the poles of
which was run a telephone line, and on that telephone line we had
about fifty series 'phones scattered along over twenty -five miles,
about half a mile apart. We were never able to get successful
service from that system. I ascribed most of the difficulty to the
fact that the talking current had to go through so many loose
contacts, so many jacks, and it is almost impossible to keep so
many contacts in good shape. With the bridge 'phone it is
necessary for the speaking current to go through only one pair
of loose contacts or jacks at each 'phone. That constitutes one
great advantage of the bridge over the series telephone. •
52 HIGH-TENSION TRANSMISSION.
The suggestion has been made that the potential between
telephone wires and ground can be reduced by introducing be-
tween them autotransformers or condensers or resistances and
connecting the middle points of these autotransformers, etc.,
to ground.
The objection to that method, it occurs to me, is that it takes
off the charging current at concentrated points. The current is
induced in these telephone wires as a distributed effect, distrib-
uted along the whole length; and if you try to take it off at
bunched points, there will be a flow of current in the telephone
wires which will introduce an e.m.f. and probably make dis-
turbance in the telephone. The remedy which I proposed is to
run a ground wire along the whole length of the telephone wire,
producing a distributed capacity which will take care of the dis-
tributed induced effect most efficiently.
Mr. Mershon: — With regard to the use of condensers on
telephone lines, it seems to me we want to keep the capacity of
the telephone lines as low as possible to get good operation of the
telephone.
If any one wanted to signal with the power lines, it would be
better to signal from neutral to ground, and receive messages
at the corresponding place at the end of the line.
I do not think the objection Mr. Lincoln makes, relative to
the use of autotransformers on telephone lines, that the current
would be drawn off at certain points, whereas it is introduced
uniformly along the telephone line, would hold, as the current
is flowing in the same direction in both telephone wires, and the
effects of the two currents will neutralize each other so far as
the telephones are concerned.
Vice-President Sheldon : — We will now proceed to the con-
sideration of the paper on " Burning of Wooden Pins on High
Tension Transmission Lines," by Mr. C. C. Chesney.
Mr. Chesney presented his paper (see page 18) and read the
following contribution by Mr. M. H. Gerry, Jr.
Mr. M. H. Gerry, Jr. : — On a certain number of high-tension
transmission lines there has been burning of the wooden pins.
On other transmission lines of high voltage, there has been no
such burning. Where burning has occurred, it has been due to
leakage of current from the surface of the insulators, coupled
with resistance conditions in the pin, such that sufficient heat
was developed to char the wood.
When thoroughly dry, wood is one of the best of insulat-
ing materials, and one of the poorest when containing sap or
moisture. The greatest objection to it is its unreliability, due to
the difficulty of removing the last traces of sap or moisture. A
thoroughly dry wooden pin, fifteen inches in length, will stand
indefinitely 100,000 volts pressure, while a green pin of the
same length, containing sap, will break down very quickly under
1,000 volts pressure. Paraffining the pins on the outside, or
coating with asphaltum or linseed oil, is of no value. If the pins
BURNING OF PINS! 53
-ire thoroughly dry, the material in which they are dipped can be
made to impregnate the entire body of the wood, thus producing
a pin of high insulation. Such a pin is of value, as it reduces the
static strains on the insulator and decreases the amount of
leakage to ground.
In order to prevent burning of pins they should have either
very high or very low resistance. With insulators having a
large amount of surface leakage, such as those illustrated by Mr.
Chesney, an iron pin is perhaps the only solution of the difficulty.
There is nothing especially mysterious about the burning of
wooden pins on high-tension lines, as it is merely a matter of total
resistance to ground and the relative resistances of the insulators,
pins, cross-arms and poles. Wherever burning occurs, it can be
remedied by altering the design, material or dimensions of the
insulators and improving the quality of the pins.
Mr. H. W. Buck: — Referring to the point which Mr. Chesney
spoke of in regard to the so-called " digesting " of pins, I have
seen many pins taken from the Niagara-Buffalo transmission
line where such disintegration had occurred, the top of the pins
having crumbled into a white powder. We have recently had
some of this powder analyzed by a chemist and it was found to
be a nitrate salt. This would look as if nitric acid had been
formed in the presence of a static discharge inside of the insulator
by the well-known atmospheric reaction and had attacked the
wood, forming the nitrogen salt in combination with the vege-
table matter of the pin.
In this connection I would like to say that about six months
ago we built an experimental single-phase line at Niagara, about
two miles in length, and operated it continuously for nearly four
months at approximately 75,000 volts. The conductors of this
line were galvanized iron wire, tied to the insulators with copper
tie wires. At the end of the experimental run, the galvanized
iron wire had turned black to a considerable depth throughout
its length. The copper tie wires had also been attacked, though
not so much as the iron. This surface disintegration was not due
to general atmosp/ieric influence, for iron wire in the same place
but not charged electrically retained its original bright condi-
tion. I believe that this action is also due in some way to the
influence of nitric acid formed by the brush discharge around the
conductor. It indicates that some trouble may be experienced
at such excessively h igh voltages where static discharge from the
line is active. This discharge probably causes a combination of
the oxygen and nitrogen of the air which, with the moisture of
the atmosphere, forms a film of dilute nitric acid surrounding
and attacking the metallic conductor.
Mr. Lincoln : — Mention has been made by Mr. Chesney and
in the communication of Mr. Gerry as to the treatment of pins.
I think the treatment of pins should be with a view to making
them durable rather than making them good insulators. The
pins should not be relied upon as a part of the insulation. As
54 HIGH-TENSION TRANSMISSION.
long as they are dry and as long as the weather is perfectly dry,
they may be most perfect insulators, but as soon as rain comes
and the pins are wet on the surface even, they become practically
useless as insulators and the entire insulation strain on the line
falls on the insulators. We should treat the pins, therefore, with
a view to preserving them rather than making insulators of them.
Mr. Mershon : — It does not seem that, as Mr. Lincoln stated
a few minutes ago, when the arms and pins get wet, the insula-
tion is all in the insulators ; because if this were the case, I do not
quite see how the sides of the pins next to the sea should
be burned, and the sides away from the sea should not
be burned. It seems to me it would be the other way. If the
insulator controls the current, the lower the resistance of the pin,
the less burning, and when the pin is charred all over there should
be less heat generated on the surface, and consequently less ten-
dency to burn. But if the pin does to some extent control the
current, the lower the resistance the greater the current over the
surface, and the more likely it is to bum, especially over any
part of it which has had it? resistance lowered.
The path of the leakage current from wire to wire of a
power transmission line may be considered as a high resistance
electric circuit, derived from a constant potential source. The
total resistance of this derived circuit is the series of the resistance
of the three elements, insulators, pins and cross-arms. The
resistance of each of these elements is that resulting from two
resistances in multiple; namely, the resistance of the element
through its substance and the resistance over its surface. The
substance resistance of all the elements is usually high, so high
in a well constructed line that it need not be considered.
The surface resistance of the three elements may or may not
be high, depending upon the surface conditions as regards
moisture, dust, dirt or other deposits. Suppose the surface con-
ditions of all the elements is such as to allow considerable
leakage. No harm will result to the insulator unless the leakage
becomes great enough to, start an arc. This is not the case,
however, with the cross-arms and pins. The leakage over their
surfaces, if great enough, will char all the surface over which it
passes. Pins are more likely to char than cross-arms, since their
surface is less and their surface resistance, therefore, higher than
the cross-arms; the result being, for a given leakage current,
more loss per unit area of pin surface than of cross-arm surface.
Any protected portion of the pin is especially liable to charring.
For, if the cross-arms and pins have their exposed surfaces pretty
thoroughly wet or dirty, so that the current passes over them with
little resistance, the wet or dirty portions may be little affected;
but if in the course of its path the current encounters any small
portion of the pin which is not wet or which for any reason has a
higher resistance per unit of length, the wood may be charred at
this point. Now, this is what happens when the pins bum. The
insulator, the lower part of the pin, and the cross-arm have their
BURNING OF PINS. 55
surface resistance lowered by moisture or otherwise, but the
upper part of the pin being protected by the insulator does not
have its surface resistance so much decreased; the consequence
is burning of the protected surface. In some cases the inner
surface of the insulator next the pin and the pin itself are so well
protected by the insulator that the current, instead of leaking
over the surface of the insulator until it reaches a point where the
insulator and pin are in contact, jumps in a brush-discharge from
the edge of the petticoat to the pin rather than follow the higher
resistance of the protected surface. As a result, the pin is burnt
at the point where the brush discharge strikes it instead of at or
near the thread. There are apparent three possible remedies
for the trouble due to charring pins.
1. Make the design and size of the insulator such that for all
conditions its surface resistance will be so high as to control the
leakage and keep it below a point which can harm the pin.
2. Make the pins fireproof, but non-conducting.
3. Make the pins conducting.
The remedy recommended in the introduction to this discus-
sion is (3). It is recommended that an iron pin be used. This
certainly would do away with the trouble of charring pins, but
whether or not it will introduce other and more serious trouble
remains to be seen. It seems to me there is a very likely chance
of trouble from the use of iron pins, due to the unyielding charac-
ter of both iron and porcelain or glass and their widely different
coefficients of expansion. Insulating material under mechanical
stress will generally break down under a lower voltage than when
not strained. An insulator or an iron pin might, when in-
stalled, be put under a considerable mechanical stress or one
which when first installed has comparatively little stress upon it
may, due to changes of temperature, be much strained; the
result in either case is increased liability to puncture.
The endeavor may be made to get around this trouble by
using a wooden thread upon the iron pins, but as shown by one
of the cuts in the introduction, the charring trouble may still
remain if this course is adopted. If a wooden cross-arm is used
with the iron pin, the seat of the charring trouble may be trans-
ferred to the cross-arm unless the pins be connected by a con-
ductor. It would seem better to adopt the first remedy and
make the design of the insulator such as to protect the pins.
Mr. de Muralt : — It may possibly interest you to know that
while the general practice in America is evidently to use wooden
pins, in Europe it is just the opposite. Practically all the high
potential installations use iron pins, and more than that, while
here very often the whole pole is treated with as little iron as
possible, in Europe there are quite frequently poles constructed
entirely of iron, with iron cross-arms and iron pins, and the only
insulation relied upon is the insulation proper. I believe this
does away with the burning of pins, cross-arms and poles. I do
not think there is very much difficulty in the way of avoiding
56 HIGH-TENSION TRANSMISSION.
mechanical strains, which have been alluded to several times
to-night, with regard to fixing the insulator in the pin. One way
to get around that is to fix the pin into the insulator by means of
a cement which will take up any such strain, and in a great many
installations that I know of a cement made of a mixture of
litharge and glycerine has been used with, as far as I know, very
good results. It seems to me that it is a very fair scheme thus
to lay the entire insulation into the insulator, and then let the
rest of the pole take care of itself. I know of one installation,
where they are operating at 26,000 volts, using American glass
insulators and iron pins and iron poles ; and of another one which
is using 25,000 volts, and has porcelain insulators, with iron pins
on wooden poles part of the way, and iron pins in walls and on
any kind of a support on the other portion of the road. Neither
of these installations has given any trouble whatsoever and they
are amongst some of the best high-voltage installations in
Europe.
Mr. Philip Torchio: — I want to suggest an explanation of
the burning of the wood between the iron pin and the porcelain
base in the Locke insulator shown in Fig. 3 of Mr. Chesney's
paper. I wish to call attention to the fact that, if two plates
are maintained at a certain difference of potential, acting as
condensers and spaced at such a distance that there will be no
discharge between the plates, but set near the limit at which the
discharge would begin and then there is inserted in the middle a
plate of vulcanized rubber, which has a higher dielectric resist-
ance than air, right away the discharge takes place between the
plates. Now, that is contrary to what might have been ex-
pected. The explanation is that before the insertion of the
vulcanized rubber plate the fall of potential between the two
plates of the condenser is a uniform straight line, but when we
introduce the vulcanized rubber plate we alter the conditions,
as we have then three condensers in series, which will distribute
the total fall of e.m.f. in inverse ratio to their capacities. There-
fore, this plate of vulcanized rubber acting as a condenser with a
larger capacity than the same amount of air which it displaces
will be charged at a smaller fall of e.m.f. between its faces than
existed before, and the e.m.f. between the outer condensers
will be increased and then the discharge begins. Now, it seems
to me that in the Locke insulator, with double porcelain petti-
coats and an oak thread between iron pin and porcelain, there
are present the conditions of several condensers in series which
might give rise to a lack of uniformity in the distribution of
e.m.f. between line wire and iron pin and cause the charring of
the wood at the base of the insulator.
Mr. C. E. Skinner: — I understand that the pins used on one
transmission line were selected with the utmost care, and were
most carefully treated, and that they have had practically no
trouble whatever in more than a year's run with a potential of
over 50,000 volts. These pins are protected from the weather
■ BURNING OF PINS. 57
by glass sleeves. We should keep in mind that this is in a
different climate from many other installations, and that a cure
for these troubles in one climate may not be a cure in other
climates.
Mr. W. N. Smith: — In the matter of wood and iron pins, it
seems to me that along with various other elements the question
of cost will govern. Iron poles in this country at this time cost
anywhere from $30 up, and a wooden pole of suitable size runs
from perhaps $7 to $20, according to size and where it can be
obtained. The size of cross-arms may be governed to some
extent by the size selected for the butt of the pin. If you deter-
mine first on the size of the shank of the pin that enters into the
cross-arm, that in a measure determines the thickness of the
cross-arm, if of wood and larger than usual. That may mean
quite an additional percentage to the number of feet of lumber to
be bought to provide cross-arms for a long pole line. Lumber is
higher than it used to be, so that there are considerations, com-
mercial as well as techincal, that these various elements of design
all enter into. The cost of selecting some particular pin because
it looks a little better may thus run into some thousands of
dollars on a long pole line.
Vice-President Sheldon: — ^We will now give Mr. Chesney
an opportunity to close the discussion on his paper.
Mr. Chesney: — I was particularly interested in Mr. Buck's
information concerning the cause of the " digesting " of the pin.
This has bothered me on a number of transmission lines. I
attributed this trouble to the formation of ozone. If it is due
to the formation of nitric acid, I am glad to know it. As far
as I know, on the particular line on which the Locke iron pins
with wooden threads were used, the burning was not serious.
The thread was punctured at one point but was in no other way
injured. In order to relieve the mechanical strain between the
iron pin and the insulator, I think it is quite possible to use a lead
thread. Litharge and glycerine have been used to some extent in
this country to cement iron pins in porcelain insulators, but
lately Portland cement has been used with quite as good results.
I understand that one of the largest new transmission lines in
Mexico is to be built with iron pins and porcelain insulators.
The pins will be cemented in the insulators with Portland cement.
Instead of iron poles, iron towers will be used, placed 400 or 500
feet apart.
58 HIGH-TENSION TRANSMISSION.
A Note on Line Insi-lation for High Voltage.
[communicated by M. H. GERRY, JR.]
The maximum practicable limit of pressure on transmission
lines has been frequently stated as fixed at a certain voltage, but
this limit has as frequently been extended, with good results.
At the present time, no considerable difficulty should be experi-
enced with 100,000 volts, and there is no good reason to fix the
limit at that figure.
The problems of insulation are becoming better understood, but
there is still much to learn. The capacity/ and the surface effects
of line insulators have received but little attention from engineers
and many of the failures are due to this fact. The form of the
insulator and the material have not, in general, received the
proper treatment. A desirable insulator for high-tension is not
merely a piece of glass or porcelain arranged to shed rain, and of
sufficient thickness to resist puncture.
The materials for construction of insulators are not so limited
as assumed in the past. Glass and porcelain have been used
almost exclusively, but from the experiments of the writer the
material of greatest promise for high-tension insulators is pre-
pared paper. Organic material, such as paper, has great advan-
tage and is well suited for this purpose. Compound insulators
in which the petticoats and water-sheds are made of metal, and
the core of glass, porcelain, paper or other insulating material, are
also feasible.
For moderate tensions, up to perhaps 30,000 volts, insulators
having metal tops and outer petticoats are not only perfectly
feasible, but are very desirable, and can be made very strong and
practically indestructible, and rauch superior to the common
glass or porcelain types now in use. For high voltages, the entire
insulator can be made of prepared paper, or of a combination of
paper with glass, porcelain or other insulating materials. Insu-
lators on these lines may be designed for almost any desired
pressure obtainable with commercial transformers, provided that
all the conditions are properly understood in advance.
The writer has tested and experimented with nearly every
type of insulator manufactured and with many special forms and
constructions, and his conclusions, as stated above, are based on
this experience, coupled with that gained from the practical
operation of the highest voltage transmission in commercial
service to-day.
[Communication after Adjournment by W. N. Smith.]
An important matter that has not been touched upon in this
discussion is the design of the pole-top pin, which, on a single
three-phase transmission line, is of equal importance with the
cross-arm pins. As in other details of line construction a variety
DISCUSSION. 59
of methods has been followed, of which some are doubtless better
than others as regards their mechanical features. In the con-
struction that has come under my observation, either the top of
the pole has a hole bored vertically to receive a bolt or the shank
of a wooden pin, or else a so-called " ridge iron " has been lag-
bolted to the pole top, with the usual wood or porcelain fittings
for carrying the insulator. Sometimes an ordinary oak bracket
is framed into the top of the pole, the roof of which is shaped to
accommodate it.
Without entering into a discussion of the relative merits of
these or other methods, it seems to me that there is enough
difference between all the methods in vogue to warrant an
attempt at standardization. This subject would, therefore,
seem to be a proper one for the careful consideration of the
Committee on High-Tension Transmission.
[Communication after Adjournment by J. R. Armstrong.]
Relative to the discussion on " Insulator Pins for High-Tension
Transmission Lines," the iron pin seemed to be spoken of favor-
ably by a great many present, but to me this iron pin has one
great disadvantage (leaving the difference of coefficients of
expansion of glass and iron out of the question) — nearly every
pin has a burr on the end, due to the way in which the ordinary
pin is manufactured.
Now, there is a tendency to a continual discharge between the
line and this burr or sharp point on the other end of the pin.
This, after a time, cuts through the glazed finish of the insulator,
and consequently causes the breaking down of the insulator.
Also in the same discussion, one of the objections raised to the
use of wooden pins was that of the corroding at the ends and
sides.
I would just like to raise the question: if nitric acid is formed
as was suggested, could not some base be used, which would form
a neutral salt with nitric acid, the pin being treated in some way
with this base.
[Communication after Adjournment by F. S. Woodward.]
During the discussion relative to the breaking down of insu-
lators and the burning of high-tension insulator pins, one possible
cause of the trouble was not stated. It may sometimes be due
to the method of fastening the tie-wire to the insulator. In
many cases I have known linemen in making what is known as
a pigtail tie, after the wire was finally twisted, to bend down the
end of this pigtail so that it came in contact with the surface of
the insulator at a point near the lower rim ; the distance between
the edge of the rim on the insulator and the end of the tie, depend-
ing, of course, upon the tie's length. This would reduce the
amount of creepage surface between the pin and the tie-wire,
which partakes of the line potential. In this connection it might
be well to state that in some eases spun-yarn, thoroughly satu-
rated in tar or asphalt or in P. & B. paint, makes a. good sub-
stitute for tie-wire, the coating practically protecting the spun-
80 HIGH-TENSION TRANSMISSION.
yam against weather effects. It might not, however, be service-
able upon a line under the conditions of voltage as described by-
Mr. Buck, where the surface of the line wire and of the ties
showed signs of reaction due to the formation of nitric acid,
which would probably affect the vegetable fibre of the spun yarn
in the manner indicated in the case of the thread of the insulator
pin. I regret that Mr. Buck did not state the size of the iron wire
used on their experimental 75,000 volt line. I recall the paper
published in the Trans action s on the ' ' Dielectric Strength of Air , ' '
by Mr. Chas. P. Steinmetz, in which he gave an account of a
number of experiments on the sparking distance between sharp
points, between spheres of various sizes and cylinders of various
sizes. The lower portions of the curves, as I recall, departed
more and more from the straight line effect as the voltage was
reduced and radius increased. It would be interesting, in this
connection, to follow out these experiments and see whether a
change in the diameter of the wire (practically being a con-
tinuous cylinder) would stop sparking or brush discharge at the
desired voltage. For instance, if the wire in Mr. Buck's experi-
ment was a No. 8 and the wire in the second experiment was a
No. 1 or a No. 2, if the increased radius would so modify the
curve that the brush discharge and the probable formation of
nitrogen would be prevented.
As a sequel to the discussion on pins and insulators, it would
be a very desirable thing to take up and standardize the cross-
arm to which these pins are attached. Also that the distance
between wires and the most desirable method of spacing same
should be outlined in the report of the Transmission Committee.
Communication after Adjournment by Henry Floy.
Fearing that the remarks of some of the speakers may have left
an erroneous impression as to the potential of telephone circuits
carried on the poles of high-tension transmission lines, I desire to
state that some measurements made by a Weston voltmeter
between the conductors of a telephone circuit placed five feet
below the conductors of a 25,000 volt overhead circuit and ground,
showed the potential to be only from 140 to 160 volts. Similar
measurements on a telephone circuit three feet below a 10,000
volt line showed only about 95 volts to ground and, naturally,
no difference of potential between the telephone conductors. It
seems to me that the voltage of a telephone circuit given as
20,000 by Mr. Thomas cannot be such potential as would be indi-
cated by a voltmeter or such as would cause particular damage,
being, I assume, simply static potential.
Referring to the suggestions made as to signaling in case of
partial breakdown of the telephone system, it has occurred to me
that as a relay to the telephone circuit, a system of wireless
telegraphy could be installed without large expense, which might
advantageously be used in transmitting signals in case of trouble
witli the telephone circuit.
DISCUSSION. Gl
Discussion at Minneapolis, Minn., April 3, 1903.
The Minnesota Branch held its 11th regular meeting Friday,
April 3d, at the Electrical Building at the State University. Six
members and 13 visitors attended.
The meeting was devoted to the four papers of the Transmission
Committee. The papers were read, and produced considerable
discussion. Prof. D. C. Jackson, of Wisconsin State University,
and Dean F. S. Jones, of the Engineering Department of Min-
nesota State University, were present. The opinion of the mem-
bers regarding the papers and new ideas brought forth were :
1st. That the proposed standardization of pins and pole con-
struction must consider not only the transmission voltage, but
particularly such local conditions as mist and dampness at inland
lakes and from the ocean, of salt storms, the amount of lightning,
etc.
2d. Regarding wooden pins, that trouble from same must be
expected in time, say after fifteen years' service, when the pins
have weakened mechanically. An iron pin would seem to be
more permanent.
3d. That wooden pins should not have a shoulder just above
the cross-arm. The use of a shoulder produces additional me-
chanical strains in the pin at the cross-arm or shoulder not con-
sidered in the formula or theoretical basis given by Mr. Mershon.
The shoulder was considered a relic from telephone lines and not
necessary or advisable where there are heavy mechanical strains.
4th. That in service, the great majority of the insulator failures
were mechanical and were due to strains produced by a poor fit
between the pin and the insulator. Manufacturers of porcelain
and glass insulators in the States produced excellent insulation,
but the threads were not of uniform size in each and every insu-
lator, as in those made by foreign manufacturers. The best work-
manship is also desired in cutting the iron or wooden threads of the
pin.
5th. That transmission lines as a whole — the pole, arm, pins,
insulators and power circuits — have many weak links, in a long
line. It is advisable where there are two or more companies,
possibly competing for the power business of a city, to have con-
necting circuits and even to operate their lines in parallel. A
somewhat similar arrangement is common among steam railways.
A competing road gives the use of its tracks to a rival during tem-
porary trouble to roadbed or at a burned-out bridge. A working
arrangement of this nature, i.e., to assist each other as far as
possible in times of trouble, would help the reputation of power
transmissions,
62 HIGH-TENSION TRANSMISSION.
Discussion at Schenectady, April 7, 1903.
Dr. F. a. C. Perrine : — There is so much in these papers, that
it is hard to enter upon a discussion of them. In regard to the
paper by Mr. Mershon, I believe that there is one element in the
strength of the pin which he has altogether neglected, which how-
ever, may possibly be neglected on account of the roofing or
rounding of the cross-arm. I refer to the element of strength in
the shoulder. The pin is discussed as a beam fixed at one end,
and in consequence the ordinary parabolic section of the beam is
brought out, because the fibers of the pin are considered to be in
tension or compression. Now, as a matter of fact, if the shoulder
is made pronounced and firmly fixed on the cross-arm, the pin is
very much increased in strength ; because there is an element of
the stress applied to the end of the pin, which is transmitted
parallel to the side of the pin and against the cross-arm.
Mr. Mershon says that usually pins break off at the shank.
This is generally the case where pins do not bear on their shoulder
in the cross-arm. In some experiments made in the West with a
number of pins, I found that if the pins were given a proper
shoulder and made to bear in the cross-arm, they did not
break at the shank, but broke diagonally from a point about at
the end of the thread crossmg the pin. The pins that were tested
were approximately the same locust pins that were mentioned in
the discussion. By giving these pins a proper bearing, the
strength was found to be increased from 700 lbs. to 900 or 1,200
lbs., with approximately the same pin.
I notice that the pins designed by Mr. Mershon correspond very
closely to the pin in Fig. 1 in Mr. Chesney's paper. Furthermore,
1 see that the pin in Fig. 1 in Mr. Chesney's paper is not given a
bearing in the cross-arm, as the shoulder is filleted so that it does
not come down to a solid bearing. The other pin in Fig. 2 is
given a solid bearing, and this pin is very much stouter than the
pin in Mr. Mershon's paper or the pin in Fig. 1. As you will no-
tice, these pins are both for the same insulator. The pin in Fig. 1
is the pin used on the Standard Company's lines and in Fig. 2 the
pin used on the Bay Counties lines. Mr. Hancock of the Bay
Counties Company designed this pin after testing a number of
pins and insulators. He found that the pin in Fig. 1 would
almost invariably break before the insulator; that the pin in Fig.
2 would practically never break before the insulator, this pin
havin, practically the same strength as the insulator. The ma-
terial is eucalyptus. Since the discussion, Mr. Hancock has
reported that the strength of this eucalyptus pin compared with a
steel wagon-axle. The axle was broken at a strain that would not
break the insulator, although the wood pin was of approximately
the same strength as the insulator.
The observation made in the discussion that Mr. Mershon's
pin is based on a uniform stress applied to the insulator, and that
DISCUSSION. 63
this is not a reasonable specification for the standard pin, is a
point that is very well taken. With lines such as are proposed
now, with spans of five or six hundred feet, the transverse stress
on a wire from one-half to three-quarters of an inch in diameter,
will be in excess of 600 lbs. With oak or locust, as specified by
Mr. Mershon, the pin will not have a strength much in excess of
600 lbs. With ecualyptus, it would have a greater strength,
eucalyptus having approximately the strength of good hickory.
In such spans of five or six hundred feet it would be necessary to
install more than one of Mr. Mershon's pins to stand the strain
from heavy cables.
In regard to the testing of glass insulators, so far as I am
aware, having had experience with a good many thousands of
glass insulators, the puncture of glass insulators by reason of
breakage after the insulator had been inspected visually and
tapped with a mallet, is very unimportant. The point that Mr.
Blackwell makes of glass insulators breaking down, due to lack
of annealing is, on the contrary, an exceedingly important one.
One of the lines in California installed a type of glass insulator
that had been well tried, but apparently it received a batch of
unannealed insulators, for before the end of the year a large num-
ber of their insulators separated and broke down; the head
of the insulator cracked off and let the wires drop. Such occur-
rences with glass insulators, are far more important and more
likely to happen than punctures. A glass that will puncture at
all, I believe to be a glass that is so bad that you could see the
defects. No insulator should be installed which has a bubble
between the wire and the pin, because these bubbles are vacuums ,
and you might as well have just so much metal in the insulator.
Mr. Lincoln's paper, is I think, the first approaching a complete
discussion of the telephone line transposition problem, and it is so
complete that I cannot sit down without commending it, without
saying that in my belief it contains the elements of the entire
solution of this very important and difficult problem. Had this
paper been printed four years ago, I believe that I know of more
than one man's life that would have been saved by it. A very
sad accident happened about a year ago : A patrolman starting
•out to work, went to the closed telephone box to report. In con-
necting this telephone to the line, he was killed. I believe the
power line was grounded, but not to the telephone line. Since
that, the company has observed the rule of seeing that the
operator is insulated as well as the line.
The question of potential to earth is the only thing that Mr.
Lincoln has not given an absolute statement of, and I am inclined
to think that that is because there is something in it that we don't
yet know. Mr. Lincoln writes of the difference of potential, but
says that that represents so small a current as to be inappreciable
If the surface of the condenser that is produced by the power fine
64 HIGH-TENSION TRANSMISSION.
and the telephone Hne and the condenser of the telephone line and
the earth is calculated, where the line is one or two hundred
miles long, the amount of current that is transmitted will not be
by any means inappreciable, and will be enough to give a great
deal of trcuble. This is the only criticism that I would have to
offer to this most excellent paper of Mr. Lincoln's.
DISCUSSION. 65
Discussion at Vittsburg, April 9, 1903.
Programme.
The meeting was called to order by Chairman P. M. Lincoln.
1. Introductory Remarks.— President C. F. Scott.
2. " Mechanical Specifications for Proposed Standard Insu-
lator Pin," by Ralph D. Mershon, read by W. K. Dunlap.
3. " The Testing of Insulators," by F. 0. Blackwell, read by
C. E. Skinner.
4. " Transposition and Relative Location of Power and
Telephone Wires, by P. M. Lincoln.
5. " Burning of Wooden Pins on High-Tension Transmission
Lines," by C. C. Chesney, read by E. M. Tingley.
The discussion was participated in by C. E. Skinner, S. P.
Grace, P. M. Lincoln, H. Etheridge, C. W. Rice, Mr. Bedell, P. H.
Thomas, B. Frankenfield, J. S. Peck and President C. F. Scott.
Mr. Skinner: — I have always been under the impression that
for glass insulators a potash glass would give better results than a
lead glass. This impression has not been thoroughly proved by
test. Mr. Blackwell says that the striking distance of a given
e.m.f. is greater at high altitudes than at low altitudes. If the
striking distance is to be used by the Institute as a measure of
the e.m.f., some figures should be obtained showing the variation
of striking distances with the variation in the height of the
baromet3r.
In early high-tension work the question of surface leakage over
the insulator was considered of very great importance, and many
of the earlier designs of insulators included an oil cup underneath
to give a higher surface resistance. As far as I am aware, this
construction has not been used on any of the long-distance trans-
mission lines in the United States, and later practice has proved
that such a device is entirely unnecessary. It is objectionable
because it is soon filled with foreign substances and defeats the
object for which it was designed.
The method of regulating the voltage of the testing trans-
former should receive consideration. There are three methods
which have been followed, viz: first, by varying the field of the
generator; secondly, by the use of a resistance in series with the
low-tension side of the testing transformer; thirdly, by varying
the voltage on the low-tension side of the transformer by means
of a regulator dial connected to a suitable regulating transformer
with a number of taps brought out from its secondary winding.
The first method can be used only where a generator is provided
exclusively for this work. In the second method a water rheo-
stat is usually employed. This gives a very smooth variation in
e.m.f., and while unwieldly and requiring constant attention
during the test, it is capable of giving very good result's.. The
third method requires that the voltage on the high-tensiori'side
be changed by comparatively small steps, which may be done
with proper regulating dials without opening the circuit. Steps
CG
IIIGII-TENSION TEA NSMISSION.
even as great as 5 per cent, are not considered particularly harm-
ful in the testing of insulators.
I am pleased to be able to show you an exhibit of insulators
intended for high-tension work. This exhibit is not complete
by any means, but shows a number of types which are in use at
the present time. Most of these insulators have been given a test
which may be briefly described as follows: the insulators were
placed on the standard-size pin, the pin being wrapped with tin-
foil. A photograph of the insulators (Fig. 1) as they appeared
on the testing rack after a snow storm is submitted as part of this
discussion. The test was made by applying the high potential
from a testing transformer, the voltage of which was regulated by
means of a regulator dial giving very small steps. The testing
voltage was applied between a " tie " made in the ordinary
manner and the tin-foil coating of the pin and the test was made
under different weather conditions. The breakdown test was
repeated at intervals for a period of some months, beginning about
the middle of February and ending about the first of July.
In no instance did a breakdown occur through the insulator
DISCUSSION.
67
itself, the break in every case being over the surface. The maxi-
mum testing voltage available was approximately 90,000 volts.
In some instances, when the insulator was dry, no breakdown
over the surface could be obtained. The following are the results
of tests on certain characteristic insulators, as shown in the accom-
panying photographs. (Fig. 2 and Fig. 3).
No. 1 — Porcelain, brown glaze:
Diameter at base 10"
Height 8f
Surface distance from wire to pin 22|"
Shortest breaking distance 12"
When dry and clean, stood 91,000 volts.
During heavy, dry-snow storm, stood 90,000 "
During moderate rain storm, broke down at . . . .86,400 "
When covered with ice and snow, broke down at. 52, 200 "
When dry, stood for ^ hr 71,500 "
Fig. 1.
During the last test the snow was piled on the cross-arm almost
to the lower petticoat.
No. 2 — Porcelain, brown glaze:
Diameter at base 7^'
Height 6|"
Surface distance from wire to pin 13^'
Shortest breaking distance 9f "
When dry and clean, stood 92,000 volts.
During dry-snow storm, broke down at 87,300
Covered with wet snow, broke down at 62,100
During moderate rain storm, broke down at . . . .68,400
When dry, stood for ^ hour 66,000
No. 3 — Porcelain, brown glaze:
Diameter at base 6f*
Height W
Surface distance from wire to pin 13"
Shortest breaking distance 7^*
68
HIGH-TENSION TRANSMISSION.
When dry and clean, stood 91,000 volts.
During dry-snow storm, broke down at 78,750
During moderate rain storm, broke down at . . . .48,600
Covered with wet snow, broke down at 54,000
When dry, stood for i hour 64,400 "
No. 4 — Porcelain, browu glaze:
Diameter at base
Height
Surface distance from wire to pin
Shortest breaking distance
6*"
4|"
8"
61"
When dry and clean, broke down at 73,800 volts.
During dry-snow storm, broke down at 78,7.')0
During moderate rain storm, broke down at . . . .53,400
Wlien coveied witli wet snow, broke down at . . .52,350
When drv, stood for i hour 55,000 "
Big. 2.
No. 5 — Porcelain, white glaze:
Diameter at base 6"
Height 4"
Surface distance from wire to pin 11-J"
Shortest breaking distance 6|"
When dry and clean, broke down at 74,700 volts.
During dry-snow storm, broke down at 70,200 "
During moderate rain storm, broke down at . . . .70,400
When covered with wet snow, broke down at . . .42,800 "
When dry, stood for \ hour 52,500 "
No. 7 — Glass:
Diameter at base 7"
Height . 6"
Surface distance from wire to pin 15^"
Shortest breaking distance 7^"
DISCUSSION.
69
When dry and clean, broke down at 74,700 volts
During dry-snow storm, broke down at 73,800 "
During moderate rain storm, broke down at 52,800 "
When covered with wet snow, broke down at . . .51,100 "
When dry, stood for ^ hour 55,000 "
No.S— Glass:
Diameter at base 7^"
Height , Sy
Surface distance from wire to pin 12"
Shortest breaking distance 7|"
When dry and clean, stood . 91,800 volts.
During dry-snow storm, broke down at 87,300 "
During moderate rain storm, broke down at . . . .62,700 "
When covered with wet snow, broke down at . . . 58,800 "
When dry, stood for | hour 63,000 "
Fig. 3.
After the insulators had been up for some months and were
well coated with dirt and soot they were given a time test on a dry
day. The time test was made by applying f of the maximum
test voltage for J hour. The figures are given under the last
heading in each set of tests. All the insulators stood this test
without any evidence of trouble, except a considerable static
discharge over some of those with the thinner sections.
I think that the burning of pins is caused in many cases by the
static discharges which appear at the wire and at the pin. If the
material can be made thick enough, so that these discharges will
not appear, the burning of the pins will probably be decreased to
a very considerable extent. I think the final solution of the pin-
burning question would be to discard the wooden pin altogether
and substitute a metal pin properly cushioned to take undue
local strains off the insulator itself.
Mr. Grace called attention to the trouble whicli the telephone
ompanies have had from electrostatic effects. As fast as one
difficulty has been overcome another is encountered, to overcome
which new methods must be devised.
The system of transposing wires in order to overcome the indue-
70 HIGH-TENSION TRANSMISSION.
tive effects of one circuit upon another was devised by the tele-
phone engineers and first used on the long-distance circuit be-
tween New York and Philadelphia.
The necessity of keeping telephone circuits in absolute balance
was mentioned and a number of instances were given where an
extremely small amount of unbalancing was sufficient to produce
serious disturbances.
Mr. Grace said that Mr. Lincoln's paper treated only of tele-
phone circuits upon the same poles with the power circuit,
whereas in commercial telephone service there were many thou-
sands of circuits and it is manifestly impossible to insulate them
to so high a degree as where there is but a single telephone circuit.
He thought that representatives from the telegraph, tele-
phone, and power-transmission companies should convene and
devise suitable means for crossing the different lines where it is
necessary.
Mr. Frankenfield commented on the effect of grounding the
neutral point of a transmission system. He also commented on
the burning of insulator pins.
Mr. Bedell recounted his experiences while testing insulators.
His general conclusions were that the question of dielectric
strength of glass and porcelain had been satisfactorily settled, as
insulators almost never broke through the dielectric but over the
surface.
Mr. Lincoln: — One interesting statement made by Mr.
Grace was that the arc circuits of the " tub system," so-called,
is one of the hardest things the telephone people have to con-
tend with. This sustains one of the arguments made in my
discussion — that the static induction gives more trouble than the
electromagnetic. The conductor in such an arc system is apt to
be at a considerable difference of potential- from the earth, and
usually in the arc circuit the equal and opposite potential is not
present to neutralize its effect as is the case with a statically
balanced transmission line. I should imagine the arc circuit
would be harder to contend with, though its potential is not so
high as that of the usual accompanying transmission line. I
should like to have Mr. Grace explain what he calls a retardation
coil.
Mr. Grace : — It is an electric choke-coil and we speak of it as
a retardation coil.
Mr. Etheridge: — I wish to refer particularly to the necessity
of studying every detail of a transmission line, with the view of
applying the latest and best possible forms of construction to
insure the stability of the medium between the step-up and the
distant step-down transformer.
Estimates are carefully prepared and the best engineering skill
applied to the erection of central plants and substations, but the
transmission line, which is subjected to the worst possible me-
chanical and electrical strains and conditions, is, generally speak-
ing, the least considered and provided for.
DISCUSSION. 71
The building of a transmission line is purely a mechanical prob-
lem, and must receive as much care and skill as the remainder of
the system, if stability of action — which is the keynote of engin-
eering success — is to characterize its operation.
The average transmission line suffers from comparison with the
midern power house and substation equipment, and as the sys-
tem is strongest only at its weakest point greater care and skil:
must be applied to that part of the system which is found outsidr
the buildings, where the most adverse mechanical and electrical
conditions are encountered.
Our worst experience in the operation of transmission lines has
been due to mechanical weakness of some of the details of the
line; particularly wooden pins and faulty mechanical design of
some of the insulators. The angles and guys have also given us
trouble on account of their inadequacy for the heavy strains put
upon them. I can safely say that electrical troubles of our line
have been entirely absent. To overcome the mechanical trou-
bles of pins and insulators, we were compelled to design and
adopt a form of pin and insulator a sample of which you will find
on exhibition here this evening, and in which the greatest
mechanical strength and other features are embodied.
Having solved the question of weak pins and insulators, we
next turned our attention to the angles of our line and to proper
guying with the result of developing a rigid and successful form
of construction. In these angles we have adopted poles of 13"
and 14" tops, 4" X 5" double oak cross-arms with f " ring bolts and
washers. The braces are f'Xl^" and 30" long, bolted with
i"Xf" bolts and washers in cross-arms and through the poles,
respectively. The cross-arms are bolted together with f" bolts
and washers with the usual making-up piece between them. The
pin-holes in the cross-arms are 1^" diameter, thereby maintaining
the strength of the arm. Great care is also exercised in placing
the arms diagonally across the angle so as equally to distribute
the strain on each pin and insulator.
The " wet-rot " of our poles at the butt received our next atten-
tion, as it became evident to us that in seven to ten years our
entire pole line would have to be rebuilt ; a feat fraught with great
danger, expense, and interruption in our service, if it did not
threaten absolute shut-down.
I developed and adopted a remedy against this " wet-rot " of
our poles. This consisted in cementing about one-third of the pole
flush to and extending about 3" above the ground line, and then
placing a fillet of pitch, asphaltum, or some such moisture-proof
material to a depth of about 8" between the pole and cement of
the ground-line, so as to separate or seal the pole from contact
with the moisture in the earth at the ground-line. This, very
effectually prevents " wet-rot " of wooden poles and oxidation of
steel poles at the ground-line. The additional expense of pre-
paring and treating our poles in this manner is very trifling com-
pared with the great expense of replacing them.
72 HIGH-TENSION TRANSMISSION.
Mr. Scott has well said that " development of detail in elec-
trical machinery has made possible very reliable forms of appar-
atus," and the same reasoning and skill must be applied to our
transmission line before the ideal electrical transmission will be
attained.
At the request of Mr. Lincoln I will explain the features of the
pin and insulator which it was my pleasure to develop. It con-
sists of a malleable iron tube 1^" outside diameter and 1 J" inside
diameter. On the outside of this tube-pin is cast a shoulder on
which it rests when placed in the cross-arm. To lock this tube-
pin to the cross-arm a flat high-carbon steel spring — on each end
of which if formed a gib — is driven through the pin until the
bottom end springs out over the bottom end of the pin and cross-
arm.
The insulator, which has a plain hole to receive the pin, and a
recess at the bottom of the hole to receive the top gib of the
spring, is then forced down over the pin until the top gib springs
out into the recess in the insulator. This combination very
securely locks the insulator to the pin and the pin to the cross-
arm; to unlock, place a screw-driver between the lower gib and
the pin, force the gib back and drive the spring out through the
pin again.
The features of this form of pin and. insulator are :
(1) Simplicity and durability.
(2) The presenting of a plain surface, so as equally to distribute
the wire pressure between the contact or bearing surface of the
pin and insulator.
(3) Secure locking to the cross-arm and ease of removal there-
from.
(4) Freedom of insulator to turn in either direction on pin and
act as a sheave to the wire when used in angles.
(5) Looseness of the insulator on the pin, avoiding the break-
ing of insulators from expansion or contraction.
(6) Locking the insulator to the pin and cross-arm, yet pre-
serving looseness and freedom on the pin.
(7) The placing of the wire groove in insulator so as to relieve
the insulator from any wire leverage and any stress other than one
tending to crush the glass or porcelain, etc.
Our telephone system is erected on the same poles and is
bracketed about 5 feet below the lower cross-arm. These lines
are absolutely quiet, the electromagnetic and electrostatic
influence being overcome by using twisted pairs of wires.
(For illustrations of pins described by Mr. Etheridge, see New
York Discussion, pages 26 to 57.)
Mr. Thomas: — As Mr. Etheridge has said, the greatest practi-
cal difficulty in the operation of high-tension transmission lines
arises from mechanical defects rather than electrical ones.
Broken pins, broken cross-arms, broken insulators and injuries
to the line from external causes vastly outnumber the electrical
failures. As is easily seen, the pin is the weakest mechanical link
DISCUSSION. 73
jf the system and when of wood of good insulating quality it is
liable to be weak. I wish to call your attention to a plant install-
ing at Mexico, which marks an improvement in pole-line con-
struction from a mechanical point of view. Five hundred foot
spans are used, which is approximately five times the length of
span usually employed elsewhere, and instead of the usual
wooden poles there are built-up steel towers. The cross-arms
and pins, I understand, are of steel, the insulators of porcelain.
This construction if well designed assures excellent mechanical
qualities, and should be watched with great interest. On account
of the small number of poles a much larger pin can be economi-
cally used for each one.
Ground wires, such as Mr. Lincoln has recommended -for
protecting the telephone circuit on a transmission line, might be
used on telephone trunk lines, parallelling transmission lines,
close to the telephone line but between it and the power line. It
is probable that a very great reduction of the static induction
from the high-tension would be obtained by the use of even a few
grounded wires as a screen. I make this suggestion to Mr. Grace.
The question of lightning arresters for telephones, and the fact
that they are- ordinarily adjusted to discharge at about 300 volts,
suggests the mention of a point in the operation on the telephone
lines and power circuits by which in some cases the service has
been very much improved. In a good many power transmission
systems where the standard telephone arrester is used on the
telephone circuit, it has been found that there is at almost all
times a sufficient unbalance of the high-tension voltage so that a
frequent discharge to ground occurs over these arresters, the
result being a leaky line and more or less continuous rattle of the
telephone. The construction of an air gap in place of the light-
ning arrester very much reduces the number of such dischai;ges to
ground and entirely prevents the high resistance leak which
usually occurs in a telephone arrester. The result is a great im-
provement in the speech.
Some of the telphone engineers here have referred to the prob-
lem of making satisfactory cross-overs between two lines. From
their point rf view the transmission line is a telephone line. The
problem is broader, however, and should include the crossing of
two high-tension lines. The National Board of Fire Under-
writers has recently adopted recommendations as to methods of
such cross-overs. They suggest three methods, but preference
is expressed for crossing by means of a pole common to the two
lines. This pole should, of course, have extra strength and extra
height, the highest tension line being carried at the top. Extra
long cross-arms are used and the difference in the height of the
poles of the upper and lower lines will ordinarily prevent any-
thing which falls from the upper wire to the ground from touch-
ing the lower wires. To prevent a wire breaking at the farther
end of one of the adjacent spans of the higher line from falling
against the lower line, a guard wire mounted on the line, prefer-
74 HIGH-TENSION TRANSMISSION.
ably insulated, should be installed outside of the extreme wire of
the lower line.
A wooden pin is burned by leakage current because either its
resistance is too high to transmit the current without excessive
heating, or because its insulation is too low to prevent the leakage.
In most cases either a better or a worse pin would not be injured.
A comparatively few per cent, improvement of the pin would in
many cases be sufficient to prevent destructive heating. There-
fore, the method used by Mr. Gerry for protecting the pin which
has been put in first-class condition, from moisture and dirt, by
means of a sleeve, is an excellent one, since it will certainly give a
considerable protection to the pin and render it oftentimes safe
where an unprotected pin will conduct enough to become charred.
Mr. Gerry's freedom from trouble from burned pin referred to by
Mr. Skinner is probably due to the fact that his pins are protected
by glass sleeves, but also it must be admitted that his line is yet
young and the climatic conditions are not severe. San Francisco
is probably one of the hardest places in the country on pins and I
think no wooden pins would be able to stand indefinitely there
without burning.
Since the difficulty of operating a telephone line on an unbal-
anced high-tension power line results from the tendency for a
high-potential to ground — equally on both telephone wires,
provided the telephone line be transposed — it may be possible to
solve the difficulty by insulating the telephone line highly and
allowing it to assume its neutral potential, and transmitting the
speech through a raising and lowering transformer at either end.
The low-tension windings of these transformers may then be
grounded, and with good insulation between the high and low-
tension windings the operation may be made very secure.
I would like to ask Mr. Grace whether it is feasible to use such a
transformer for transmitting telephonic speech.
The same sort of result might be attained by the use of con-
densers, two in series with middle grounded, connected between
the wires of the insulated telephone line, the telephone receiver
or transmitter being connected between the ground plates of the
two condensers. For this purpose it would probably be necessary
to use a double winding, either on telephone-spool or choke-coil,
so that the charging current to the condensers would have its
effect on the telephone circuit neutralized.
Mr. Grace : — The use of the transformer, as suggested by Mr.
Thomas, is feasible.
Mr. Peck:; — In his paper on the testing of insulators, Mr.
Blackwell says: " There should be but one transformer used to
step up to the highest potential required and its reactance should
be as low as possible. A number of transformers in series is
particularly bad, as it gives poor regulation and leads to great
uncertainty as to the actual potential to which an insulator is
being subjected."
In the discussion at New York, Mr. Mershon called attention to
DISCUSSION.
75
the advantages obtained by the use of a number of transformers
in series for obtaining a high voltage, saying that it was possible
to obtain such a series having a good regulation ; and great point
in its favor was that in case of accident to one transformer of a
series, the remaining transformers could be used to deliver a some
what lower potential.
There is an idea more or less generally prevalent that it is
possible to obtain without danger a high voltage by connecting in
series a number of transformers wound and insulated for a low
voltage, as long as cases are insulated from each other and from
the ground. Fig. 1 shows such an arrangement, where three
10,000 volt transformers are connected with high-tension winding
in series for giving 30,000 volts.
It will be at once seen that there is a strain of 30,000 volts at
the two points (A) and (B). The normal strain for one trans-
former is 10,000 volts, so that the outside transformers of the
series are subjected to three times normal voltage strain be-
r
Low Voltage
Ivwwww kvwwwwwJ kwwwwA
10,000 V.' ' 10,000 V. ' '10,000 V,
-aOjOOO-Vr-
Fig. 1.
tween primary and secondary windings. If there were ten
10,000 volt transformers connected in series for 100,000 volts, the
strain across the outer transformers of the series would be 100,000
volts, ten times normal.
In the operation of a number of transformers in series for ob-
taining a high voltage, there are much more severe internal
strains introduced than where the transformers are used for a
low voltage. This strain occurs between turns and layers and
comes principally on the outside coils of the outside transformers
of the series. In designing transformers for connecting in series
it is therefore necessary to insulate each transformer not only
between high-tension and low-tension windings, but between
turns and layers of each winding, in the same manner that would
be required were the transformers to furnish alone the full voltage
of the series.
On account of the large amount of insulating material de-
manded between high-tension and low-tension windings, it is
76 HIGH-TENSION TRANSMISSION.
extremely difficult to make these transformers with good regula-
tion on inductive loads.
The cost of small transformers for very high- voltage work is,
within certain limits, almost independent of the capacity; so the
difference in cost between one transformer of the series and a
single transformer wound for the total capacity would be very
small.
It is true that the outer transformers of a series may be more
lieavily insulated than the others, making a reduction in cost on
the inside transformers, but this affects the interchangeability
of the transformers and the extra cost of manufacturing trans-
formers which differ slightly from each other will probably more
than counterbalance the saving in insulation.
The question of a spare unit is undoubtedly of importance, but
I believe that in general it will be cheaper to purchase two trans-
formers, each wound for the full testing voltage, than to buy a
large number of transformers which are to be connected in series
for giving the desired voltage. Where two transformers, each
wound for the. full testing voltage, are purchased, one will of
course be held as a spare and may be used as a voltmeter trans-
former for obtaining the exact voltage applied to the apparatus
on test.
When a number of transformers are in series, the voltage
measured across the high-tension winding of one transformer will
not be an accurate indication of the total voltage on the series.
Mr. Rice called attention to the importance of uninterrupted
service and to time tests on insulators. He predicted that the
highest transmission voltage would very soon be generated
directly by the dynamos, without the use of raising transformers.
He also thought that the shoulder on the proposed pin was too
small as the side strain would cause the shoulder to cut into the
cross-arm, thus enlarging the hole so that the pin would finally
pull out.
Mr. Scott: — I recall my first experiments on the relation
between the telephone and a high voltage. In the laboratory a
telephone was connected in circuit between a high-tension ter-
minal and a short length of wire. It gave a vigorous sound which
was attributed to the flow of current to the wire acting as a con-
denser. The wire was disconnected and the telephone still
responded. The wire was then disconnected from the telephone
circuit and was connected to the insulated magnet. The tele-
phone still responded.
Some measurements upon the potential generated on an insu-
lated wire not far from a high-tension circuit which were made
by Mr. Tingley, who is here this evening, are reported in a paper
on High-Voltage Transr^ission presented before the Institute
by me in 1898. These experiments show that a single insulated
wire not far from a high-tension wire may have a potential suffi-
cient to cause a spark to jump over a> considerable gap to the
earth.
DISCUSSION. 77
I had an opportunity a few years ago to inspect the burning
of pins and cross-arms on a 10,000 volt transmission Hne on the
Pacific Coast, which ran for some distance close to the shore.
Large holes were burned in some of the cross-arms and poles.
The burning was particularly apt to occur at the ends of the iron
braces between the pole and the cross-arm. There was little
doubt but that particles of sea water as ' ' fog ' ' were carried by the
wind and deposited salt upon the poles and cross-arms. I under-
stand that this difficulty has been avoided by placing wooden
frames over the insulators on the ocean side.
Mr. I. Sternefeld of Mexico has called my attention to the
deterioration of copper wire due to the salt air from the ocean.
He says that he has found a satisfactory remedy in an insulated
coating consisting simply of cotton dipped in a solution of minium
and linseed oil.
It is notable that megohms, which used to be considered of
prime importance in the testing of electrical apparatus, has not
been mentioned in the discussion this evening. The problem in
line construction is primarily to prevent disruptive and disastrous
breakdown. It is not the ohms but the volts which are of first
importance.
The collection of insulators before us this evening, containing
some early forms as well as recent ones, small insulators as well as
big ones, indicates the evolution which has taken place in insu-
lator construction, both in materials and form during the last tea
years.
The insulator problem, as presented in the discussion this even-
ing, is at the present time primarily, a mechanical problem.
Electrically, it is partly one of materials and partly one of geom-
etry. There is an intimate relation between geometry and volt-
age in insulator design. There is also the commercial problem.
High-tension tests upon apparatus, particularly transformers,
is an important matter. The conditions prevailing at high volt-
ages are to my mind different from those at lower voltages. Low-
voltage apparatus may probably be tested at several times its
operating pressure. The margin between the normal pressure
and the test will be but a few thousand volts. If, however, trans-
formers for 40,000 or 50,000 volts be tested at double pressure the
margin is also 40,000 or 50,000 volts. The purpose of making a
test of this kind is to determine first whether the design is satis-
factory in giving sufficient surface distance and the like, and
second to detect flaws in material or in construction. A moment-
ary or short test is in general sufficient to determine these points.
The prolonged test may have a deleterious effect upon the insulat-
ing materials by weakening them. The test may result in a
breakdown due to conditions entirely abnormal to service. On
the other hand, although there may be no breakdown the ma-
terials may be left in a condition weaker than tney would have
been if the test had not been prolonged.
78 HIGH-TENSION TRANSMISSION.
Mr. Budd Frankenfield : — Speaking of the dependence of
transmission systems on the telephone in time of emergency,
recalls an incident that came under my observation on the coast.
It belongs in the category with the somewhat disastrous accidents
that sometimes occur when too great reliance is placed on auto-
matic devices.
A fire occurred in a city that received power from a long-
distance transmission system. The fire caused havoc in the
secondary network, and the substation attendant pulled all his
switches in the emergency, without first notifying the power
house. At the power house the governors happened to be off
duty and the impulse wheels took on speed. Instead of taking
recourse to the " Armstrong system " and shutting down the
plant as he might have done, the power station attendant ran to
his telephone booth to call up the substation.
He never got into communication ; for there was a crash which
brought him out of the booth to gaze in open-eyed wonder at the
roof above — ^the fly wheel had gone soaring heavenward and it
left a great hole in its wake. Here is an instance where it had
become so natural to use the telephone in every emergency that,
what is ordinarily a blessing, proved a source of danger. The
moral is to use " horse sense " even when surrounded by modern
conveniences.
In regard to the suggestion that the ground be brought near
the telephone line by means of an earthed conductor placed in
proximity, I would like to recall the fact that grounding the
neutral of a Y. connected transformer system has this effect, as
stated in the paper, that the telephone line tends to assume the
potential of the neutral point of the transmission system; and
the grounding of this point will virtually bring the telephone line
to the potential of the earth. It seems to me a method worthy
of careful consideration.
It has been suggested that by using an iron insulator pin burn-
ing would be avoided because of the low resistance of the pin;
and it has been urged in opposition, that the wooden pin has
some give to it and is less likely to break insulators. Why not
combine all the good qualities in one pin, a wooden pin with a
metallic coating? Cover it with foil, paint it with a metallic
paint, electroplate it if need be — do anything to make it a good
conductor. A study of the Redlands type of pin, which is said
to have shown deterioration only at the wooden thread and
which is said to have caused no burning of cross-arms, is an indi-
cation of the result to be expected with a metal-coated pin — no
burning at all.
A paper presented at the 20th Annual Convention of
the American Institute of Electrical Engineers,
Niagara Falls, New York, July 1, 1903.
METHODS OF BRINGING HIGH-TENSION CONDUCTORS
INTO BUILDINGS.
BY C. E. SKINNER.
One of the points in the design of high-tension transmission
lines which seems not to have received general attention is the
method of supporting and insulating the conductors which
connect the transmission circuit with the apparatus in the gen-
erating stations and substations. Each engineer follows the plan
which seems to him best for his particular set of conditions. In
some cases the line is brought through a hole in the wall; in others
through an elaborate system of tubes placed in the wall ; in others,
through a piece of insulating material of some kind set in the wall ;
in others, the line is entered through an elaborate tower built
for the purpose on the top of the building; in still others, it is
taken directly through the roof of the building.
It is manifestly impossible to prescribe any fixed method for
all voltages and all locations, as the requirements of each plant
are varied by the local conditions, but much would be gained if
the general requirements were outlined in such a way that
designers of btdldings and designers of plants could follow some
general and accepted scheme which is known to be satisfactory
for any given set of conditions. It is the purpose of this paper to
discuss the general requirements rather than to give specific
designs, although specific methods must necessarily be referred
to in this discussion.
The method to be followed will depend on the following con-
ditions:
(1) The voltage of the transmission circuit.
(2) The climate in which the plant is operated.
(3) The size of the high-tension conductor.
79
80 HIGH-TENSION TRANSMISSION.
(4) The kind and height of building used.
(5) The conditions of approach to the building and the location
of the apparatus in the building to which the high-tension line is
connected.
The requirements which must be met are:
(a) The Maintenance of Proper Insulation of the Circuit. — To
maintain proper insulation, it is necessary either to allow sufh-
cient open space about the wire to prevent any possibility of the
current striking across to the walls or surrounding material; or
some insulating medium, such as a tube, must be applied to the
wire to give the proper insulation.
(b) The Prevention of the Entrance of Rain, Snow, Cold Air and
Dust. — The entrance of moisture, snow, and dust, should be
prevented both on account of damage to the contents of the
building, and on account of the weakening of the insulation at
the point of entrance. In most climates it is necessary that all
openings be closed for at least a portion of the year.
(c) The Proper Mechanical Fastening of the Line Wire. — The
end-strain of the line must be taken up, and it is often con-
venient to combine the plans for taking up this strain with those
for entering the building. This is particularly true where the
transmission conductors are very large. It is also necessary to
hold the wire in a fixed position where it passes through the
opening into the building. This requires a more rigid line con-
struction than is necessary away from the building.
{d) Reliability and Simplicity of Construction. — It is self-
evident that the construction must be such that it will be
reliable under all circumstances. There are usually a sufficient
number of troubles on high-tension transmission lines due to
circumstances beyond the control of the engineer, without intro-
ducing any extra risk at the point where the wire enters the
building. Usually, as in most other work, the simplest form of
construction will be found the most reliable.
In general, wires are best brought through the walls of the
building. The simplest form of construction consists merely of
an opening in the wall sufficiently large to allow the proper air
insulation between the wire and the wall, this opening being
suitably protected from rain either by means of a large pipe set
in the wall, sloping outward, or by a sufficint extension of the
roof above, or both. The requirements of this form of construc-
tion are that the wire be a sufficient distance from the pipe, so
that there will be no possibility of striking across under any
HIGH-TENSION CONDUCTORS.
81
conditions. The pipe should always be considered as " ground,"
regardless of the construction of the building. The cross-arms
holding the wire inside and outside of the building should be
sufficiently near and so braced that the wire will remain central
in the pipe. This construction can be used to advantage only
in dry, warm climates.
Fig. 1.
In most climates provision must be made for keeping out rain,
snow, etc. With potentials-of 15,000 volts or lower a disc of glass
or other fireproof insulating material placed over the wire at the
inner end of the pipe will usually accomplish this purpose. In
this case the tube must be sufficiently large so that the surface in-
sulation over the insulating disc used will be ample to prevent
trouble under the worst conditions which may occur. When
there is any danger of condensation of moisture due to differences
82 HIGH-TENSION TRANSMISSION.
of temperature inside ana outside of the building, two discs a
little distance apart should be used. These discs may be cut so
as to be placed in the pipe itself, or they may be cushioned and
simply swung on the wire, lying against the ends of the pipe. The
surface insulation of the discs used should never be less than that,
of the line insulators, and as they will usually be less advantage-
ously placed than the insulators, extra distance should be al-
lowed, if possible.
With potentials above 15,000 volts, this form of construction
becomes unsuitable on account of the large size of opening
required to give the necessary insulation distance over the discs.
This may be true even with potentials below 15,000 volts under
very adverse conditions. For the higher voltages, a long insulat-
ing tube of small diameter and very heavy wall may be placed
over the wire and passed through a slab of insulation set in the
wall of the building, the whole being protected from driving rain
by an extension of the roof. The insulating tube should slope
outward in all cases. Some form of drip point should be pro-
vided on the wire just outside the end of the tube. The insula-
tion slab holding the tube should be large enough to prevent
actual breakdown even though the tube is broken. Both tube
and slab should be of fireproof material. This form of con-
struction has been successfully used for potentials as high as
50,000 to 60,000 volts. The chief difficulty is in securing the
proper insulating tubes. Glass and porcelain are electrically
the best materials for the purpose, but when these are used it
is usually necessary, on account of their lack of mechanical
strength, to take up the end strain outside of the building by
a suitably guyed pole.
The tower-construction may be necessary where the building
is low, and the line wires must be carried at a considerable ele-
vation in the immediate neighborhood of the building. It is
generally very cumbersome and unsightly, and the bringing of
the wires through the side of the tower presents the same problem
as bringing them through the side of the building.
The bringing of the wires directly through the roof of the
building, while possible, requires that extra precautions be
taken to secure sufficient insulation and to keep out all moisture.
This method, however well carried out, will probably constitute
a danger point in the system.
In general no combustible material should be used near the
line wire, even when separated from it by insulating material
HIGH-TENSION CONDUCTORS.
83
sufficient to withstand the strain. Leakage or brush discharge
is liable to cause burning sooner or later, and such burning is
more serious at the building than the burning of a pin or cross-
arm on the line.
The accompanying illustrations, Figs. 1 and 2, are intended to
show diagrammatically the two general plans recommended in this
paper. Both plans, practically as shown, are in successful use
Fig. 2.
by important transmission plants. It is expected that each
engineer will find it necessary to make changes in details to suit
his particular case, but it is believed that the plans proposed
may be made effective for any transmission circuit.
The method of bringing high-tension wires into buildings
should be carefully considered at the time the building is designed
and proper provision made. It often happens that this point
84 HIGH-TENSION TRANSMISSION.
IS given no consideration whatever, and the result is an unsightly
and unsuitable arrangement made after the completion of the
building and at an increased expense.
It is hoped that those having practical experience with the
design and construction of this particular feature of the trans-
mission line will take an active part in the discussion of this
paper, and that by this means the Institute may be able to
furnish general recommendations covering this subject.
HIGH-TENSION CONDUCTORS.
85
Discussion of Mr. Skinner's Paper.
Mr. Skinner: — I have here several communications which I
will read.
Mr. Henry Floy: — Because of its simplicity and reliability,
the writer believes there is nothing quite equal to a plain but
generous hole in the wall through which the wire rigidly sup-
ported, may pass. This form of construction modified as here-
after shown, is applicable to any voltage, and almost any climate.
I consider that the tise of glass plates, as suggested by Mr.
Skinner in Fig. I., or conductors insulated for a portion of their
length as in Plan II., are more or less objectionable because of
the constant menace of leakage and grounding of the system,
through the wall of the building. The accumulation of dust or
moisture on the glass plates, or the deterioration of rubber or
paper insulation due to exposure and weather will sooner or later
end in a shut-down; glass tubes and plates are always breaking
and never make a really good mechanical job.
If the station is provided with an overhead traveling crane, it
will usually be found mora convenient to bring the wires into the
building through one of the walls rather than into a tower.
Having tried several different methods, none of which were
wholly satisfactory, the writer devised the scheme shown in the
accompanying sketch, which explains itself. This form of con-
struction has been successfully used in a concrete-steel building,
where the roof beams of concrete were carried beyond the walls
86 HIGH-TENSION TRANSMISSION.
of the building and made to support a gallery, which serves as a
lightning-arrester house; thus, the satisfactory introduction of
the wires into the building and a proper fireproof room entirely
separated from the station for the location of the lightning
arresters, is provided. The iron brackets on which the wires are
first supported, may be set either in the floor of the gallery or in
the wall of the station. In either case all water drips from the
wires before the latter turn vertically to pass through the floor
of the gallery. At the same time any small amount of rain, snow
or dust which may blow up into the gallery will not continue on
through the second hole into the station. Moreover, the two
apertures, one leading into the gallery and the other from there
into the station, being at right angles to each other, prevent any
large amount of cold air entering the station. One building pro-
vided with this form of admittance was not particularly uncom-
fortable though the outside temperature was as low as 27° Fah-
renheit below zero. The maintenance of proper insulation is
always insured; proper mechanical fastening of the line wires
secured, and the reliability and simplicity is all that could be
desired.
Mr. Skinner: — It should be noted that Mr. Floy's plan does
not contemplate in any way taking up the end strains of the line
wires. This must be done away from this point.
The other communication I have is from Mr. 0. H. Ensign,
Chief Electrical and Mechanical Engineer of the Edison Com-
pany of Los Angeles, California.
Mr. 0. H. Ensign:— We use, for 30,000 volts, plain 12-inch
sewer-pipe wide open. Our temperature never goes to zero. It
is cold only for short periods. I do not believe that unless con-
siderable protection is given in the way of extension of the build-
ing, any sort of glass plate or marble supporting special insu-
lators would be satisfactory, exposed to the weather.
Mr. Skinner: — Here is another discussion by A. L. Mudge.
Mr. Mudge: — Would suggest that the terra cotta should be
closed at outer end to prevent birds and insects getting into,
or building nests in, the pipe. I find that a good ice and snow
break on a sloping roof is V-shaped, and is much stronger than
a single horizontal strip and also tends to let the roof free itself
of snow. These strips can either be made of wood or of two
lengths of angle iron bolted to the roof.
President Scott: — Another from Mr. F. C. Pierce.
Mr. Pierce: — Referring to the article : Page 80. Art. (5), (C),
I do not believe in allowing the wall of the building to take the
strain of the line, the last poles of the line should be braced or
guyed ; the number of poles guyed being determined by the num-
ber and weight of the line wires. In all cases I have seen, the
wall, even if very heavy, will eventually come loose or bulge.
Where the strain is taken on the line; a X-arm just outside and
one just inside the wall, fastened rigidly to the wall, will hold the
wires in the centre of the slab of insulating material and exert no
strain thereon.
HIGH-TENSION CONDUCTORS.
87
I enclose rough sketch of our method of entering wires in the
power house.
We found it necessary in cases where we enter under the eaves
as in the sketch on p. 83, Fig. 2, to put a false dormer above
the entrance, as otherwise the ice and snow slides down, catches
on the wires and accumulates between the wires and eaves until
the wires .are either broken or pulled out of place.
The substation wires enter the gable ends. The slab of insu-
lating material is 12"x 12" plate glass with 2" hole through center.
Since putting the dormer on power house we have had no trouble
whatever from our entrance wires.
[Discussion Contributed by J. Harisberger.]
My experience has been with the construction as shown in
sketches 1 and 2, pages 81 and 83. The Snoqualmie Power
Company adopted at the very beginning the arrangement shown
in Fig. 2, and with all of its high-tension troubles, it has yet to
experience its first trouble with this style of construction for
entering buildings. In some of the buildings the wires enter with
the construction shown in Fig. 1 and in every instance when the
high-tension lines became grounded for one reason or another,
there was a discharge across the glass plate to the terra cotta
pipe and which is evidence, in my opinion, that with a voltage
as high as 30,000 it is not the best, unless a terra cotta pipe of an
unpractical diameter is used,
88
HIGH-TENSION TRANSMISSION.
[Communicated by M. H. Gerry, Jr.]
Mr. Skinner has stated the essential reqiiirements for entering
high-tension wires. There are a number of excellent methods in
common use, all of which give good results when properly ap-
plied. Fig. No. 1 is an excellent construction in use in several
plants operating at 40,000 volts. This arrangement consists of a
double, or triple, window sash set in an ordinary frame, the glass
having openings in the centre in which are placed insulating
bushings, or tubes. A water shed to keep the rain from the glass
is sometimes added,
Fig. No. 2 is a method frequently advocated, and in use for
moderate pressures to a certain extent. It can be made to give
good results, but involves special building construction.
HIGH-TENSION CONDUCTORS.
89
Fig. No. 3 IS a common method of entering high-tension wires
through tile pipes. This method is an excellent one, and will
give good results even up to pressures of 30,000 volts. En-
trances of this design should always be made, if possible, through
gable end of the building and not under the eaves, as shown by
Fig. 3
Mr. Skinner. If impossible to enter at the end of the building,
then a rain-shed should be provided over the wires, this being
especially essential in cold climates, where ice forms readily.
Fig. No. 4 is a simple method of entering high-tension wires as
applied to an iron building. The glass tubes shown are four feet
in length two inches in diameter, and from five-eighths to three-
fourths of an inch in thickness. This method is now in regular
use at 50,000 volts,
Fig. 4
Figs. No. 5 and No. 6 are methods of entering wires vertically
through the roof. Fig. 7 is a detail of the roof insulator, used in
connection with the arrangement as shown in Fig. No. 6. The
drawings show the construction clearly and require no explana-
9f
HIGH-TENSION TRANSMISSION.
Fig. 5
..-'
^
— GALV. IRAK CONe
«,600 VOLT
F
LINE y
END ELEVATION
Fig. 6
^
t^^
60,000 VOLT LINE
_PAPER CONB
_ PARAFFINED WOOD
_GALV IRON
.^APER CYLINDER
OUtSIDE OF
GLASS TUBE
END ELEVATION
HIGH-TENSION CONDUCTORS.
91
tion. These vertical entrances are in use at the Canyon Ferry
Plant of the Missouri River Power Company, and give good
satisfaction. The above methods are selected as representing
current practices. There can be no one method of entering high-
RUBBER
TAPE
WOOD PIN
PAPER CONE
PARAFFINED WOOD
PABAFFINED WOOD
WOOD PIN
WEDGED AT ENDS
Fig. 7
section through
50,000 volt roof
insulator
tension wires, it, is always a question of engineering detail,
which should receive special treatment in each particular case.
President Scott: — Mr. Skinner's paper, on the " Methods
of Bringing High-Tension Conductors into Buildings," is open
for discussion.
Mr. Mershon: — I have used a number of different methods
of bringing wires into buildings, some of which have already
92 HIGH-TENSION TRANSMISSION.
been described. The method of a tile and a flat glass plate,
has been used, I think, quite a long while; also that of a glass
tube in a wooden bushing going through the wall, for voltages
of 25,000 or 30,000. The latter is a good method of bringing
wires into buildings except for the difficulty of getting glass
tubes. Some times I have had no difficulty in getting satis-
factory glass tubes; at other times tubes obtained from the
same manufacturer will all go to pieces if, being warm, they are
subjected to a blast or draft of cold air, such as would result from
opening the door of the station. So I have come to feel a little
bit afraid of the use of glass tubes.
Now, as to the size of the glass plata and the distance which the
voltage will go over it. Some time ago I had occasion to install
a tile and a glass plate arrangement because there was not time
to get anything else, and the largest tile obtainable was 24 inches.
That size was put in on a 50,000 volt line, which has been in
operation in all kinds of weather for four or five months without
any trouble. At times the frost gets so thick on the glass that
you cannot see through it and, if the line has been shut down for
a little while and a great deal of frost has collected, there is a
discharge over the glass until the frost is melted; but after it is
melted near the wire the discharge stops almost altogether.
Although we have had no trouble at all in this case, I think a
greater distance than 12 inches over the surface of the glass plate
from the wire to the tile in a brick wall is advisable for this
voltage. I think this question of entering buildings is a good
deal like the question of insulators, in that it depends somewhat
on the climate. There are places where the climate is such that
the method I have just described for a 50,000 volt circuit would
undoubtedly give trouble.
Mr. R. F. Hayward: — There is no doubt that the question
of climate cuts a very big figure in the selection of the methods
for entering buildings with high-tension wires. I think this
method of using a tile is open to objection, and a good deal
of trouble comes from it. I do not think that any outlet which
has for its protection a covering for building outside the power
house where the wire comes in, then up and then through, is
very nice, for the reason that birds do get in. The most suc-
cessful outlet that I know of is one that was put in at the Murphy
mill and has been running on 40,000 volts for, I think, four years.
There is a brick wall in the gable end. The outlets are, I think,
four feet apart. The holes in the brick are, I think, 18 inches.
They may not be more than 14 inches. In those are set two
plates of glass, each plate of glass flush with the outside, then
another flush with the inside, of the brick; a hole about 2^ inches
in diameter drilled through this and another glass tube placed in
it. There was great difficulty, as Mr. Mershon has mentioned, in
getting good glass, but they have got it, and that glass has never
broken. There has never been a short-circuit or a breakdown,
and that gable end faces the southwest storms, where all the
HIGH-TENSION CONDUCTORS.
93
sleet and rain comes from. We are using that kind of outlet
for all our work in Utah, only instead of using the glass tube we
are going to use porcelain tubes, because I think we can get them
stronger, and we shall simply increase the size of the plate glass
to about two and even three feet square. I think that people
do not appreciate how efEective in practice a simple piece of
plate glass is. On 16,000 volts I have a piece of 12-inch plate
glass with a f hole drilled in it and wires passing right through,
and have never had the slightest trouble, although we frequently
have severe storms in winter. I think that the most important
thing in outlets is lots of space and not cumbering the outside of
your building with any extra structure. Leave it clear, so that
nothing can get up against it, and where everybody can see it.
Mr. V. G. Converse: — I am hardly prepared for an im-
promptu discussion, but I have a few ideas on this subject, one of
which I think is of the utmost importance with very high volt-
ages. It is that the insulation into a building should of itself be
protected. It should be protected so that anything coming in a
1/6 CoMvcnsi
horizontal line, such as rain, snow or dirt that is blown will not
decrease the resistance of the insulation. Two figures show the
extension of the roof brought down to such a point that to my
mind it leaves off just where it begins to be of value.
94 HIGH-TENSION TRANSMISSION.
The tile shown in Fig. 1, seems to me to possess a very bad
feature in being left open on the exposed side. This construction
may suffice, and I know of several cases where it is in use, but it
certainly is open to the objection of being free to receive any-
thing that may lodge in it. I think that Fig. 2 is a much better
construction, but it could be improved upon by using several
tubes, rested one within the other. Mr. Mershon has stated the
objection to glass tubes, and I would recommend the substitution
of porcelain. I do not think that porcelain is always a good
article to use, but it is in this case. Suitable glass tubes are not
made in this country and are very difficult to get anywhere,
while porcelain tubes are a standard article of manufacture and
they can be gotten in lengths up to three feet, I believe, and in
a variety of diameters, which will nest very satisfactorily. I
would make the further suggestion with reference to Fig. 2, that
instead of one glass plate, there be two glass plates, spaced some_
five or six inches apart. This will give additional support, and
afford an inside space which should tend to prevent the accumu-
lation of frost. As to the point of the extension of the gable, as
first mentioned, I think that there is the insulation of the whole
structure. To my mind, the most uncertain point of the insula-
tion in Mr. Skinner's second figure is the surface distance from
the outer end of the tube over the glass plate. This cannot be
very many inches and should be protected. I would advise that
the gable be extended down to a point considerably below the
wall insulation. The line wires should be carried from the
anchor pole to a point several feet below this gable, and up to the
tube insulators and into the building. The lines may be held in
this position by a bracket supported on the wall, below the gable.
If the lines are heavy they may be further supported by line
insulators within the gable, so that there will be no strain on the
tubes or glass plates. I furnish a sketch embodying my ideas.
Mr. p. H. Thomas: — To my mind Mr. Converse's suggestion
of a rain-shed is an excellent one. By extending the roof a con-
siderable distance from the wall and running it low down, build-
ing a bafifle-plate from the ground up, leaving just sufficient open-
ing to carry the wires in, and carrying the wires down and up as
he suggests, you get the conditions of an indoor inlet at the main
wall, where the plate glass and tubes are used. With the possible
exception of the temperature outside, the conditions or interior
construction will be admitted to be very much superior to those
out of doors. Now, by changing the usual out-door inlet to an
indoor inlet nine-tenths of the trouble would be avoided , and this
can be easily done by the rain-shed spoken of. Sometimes it
might be more convenient to obtain the protection by bringing the
the rain-shed inside the building; that is, have a large opening in
the wall and building a small room or large box up near the top,
for bringing in the wires and then putting the true inlet on the
farther wall, where it would be thoroughly protected from the
weather.
HIGH-TENSION CONDUCTORS. 95
There is one other point; ordinarily, I think a great deal will
be gained in the long run by mounting the true high insulating
inlet in an insulating panel, made as nearly fireproof as possible —
something of the nature of marble would of course be the best —
but with a large number of substations this would be too ex-
pensive. For a great many climates, it would be wise to use a
wooden panel in which to mount the glass or porcelain inlet.
This panel in such a case should if possible be made of a number
of different pieces of wood with the grain running in different
directions, and should of course be as well treated and prepared
as possible. There is a certain danger of fire, but this is a
minimum, I think, with good construction, and with the rain-
shed of which we have spoken.
Mr. p. M. Lincoln: — There is just one point in the scheme
mentioned by Mr. Converse that I would like to bring up, and
that is the matter of taking up end strain. If you adopt that
scheme, you have got to take up your end strain on the line
outside of the building. That means taking it up on the stan-
dard insulators with the usual pins. Unless there is a special
construction it is difficult to take up the strain on a heavy line
in that manner. The end strain should be taken up by a strain
insulator inside, as represented in Mr. Skinner's sketch No. 1.
The great advantage of that to my mind is that the end strain
of the line is taken by the insulators mounted inside the building,
and you can put your insulator in any position, without having
petticoats in such a position as to fill up with water and become
useless.
[Communicated after Adjournment by Dr. Louis Bell.]
For all high voltages, I prefer the arrangement shown in Fig.
2 in Mr. Skinner's paper. It is thoroughly effective and has
the great merit of demanding ample space between wires. A
mania for compactness has been responsible for more trouble
in high voltage systems than any other one cause with which
I am acquainted.
Wire towers for high potential lines should be avoided, first,
last and always, together with tunnels, conduits and every other
device for getting high-tension wires compactly stowed away out
of sight. My own personal rule is to use wide spacing and to
carry all wires in obtrusively plain sight until they get out of the
building and go upon the line proper.
The high voltage wires themselves and all their connections
should be so placed that their whole arrangement is evident from
a cursory glance, and the higher the voltage the more need for
caution in this respect.
A paper presented at the 20th Annual Convention of
the American Institute of Electrical Engineers,
Niagara Falls, N. Y., July 1, 1903.
THE GROUNDED WIRE AS A PROTECTION AGAINST
LIGHTNING.
BY RALPH D. MERSHON.
Some of the transmission lines of this country have installed
upon them as a protection against lightning one or more wires
strung parallel to the power wires and grounded at intervals.
There is a difference of opinion amongst those operating such
lines in different parts of the country as to the efficacy of this
device. The importance of the subject makes it desirable to
have an expression of opinion upon it from those members of
the Institute who have had experience in operating such lines
or who have given the matter close consideration. This can
perhaps be best arrived at by a discussion on the subject.
Theory.
There are three ways in which lightning can affect a trans-
mission line; by a direct stroke, by electromagnetic induction
and by electrostatic induction. Protection against the first of
these would be almost impossible, certainly impracticable.
Fortunately, lines are not often struck by lightning. The
second, electromagnetic induction, is, in the opinion of the
writer, a theoretical possibility — nothing more. It is against
the effects of the third, electrostatic induction, that lines are to be
protected, whether by lightning arresters or by grounded wires.
The theory of the electrostatic induction action may be ex-
plained with practical accuracy as follows: The whole trans-
mission system, line, transformers, etc., may be regarded as an
electrostatic conductor, insulated from the earth. Suppose a
96
GROUNDED WIRE. 97
cloud heavily charged with, say, a positive charge, to move up
to the region over the transmission line. There will be a posi-
tive charge " set free " on the transmission system and it will
have a tendency to pass to earth. It will pass to earth by grad-
ual leakage over and through the insulation of the system if the
approach of the cloud is slow enough to give time for such
leakage; if not it may puncture the insulation and thus pass to
earth. The intensity of the charge will depend upon the poten-
tial at the line wires due to the charge of the cloud. Suppose
there be near the transmission wires other wires parallel to them
and grounded at frequent intervals. They will also be subject to
the inductive action and the charge set free upon them will pass
to earth as fast as liberated, the " bound " charge of the opposite
sign of that of the cloud remaining and depending for its magni-
tude on the potential due to the cloud and the electrostatic
capacity of the grounded wires. Under these conditions the
intensity of the charge on the transmission wires will no longer
depend only upon the potential at them due to the cloud, but
upon the combined action of the charge of the cloud and the
bound charge of the grounded wires. In other words, the
potential of the line wires will be equal to the difference of the
potentials due respectively to the cloud and the grounded wires
and will in general be less than that due to the cloud. This
action constitutes what may be designated as the " shielding
action " of the grounded wires.
Return now to the condition where with no grounded wires
the system has been gradually charged and the charge has
gradually leaked away, leaving a bound charge of negative sign
on the system.- Suppose now the cloud be discharged by a
lightning flash to earth. The potential due to it at the trans-
mission wires is now zero and there is consequently left upon the
transmission system the negative charge which was previously
" bound " but is now " free " and which has a tendency to pass
to earth and will probably do so suddenly, since the charge has
been rendered free suddenly. Its passage to the earth may
mean a puncture of the insulation of the system. If, however,
we assiime that the grounded wires are again present and the
charge bound on them by the cloud and set free upon them by the
lightning flash can readily pass to earth, there will be less ten-
dency towards ■ the puncture of the insulation of the system
because of the fact that, as previously explained, the impressed
potential of the line wires before the flash is less with the grounded
98 HIGH-TENSION TRANSMISSION.
wires than without them. If the charge on the grounded wires
cannot pass readily to earth the charge on them will tend to
set free a negative charge on the line wires, which will be added
to that set free on the line wires by the lightning flash. The
worst condition would be that under which the charge on the
grounded wires could not pass to the ground at all, in which case
the sum of the two charges on the line wires will be just equal
to that which would have existed if there were no ground wires.
The passage of the charge from the grounded wire to ground will
always be more or less obstructed by the inductance of the dis-
charge path, the efEectiveness of this inductive obstruction
depending upon the suddenness with which the cloud discharges.
This inductive action of the ground wires due to the charge left
upon them we will designate as the " direct action " of the
wires.
The " shielding action " of the ground wires may be calcu-
lated by making assumptions which will approximate to a
degree those which obtain in practice, but the calculation of the
" direct action " is less satisfactory since it involves a number
of assumptions, all more or less speculative in their nature.
This is due amongst other things to the fact that we cannot know
how long the lightning flash will last or whether it will be oscilla-
tory or not. Furthermore, we do not know what the dielectric
strength of the insulation of the system will be for periods of
time so short as those involved under the conditions mentioned.
We do know, however, that under the worst conditions that can
obtain the insulation stress due to the " direct action " of the
grounded wires can be no greater than though they were not
present and will in general be less. We also know that whatever
be the maximum value of this insulation stress it will diminish
rapidly either in an oscillatory or non-oscillatory manner, the
rapidity of the diminution depending upon the freedom of the
discharge path from obstruction. It is to be noted that the
time-element of dielectric strength is not involved in the calcula-
tion of the " shielding action " to the degree that it is in the
" direct action " ; since in the former case the charge comes on to
the system more or less gradually and we may assume without
great error that ordinary values of dielectric strength hold.
In order to get an idea as to the magnitude of the " shielding
action " let us calculate its effect under the most simple condi-
tions. Suppose we have two No. 00 wires stretched side by side
on a pole line 20,000 feet in length, the wires being one foot
GROUNDED WIRE. 99
apart. Call these wires a and b. Suppose first that both wires
are insulated from ground and that the space occupied by them
is raised by the inductive action of a cloud to a potential v above
the earth. The expression. for the potential of a long cylinder
or wire of length / and diameter d, having upon it a charge
whose density is to cause any particular damage, as the apparatus must
have a strength considerably above the contract test in order
to pass either without giving trouble.
In regard to applying the voltage, it is sufficient on low-tension
apparatus, say, tests up to six, eight or ten thousand volts, to
simply switch in the potential at which the test is made. There
will be a rise of the e.m.f. across the testing terminals, but the
factor of safety, if you may call it such, will be sufficient, or
should be sufficient to stand this rise ; and where hundreds and
even thousands of tests are made every day, as they are in the
large factories, it becomes quite a serious loss of time, in making
the tests, if considerable time is taken to bring up the voltage.
For the higher potentials, it is necessary to raise the potential
gradually, and there are various schemes for doing this. One
of the best is to have control of the generator. That is not
always possible. Where we are obliged to make the test from a
constant potential system, then it is necessary to introduce some-
thing in the nature of water resistance or of a step-by-step
method, using very small steps. Where the capacity of the
apparatus to be tested is quite small, such as insulators or small
sets of cable, steps as large as 5 per cent, do not seem to be ob-
jectionable. Where the static capacity of the apparatus under
test is large the steps must be smaller to prevent surges in the
testing circuit.
Mr. Mershon: — I thoroughly agree with what Mr. Peck
and Mr. Skinner have said. I have no love for what might
be termed an " egg-shell " transformer. It seems to me that
we want something that is going to stand a little rough knocking
about. If we have to handle 40,000 and 50,000 volt trans-
formers so gently, what is going to happen when we get up to
the voltages that are being talked about 100,000, perhaps?
As regards the question of injury to the apparatus under test,
at, for instance, double potential test for a minute. The problem
is simply this, that we want to get apparatus which will meet and
withstand the conditions of practical operation. Now we cannot
state accurately and explicitly what those conditions are. There-
fore, we cannot formulate explicitly any tests which will show
whether or not the apparatus will meet them. The best we can
do is to adopt tests which, in the light of experience, will probably
come somewhere near telling us whether the apparatus is going
to meet the practical conditions. It seems to me that a double
potential for one minute is not any too high, and I can tell you
that it is very comfortable to know, under some conditions that
obtain on transmission lines, that your transformers have stood
such a test.
DIELECTRIC STRENGTH. 131
In regard to when and where the test shall be made, I want to
emphasize what Mr. Peck says. It seems to me that the test
should be made after the installation of the apparatus. We
want apparatus that is going to stand the conditions to which it
is subjected after it is installed.
The stand taken by Mr. Peck regarding the improvement in
the condition of the apparatus after installation, I agree with
entirely. Presumably the manufacturer gets his apparatus in
the best possible condition before it is tested. It is not fair that
the severity of the test should be reduced in any way because
the condition of the apparatus is going to improve with time,
when in the meantime the apparatus may be damaged by light-
ning or other disturbances on the line, and the burden of that loss
fall upon the purchaser.
Mr. Dunn: — ^What we need to solve a good many of these
questions is data on the relation between the elastic limit of
insulating materials and their ultimate break-down point, just
as we have that data for mechanical properties of various mate-
rials. To refer to the case mentioned by Mr. Lincoln, I think
it would be good engineering for Mr. Stott to try to break the
suspected base of the generator with a reasonable excess of
strain over what it was expected to stand regularly.
Insulation testing is of two kinds. One, as I said before, to
determine whether the insulation is present. This is necessary
even if a manufacturer is honest, because in putting conductors
into slots and wires around cores, considerable mechanical
pressure and hammering has to be used, which is liable to break
the insulation or subject it to such pressure that its properties are
injured. The other kind of testing is to determine whether
insulation which we believe present is good. In this test we
apply a stress that is above the elastic limit. If we could deter-
mine that the elastic limit of the insulation was say one-third of
the ultimate limit, it would be proper for us to use a high potential
test within the former limit. The stresses we put on apparatus
in factory tests now are above that limit, and we keep them on
but a short time in order not to damage the insulation too much.
Such tests, I think, are bad. If one of the results of this dis-
cussion were the collection of data on elastic lirnits, it would be
of great benefit.
Professor Langsdorf: — There is another kind of test,
which so far as I know has never been applied to insulating
material. It is analogous to those which are made upon metal,
and recently upon cement, to determine the effect of fatigue.
I have recently seen a curve which was made from the re-
sults of tests of this nature on cement that looks something
like this (indicating); the number of repetitions necessary to
produce failure are plotted as abscissae, and percentages of the
normal breaking load as ordinates. The curve is apparently
logarithmic and approaches an asymptote passing approximately
through the 50 per cent, division on the scale of ordinates ; this
132
HIGH-TENSION TRANSMISSION.
would mean that the factor of safety as ordinarily understood is
only half the assumed value ; so that if tests of this nature could
NUMBER OF REPETITIONS
be made on insulators we might get a little more light upon the
value of the factor of safety.
Mr. Henry Pikler: — When we are testing electrical appar-
atus we assume a sine wave e.m.f. This is true as long as the
step-up transformer is directly connected to the terminals of
the generator which furnishes the sine wave high voltage, but as
soon as we use resistances in series with the transformer in order
to control its terminal voltage the wave-shape of the e.m.f.
changes. You know very well that the hysteresis, or more
correctly, the change in the permeability during one cycle of
magnetism distorts the wave-shape of the magnetizing current ;
but if we have it in the circuit besides the transformer, a series
ohmic resistance, then this will cause the distorted current to
change again to a sine wave. And when a sine wave current
excites the transformer, its induced e.m.f. will be no longer a
sine wave but a highly peaked wave, and we subject the tested
apparatus to a voltage which is perhaps 20 per cent, higher
than we are calculating on. I made some experiments in this
regard, and I found that the more the energy consumed by the
ohmic resistance comparatively to the energy consumed by
hysteresis in the transformer, the less will be the distortion of
the current wave, it will become more and more sinusoidal. But
if the transformers get a sinusoidal magnetizing current, its
induced e.m.f. wave will be distorted, assuming as a limit a
perfect sine wave shaped exciting current. The induced e.m.f.
wave of the transformer will have exactly the same shape as the
exciting current curve has, when the current drawn from the
sine wave generator is only that due to the transformer, the
secondary of which is open.
It has been suggested that we should know the relations be-
tween the ultimate strength and the elastic limit in insulating
materials. The insulation engineer has a very difficult problem
to handle. With low voltages it is fairly simple; but when we
get up to the higher voltages, there arises a new order of affairs.
One of the things to guard against particularly is that we do not
DIELECTRIC STRENGTH. 133
encounter unawares a new kind of phenomenon. For example,
when we test at two or three times normal voltage, we are simply-
endeavoring to determine the breaking down strength. Some
new phenomenon like dielectric hysteresis may come in to
produce heating, or in suddenly applying the voltage for test
there may be some sudden rise of voltage which was not antici-
pated. It is things of this kind, these incidental and unexpected
things, which we must guard against particularly.
Mr. Thomas: — I will take only a moment or two. The
building and testing of high-tension apparatus, transformers
or generators, is an extremely intricate and complicated problem,
and no person who has not worked on a design and used such
material can have any real appreciation of the difficulties in-
volved. These criticisms and recommendations, if we may call
them such, which I have drawn up here, are based on a very long
line of experience, tests, actual apparatus troubles, and repre-
sent a very careful consideration of all the data.
Mr. Peck began by calling attention to the fact that the
apparatus is likely to get strains on layers near the terminals of
the transformers during the early testing of the line and that tests
ought to be made in apparatus purposely to apply these strains.
This would certainly be very desirable on the face of it, and is
desirable if it can be carried out practically. But this great
difficulty is met; Suppose you make the test and our trans-
former fails to stand it. You can't always know the fact. A
spark occurs between two layers inside somewhere, and since the
apparatus is, in all probability, not in a position to be supplied
with generator current to the full capacity of the system, your
insulation is punctured, the spark passes and ceases, stops, and
you think the transformer is all right. You go ahead and a
little later a strain of much less magnitude comes along and
when conditions are favorable for that fault to be developed, and
the general apparatus breaks down. That is one of the diffi-
culties.
[Contributed after Adjournment by Dr. Louis Bell.]
I do not think it wise for a purchaser of apparatus to place
much reliance on over- voltage tests set forth in contracts, save
in the case of line insulators, switching and such-like simple
apparatus. In other cases such tests ought not to be long con-
tinued, and should not be made until the apparatus has success-
fully stood a full load test and recovered therefrom. Then a
moderately severe over-voltage test can be usefully applied,
merely to try out the insulation as a whole. I do not concur that
a disrupture test is unfair because it may subject to severe
strain parts of the insulation which normally receive in com-
mercial working only a moderate straii.. The disrupture test
ought to try out these very points, for danger to insulation from
minor lightning discharges, resonance and the like frequently
catches apparatus at just these weak points, since trouble usually
comes from abnormal, not ordinary, conditions. Personally, I
134 HIGH-TENSION TRANSMISSION.
attach some value to an overload test at a voltage somewhat
greater than will ever be demanded in practice, with carefu)
insulation measurements before and after.
[Contributed after Adjournment by Mr. P. G. Gossler.]
The grounded wire method of protection against lightning has
been used on the transmission lines of the Montreal Light, Heat
& Power Company for the last four years, with very satisfactory
results. For three years the transmission lines were operated at
two-phase, 12,000 volts and for the last year at 3-phase, 25,000
volts.
The 2-phase transmission lines consisted of duplicate lines run
from Chambly to Montreal, the total distance being about 17
miles for each line of which 14^ miles were aerial and 2J miles
single-conductor rubber-insulated underground cables. The
underground cable was divided up in three sections, the first
section was about a mile and a half from power house, the
second about 15 miles from the power house, and the third at
the Montreal end.
The present transmission lines consist of duplicate lines, 17
miles for each line of which 15^ miles is aerial, and 1^ miles under-
ground cables at one end. Three lines of barb wire are run on
pony glass insulators on each pole line, two lines being run on
the ends of the top cross-arms 32 inches from the line wire, and
the third on a pin on the top of pole.
The barb wire is composed of two twisted No. 12 B.W.G.
galvanized iron wires with one four point barb every five inches,
and is connected at each pole by means of a soldered joint to the
ground wire. This ground wire is stapled down the face of the
pole and is twisted several times round the butt, after running
through an iron pipe about 8 feet long, which projects above the
level of the ground, preventing the wire from being cut or
broken, as well as affording an additional ground.
As the poles are set 90 feet apart the barb wire lines are
grounded about fifty-eight times per mile ; this frequent ground-
ing being one of the most important points in the protection.
It has been the general opinion that ordinary barb wire lacks
good mechanical properties, is liable to corrosion and to cause
interruption to the service by breaking and becoming tangled
with the transmission wires.
This has not been our experience. In the line described above,
ordinary commercial barb wire was used and we have only
experienced two cases of the barb wire breaking. In both cases
it fell clear of transmission wires and did not become entangled
with the conductors. We are of the opinion that our freedom
from mechanical troubles has been due to the care exercised
when stringing the line, and also fastening to a glass insulator,
instead of stapling to the cross-arms and top of poles.
We also use the Westinghouse low eqtdvalent a.c. lightning
arresters, in conjunction with the barb wire. Banks of arresters
being located at both ends of the aerial lines.
GROUNDED WIRE. 135
We have undoubted proof of the usefulness of barb wire
protection as applied to our system. The first year and a half
of operating our 12,000 volt Chambly Plant we did not have any
protection against lightning but the barb wire. The first summer
we had the opportunity of watching the effect of a very severe
stormwhich traveled from Montreal to Chambly, passing over
the district through which our transmission lines run; this
storm did considerable damage in Montreal, shattered several
trees along the transmission line, and also damaged the local
lines in Chambly, but no trouble was experienced on the trans-
mission lines.
So satisfied are we of the usefulness of barb wire as a protection
that we have installed it on many of our local 2400-volts circuits
in and around Montreal, with satisfactory results.
A paper presented at the 20th Annual Convention
of the American Institute of Electrical Engineers,
Niagara Falls, July 1st, 1903.
CHOICE OF FREQUENCY FOR VERY LONG LINES.
BY P. M. LINCOLN.
Although other frequencies are in use in this country, there are
only two which by the extent of their use can be called standard,
viz.: 60 and 25 cycles per second. Without discussing the rela-
tive merits of other frequencies, the question now presented is,
which is the better frequency for a very long line, 60 or 25 cycles
per second, considered purely as a transmission problem.
In the present state of the art, 200 miles may be considered as
very long for a transmission line. Although longer ones have
been proposed, only one of this length has been put into actual
operation and no other line approaches this length. The reason-
ing which follows will, therefore, be made to apply to a typical
line 200 miles long.
Frequency has a direct bearing upon voltage regulation and
charging current and its influence on a possible condition of
resonance may also be profitably discussed.
1st. Voltage Regulation.- — The difference between the voltage
at the transmitting and the receiving stations, termed the
" drop," is dependent upon several elements, among which are
the resistance and the inductance of the circuit. The volts for
overcoming the resistance are the same as would be required for
sending a direct current equal to the normal alternating current
through the line, if it be short-circuited at the receiving end.
The volts for overcoming the inductance at any frequency are
measured by the pressure which would be required for sending
the alternating current at that frequency through the short
circuited line, if the ohmic resistance were negligible. The
inductance volts are directly proportional to the frequency.
The difference in voltage between the transmitting and receiv-
136
CHOICE OF FREQUENCY.
137
ing stations, or the " drop," is a function of the resistance volts,
the inductance volts and the power factor of the load.
Consideration of voltage regtdation at the receiving end limits,
according to best practice, the resistance volts in a transmission
line to about 15 per cent, as a maximum, and the same con-
sideration should keep the inductance volts within a maximum
of 20 per cent. This will mean a line regulation of about 24 per
cent, with a load power factor of 85 per cent. Best economy
may reduce the resistance element below the maximum given.
The resistance volts may be reduced to any given amount
by the addition of copper, while inductance volts are little
affected by increasing the size of wire. An increase in size of
conductor which will reduce resistance volts by one-half will
reduce inductance volts only about 5 per cent. The matter of
inductance volts, therefore, constitutes a limit to the amount of
power that can be delivered over a single line. This considera-
tion will limit the amounts of power which can be delivered by a
three-phase line 200 miles long to approximately the following :
Table Showing Limits of Transmission Line Capacities.
Voltage at
Power Delivered with 20% Inductance Volts.
Receiving End.
200 Mile, 3-Phase Line.
60 Cycles.
25 Cycles.
20,000 Volts
500 k.w.
1,250 k.w.
30,000 "
1,125 "
2,800 "
40,000 "
2,000 "
5,000 "
50,000 "
3,125 "
7,800 "
60,000 "
4,500 "
11,250 "
80,000 "
8,000 "
20,000 "
For longer or shorter lines the k.w. in the above table may be
decreased or increased in direct proportion.
If the amount of power to be transmitted is large, the multi-
plication of lines necessary at 60 cycles unduly increases expense
both of pole lines and of right of way for same. This point is
evidently in favor of the lower frequency.
2d. Charging Current. — Charging current is, of course, a
direct function of frequency and voltage and to a sUght extent
of line construction. At 60 cycles the apparent energy repre-
sented by the charging current in a 200-mile three-phase line is
practically equal to the ultimate capacity of that line as limited
by the 20 per cent, inductance volts consideration. At 25
cycles it is only about 15 per cent, of the ultimate capacity a&
limited by the same consideration. In a 60-cycle installation.
138 HIGH-TENSION TRANSMISSION.
therefore, it is necessary either to operate the generators on such
a line at about full current output all the time, no matter what
the load, or to compensate for the charging current in part or in
whole by the installation of choke coils, either horn of which
dilemma is not pleasant to consider. The problem of taking
care of the charging current at 25 cycles does not enter the dis-
cussion as compared with 60 cycles.
The effect of a large charging current on the regulation of the
generator should also be considered. As is well known, a line
charging current, when circulating in a generator armature, has
the effect of assisting the field ampere turns to magnetize the
fields. The percentage of magnetizing done by this charging
current depends upon its amount and the inherent regulation of
the generator. Since the charging current depends upon the
voltage, the generator exciting power of the charging current also
depends upon the voltage. The effect of sudden load changes,
therefore, which tend to change the voltage delivered, will in
turn affect this element of the excitation. That is, to a certain
extent, the generator assumes the regulation which inherently
belongs to a d.c. shunt generator. The effect of large charging
currents on generator regulation is, therefore, not toward an
improvement.
3d. Resonance. — As is well known, every combination of a
condenser and choke coil in series has a natural period of oscilla-
tion, whose value depends upon the square root of the product
of the condenser capacity by the choke coil inductance. If a
frequency of its natural period be applied to such a combination
resonance will occur. That is, a small exciting force of the proper
frequency will cause comparatively large currents to circulate
between the condenser and the choke coil and therefore com-
paratively large voltages across both the condenser and choke
coil. This is an example of resonance in its simplest form.
A transmission line possesses both capacity and inductance
and therefore the possibility of becoming resonant under cer-
tain conditions. The fact that both the capacity and induct-
ance of a transmission line are distributed throughout its entire
length, and the disturbing effect of concentrated inductances and
capacities at transmitting and receiving stations, makes the
problem of determining under what conditions resonance will
occur an extremely intricate one. A first approximation may be
obtained, however, by assuming that the inductance and capacity
of a line are concentrated instead of distributed, and omitting the
CHOICE OF FREQUENCY. 139
effects of translating devices. Under this assumption, we may
consider that the capacity of a distant portion of the Hne is in
series with the inductance of the intermediate portion.
The natural period, that is, the applied frequency at which
resonance will occur between the parts of a transmission line,
will be a minimum when the two parts are equal, or each is equal
to one-half the total line. The number of natural periods above
this minimum is infinite, since it is possible to divide the line
into two parts, the inductance of one of which multiplied by the
capacity of the other may be any quantity less than that ob-
tained by dividing the line into two equal parts.
The minimum period of a 200-mile line is approximately 200
cycles per second. There is, of course, no danger that the
fundamental applied frequency will produce resonance until the
length of line largely exceeds 200 miles, but the same cannot be
said of some of the harmonics if they are sufficiently prominent.
The lower the fundamental frequency, the less is the danger from
this source. So far as the writer is aware, no actual trouble has
ever been experienced in existing plants from this source even on
the longest lines and highest frequencies in use, but it neverthe-
less constitutes an advantage for 25 over 60 cycles that cannot
be dismissed with a scofE.
It is a fact that the longest transmission line in the world — the
Bay Counties line in California — as well as the highest voltage
line — the Missouri River Power Company in Montana — are both
operating at 60 cycles. These facts, however, do not detract
from the force of the preceding reasoning.
It is not claimed that this discussion contains all of the argu-
ments pro or con. The bringing out of additional points as well
as the soundness of those presented, is left to the discussion
which it is hoped the above will provoke.
140 HIGH-TENSION TRANSMISSION.
Mr. B. a. Behrend: — Mr. Lincoln's figures indicate clearly
that, with a given amount of material in a long line, more power
can be transmitted at 25 cycles than at 60 cycles. Mr. Lincoln
calls attention to the possible danger of resonance as pro-
duced by the higher harmonics superimposed upon the funda-
mental used for the transmission. Mr. Lincoln says: " The
fact that both the capacity and inductance of a transmission line
are distributed throughout its entire length, and the disturbing
effect of concentrated inductances and capacities at transmitting
and receiving stations, makes the problem of determining under
what conditions resonance will occur an extremely intricate one.
A first approximation may be obtained, however, by assuming
that the inductance and capacity of a line are concentrated
instead of distributed and omitting the effects of translating
devices."
I showed in a brief contribution to M. Leblanc's paper at the
Convention of the Institute last year that the natural period of
oscillation of a transmission line with distributed capacity and
self-induction can, without difficulty, be calculated. The method
in my contribution requires no extraordinary mathematical
knowledge beyond simple differential equations, and I have
shown on page 1213 of our volume XIX of 1902 that the funda-
mental of the natural frequency of oscillation of the line is;
1
4x\/LC
while the natural frequency, if we assume the capacity and self-
induction to be concentrated, is equal to.
2^1 VL.Ci
The discharge frequency of a long line with distributed capacity
and self-induction is, therefore, greater than if the capacity and
self-induction were concentrated.
Although this is all very interesting, I feel somewhat skeptical
about the practical importance of this resonance. It may be
possible that such resonance occurs on long transmission lines,
but I should prefer to suspend judgment on this point until the
facts had forced themselves upon my attention. I cannot help
thinking of the unreasonable importance which at one time
used to be attributed to the wave-form of alternating current
generators a case which has almost entirely broken down. But,
at one time, the wave-form was the scapegoat for all sorts of
mistakes made and a perfect bugbear to the designing engineers.
In considering the question whether a frequency of 25 or 60
cycles is preferable for power transmission purposes, we should
not confine our attention to the line itself, but we should take
CHOICE OF FREQUENCY. 141
into consideration the generating plant, the transformers and
the substation as well. In regard to the generating plant and
the transformers, there can be no doubt that a trequency of 25
is rather lower than desirable. In regard to the substation
apparatus, a frequency of 25 is as high as desirable for rotary
converters, while it is too low for lighting. Is not, after all, then,
Mr. Lincoln's problem the same that has been argued for fifteen
years, viz., the problem of the most favorable frequency?
I may add to Mr. Lincoln's statement to the effect that the
longest lines, as the Bay Counties and the Missouri River, are
operated at 60 cycles, that the first long distance transmission
line of 115 miles in length between Lauffen and Frankfort,
which was built in 1891, was operated at a frequency of 50.
Mr. F. G. Baum : — The first criticism I have to make on this
paper is that it confines the discussion of the choice of frequency
to the transmission line.
Unquestionably, so far as the line is concerned, the lower the
frequency the better the regulation, and the greater the capacity
of the line, limiting the capacity of the line by the inductive volts.
But the fallacy of reasoning that a low frequency is, therefore, to
be used, becomes immediately evident if we pass to the trans-
formers, where the higher the frequency, the smaller the weight
and cost, and the greater the efficiency.
The best frequency for the generators is, of course, dependent
upon the speed at which they are driven, and on their capacity.
With slow speed engines, low cycles would no doubt be prefer-
able, but in water power plants, operating at speeds from 300
to 500 r.p.m., with peripheral speeds of about 10,000 feet per
minute, according to the head of water used, the best frequency
for the generators will be higher than when driven by low speed
engines.
A power company at the present time, in California at least,
if it is to be a success, must sell a good proportion of its load to
small towns for lighting, etc. These towns being already
equipped with 60 cycle apparatus, practically force the power
companies to supply that frequency.
As to the limits of the percentage of resistance pressure or
copper loss, I believe 15 per cent, as a maximum is a little high,
and a satisfactory system should probably not have over 10 or at
most 12 per cent. The limit of 20 per cent, for the reactance
pressure is, I think, a little low. As it is possible generally to
have pretty fair contrdl of the power-factor of the line, a maxi-
mum of 30 per cent, for the reactance pressure would, I think,
not be excessive, and would give satisfactory service.
The charging current is not difficult to handle. If the load is
to be mostly induction motors, the charging current will improve
the power-factor of the generators. However, a 30 cycle system
would be better than 60 cycle so far as handling the charging
current is concerned.
Undoubtedly if our lines are to increase in length to 300 and
142 HIGH-TENSION TRANSMISSION.
up to 500 miles, we must operate at less than 60 cycleS; in order
to reduce the reactance volts and also on account of coming into
resonance with the line.
President Scott: — This paper is another example of what
was referred to this morning in another connection ; namely, the
new class and order of phenomena which may appear when the
voltage is changed. The various points which have been taken
up in this paper; namely, regulation, charging current and
resonance, have little or nothing to do with the choice of fre-
quency at low voltages. For instance, in an installation of an
isolated plant, or one for short distances, in which the voltages
are not more than a few thousand. But when the higher voltages
and the longer distances come in, then these new problems
appear; new elements have very great importance, sometimes
they are even the limiting conditions. The subject is one which
is open now for general discussion.
Mr. Mailloux: — It seems to me that in a matter of this
kind the consulting engineer is confronted more by conditions
than by theories. If he has to consider locations where the
electrical energy is to be used principally for lighting, he must
of necessity adopt a frequency that will be compatible with
satisfactory lighting. In all the cases which I have had to deal
with in long-distance transmission thus far, that condition has
been imposed by the facts and circumstances of the case. It
has been necessary to make provision for a current capable of
giving satisfactory lighting, because the bulk of the current was
intended to be used for that purpose. Now the question it
seems to me, therefore, would be, in striving to obtain a com-
promise between extremes, to determine what is the minimum
frequency that is satisfactory for lighting purposes. Experi-
ments have been made with the various frequencies in Europe.
There are many plants which are furnishing or attempting to
furnish lighting current with frequencies as low as 40. I have
seen several of those plants, and I must say that I do not consider
them satisfactory. One can see stationary objects very well,
but moving objects seem to have a jerky motion which is un-
pleasant and even annoying. I would like to know if any of the
gentlemen present have had experience with frequencies as low
as 50. I* has occurred to me several times that perhaps a
frequency of 50 might be a satisfactory compromise. We all
know that 60 is perfectly satisfactory for lighting, but it would
be very interesting to know what experience has been had with
frequencies lower than 60, in this country.
Mr. Stott: — As to the frequency at which incandescent
lighting becomes impossible, I think that point comes at just
about 20 cycles, from some experiments which have been carried
out. Twenty-five cycles, with a low efficiency lamp, taking
about 4 watts per candle, and with a voltage not to exceed 110,
where the filament is con:paratively heavy, is quite satisfactory.
We have tried the experiment of having direct current lighting in
CHOICE OF FREQUENCY. 143
the draughting room and then without notice throwing it over
on the alternating current, and no one knew anything about it;
and this certainly demands the best light possible.
President Scott: — You are using it in the elevated stations
in New York.
Mr. Stott: — Yes; we have about 30,000 incandescent lamps
run now on 25 cycles, and very few people notice the fluctuation.
I think it depends a good deal upon the voltage regulation and
also upon the fact that low efficiency lamps are used.
Mr. Mailloux: — How about the Nernst lamp?
Mr. Stott: — I have no information about the Nernst lamp.
I understand 25 cycles is rather low for it. In reference to the
general proposition of frequency, it seems to me that it is a local
condition which must be considered in connection with every
individual proposition, which is brought up.
Mr. Mershon: — Mr. Lincoln considers his subject purely as a
transmission problem. It is not very often that you get a chance
to consider the engineering of transmission from that standpoint.
You generally have to take into account certain conditions that
have to be met. You cannot select the frequency of your appar-
atus just as you chooge. Now, in many of these cases — I guess
it has been true of all the California plants — I think it is true
of most all the transmission plants that have been put in — the
condition to be met first was that of delivering power at 60
cycles. The transmission enterprises could not have existed,
probably, if you had insisted on putting in the 25 cycles, in that
there would not have been enough immediate prospective market
to have made it possible to finance the enterprise, and in order
to get this market, and get it as soon as the plant was in opera-
tion, it was necessary to deliver 60 cycles. In such a case, the
question comes down to whether or not it is better to transmit at
25 cycles and use frequency changers for 60, or whether it is bet-
ter to transmit at 60 cycles and use synchronous motors to raise
the power-factor of your load, or even bring up the drop in your
line to approximately that of the copper drop. If you consider
the question of the investment in these cases, you will find that
the 60 cycle plant shows up much more favorably. Take, for
instance, the use of motor generators for changing your frequency
from 25 to 60 cycles — you would require, with a power-factor of
85, which is the one Mr. Lincoln has taken, approximately 220
per cent, in actual machine capacity, counting both motor and
generator, and the fact that your generator has got to be able to
take care of a power-factor of 85. If you are using synchronous
motors and bring your power-factor up to unity, it will require
about 53 per cent. Now, that represents not only the cost of the
■machines, cost of the switchboard apparatus for handling them
and cost of station room for installation of machines, but in addi-
tion to that there is the question that has been mentioned of the
less cost of the transformers for 60 cycles. As regards the ques-
.tion of the charging current on 60 cycles, if synchronous motors
144 HIGH-TENSION TRANSMISSION.
were used, you would be able to get a greater amount of power
over a single line than Mr. Lincoln has calculated. Besides, you
could reduce the effect of the capacity current on the generator
by means of these synchronous motors, by keeping some of them
running at light loads just as you would have to do in case of
frequency changes. I cannot see that the capacity current of
the line will seriously affect the generator regulation. The
generator excitation depends upon ampere-turns either in the
field winding or the armature winding. To the over-excitation,
required to neutralize the armature-reaction of a given lagging
load, is due, mainly, the rise in voltage when such a load is
thrown off. If the same lagging load be carried but in conjunc-
tion with a charging current, such as brings the power factor at
the generator terminals to unity, the unity condition is due to the
fact that the reaction component of the lagging load has been
neutralized by the charging current. When, therefore, the lag-
ging load is thrown off, there is left on the generator the charging
current whose effect on the generator magnetization is about
equal to, in fact somewhat less than, that of the over-excitation
previously referred to. True, the rise of voltage tends to in-
crease the charging current which in turn tends to increase
somewhat the voltage rise, but this cumulative action will be held
in check by the fact, just referred to, that ampere-turns in the
armature are less effective in raising voltage than an equivalent
number of ampere-turns in the field.
As regards the question of frequency in lighting, I think there
is an element to be considered that has not been mentioned,
namely, personal peculiarities. I have tried in a number of cases
to find out the impression made on different people by low fre-
quency lighting. At 25 cylces, if I endeavor to do so, I can
notice a flicker in any 25 cycle installation I have ever seen, but
it does not bother me. Some people say that it annoys them at
all times, and some people say that they can even see the flicker
in the case of frequencies considerably above 25 cycles. I
think, however, that the majority of people cannot notice any
effect from 30 cycles. Possibly they could with quick move-
ments of illuminated objects, but I do not think that with the
ordinary movements of every day life they would notice any
flicker at 30 cycles.
Mr. Rushmore: — An interesting instance came to my notice
some time ago in talking with an engineer of one of the large
transmission systems. On some of their new lines, he said that
they were using a maximum distance between wires for the
purpose of obtaining the greatest possible line inductance, the
rise in voltage being greater than was desirable.
The form of e.m.f. curve has been mentioned as being some-
thing about which we need at present concern ourselves but
little. This is quite opposed to my own view. The capacity
charging currents on these high voltage lines very considerably
amplify any harmonics which may exist in the original wave.
CHOICE OF FREQUENCY. 145
Under such conditions, it is necessary that the wave form ap-
proximate closely that of a sine function. In modem generators
this is the case, which perhaps explains to some extent the
reason why but little is heard on the subject.
Mr. Lincoln: — Mr. Mershon advanced the idea that syn-
chronous apparatus could be operated at the receiving end of
the line to compensate for the inductive drop. I wish to take
issue on that point. It is possible so to operate synchronous
apparatus that the current at the receiving end of a transmission
is either lagging or leading with respect to the e.m.f . at the will of
the operator. That is, the inductive "drop " in the transmission
may be made to subtract from or add to the generator volts at
the will of the operator. This fact, however, is not going to help
line regulation, that is the change in receiving end voltage for a
given load change — ^unless the field strength of the synchronous
apparatus can be changed automatically with load. The limiting
factor in very long lines is regulation and I do not see how Mr.
Mershon's scheme of putting synchronous apparatus at the end
of the line helps regulation. And for the same reason I would
differ from Mr. Baum where he places the real loss in a trans-
mission line at somewhat less than I have. I have placed it at
15 per cent. He says it is not over 10 per cent, or 12 per cent.,
and he places the inductance drop at 30 per cent., instead of 20
per cent., as I had it. That inductance drop is going to have an
important influence in the regulation of the line, and if we are
going to limit our regulation to 25 per cent., I don't see how you
are going to allow 30 per cent, inductance drop, particularly with
loads of low power-factor.
Mr. Mershon: — I cannot quite agree with Mr. Lincoln. The
action of a synchronous motor with a constant excitation is
similar to that of a condenser so long as the voltage impressed
upon the motor does not vary, but as soon as the voltage begins
to vary the similarity ceases. If the voltage rises on a condenser
the condenser takes more current. If the voltage rises on an
over-excited synchronous motor the motor takes less current.
The voltage may rise to a point where the motor will take practi-
cally no current or it may increase to a point enough greater
than this so that the motor instead of taking from the line a lead-
ing current, it will take a lagging current tending to pull down
the voltage, or rather, limit the rise. The action of the idle syn-
chronous motor is therefore corrective which a condenser would
not be. This corrective action of a synchronous motor will
depend for its amount on the inherent regulation of the motor.
If we chose to go to extremes we might make the synchronous
motors dominate the system completely as regards the delivered
voltage and might keep the voltage variation as low as we
pleased by employing motors with very low inherent regulation.
Dr. Perrine:— I would like to say that whether it is pos-
sible or not to regulate a line with a synchronous motor as
the last speaker describes, it has never been done; but the
146 HIGH-TENSION TRANSMISSION.
regulation of the line by means of an automatically excited
synchronous motor has been done and was described by Mr.
Baum in his paper presented before the meeting last year, where
he showed how he regulated by means of an automatic exciter
the voltage of the Bay Counties line at Oakland, overcoming the
effect of capacity and inductance on the line by means of syn-
chronous motors.
Mr. H. a. Stores : — If the discussion need not be limited
to 200 mile lines, there are one or two points which might
be of interest. First, as regards the highest frequency which
will produce a noticeable flicker in the lamp. A number of
years ago in the laboratory at Columbia College we had a small
rotary converter which was under control so that we could pro-
duce alternating currents of any frequency we desired, and we
made a good many tests with 15 or 20 students at a time, in order
to determine what fiequency could be detected. The condition
is quite different from what it is to go where a system is being
operated at 25. You know the frequency, and you look at a
lamp, and you say, yes; you can see the flicker of the light.
But if you start with a high frequency and gradually lower it,
telling everybody to keep his eye on the lamp, different men will
at different instants say that they detect a flicker ; and if, as you
repeat that experiment, the same man detects a flicker repeatedly
at the same frequency, why that is pretty good proof that he
does detect the flicker. Under other conditions there is a good
deal of imagination about whether you detect the flicker or not.
As a result of a good many experiments of that kind, with lamps
of various efficiencies, we found that 20 or 21 was about as high
a frequency as any man could detect repeatedly. In fact, the
majority could not detect a frequency of 20.
President Scott: — I would hke to call attention to one thing.
We are here dealing with certain engineering problems. We
have a paper here which deals with the engineering question.
What are the factors in connection with a line, a very long line,
which bear on the determination of frequency ; and we have got-
ten off from that into a whole lot of commercial things which
have nothing to do with this question. What have incandescent
and arc lamps to do with this ? Mr. Lincoln has shown us here
that certain facts prevail if we want to transmit at 50,000 volts,
200 miles. If we get beyond 3,000 kilowatts, we are going to
exceed certain engineering limits which he has assigned, and he
has done well to call our attention to those things, and bring
them in as an engineering problem. The specific application
will come in somewhere else.
Mr. Mershon: — Mr. President, will you allow me to take
issue with you in six words.
President Scott:— In a moment. I call attention to tbi&
at this time, so that in this discussion we may endeavor to
keep in on the plane of engineering rather than commercialism ;
not that the commercial is not important, but that the other is
the important thing here. Now, in six words, Mr. Mershon,
CHOICE OF FREQUENCY. 147
Mr. Mershon: — 1+ seems to me that if you confined this
question of frequency to the transmission line alone, there would
not be any discussion. We would agree on the 25 cycles or
perhaps on direct current. It seems to me that an engineering
problem is always more or less commercial. A physical problem
is not an engineering problem until it is commercial ; it is simply
scientific.
A paper presented at the 20th Annual Convention of
the American Institute of Electrical Engineers ^
Niagara Falls, N. Y.. July 1st. 1903.
Y OR A CONNECTION OF TRANSFORMERS.
BY F. ^. BLACKWELL.
The two alternative methods, Y or A, of connecting trans-
formers to a three-phase system, come up for discussion with
every three-phase installation. A general statement of the ad-
vantages and disadvantages of both connections, as they appear
to the writer, is given here with the hope that those engineers
who have had most experience with power transmission will
contribute their views on the subject.
Transformers.
Assuming that three transformers are to be used for a three-
phase power transmission, and that the potential of the line is
settled, each of the transformers, if connected in Y, must be
wound for — or about 58 per cent, of the line potential, and
for the full line current. If connected in A, each transformer
must be wound for the line potential and for 58 per cent, of the
line current. The number of turns in the transformer winding
for Y connection is, therefore, but 58 per cent, of that required
for A connection and the cross section of the conductors must be
correspondingly greater. The greater number of turns in the
winding, together with the insulation between turns neces-
sitates a larger and more expensive coil for A connection.
The larger coil calls for a longer magnetic circuit and conse-
quently a larger and heavier transformer throughout. This is of
no importance when the potential of the coil is low or when the
transformer is large and the current high. In fact, in trans-
formers in which the current is heavy it is usual to divide the
conductors into several multiple circuits for ease of handling and
148
Y OR DELTA CONNECTION.
149
to avoid eddy current losses that occur when the cross section of
the conductor is too large. A few turns more or less in the wind-
ing under such conditions is, therefore, immaterial.
In transformers of small capacity wound for high potential, the
cost and weight are both considerably in favor of the Y connec-
tion of the high potential coils.
Where it is desired to secure the smallest transformers that can
be wound for any given potential, the minimum size of wire that
can be employed in the windings of the high potential coils and
give sufhcieat mechanical strength, is the limiting feature. A
transformer practicable for Y connection may be smaller there-
fore than can be commercially considered for A connection.
The Y connection requires the use of three transformers, and
if anything goes wrong with one of them the whole bank is
disabled. With the A connection, one of the transformers can
0g. I step Down Tran5former'For 400O Volt Y Distribution
be cut out and the other two still deliver three-phase power up to
their full capacity; that is, two-thirds of the entire bank.
Combined three-phase transformers are generally of small size
and on that account are preferably Y-connected on the high
potential side.
Grounding the Neutral.
If the common connection of transformers joined in Y is
grounded, the potential between windings and the core is limited
to 58 per cent, of that of the line, and the insulation between the
windings and core might be proportionally reduced. The same
argument applies to the transmission circuit and would allow the
size of the line insulators to be reduced.
The saving that can be made in insulating transformers by
grounding the neutral is not great with large transformers, but is
important on small ones, as the space taken up by the insula-
tion for any given potential is relatively greater in a small
150
HIGH-TENSION TRANSMISSION.
transformer. Under normal conditions, the potential between
any conductor of a three-phase transmission circuit and the
ground is 58 per cent, of the line potential, with either Y or A
connection, but the neutral may drift so as to increase the
potential with an ungrounded system. If one branch is partly
or completely grounded, the potential between the other two
branches and the ground is, of course, increased and may be
the full line potential. With a grounded neutral Y system,
a ground is a short circtdt of the transformers on the grounded
branch and the transmission becomes inoperative.
From the point of view of safety to life and prevention of fires
this is a desirable condition, especially if the low tension distribu-
tion is also grounded. If the high tension circuit makes contact
with the ground or low potential system, it can be immediately
cut out by fuses or automatic circuit breakers.
Fig. 2 Step Down Transformer For ^00\/o/-L Y Distribution
The difficulty is that a power transmission with grounded
neutral is likely to be frequently shut down by temporary
grounds, such as would be caused by a tree blowing against
one of the wires. Even if the circuit is not opened, the drop
ia the pressure due to the sudden " short " on the line will cause
synchronous apparatus to fall out of step. Under the same con-
ditions a system without a grounded neutral would give uninter-
rupted service.
Unstable Neutral.
If two transformers are connected in series, there is no cer-
tainty that they will divide the potential equally between them.
A system in which all the electrical apparatus is connected in Y
has somewhat the same characteristics. The neutral may drift
out of its proper place and there will be unequal potentials be-
tween it and the three conductors of the circuit, due to unequal
loading and differences in the transformers or transmission cir-
Y OR DELTA CONNECTION.
15]
cuits. Such unbalancing would cause unequal heating of the
transformers and if a four-wire three-phase system of distribution
were employed, would seriously interfere with the regulation of
the voltage. In transformers, therefore, have Y secondaries, it is
desirable that the primary should be A connected. Two systems
in common use with which A primary windings should be used,
are shown in Figs. 1 and 2.
Rise of Potential.
The high potential windings of transformers are necessarily
of high reactance, and if left in series with a circuit of large
capacity, as shown in Figs. 3, 4, 5 and 6, the leading charging
current flowing over the reactance may set up extraordinarily
high pressures. Figs. 3 and 4 represent Y connected banks of
three transformers, each connected so as to cause such a rise of
potential. In Fig. 3 the primary of one trasformer is excited by
a generator, the primary of the other two transformers being
^/9-3
Fig. 4.
open-circuited. In Fig, 4 the primary of one transformer is. open
circuited, the other two being connected to the generator. Figs.
5 and 6 show T connected banks of two transformers, which
might be used to transform from either two-phase or three-phase
to three-phase or vice versa, and are similar in action to Fig. 3.
If in any one of Figs. 3, 4, 5 or 6 the secondaries are connected to
a long distance transmission circuit, a pressure of many times the
normal potential will be set up between a and b, and between
B and c, that between a and c not being affected.
It is theoretically possible for a potential 100 times that for
which a transformer is wound, to be caused by opening the
primary switches of one or more of the transformers of a bank
connected in Y before the secondary switches are used. Of
course, actually, the current jumps across the insulation at some
point in the system before there can be any such increase in
pressure. If there are a number of banks of transformers in
parallel, this phenomena cannot occur except when all but one
152
HIGH-TENSION TRANSMISSION.
bank are disconnected. This source of trouble could be obviated
by employing oil switches on the high potential side which dis-
connect the line before the low tension switches are used, or
by triple pole switches on the primary which open all three
branches of the bank of transformers at once.
The selection of Y or A connection of transformers for long
distance transmissions should only be determined after a careful
consideration of the conditions in each case.
There is little choice between Y or A without a grounded
neutral.
f'/gS
Fig. 6 >
In small installations, the cheaper cost of transformers for Y
with a grounded neutral will be a determining factor. Larger
plants will be guided by the greater importance of giving unin-
terrupted service and will not employ a grounded neutral unless
demanded on the score of safety.
Where the amount of power is great and the system extensive,
A connection will be generally preferred on account of its avoid-
ing the possibility of rises of potential from any cause. Many
plants can have advantageously a mixed system with both Y and
A transformers, each installation of transformers being con-
sidered by itself.
Y OR DELTA CONNECTION. 153
[Contribution to Disscussion on F, 0. Blackwell's Paper
By J. S. Peck.]
Mr. J. S. Peck: — In his paper, " Star or Delta Connection of
Transformers," Mr. Blackwell refers to the grounding of the neu-
tral points of a transmission system, for the purpose of limiting
the strain between line wires and ground, and mention is made
of the fact that the neutral point is likely to drift out of position
and cause unequal voltage strains upon different parts of the
circuit.
The question of grounding or not grounding the neutral and of
the best method of connecting transformers is one of great im-
portance, and it is the object of this paper to point out some of
the conditions, both normal and abnormal, which arise with
different systems of connections with and without grounded
neutral.
By the grounding of the neutral point of a transmission system
it is sought:
First: — To limit the strain from line wires to ground.
Secondly : — ^To limit the strain between high-tension and low-
tension windings of the transformers, also between high-tension
windings and iron core.
There are a number of different ways of connecting trans-
formers for transmission work:
Single-phase, 2-phase, 3-phase-delta, 3-phase-T, 3-phase-V
2-phase-3-phase, 3-phase-star, 3-phase-star-and-delta.
Consider first the case of a single-phase transformer un-
grounded, with high-tension and low-tension voltages taken for
convenience as 10000 and 1000 respectively, (see Fig. 1). There
is evidently a maximum strain of 10000 volts from one high-
tension line wire to the other. If the circuits are insulated and
symmetrical there will be a strain of 5000 volts from each line
wire to ground, and from each extremity of the high-tension
winding to the low-tension winding and to the iron core.
If, however, the circuits are not symmetrical, the full strain
will not be equally divided, and if in an extreme case one high-
tension wire is grounded there will be a strain of 10000 volts from
the other line wire to ground; similarly, if one extremity of the
high-tension winding be connected to the low-tension winding or
to the core, there will be a strain of 10000 volts from the other
extremity of the high-tension winding to the low-tension winding
or to the core.
The actual strain between adjacent high-tension and low-
tension windings is equal to the high-tension voltage plus or
minus the low-tension voltage, depending upon the arrangement
and connection of the coils; but as the low-tension voltage is
usually a small percentage of that of the high-tension, it is custo-
mary to assume that the strain between windings is equal to that
of the high-tension voltage alone.
If the middle or neutral points of high-tension and low-tension
windings are grounded, the -iron core being also grounded (see
154
HIGH-TENSION TRANSMISSION.
Fig. 2), then as long as the circuits are in balance the voltage
strains will be the same as with the windings ungrounded, and
balanced ; but in case of a ground on either high-tension or low-
-1000V.
f lOOOO V.
Fio. 1
single Phase
1000 to 10000 voItB
Maximum Strain to Ground
10000 volte
tension line, or in case of a connection between high-tension and
low-tension windings, a portion of the windings will be short-cir-
cuited. This will, in general, blow fuses or open circuit-breakers,
thus cutting the transformer out of service ; or the voltage of the
G
J_
i
_L
FlO. 8
Single Phase Grounded Neutrals
1000 to 10000 volts
Maximum Strain to Ground
9000 volts
system will be lowered to such an extent as to call attention to
the trouble.
Thus, on a single-phase transmission system, the grounding of
Y OR DELTA CONNECTION.
155
the neutral point of primary and secondary windings will limit
the strain from line to ground, and from either extremity of high-
tension to low-tension and iron to approximately one-half the
normal voltage of the system. If the neutral of only one winding
is grounded, the strain from this winding to ground will be limited
to approximately one-half of its normal voltage, but the strain
from the ungrounded winding to ground and to iron and to the
grounded winding will not be thus limited.
In considering other systems, the voltage strains between
primary and secondary will not be mentioned, as these strains
are easily calculated when the voltage on the transformers and
the strain to ground is known. A short-circuit on a system will
be assumed to cut out the trasformers.
Fig 3
2-Phas6-3-Wlre
1000 to lOOOO volts
Maximum Strain to Ground
14000 volts
Two-Phase, Four-Wire System.
The 2-phase, 4-wire system is practically a double single-phase
system, and the conditions for grounded and ungrounded neutral
will be the same as for single-phase.
Two-Phase, Three-Wire System.
The voltage across the two outside wires is 1.4 that between
the middle and either outside wire. The connections and volt-
ages are shown in Fig. 3, which assumes 1000 to 10000 volt trans-
formers.
A ground on the middle wire will give a strain of 10000 volts
between each outside wire and ground, while a ground upon an
outside wire will give a strain of 10000 volts from middle wire
to ground, and of 14000 volts from the other outside wire to
ground.
156 HIGH-TENSION TRANSMISSION.
The neutral point for this system may be obtained from the
middle point of an auto-transformer connected across the trans-
former windings. In this case, a ground upon any line wire will
cause a short-circuit on the transformers, thus limiting the strain
to ground to approximately .7 normal line voltage.
Thus, with a 2-phase-4-wire or a 2-phase-3-wire-system,
grounding the neutral limits the strain from line wires to ground,
in the first case to one-half normal voltage, in the second case
to .7 normal voltage.
In general, the method of obtaining the neutral point by means
of auto-transformers is not feasible on high-tension systems on
account of the comparatively great cost of an auto-transformer
wound for the high-tension voltage, and it will not be further
considered in this discussion.
1
1
1
1
i
A AA A A aXa A A A A_
^\ /vyv /\
.yK/\ 1
o
o
o
o
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/ W WW VV vV V v^
J^
r* ^— ^^ v -v -v
t
■^
1 l_
X
—A o
1
o
\ '-J
C J
\ o
1
o
1 L
7 r^ ^^
\ o
1
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o
\ / h
_r <
I
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o
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1— 1 -^
■1
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1
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Fig. 4
a-Phase Delta Co
1
1
\
nnectlon
1000 to 10000 volts
Maximum Strain to Ground
10000
volt
8
Three-Phase, Delta System.
With this system shown in Fig. 4, the strain from any line wire
to ground is, with the system in perfect balance, 58 per cent, of
the line voltage. In case of a ground on any line wire, the -two
remaining wires are raised to full line potential above the ground.
With this connection one transformer may be cut out, leaving
two connected in V, and the above conditions will not be changed.
Three-Phase, " V " System.
With transformers connected in V, the strains will be the same
as when connected in delta.
Three-Phase, " T " and Two-Phase-Three-Phase System.
With either the T or 2-phase-3-phase connection the voltage
strains with ungrounded neutral are the same as for the delta
system. The neutral point may, however, be obtained from the
teaser winding (see Figs. 5 and 6), in which case a ground upon
any Une wire will short-circuit portions of the windings,
Y OR -DELTA CONNECTION.
157
With the 3-phase-T and 2-phase-3-phase connection the
grounding of the neutral Hmits the voltage between line and
ground to 58 per cent, of normal.
Star System.
With transformers connected in star the conditions are very
similar to those where two transformers are connected with
primary windings in series and also the secondaries in series.
Fig. 7 shows such a series combination, neutral not grounded.
Fig. 5
Three:pliaseT System. 1,000 to 10,000 Volts". Neutral Grounded^
.Maxinmni_StrainAoGround_5800 Volts.
Fio. 6
TWQrPb^e?r-Three-Pbase System. ' IQOO to 10000 Volts. IJeutral Grpnndedji
M aximu m Strain to Grognd 5800 Volts
The total line voltage will divide with approximate quality
between the two transformers. Between line wires and ground
there will exist the same strain as with a single transformer, hav-
ing the same total voltage; but if one transformer be short-cir-
cuited, the full voltage will be concentrated upon the other trans-
former so that the internal voltage strains on this transformer will
be doubled and its iron loss greatly increased, through the strain
from line wires to ground may be the same as before.
158
HIGH-TENSION TRANSMISSION.
If the series connection between the two transformers be
grounded (Fig. 8), and a ground occur on either Hne wire, the
transformer connected to this wire will be short-circuited and the
FlO. 7
Two Transformers — 1000 to lOOOQ Volts. PrimarifS
and Secoodanes in Series. Each Transformer takes
approx. i Line Voltage.
TT —
.NEUTRAL
G
' S
> >
1
^ 1
!
> 1
1
> 1
f
FiO. 8
Two Transformers, Primaries and Secondaries in Series.'
Neutral Grounded Ground on Outside Line Wire Short
Circuits Adjarent Transformer and Gives DoubliVoUage
on Other Transform2r. Full Voltaje Strain to Ground.
other transformer will take the full voltage of the circuit and the
ungrounded wire will be raised to full line voltage above ground.
Unless the leakage current of the transformer working at
Y OR DELTA CONNECTION.
159
double voltage is sufficient to open the circuit, the transformer
may continue to operate indefinitely under the above conditions
provided it does not break down, due to excessive heating or to
the double voltage strains to which it is subjected.
In Fig. 9 is shown a star-connected group of transformers with
the neutral point of the primary and of the secondary, and also
that of the generator, grounded. In this case no excessive volt-
FlO.9
0600 V.
t
>
""A
o
■** s
o
1
t
1-
♦
Three-Phase Star System. Line Voltage 1000 and 10000 Volts. Transformer Voltaoe
CSC and-fiSOO. Grounds on Neutrals of Generator and Transformers. Max. Voltages per
Transformer S800, Max. Voltage to Ground 5800.
age can occur on any transformer, and the strain from any line
wire to ground is limited to 58 per cent of full line voltage, for a
ground on any line or a short circuit in any transformer will
short-circuit the generator.
Fig. 10 shows the same system of connection but with the
generator ground omitted. In this case a ground upon a
primary or secondary line will short-circuit one transformer of
the group and the two remaining ones will be operated at 73 per
cent, above normal potential; also the strain between the un-
grounded wires and the ground will be that due to the full line
voltage.
FlO. 10
Three-Phase Star. Primary and Secondarv Neutrals grounded. Line
Voltage 1000 to 10,000. Normal transformer voltages, S80 and SSOO. Ground
on one line wire short circuits one transformer, increases voltage on other
transformers 73%, raises two line wires 10,000 volts above ground.
Thus for a star connected system the grounding of the neutral
points is of no value in limiting the voltage strains on the system
unless the neutral point of the generator be also grounded ; in
fact, the grounding of the transformers without the grounding of
the generator increases the chance for trouble, since a ground
upon any line wire increases by 73 per cent, the voltage of two of
the transformers.
160
HIGH-TENSION TRANSMISSION.
Star-to-Delta System.
Fig. 11 shows a star-to-delta system. With this method of
connection no excess voltage can be obtained on any transformer,
and not more than full voltage strain to ground, provided the
delta remains closed ; but with the delta open at one point and a
Fig. 11
Star to Delta System.
Line Voltages 1000 and 10000.
Transformer Voltaees, 580 and lOOOOv
short-circuit on one transformer (Fig. 12), the voltage on thetwo
remaining ones -^ill be increased 73 per cent, and across two sides
of the delta there will be three times normal voltage. Thus, on a
10000 volt circuit, 30000 volts may be obtained in case a trans-
former is short circuited and cut out of the delta.
This excess voltage across the two sides of the delta is due to
the fact that a short-circuit on the star changes the angular
position of the voltages from 120° to 60°, which in turn changes
the angular position in the delta from 60° to 120°.
Delta-to-Star System.
With this system it is impossible to obtain voltages higher than
normal upon any transformer or between any two line wires. A
short-circuit in one transformer may, however, cut it out of the
1
§
I
VOLTS
r^llr
1
V_|l''^
§
PRIMARY
%^
FI8.12
Same as Fig. 11 except that Delta is opened and one transformer rhort
cireuited. Voltage' of two transformer increased 73%. Voltage betvreen.
two fine -wires increased 200%.
delta but leave the star-connection intact. In such a case the
voltages will be as shown in Pig. 13. Two of the transformers
operate at normal potential, with normal potential between two
of the line wires, but with 58 per cent, of normal between th6
other wires.
Y OR DELTA CONNECTION.
161
Star-to-Delta, Raising. Delta-to-Star, Lowering.
In Fig. 14 is shown a transmission system with raising-trans-
formers connected star-to-delta, and lowering-transformers con-
nected delta-to-star. The voltages obtained across transformers
and across line wires are shown. The neutral points of the low-
tension windings of both raising and lowering-transformers are
grounded, generator neutral not grounded.
Three-Phase Delta to Star System. Line voltages 1060 and 10000.
Transformer voltage lOOOjand 5800 One transformer short circuited and cut
out of Delta. Two transformers continue to operate at normal voltage,
giving 10000 volts across two line wires. 6800 volts across others.
Fig. 15 shows the voltaiges which will be obtained with a
ground on one low-tension lead which short-circuits one trans-
former. The high-tension side of this transformer is cut out of
the delta. The voltage across the other transformer is increased
73 per cent, and the phase relation changed from 120° to 60°, the
voltages being as shown in Fig. 12. On the lowering-delta, three
times normal voltage is impressed on one transformer and 73 per
cent, above normal voltage on the other two. The voltages
obtainable across the star on the lowering-transformers are
readily understood from the figure. It will be noted that across
one phase there is normal voltage and across the other two phases
..._„,, ^,,_
1 Ik
A ?
' rV
tf^^WwCb °
f ) T
g J
*i
s
s
1
-4
*
Fig 14
Star to Delta Raising Delta to Star Lowering Neutral of Raising
and Lowering Transformers grounded.
Line Voltages 1000 to 10000 to 1000. Transformer Voltage 580 to 1000 to 680.,
2.7 times normal voltage. It is probable that a transformer sub-
jected to three times normal voltage would take so large a
leakage current as to blow fuses.
With this system of connections, grounding the neutral point
of the star without a ground upon the neutral point of the gen-
erator is of no use in preventing unequal and excessive strains on
the transformers and from Hne wires to ground. Should the
162
HIGH-TENSION TRANSMISSION.
delta on the raising -transformers be kept closed, it is obvious that
a short-circuit on any raising -transformer would short circuit the
generator, but the above condition is one which might very
possibly occur where switches or fuses are placed inside the delta.
Delta-to-Star, Raising. Star-to-Delta, Lowering.
Fin. 15
Same as Fig. 14, except that one raising transformer is short■ A
1
8 / \
>
§1 / \
o
T
>l
. -i
4
St },
Fig. 16
Delta-to-Star Raising. Star-to-Delta, Lowering.
Line voltages 1000 to 10000 and 1000
5800 to .1000.,
--„- Neutrals not grounded,
transformer voltages 1000 and
above normal ; that on one transformer 73 per cent, above normal
and on the other it is normal.
If the neutral points of raising and lowering transformers are
grounded the abnormal conditions shown in Figs. 17 and 18
cannot be obtained, for in this case, with the lowering -delta closed
Y OR DELTA CONNECTION.
163
as in Fig. 17, the fuses will be blown when a lowering-transformer
is short-circuited; and with the delta open as shown in Fig. 18,
a short-circuit in the lowering-transformer will short circuit the
generator.
Some abnormal conditions which may be obtained from a few
of the possible combinations of transformers have been given
Fig. 17
Same as Pig. 16. except that raising Delta is open and one transformer
snort circuited. Vbltage on, lowering transformers less than normal. Note
the extent to which the Delta is distorted. If neutral points of raising and
lowering transformers be grounded, this distortion cannot occur, as fuses
will blow when raising transformer is short circuited.
above. These abnormal conditions are produced by combina-
tions which are accidental or unusual ; but it is the accidental or
unusual condition which must be taken into consideration and
guarded against, if trouble is to be avoided. Some of the condi-
tions which are shown, undoubtedly have occurred in practice
and are possibly responsible for some of the troubles on high-
voltage transmission systems.
It is obvious that a large number of combinations of raising and
lowering-transformers in addition to those given above may be
obtained, and in the following tables it has been endeavored to
give the most common of these combinations and to show the
abnormal conditions which are obtainable.
Resonance. — The abnormal voltages given above are those
which are obtained from the generator pressure through direct
Fig. 18
Same as Pig. 16. except that lowering Delta is open and one transformer
short circuited.
Voltages on raising transformers normal and 0.
Voltages on lowering transformers normal, 73% above normal and 0.
Voltages across secondaries normal, 73% above normal and>165% above normal.
transformation. Mr. Blackwell, in his paper, " Star or Delta
Connection of Transformers," has called attention to another
cause which may produce abnormal voltages, i.e., Resonance.
This is particularly liable to occur when a high inductance, such
as the winding of an idle transformer is in series with a large
capacity, such as that of a transimssion line.
164
HIGH-TENSION TRANSMISSION.
In the tables below, where the combination is such as to give
an idle transformer in series with an active transformer and a
transmission circuit, it is indicated in the column headed "Reso-
nance."
Table I.
Systems op Connecting Transformers with Voltage Strains
Obtainable.
Single Transformation.
Maximum Voltage.
Possi-
bility
System.
Neutral.
Per
Be-
To
of ■
Trans.
tween
Ground
Reso-
%
Wires.
%
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nance.
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2-phase-4-wire
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100
100
50
No.
Single phase or
2-phase-4-wire
(6) No Ground.
100
100
100
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2-phase-3-wire
" "
100
140
140
Yes.
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" "
100
100
100
No.
3-phase V
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100
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100
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or 3-phase T . .
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100
100
58
*'
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(6) No Ground.
100
100
100
*'
3-phase-Star. . .
Grd. or not Grd.
173
100
100
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100
100
58
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Open or Close
100
100
100
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173
300
300
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" Closed.
100
100
100
No.
Delta to Star....
(a) Grd. Delta
Open.
100
100
100
"
"
(6) Grd. Delta
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100
100
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168 HIGH-TENSION TRANSMISSION.
In the above tables, it has not been attempted to show all the
operating conditions with each of the combinations. The re-
maining ones may, however, be readily worked out.
In addition to the combinations given above there are the
2-phase-3-phase, 3-phase-V and 3-phase-T connections which
may be used at either the raising or the lowering ends. When
used for raising- transformers, these combinations will deliver their
proper voltages to the line provided the proper voltages are im-
pressed on their primary terminals, as it is impossible by short-
circuiting one transformer to raise the voltage of the other.
When used as lowering-transformers these combinations will
supply to the secondary circuits, voltages of proper amount and
bearing the proper phase relation to each other, provided the
voltages impressed on the primary side are of proper amount and
proper phase relation to each other. If, however, the voltages
applied to the primary are distorted then the voltages delivered
by the secondaries will be correspondingly distorted.
Grounded Neutrals. — It will be noted that in many cases the
grounding of the neutral points of a transmission system limits
the voltage strain to ground and the voltage which may be ob-
tained across any transformer, and in such cases grounding would
seem advisable. This is notable in the case of the star-system
with grounds on transformer and generator neutrals. There is,
however, a danger arising from this grounding which should be
carefully considered. In case of trouble on the circuits, current
may flow through the ground to the neutral ; in thus flowing it
will naturally take the path of least resistance, so that if telephone
or telegraph lines, which have normally low resistance to ground,
parallel the transmission circuit, the current will flow along these
wires, often with disastrous results to the circuits.
Two cases of trouble are particularly liable to give these con-
ditions :
First: — Where the neutral points of the high-tension windings
of raising and lowering-transformers are grounded, the opening of
one or two of the three transmission wires will cause currents to
flow through the ground.
Secondly: — A high resistance ground on a transmission wire
will partially short circuit a transformer and cause current to flow
through the ground to the neutral.
Some plants have been able to operate satisfactorily with
grounded neutrals; with others this grounding has caused great
disturbance on telephone circuits, and in one plant it is reported
that the blowing of a fuse on one of the high-tension wires put out
of service the telephone systems in " ten counties." Thus, while
grounding of neutrals may be permissible in certain localities it
may not be allowable in others ; and in laying out a plant it would
seem to be advisable so to arrange the apparatus that it may be
safely operated without grounding the neutrals.
An examination of the tables given on the previous pages indi-
cates that the delta-system is the one giving the minimum chance
Y OR DELTA CONNECTION. 169
of trouble. Under certain conditions, however, the star and star-
delta systems will give satisfactory service.
The choice of a system of connections for any high-voltage
transmission system is evidently a matter which should be care-
fully considered, account being taken of the possibility of obtain-
ing excessive voltages under accidental conditions, the chance of
trouble on parallel circuits, due to grounded neutrals, and the
possibility of obtaining resonance when switching or under other
similar conditions.
President Scott: — The question of grounding one point of a
transmission line is a very important one, and it is one which has
received a good deal of attention during the last few years. I
remember when some engineers with whom I was acquainted
went West to visit transmission plants, I asked them to look
into that point particularly, and from the evidence which they
got, and from the evidence that I obtained when I took a trip
West some time ago, and from what I have heard since, I have
concluded this — that some plants grounded the neutral, and its
engineers considered it safe and would never think of running
in any other way, while the engineers of plants which did not
ground the neutral would never think of doing such a thing. It
is an important question; it is partly theoretical, it is largely
practical and one which is not yet settled. We should like
particularly to hear from out western friends on this point. The
subject is open for discussion.
Mr. Hayward: — As you say, Mr. President, this has been a
subject of discussion for a good while, as to whether to ground
or not to ground, and our friend Mr. Nunn has been operating
his lines grounded from the very start, but I believe Mr. Gerry is
operating without ground. We, with our 16,000 or 17,000 lines,
have operated with a double delta connection without any
grounds on. The experiences we have had without grounds are,
of course, that you may have a short circuit on one wire, and the
wire down, and you could still keep running. Still, I believe —
and this is only an opinion — that when we get up to any very
high voltage, after all it is better to ground the neutrals and
keep them grounded everywhere. It is better, I think, to avoid
any chance of these extra high voltages that may occur, and I
want to say very emphatically that they have occurred in
practice, where some of the conditions mentioned by Mr. Peck
and some mentioned by Mr. Blackwell have held. I therefore
think that it is probably best to ground every neutral point. We
are changing from a delta-delta connection to what will be a Y
to delta connection and various other connections which we have
not been running hitherto, simply because we are changing our
voltage on the high tension lines from 16,000 to 28,000, and we
intend to change our distribution in Salt Lake City from 2,300
volt to Y-connected 3,800 volt. Of course, we all recognize the
difficulty of a single short circuit on a line with grounded neutral
single breakdown on the line with grounded neutral—
170 HIGH-TENSION TRANSMISSION.
means short circuit. Yet, after all, we have to recognize this,
that our lines must be made so that they will not break down.
There is just one point — the rise of potential mentioned in Mr.
Blackwell's paper, page 151 — the conditions holding in Fig. 3 or
4, I don't know exactly which, actually occurred in testing a
transmission line in 1897. The conditions were that we had 37
miles of line. We connected the two circuits on the pole line to-
gether solidly, making a line out and back of 74 miles. We got a
delta-star connection and tried to see what the charging current
on the line was. Having tried with the three switches closed, we
then thought we would like to see what it would be with only two
switches closed; and as soon as we got up to about 25,000 or
26,000 volts an arc jumped across the wires, 12 inches apart.
Not only did it do it once, but it did it every time. That is the
condition mentioned by Mr. Blackwell right here. If you get
the conditions that are laid down here they will occur sooner or
later in practice, and they will find out your weak spot.
President Scott: — Mr. Gerry, we turn now naturally to you.
Mr. Gerry: — I do not know, Mr. President, whether I can
add anything of value to this discussion. The selection of either
the s^ar or the delta system of connecting transformers is, to a
certain extent, a matter of engineering detail. I say this for the
reason that I believe satisfactory results can be obtained by the
use of a star connection, although not quite as good results as by
the use of a delta connection, on a transmission line. The points
of advantage and disadvantage have been referred to generally
by Mr. Blackwell and Mr. Peck. The points brought out by
Mr. Peck are of great interest, but a plant can be arranged in such
a manner as to avoid practically all the dangerous conditions
outlined for a plain star system. It is possible to provide,
switching devices of such a nature that all three transformers
will be cut out automatically, at the same time, in case of trouble
with any one; or if a ground appear on the system, and this
should always be done on a star connected transmission line,
even if the neutral be grounded at the generators in addition to
grounding at the transformers.
Mr. Peck, in introducing his discussion, says: " By the ground-
ing of the neutral point of a transmission system, it is sought,
first, to limit the strain from line wires to ground." Only a
short time ago that was considered of great importance as reduc-
ing the strains on the insulation of the line. As a matter of fact,
that does not limit the possible strain on the insulators to the
pressure from wire to neutral. Even with all the neutrals
grounded at the ends of the transmission lines, it is possible,
owing to the resistance of the ground circuit, to have on the
insulators the full line pressure between wires. In other words,
even with a grounded neutral at the generators, it is possible
locally, at points on the transmission line, to have the same
pressure between the ground and any one line, that you have
between any two wires of the circuit. Mr, Blackwell, in referring
Y OR DELTA CONNECTION. 171
to the advantages of a grounded neutral, in several instances
states that in case of trouble, such as a ground on one of the
wires, the result will be immediately to open the automatic
devices and cut off the transformer coils from the line. Now,
the same result can be accomplished with a delta connected
system, by means of suitable automatic devices and without
throwing a short circuit on the system.
There are a number of operating advantages of the delta con-
nection, one of which I will mention. A transformer may be
cut in and out of service, in and out of delta, with very great
convenience and with no disturbance of the system, and con-
siderable operating advantage is thereby obtained, especially
where the number of transformers is limited. It has just been
suggested that one advantage of the star system is that it is
possible to put in transformers connected in delta, and after-
wards increase the voltage by changing over to a star connection.
As a rule, however, I believe it would be better to arrange the
switches for delta connection, and accomplish the desired result
by double winding the transformers, operating the coils at first in
parallel, and later in series.
Mr. Converse: — Mr. Hayward referred to the plant of the
Telluride Power Company. I have had considerable to do with
the transformers of that plant. It is an old plant, at least we
consider it so now. I would say that those transformers were
built for star connection on a high-voltage and a low-voltage,
and we have had some results there. A great many things
have happened there, and I would ask Mr. P. N. Nunn, Chief
Engineer of the Telluride Power Company, who is here, to tell
us something of them.
President Scott: — I had it in my mind to call on Mr. Nunn
very shortly. Mr. Nunn's work has figured largely in our
Institute, both in papers which have been presented and in
discussions from time to time; but Mr. Nunn himself, who has
been so intimately connected - with a great deal of this high-
voltage and pioneer work, has not been very much in evidence.
We are very fortunate in having him here.
Mr. p. N. Nunn: — In our Utah system, star connected
transformers with grounded centers have been the rule, although
the initial transmission employed three-phase two-phase step-
down transformers.
Transmission difficulties have been chiefly traceable either to
outside interference with our lines, or to the opening of circuits,
especially by fuses. The line system is rather complex, the
main transmission consisting of duplicate three-phase, three-
wire, 40,000 volt lines extending from the Provo to the Logan
power house, a distance of approximately two hundred miles,
through the several markets of Salt Lake Valley. These are
divided into sections, and so arranged that a defective section
will cut out without interrupting the whole system. Until
recently we have been obHged to protect these sections, as well
172 HIGH-TENSION TRANSMISSION.
as our generating and substations, with fuses and to switch at
the same points with air-brake switches. Neither of these de-
vices has been satisfactory. The blowing of a single fuse is often
followed by the blowing of others, sometimes at distant points,
and the opening or closing of switches sometimes produces the
same result. It seems imperative that all wires of a circuit
should be opened or closed simultaneously, and in this respect
the automatic triple-pole oil-switches, with time-limit attach-
ment, which are now being installed, should prove invaluable.
The mere opening or closing of circuits may have caused ex-
cessive rise of voltage, as we certainly have had at times some
abnormal rises. I recall clearly one instance when current
jumped a full eight feet from a conductor to the steel framework
of the roof of the station. This may have been due to atmos-
pheric disturbances, although there were no indications of
lightning.
From the first we found that a ground on one line did not short-
circuit the generator, and noticed that the first indication of such
a ground was the arcing of the current over the lightning ar-
resters. Investigation of the conditions led to the discovery
that we had full line voltage between the remaining lines and
ground, which accounted for the disturbance on the arresters,
and also full line voltage on the active transformers, instead of
the normal 58 per cent, of line voltage. No transformers have
ever been burned out due to this condition, and no serious incon-
venience has been suffered so far as I know.
This plant has been in operation nearly six years, employing
as stated, star-connected, grounded center transformers and on
the whole has been, I think, a pronounced success. Whether
the difficulties mentioned have been aggravated by the connec-
tions of the transformers, or whether we would have suffered less
with delta-connected transformers, I do not know.
President Scott: — I would like to ask Mr. Nunn about one
point. You have grounded the central point of the high-tension
system. Is the central point of the generator grounded pri-
marily ?
Mr. Nunn : — The central points of both low and high-tension
winding of the step-up transformers are grounded. The gener-
ator winding is not otherwise grounded.
Mr. Thomas: — Mr. Blackwell's paper contains a statement on
page 151 which I think needs a little further explanation — the
last paragraph:
" It is theoretically possible for a potential 100 times that for
which a transformer is wound, to be caused by opening the
primary switches, etc."
Of course this is true if we neglect all true energy losses in the
system, but there is inherently linked with the condition which
he speaks of here an energy loss which must necessarily limit this
rise of potential very materially. That will probably bear a
little further analysis.
Y OR DELTA CONNECTION. 173
The conditions of resonance at normal generator frequencies,
as shown in most all these discussions, requires that the leading
current to a transformer line pass through a transformer in
one wiiiding, the other winding being open circuit The only
way it is possible to get a high enough inductance to meet the
condition for resonance is by means of iron in the magnetic
circtiit in the transformer. As we all know, there is a con-
siderable true loss represented by the energy taken by an open
circuited transformer — open circuited, I mean, in the other
winding. In some designs I have looked over, this true loss is
almost as great as the apparent loss, though not quite so great.
In other designs the true loss, I presume, may be half as great
as the apparent loss. Now, the resonance results from the
action of the potential from some generating source, which
builds up oscillations in the oscillating circuit. This generator
must supply the true loss. If the true loss is nearly half the
total apparent energy, taken by the transformer when connected
across the mains, — I mean the total energy, now, considering
impedance — then if we should by resonance increase to double
this true loss by increasing the voltage on the transformer, no
higher potential can be built up, because all the true energy
supplied by the generator is absorbed. This can be made a
little clearer by considering the formula which gives the result
of the current in the circuit containing inductance, capacity and
resistance when conditions are right for resonance.
T, r^ ^ General Voltage
Resonance Current = — , ° ~
X Sin
(^— ■^')
This formula states that the current equals the potential
applied from the generator, divided by the true impedence of
the circuit, which can never be less than the ohraic resistance i?.
If this allows only double current on normal voltage, resonance
can cause no greater rise. Since the ratio between the true loss
and the apparent loss of transformers changes materially with
changing induction in the iron, and when above saturation the
magnetizing current goes up very fast in proportion to the true
energy current turns, it follows that perhaps the resonant current
may haVe to increase several times to cause a doubling of the
true loss. This suggests another point if you have the proper
frequency for resonance, before e.m.f. is applied, assuming
normal magnetic induction in the iron of the transformer. Then
if resonance builds up the voltage to perhaps three or four times
normal potential, the induction of the transformer has also
. changed very materially on account of the greater magnetizing
174 HIGH-TENSION TRANSMISSION.
current causing a great lessening of permeability and a reductioi
of the inductance as a choke-coil. Consequently the natura
frequency, of the generator, which should give resonance wilj
perhaps be several times larger than before the rise of potential
started. It is thus quite unlikely with this type of choke-coil
that resonance would reach a very high value, even if it were not
limited by the true loss. However, when the inductance through
which the resonance occurred is not denied for a closed magnetic
circuit, as in the case discussed, the true loss is a very small
percentage of the total apparent energy and no low limit to the
resonance rise can be thus assumed.
In regard to static resonance — I mean -resonance at very high
frequencies, where choke-coils without rim coils might have the
proper resonance values — it seems to me there is little danger of a
very considerable rise, because, so far as I know, there is no
source of continuous, constant value alternating e.m.f. at a very
high frequency. Most discharges we get are perhaps oscillatory,
but they lose their intensity very rapidly, two or three oscilla-
tions, only, probably, having anywhere near the maximum
values of potential.
I would like to ask Mr. Mershon, in the absence of Mr. Black-
well, whether Figs. 5 and 6 on page 152 should not show a
ground on either line A or C, or some form of unbalancing. As
those stand, I do not believe that resonance can occur. For
instance, in Fig. 5, we have the natural tendency when the gener-
ator excites the lines for changing current to pass from B to A
and from B to C, but these currents will be equal if there is no
unbalancing, and since they pass in opposite directions, through
the halves of that idle transformer, there would be no choking
effect except the small amount due to the magnetic leakage of
the transformer. In Fig. 6, the natural tendency is, for the
charging current to pass from A to C, and even if the line B is
connected at the middle point of the transformer, it is naturally
at earth's potential and would never receive any charging cur-
rent at all. Of course, if either line is then balanced or grounded
there then appears a condition for resonance. Am I right in this
conclusion ?
Mr. Lincoln: — Just one point; I was going to mention a
number, but Mr. Thomas has got in ahead of me on the others.
One point struck me in connection with the statement of Mr.
Blackwell, that theoretically 100 times normal potential was
possible in a condition of this kind — resonance. In that con-
nection I was very much interested in reading a contribution
by Mr. M. I. Pupin, contributed to the Transactions of this
Institute in 1893, in which he showed how very difficult it was
to maintain resonance with iron circuits. He showed that
resonance, where there was no iron in the inductance, was very
marked, but as soon as iron was introduced into his coils the
difficulty of obtaining resonance conditions became extremely
marked and very difficult to obtain; and that same condition
F OR DELTA CONNECTION. 175
would, I think, apply here, where you have iron in the circuit of
the choke-coil, and would prevent a rise in voltage anywhere near
approaching that stated by Mr. Blackwell.
Mr. Peter Junkersfeld: — In Chicago we have been operat-
ing a 4-wire-3-phase-60-cycle overhead system with a grounded
neutral for about three years. The generators are star con-
nected, and the common point is connected to the ground. It
has been very successful from the start. We, however, ground
in the station only, and do not ground any other point of the
primary system. The neutral, on the secondary of transformers,
is also grounded.
In our underground system, which is operated at 9,000 volts
and 25 cycles, we likewise operate now with the grounded neutral.
For the first four or five years' development while the voltage was
only 4,500, we had step-up transformers and they were con-
nected in delta, but the next step beyond tnat was to double the
voltage to 9,000 and install line voltage generators, which have
been operated with the grounded neutral. There is one thing
though that we have discovered, or rather which has been
brought to our attention very forcibly. That is, the necessity
of doing away with single-pole switches and fuses, and things of
that sort. We have nothing but straight 3-pole oil-switches.
We have no plug change-overs, or fuses or single-pole switches.
Those have all been done away with, and we believe it is very
necessary to do so.
I might say that a great many of the conditions that are laid
down here by Mr. Peck and Mr. Blackwell, as Mr. Hayward very
forcibly brought out, do occasionally occur in practice, and that
is something which needs a great deal of attention. As regards
the delta or star-connection, in our experience we have found
that the number of transformer troubles are after all compara-
tively few. In six years I can recall only four, possibly five,
cases of serious transformer trouble in substations. With the
increase in the number of transformer and rotary converter
units feeding an interconnected network, we have come to the
conclusion that the advantage of having delta-connected trans-
formers in order to be able to cut out one of the bank and operate
with two, is not very great. In the earlier history, when our
installations were small and few in number, it was an advantage
to have the delta-connected outfit, but with a larger number
that advantage disappears, and to-day we are installing Y-con-
nected 3-phase transformers, the idea being that these trans-
former accidents occur very rarely, and When they do occur a
whole unit is usually shut down, in any event for a short time,
and we can then just as well afford to have it shut down until
such time when the whole 3-phase outfit can be replaced.
Mr. Mershon: — Mr. Gerry said something in regard to auto-
matic means for cutting banks of transformers free on both sides.
That would mean reverse circuit-breakers, and it would mean
not only reverse circuit-Ureakers, but it would mean 40,000 our
176 HIGH-TENSION TRANSMISSION.
50,000-volt circuit-breakers. Mr. Gerry knows something about
automatic circuit-breakers for 40,000 and 50,000 volts. I would
like to hear from him in regard to that.
Mr. Gerry: — My remarks just now were intended to indicate
that with proper arrangements, either the star or delta con-
nection might be used with good results. If star connections
are used on high voltage transformers, in fact on any transform-
ers, it is desirable, in order to obtain proper safety, to have
devices which will open all three legs of the circmt at one time
but if the delta-connection be employed, you may use single-
pole switches. For this and other reasons, up to the present
time, I have always considered that there were advantages in
using a delta-connected system. Single transformers may be
conveniently switched into and out of service; single-pole
switches may be employed if desired and at the same time all
those excessive potentials mentioned by Mr. Peck will be avoided
and resonance will not be likely to result. In other words, a
plain delta is at once a flexible and safe arrangement to adopt.
In reference to high-tension circuit-breakers for transmission
lines, the time is coming, if it be not here already, when an oil-
switch can be obtained, together with reverse current and over-
load operating devices for any voltage and capacity, which will
open all three legs of a circuit. Mr. Nunn touched upon this
subject just now, and it is of great importance, especially with a
star-connected system. Whether the star connection is the
more desirable is another question, but I do not consider it vital
in connection with operation, if proper precautions are taken. I
do, however, consider the proper arrangement of switches, with
either the star or the delta, a very important problem in con-
nection with the system.
Mr. A. L. Mudge: — Page 149, lines 16 and 17, the words "And
the other two still deliver 3-phase power up to their full capa-
city, i.e., two-thirds of their bank," should read, I think, as fol-
lows: "And the other two still deliver 3-phase power up to 86.6%
of their full capacity, i.e., 57.7% of their entire bank."
Mr. J. E. Woodbridge: — The special case of high-tension
distribution of power for the operation of rotary converters
brings up some considerations not mentioned in Mr.Blackwell's
Introduction.
In distribution of this kind the secondary voltage of the step-
down transformers is so low that there is no advantage in a
Y-connection of the secondary coils. In fact, this would prove
a positive disadvantage. For this reason a delta connection
of the secondary windings is to be preferred for 3-phase con-
verters. With the primary windings connected Y and the
secondaries delta, operating synchronous machinery, there is no
instability of the neutral. While it is true that a Y-delta con-
nection of three transformers with no neutral lead throws the
whole bank out of service if one is disabled, the grounding of the
high-tension neutral of both the step-up and step-down banks
Y OR DELTA CONNECTION. 177
gives a radically difEerent condition. With this connection one
transformer of the three may be taken out of service and the
remaining two will continue to deliver 3-phase current just as
will two transformers connected delta-delta on a 3-phase system.
It will be noted that when one transformer on a Y-delta con-
nection with grounded neutral is taken out of service, one of
the three line wires is also open-circuited. Thus not only does
this connection allow service to be resumed with one transformer
crippled, as soon as this transformer can be disconnected, but it
allows service to be continued with one line wire in trouble,
either broken, crossed with another wire, grounded or attached
to a punctured insulator. It has often been claimed for the
delta-delta connection of transformers that the ability to operate
on two in case of trouble with the third is a great advantage.
There are now in operation in this country many railway distri-
bution systems with lines of moderately high-tension, 10,000 to
15,000 volts, put up on trolley-supporting poles along the right
of way, which frequently is the public highway, with many
trees and maSiy turns, and lacking the substantial and carefully
worked out details of the lines of heavy transmissions. These
railway distribution plants, so built, are subject to unavoidable
line troubles many times more numerous than transformer
breakdowns. It seems to the writer that any connection of the
transformers which allows operation with one line wire in trouble
is much more valuable in such cases than any which simply
provides for transformer troubles.
The drop on a 3-phase line with grounded neutral is increased
just 50 per cent, when one line wire is thrown out of service, the
other two being used on Y-delta connected transformers; this
being based on the assumption that the ground or track return
has a negligible resistance in the high-tension transmission. The
writer has operated a railway substation in this way on two wires,
starting a rotary converter as an induction motor by means of
alternating currents applied directly to its armature, and carrying
the load with two wires in service with no apparent difference in
the operation from the usual results obtained with all three wires
in service. In fact, much to the writer's surprise, there was no
apparent eflect on the telephone line which was on the same
poles with the high-tension line for several thousand feet, one of
the three high-tension wires being completely disconnected at
both ends. At one time while operating in this way the trans-
mission line became reduced to one active wire and ground,
owing to the melting out of a temporary low-tension connection.
The substation continued to carry its load and the trouble was
not noticed for some time.
It is also of interest to note in this connection that 6-phase
rotary converters supplied from diametrically connected trans-
formers will start and carry load satisfactorily when supplied
with power on two diameters only. With a Y diametrical
connection of the step-down transformers and with a grounded
178 HIGH-TENSION TRANSMISSION.
neutral the cutting out of one transformer would of course
reduce the supply of the 6-phase converter to two diameters.
It is almost needless to state th^t a 6-phase converter with
double-delta low-tension connection would operate satisfactorily
on two transformers.
Referring somewhat more in detail to the advantages and dis-
advantages of a grounded neutral, an investigation of the action
in case of a punctured or broken line insulator is of interest, as
most of the serious line troubles come from insulator breakdowns
causing the burning off of cross-arms or pole tops which fre-
quently results in complete shutdown. With no ground on
the neutral, the puncturing of an insulator generally manifests
itself as a ground on the system. To guard against burning of
cross-arms or poles, it is possible to solidly ground the faulty
phase, thus removing all electromotive force from the faulty
insulator, but this method seems open to the objection that if one
insulator will break down under the Y voltage of the system, it
is inadvisable to subject two-thirds of the total number to nearly
twice this voltage. Some lines are now being built with a fourth
wire with switching arrangements at each end of same, so that
in case of trouble on one wire the fourth can be connected into
circuit in place of the faulty conductor. With a grounded
neutral the question arises whether a broken insulator would
cause sufficient leakage to open the circuit through overload, or
would burn off cross-arm or pole-top without giving previous
notice to the station attendants. A ground wire on the poles
electrically connected to an iron pin in each insulator would
make a short circuit of each insulator breakdown, and would
prevent burning off of pole tops. With instantaneously acting
autometic switches it would also prevent what is sometimes
worse, i.e., the burning apart of transmission wires and dropping
of same across other circuits or to the ground.
Another factor that is affected by the grounding of the neutral
is the protection against lightning. On a line with no ground
of the neutral it is essential to have enough gaps to prevent a
discharge under the full rated voltage between wires. This
voltage is applied when one corner of the circuit becomes
grounded. It is also necessary to provide enough resistance in
each branch of the discharge path to prevent an arc holding when
a discharge occurs under this voltage. With grounded neutral
the maximum voltage between any one wire and ground is
reduced nearly 50 per cent., allowing material reduction of the
number of gaps and resistance in the discharge paths.
From the above consideration the writer believes that extra
high voltage systems, that is, those with working pressure
between wires of over 25,000 or 30,000 volts, should have the
high-tension windings of their step-up and step-down trans-
formers Y-connected with the neutrals grounded.
(Communicated after Adjournment by Dr. Louis Bell.)
Note on Mr. Blackwell's Paper.
It should be noted that the Y systems, which are immensely
Y OR DELTA CONNECTION. 179
valuable in saving copper, also entail some additional care, as is
the case with all copper-saving connections. In practice I have
found that mixed delta and Y connections are desirable and
tend to steady the regulation. I believe in the grounded neutral
as a safety measure, but sources of accidental grounds should be
followed up rigorously and carefully eliminated. In using Fig. 1,
this is especially necessary, and it is a good thing to ground
through light fuses or lightly set circuit-breakers, but one usually
has to ground this system since its main use is in making long
runs where high voltage lines are barred, and the Fig. 1 connec-
tion carries one below the prohibitive restrictions placed arbi-
trarily to allow old arc machines to run while blocking modern
distributions.
A faper presumed at the 20th Annual Convention
of the American Institute of Electrical Engi-
neers, Niagara Falls, N. Y ., July 1, 1903.
ELECTRIC CABLES FOR HIGH VOLTAGE SERVICE.
BY HENRY W. FISHER.
In the early part of the last decade there was a general belief
among electrical engineers that rubber-covered cables ■^ould be
used almost exclusively for high-voltage service and paper-
insulated cables for comparatively low voltages. With the im-
proved manufacture of the latter, opinions have changed so that
some engineers prefer paper to rubber, stating that in their
experience the life of paper cables is longer than that of rubber
cables. To account for this they believe that the strain caused
by very high voltages gradually deteriorates the rubber by some
kind of electrolytic action, or by a purely physical action, or by a
tendency for static discharges gradually to penetrate farther and
farther until a breakdown occurs. In substantiation of their
claims they give instances where rubber cables have broken
down one after another in service without any apparent cause.
On the other hand, there are engineers who claim that they have
operated rubber cables at high voltages continuously without any
trouble. The ability of a rubber-insulated cable to withstand
high voltages depends upon the ingredients entering into the
composition of the rubber compound. The dielectric strength
to resist electric pressure becomes greater within certain limits
with increased percentages of pure Para or other high-grade
rubber; and there is good reason for believing that when lead-
covered cables are employed, the life of rubber-insulated cables
is lengthened with increased percentages of such rubber. This
subject should naturally be treated under three headings
180
HIGH VOLTAGE CABLES. 181
First: Manufacture of cables.
Second; Installation of cables.
Third: Operation of cables.
First : Manufacture of Cables — In the manufacture of paper-
insulated cables for high voltages, great care has to be exercised
in selecting the right kind and quality of material, and also in the
methods of construction and impregnation of the paper with
insulating compound. The most experienced engineers now
realize that cables saturated with oily compound can better be
handled without injury to the dielectric, and also resist better
high voltages. The use of oily compound is, however, accom-
panied with lower insulation resistances, and consequently
many engineers who think they are adopting the best practice
by specifying several hundred megohms per mile, are in reality
inviting bids on an undesirable type of cable. The best cables
either with paper or rubber insulation should be able to resist
comparatively high voltages for an extremely short period of
time. Such voltages are obtained at the time of making or
breaking the circuit, or during short-circuits. To illustrate: If
a cable of inferior material and construction be subjected to a
gradually increasing voltage till a breakdown occurs, and then
after removing the burnt-out part the operation be repeated, a
second breakdown will almost invariably occur at much lower
voltage than at first, showing that the cable was injured by an
impulsive rise of voltage at the time of the first burn-out. With
the best cables the difference between successive voltages applied
as above is much less than is the case with inferior cables, and
at the same time the former withstand very much greater volt-
ages for the same thickness of insulation. If the question of
expense is not a consideration, paper insulated cable can be made
of remarkable dielectric strength. On one occasion the writer
designed such a cable with a thickness of insulation capable of
ordinarily withstanding 16,000 volts. Extraordinary care was
exercised in the manufacture of this cable, and when tested
48,000 volts were required to break it down, and during successive
tests the voltages applied scarcely varied 1,000 volts from the
above figure, showing a very great uniformity. Such a cable
would have a greater dielectric strength than that of ordinary
rubber cables, and at least equal to that of rubber cables with
high percentages of Para, and would cost fully as much as the
latter.
In the manufacture of rubber cables, care has to be used in
182 HTGH-TENSION TRANSMISSION.
selecting the best and proper materials ; and the work of mixing
them and masticating and appyling the rubber must be done
uniformly well, and the process of vulcanization must be carried
on at the right temperature and for the right length of time to
suit the particular compounds. After being made, all high
voltage cables should be subjected to the usual test for insulation
resistance and electrostatic capacity, and also to voltage tests
of double the normal working e.m.f. Even if this test is not
specified the manufacturer should apply it for his own protection.
Second: Installation of Cables. — This work must be done by
well-trained men, as a small amount of carelessness may mean
much trouble and expense. When the cables are pulled into
ducts great care must be exercised to prevent abrasion of the
lead cover, and no sharp bends must be made because in so doing
the insulation may become injured or cracked. It is advisable
not to pull paper insulated cables into ducts during extremely
cold weather, because of the possibility of cracking the insulation.
If such work of installation has to be done, the reels of cable
should be kept in a warm place over night, or else put under a tent
for a few hours and kept warm with plumber's furnaces placed
so as not to overheat the cable at any point.
The work of jointing the cables must be done by good jointers
who are in turn carefully watched by an experienced foreman.
Different companies make different forms of joints, but after a
reliable one is adopted the work should be systematic and accord-
ing to definite directions in all particulars. By so doing, remark-
able records of perfect workmanship have been made. After
complete installation each cable should be subjected to double
the working voltage, but this voltage should not be applied or
broken suddenly because by so doing unnecessary strains would
be imposed upon the cable.
Third: Operation of High Voltage Cables. — This is a subject
that could better be presented by the operator of the electric
light and power plants where cables are employed. However,
as one of the objects of this short paper is to invite discussion, it
may be well to state that a perfect protective device for cables
and auxiliary apparatus would lessen to a very large extent the
troubles of the operator incident to impulsive rises of voltage
from switching and short-circuit. On several occasions and in
different power houses, discharges have been seen to take place
over the surface of switchboards at the time of short-circuits in
cables,, transformers, switches, etc. On some of these occasions
HIGH VOLTAGE CABLES. 183
the rise in voltage necessary to make said discharges was esti-
mated to be about four times the normal working voltage. At
such times the original cause of the trouble cannot always be
ascertained because frequently cables are burned out in several
places, and transformers and apparatus injured at the same
time. This kind of phenomena seems to be more prevalent and
dangerous where air-lines connect with cables. It will therefore
be seen that an efficient device which would protect cables and
accessory apparatus from such excessive rises of voltage would
be of incredible value to operators.
The question of the carrying capacity of cables is often not
considered as carefully as it should be. With a great many
cables all carrying normal currents are in one duct-system, the
middle and top ones are apt to become very warm. The differ-
ence between the temperature of the conductor and that of the
duct may be nearly as great as the difference between the tem-
perature of the duct and that of the surrounding air, although
generally speaking the former is the least. The carrying capacity
of cables as frequently recommended is entirely too great when
many cables are in the same duct-system.
There is a very great difference in the radiating power of dry
and wet-ducts, and in the heat conductivity of different soils,
and so it is impossible to give set rules governing all cases. Under
no circumstances should the temperature of the conductor be
allowed to reach 90° Centigrade; and if twice the maximum
difference of temperature between any duct and earth added to
the temeprature of the earth is nearly equal to 90° there is reason
for apprehension.
The above remarks do not apply to rubber covered cables,
which should never be heated to over 65° or 70° C.
Moreover it is not desirable nor economical to heat paper
insulated cables to 90° C, and the only reason for mentioning
this figure is because such cables can withstand this tempera-
ture for a considerable length of time without deterioration.
A i>aper presented at the 20th Annual Convention
of the American Institute of Electrical Engi-
neers, Niagara Falls, N. Y., July 1, 1903.
THE OPERATION AND MAINTENANCE OF HIGH-
TENSION UNDERGROUND SYSTEMS.
BY PHILIP TORCHIO.
The following notes apply mainly to moderately high-tension
systems as installed in large cities in the last few years.
(1) Independent vs. Parallel Operation of Feeders at
Substations.
By proper selection of size of feeders and transforming units
at substations, each feeder can be operated to supply normally
an independent group of transforming apparatus. In case of
emergency the same apparatus can be arranged to be fed from
other feeders through an emergency bus. This arrangement of
independent operation of feeders has in most cases the disad-
vantage of not allowing the full use of the copper investment at
light loads, but it has the following advantages.
(a) The short-circuit current fed back from the substation bus
bars into a faulty feeder is limited by the reactance of at least
two sets of transforming apparatus. This will materially help
the final clearing of the short-circuit.
(b) In rotary converter substations the independent groups of
transforming apparatus can be fed from different bus bars or
from different generating stations, thereby increasing the re-
liability of service.
(2) Testing of Cables.
(a) Periodic insulation tests are valuable as they furnish
indications of abnormal conditions and often lead to the detection
of faults on the systems. The instruments usually used in con-
nection with insulation tests are a D' Arsonval galvanometer with
184
UNDERGROUND SYSTEMS.
185
shunt, and a battery of from 70 to 100 volts. Periodic tests
should be made at least once a week on each feeder, and oftener
under abnormal conditions.
(6) High- voltage tests of dielectric strength of insulation should
be carefully applied or possibly avoided entirely. Experience
has demonstrated that failure of cable feeders are almost uni-
formly due to defective joints or mechanical injury to the cable.
The record of all high-tension cable faults of a New York com-
pany for a period of five years is as follows:
Location of Faults on High-Tension Cables.
Made manifest by open-
ing of- circuit -breakers
during operation.
Made manifest
by low insula-
tion test.
Reported by Line
Inspectors.
1 in splice.
1 nail driven into cable
(external mech. in-
jury.)
1 in sharp bend in man-
hole.
1 in damaged sleeve
(external mech. in-
jury-cause unknown.)
1 in bend in small man-
hole.
1 wet end of cable (ex-
ternal injury due to
water leak.)
1 wet end cups caused
by steam (external
mechanical injury.)
1 steam in substation
(external mech. in-
jury.)
1 in splice.
1 in splice.
1 in splice.
1 in splice.
1 leak of steam to
cable end.
1 injured in man-
hole by arc cable
burnout.
1 damaged in man-
hole by A. C. light-
ing cables burnout.
1 damaged by out-
side parties doing
subway work.
1 damaged as above.
1 damaged as "bove.
9
4
5
Note that of the nine faults made manifest during operation,
five were due to extraneous mechanical causes and four to de-
fective installation.
186
HIGH-TENSION TRANSMISSION.
The operating voltage of this system is 6,600 volts.
The lengths of high-tension cables in operation on December
31st of the first and last year covered by the record were 3.2 and
84.6 miles, respectively. The cables of this company have not
been subjected to high-pressure test in subways.
This table shows that only four cable breakdowns out of 18
faults on high-tension cables could possibly have been prevented
by having applied high-pressure tests to the cables originally. It
cannot be determined how successful such tests would have been
in other respects, as the testing strains might possibly have
lowered the dielectric strength of the insulation at points other-
wise perfectly safe for operating at the normal pressure. Note
must also be taken of the fact that no failure of the cable proper
has yet been recorded in this large system, now operating over 85
miles of high tension cables.
Fio. I.
(3) Indicators and Protecting Devices.
(a) Ground detectors with annunciator relay and drop-signal
are desirable features of a high-tension switchboard equipment.
The diagram (Fig. 1) shows an arrangement for a three-phase
installation.
(6) Grounding of the neutral of high-tension generators is ad-
vocated by many engineers, and apparently it has given satisfac-
tion wherever it has been tried. The objection to the heavy
short-circuit current from one leg to ground has been overcome
by the suggestion of grounding through a non-inductive resist-
ance, thereby limiting the short-circuit current to a pre-deter-
mined amount. The experience of the companies so operating
will be of great value.
(c) Spark Arresters. — It seems impossible always to guard
against the appearance of high voltages due to sudden change
UNDERGROUND SYSTEMS. 187
of load, grounds, short circuits, etc., and, especially in the
latter case, spark-arresters will greatly increase the safety.
Thq'se devices are preferably connected " delta " on system
without grounded neutral and installed at the generator end
as well as substation end. of every cable and at every other place
where the cable is looped into a substation or joins an overhead
line.
(4) Apparatus and Methods for Care of Cables.
A new cable should not be connected to the main bus bars
without being previously tested with full working pressure. This
is sometimes accomplished through a suitable transformer
properly fused or by inverting a rotary converter with a fuse on
the low tension side.
A defective feeder often requires the application of high-
voltage for breaking down the defective insulation and creating
a low-resistance path for sending through it a direct current for
the purpose of locating the fault by the compass method applied
to the cable in successive manholes. To break down and charge
the insulation requires about two amperes for paper and five
amperes iot rubber-insulated cables, applied for about five
minutes. The regulation of the amperage could very conveni-
ently be obtained by the use of a reactive coil, or what amounts
to the same, a transformer of sufficient internal reactance to limit
the current on short-circuit. But while there may not be much
danger of resonance phenomena when using reactive coils, still
there is some dari'ger and it is, therefore, safer to limit the short-
circuit current hf resistance. Fig. 2 shows the connections of a
rheostat intended to limit the short-circuit current to 2i and 5
amperes at 6,600 i volts.
(5) Rules.
In a large system it is important to devise a set of rules for the
guidance of the men in the different departments. These rules
must be rigidly complied with so as positively to eliminate any
danger to men making tests or repairs to cables or switchbards.
(6) Maintenance.
It is not feasible to estimate accurately the life of high-tension
cables and what will be the cost of maintenance after several
years' installation. The cost of repairs for the first years is
merely nominal, and the only other items of maintenance are the
expenses for the periodic inspection and testing and minor details.
188
HIGH-TENSION TRANSMISSION.
A paper presented at the 20th Annual Convention
of the American Institute of Electrical Engi-
neers, Niagara Falls, N. Y., July 1, 1903.
THE USE OF AUTOMATIC MEANS FOR DISCONNECTING
DISABLED APPARATUS.
BY H. G. STOTT.
This subject may preferably be divided into three sections, as
follows:
(a) Generating apparatus.
(6) Transmission apparatus,
(c) Receiving apparatus.
(a) Generating Apparatus. — That no overload device should be
used in the generating plant to disconnect disabled apparatus
may be stated as a general proposition.
Experience has probably been responsible for the evolution
of the art to a point where it has become not only possible, but
necessary to eliminate all overload devices.
Only a brief statement of the reasons for abandoning the use
of overload apparatus will be necessary.
In case of an accident to one generating unit, the other units in
multiple with it will immediately begin to force current into the
disabled one, and the increased load on the good units, due to
their normal load plus the short-circuit current supplied to the
crippled unit will, in all probability, trip all the circuit-breakers
simultaneously, thus interrupting the service.
Without automatic circuit-breakers the overload on the good
units would cause the potential of the system to fall so low that
the service would, in all probability, be as completely inter-
rupted as in the former case, unless the attendant succeeds in
locating and disconnecting the crippled unit immediately.
189
190 HIGH-TENSION TRANSMISSION.
Should he fail to do so, the service will inevitably be inter-
rupted, and a great deal of damage done to the crippled unit by the
cvirrent from the good machines.
It is then evidently necessary to have some means of dis-
criminating between a current coming out of the machine and
one going into it. Modern apparatus can safely carry 200 per
cent, or more load for a few minutes, but if a unit has become
crippled it will immediately cease to be a generator and become
a receiver. All that is necessary to do then is to install on each
generator a suitable circuit-breaker which will operate only when
the direction of flow or energy through it is reversed.
This type of safety device has been developed for both d.c. and
A.c. apparatus so that it operates quite satisfactorily.
As an additional precaution in large plants, a second reverse-
current relay should be installed which will merely light up a
letter or number in front of the operator so that in the event of
the failure of the first automatic device the faulty machine may
be quickly disconnected by hand. These reverse-current relays
should have a time-element and current -limit attachment,
which should be set for not less than three seconds, so that a
slight reverse current, or one of momentary duration, such as is
liable to occur at the moment of multiplying, will not operate the
circuit-breaker.
(b) Transmission. — ^When transmitting power through over-
head and underground cables, it is essential to successful opera-
tion to be able automatically to disconnect the feeders from (1)
the generating station, and (2) if there are duplicate transmission
lines, from the receiving station.
(1) At the generating station this should obviously be done by
an overload circuit-breaker whose operation is delayed by a
time-element which may be set at from one to ten seconds ac-
cording to the local conditions.
This is all the protection necessary or desirable where only one
transmission line exists.
(2) With two or more transmission lines in multiple, an
entirely different set of conditions exist as in case trouble de-
velops in one, current will be fed back from the receiver end into
the fault through the good feeders ; the result will be that all the
feeder overload breakers at the generating station will trip, thus
shutting down the entire line and, in all probability, shutting
down all synchronous receivers on the system, due to the result-
ant fall in potential.
DISABLED APPARATUS. 191
Reverse-current relays at the receiver end of the feeders
operate satisfactorily, provided the fault is not severe enough to
drop the potential.
If, however, the fault amounts to a short-circuit the potential
at the receiver end will fall so low that the potential coil of the
differentially-wound relay will not receive enough current to
enable the relay to operate.
Reverse-current relays on the receiving end of feeders are not
as yet to be depended upon, but recent improvements give
promise that we may soon expect to find a satisfactory solution
of this important problem.
When only two feeders are in use a method devised by Mr.
L. Andrews, of England, seems to be very satisfactory. At the
receiver end the two feeders are connected together through a
choking-coil wound entirely in one direction. The current is
drawn from a tap in the centre of this winding. Under normal
conditions the feeders supply equal current through each half of
the winding to the tap, but as the currents pass in reverse direc-
tion through the winding the resultant flux is nil and, therefore,
the resultant inductance is nil, the only loss being that due to
the ohmic resistance of the coils.
Should a short-circuit occur in one of the lines, the current
from the other line will flow through both halves of the reactive
coil in the same direction, thus producing a strong choking effect
and limiting the current to an inconsiderable amount.
As the overload circuit-breaker on the faulty feeder at the
generating station will trip immediately, it is then only neces-
sary for the attendant at the receiving station to open-circuit the
section of the reactive coil connected to the faulty cable and
short-circuit the other half connected to the good cable. This
device, I am informed, has given excellent results in England, but
for obvious reasons would not be suitable for more than two
feeders.
Where possible, the safest plan at present is, in the writer's
opinion, to run the feeders entirely separate at the receiving end,
only putting the d.c. end of the rotaries in multiple; or in cases
where low tension alternating current (2000 volts or less) is sup-
plied, putting the secondaries in multiple. If, under these
conditions, reverse-current relays are installed at the receiving
end of the feeders they will operate very satisfactorily as the
reactance of the rotaries and transformers will be sufficient to
limit the reverse current in the faulty cable, thus allowing the
192 HIGH-TENSION TRANSMISSION.
reverse-current relays to operate as there has been no serious
fall of potential.
The greater the number of feeders used between the generating
station and the substation the better this method becomes, as,
for instance, with two cables a fault in one will only reduce the
capacity 50 per cent, until .the operator can synchronize all the
apparatus, which was running on the faulty cable, and as the
apparatus and converters will continue to run at full speed only a
few minutes will be necessary to synchronize on the good feeder,
which will in the meantime carry the whole load, so that no
interruption to service will occur. With three cables this would
mean a loss of capacity of 33.3 per cent., and with four cables
25 per cent., etc.
(c) Receiving Apparatus. — This should. be treated in exactly
the same way as the generating apparatus, namely: use reverse-
current relays only to operate the circuit-breakers on the rotaries,
etc., and use time-element overload relays only on the low-ten-
sion feeders leaving the substation.
The above remarks apply generally to both d.c. and a.c.
apparatus, with the exception of the part devoted to transmission
apparatus, which, of course, only applies to a.c. transmission.
DISABLED APPARATUS. 193
Discussion of H. G. Stott's Paper on " The Use of Auto-
matic Mjans for Disconnecting Disabled Apparatus."
By W. F. Wells.
Mr. W. F. Wells: — Recent experience with 6,600 volt,
revolving field apparatus in central power station practice has
proved that automatic disconnective devices are not necessary
in order to insure reliable operation of the system to which
current is supplied and that capable operators with good judg-
ment can handle any cases that may arise better than automatic
devices could be expected to operate.
The instruments and controlling devices on each generator
should be placed close together, and their positions so related
that there could be no possible chance of the operator when
noting the indication on the instrument of one generator, becom-
ing confused and by mistake opening the switch of another
machine.
In the station referred to each generator is equipped with an
overload relay whose secondary is connected to a red lamp only,
and the following indicating instruments, wattmeter, power
factor indicator, field ammeter, voltmeter and two ammeters.
The first indication of any trouble is generally a drop in bus
pressure, unusual noise from the generators, or lighting up of the
overload lamps. A quick survey of the instruments enables the
operator to determine if the trouble is on the generators or
feeders. If on uhe generators, the wattmeter or power-factor
indicator shows if current is reversed in any one of them, and the
field ammeter shows if the reversal is due to open field circuit
'or loss of motive power. The character of the swing or vibration
of the needles will show whether the trouble is due to some
accident affecting the angular velocity, such as break in valve
motion, or if it is due to faulty governor, cut off of steam supply
or broken vacuum.
After a short experience in any such station equipped similarly
to the one mentioned, the operator is able almost immediately
to locate the cause of the trouble, and if he thinks advisable, open
the circmt-breakers before any automatic device would operate,
if properly protected by a time-limit element.
During the past eighteen months eight generators have been
operated a total of 25,000 hours and a careful anlaysis of every
accident or mishap that has occurred has failed to show any
necessity or even desirability of automatic disconnective devices.
It is alrnost needless to add that the station was free from acci-
dents that might have been caused by faulty operation of unre-
liable devices, and there was no expense incurred for maintenance
and repairs of such devices.
In the transmission apparatus, it has been found best to set the
time-limit overload relays on the feeders in the generating station
for two seconds and at about two and one-half times normal load.
During the entire time that the station has been in operation,
a period of neariy two years, it has always been the practice to
194 HIGH-TENSION TRANSMISSION.
run the high-tension feeders on what Mr. Stott refers to in his
paper as the safest plan; i.e., entirely separate at the receiving
end, only putting D. C. ends of the rotaries in multiple. But
as practically all the substations are equipped with large storage
batteries, which are also in multiple with the rotaries, it has been
found best to operate without reversed-current relays, but de-
pend on the operator in the substation opening the circuit-
breakers when necessary. Here as well as in the generating
station, the operators very quickly learn to read from their
instruments the nature of the trouble, and the disturbance to
the system caused by any accident is always less than it might
have been had automatic devices been depended on.
In the substations, the receiving apparatus converts the alter-
nating current to 260 volt direct current and here the only
automatic device is an overload-relay on the high-tension
feeders, and a centrifugal device which opens both alternating
current and direct current switches of the rotary if its speed ap-
proaches too close to the danger limit. On the direct current
feeders there are no automatic devices.
In general, on the entire system there are in use no automatic
disconnective devices except those operated by the time over-
load relays on both ends of the high-tension feeders, and by the
centrifugal speed limit device on the rotaries in the substations.
Discussion of H. G. Stott's Paper by Mr. Carl Schwartz.
Mr. Carl Schwartz: — As to the reverse-current relay for the
generator circuit, I think that this relay should operate a lamp
and then maybe in addition a bell signal in order to call the
attention of the operator, so that he could take as quickly as
possible suitable steps to bring the load back to the generator or
disconnect this unit if it is unable to work. A reverse-current
relay, opening the generator oil-switch, is in that case not very
essential and could be left out entirely; but if it is applied it
should be provided with a time and current -limit relay. The
exciter generator circuit must contain a reverse-current circuit-
breaker acting as soon as the generator begins to run as a motor,
the supply of the generator field being maintained by a storage-
battery.
Referring to the transmission lines, I would say that at the
generator end, overload relays with a time limit device will be
generally sufficient. It is important that the overload as well
as the reverse-current devices for the feeder lines are connected
to each phase, as burnouts between one conductor and the lead
cover, not afEecting the other phases of a three-conductor cable
line, may occur. I refer here especially to the star-connected
system.
Discussion of Philip Torchio's Paper on " The Operation
AND Maintenance of High-Tension Underground Sys-
tems," BY Mr. Edward P. Burch.
Mr. Edward P. Burgh: — Referring to the testing of insulation
of high-voltage cables, the writer would add his experience with
UNDERGROUND SYSTEMS. 195
two very successful 12,000 volt three-phase cables, one 9.5 and
one 7.0 miles long, used by a Minneapolis company for three and
five years respectively.
Experiments were made on short lengths of these paper
cables_ by stripping off the lead sheath and partly immersing
them in water, the full potential being on the three legs of the
tri-phase cable. It was found that it usually took several days
before water impregnated the paper insulation to such an extent
as to cause a short circuit between the legs.
Now most of the cable faults are due to mechanical causes such
as a damaged lead sheath or to chemical deterioration of the
sheath due to electrolysis from a direct current circuit. In both
cases moisture finally, from a day to a week, works through the
paper insulation and a cable break occurs. Manhole inspection
for the exact location of electrolytic troubles generally proves
valueless. Mechanical troubles at or between manholes are
generally classed as " accidents."
Tests of value were regularly made on these 12,000 volt cables,
using 600 volts direct current. The scheme is to charge the
cable legs and then to note the electrostatic discharge through an
ordinary Weston direct current voltmeter. The cable terminal
switches were of course open at the station and at the sub-
station. If the electrostatic discharge is large, one may safely
conclude that the cable is not in bad condition. If the discharge
as indicated by the swing of a voltmeter needle, is weak, this is
due, to the fact that the charge has leaked off through faulty
insulation. The indications are, in general, reliable.
In railway power houses regular testing, between 2 and 5 a. m.,
thus furnished indications of the condition of the cables. It is
of some real value to an operator to know that a certain cable is
weak and may blow out.
Ground detectors sometimes give negative results. The indi-
cations on the scale of the commercial switchboard instrument
are too rough to be of great value.
Cable testing sets of the D'Arsonval galvanometer type are
generally too sensitive for power station work.
High-voltage tests of cables in service are considered of doubt-
ful value.
Discussion of Philip Torchio's Paper on " The Operation
AND Maintenance of High-Tension Underground Sys-
tems," Mr. W. G. Carlton.
Mr. W. G. Carlton: — The experience of the Chicago Edison
Company with its high-tension-three-phase cables has been simi-
lar to that of the New York Company mentioned by Mr. Torchio.
At present they are operating about 45 miles of three conductor
cable at 9,000 volts. The first of these cables was installed
about five years ago. The voltage used at first was 4,500 but
about one and one-half years ago it was changed to 9,000.
There have been seven cases of trouble on these cables: Four
were caused by mechanical injuries to cables in manholes; one
196 HIGH-TENSION TRANSMISSION.
by a burnout on an adjacent cable; one by a defective joint, and
one by electrolysis causing a hole to be made in the lead sheath
of the cable. With the exception of the defective joint none of
these troubles would have been avoided by using high pressure
tests on the cables.
The neutral points of the high-tension generators are grounded
direct, no resistances being used to limit the flow of current.
Two cases of trouble already referred to, one due to mechanical
injury and one to electrolysis, resulted in one conductor of the
cable burning to grcund, and the other two being left in good
condition. One of these cases occurred within 3,000 feet of the
generating station. The overload coils on the oil-switch worked
and cut out the line. Rotaries in two large substations were
running from this line but they merely dropped their load and
did not feed back into the cable. Immediately after the trouble
occurred the line tested clear and 9,000 volts was applied for
about 10 minutes. When the trouble was located it was found
that about 6 inches of the copper in one line was gone, and there
was an irregular shaped hole in the lead approximately three by
six inches.
The second case of trouble occurred about four miles from the
generating station and was manifested by a motor generator
operating from this line, making a peculiar noise. It was after-
wards found that this was due to its running as a single-phase
instead of a three-phase motor. The operator at the generating
station had not noticed any trouble. One copper was found
burned open and there was a hole in the lead approximately the
size of a half dollar.
These two cases of trouble are possibly unusual in that very
little damage was done. I believe however if we had been operat-
ing without a grounded neutral the chance would have been
greater for more serious trouble owing to the displacement of the
neutral that would have occurred.
President Scott: — We shall be pleased to hear from Mr.
Eglin.
Mr. Wm. C. L. Eglin: — Our experience is different from
that of other large companies in that we use a higher frequency
and as we started with 60 cycle rotaries before they were properly
developed, it necessitated the use of direct current circuit-
breakers on the direct side of the rotary converters, for the reason
that these rotary converters were installed in stations with
storage-batteries and also with other similiar units. With hand
operation the current on the direct current side of the rotary
would flash over before the operator had time to open the circuit-
breaker, and with a large battery in the station it generally
resulted in wrecking the rotary, at least wrecking the brush-
holders. There were very few of the brush-holders left after that
flashing took place ; so that we have used circuit-breakers on the
direct current side of all rotaries since that time. If we had
machines with effective bridges it is possible we would not have
UNDERGROUND SYSTEMS. 197
used the automatic circuit-breaker on the direct current side of
the rotary.
The only other protective device is an automatic speed limit
device to prevent speeding up beyond a predetermined speed.
One feature that I feel has not been discussed, and I was sorry
it didn't have more discussion in connection with the paper last
night, is the limiting of current on the high-tension feeder. I
feel that with the growth of the size of generating stations and
all of the feeders being run in parallel on a large generating sta-
tion, we must provide some means for limiting the amount of
energy that can be put in to any short circuit of a high-tension
cable. Our own practice has been to subdivide the feeders at the
substations so that at the substation ends the feeders were not
tied together. I think our operation has been much more suc-
cessful since this has been done. We had conditions similar to
those that are spoken of by the high-tension people ; that is, that
we had the cables break down when they were tied together at the
substation end, and a number of other cables would break down
for some unexplained reason. Last winter we ran through with
all of our cables separated at the other end, and if a cable broke
down, that was the end of the trouble; no other cable would
break down due to the disturbance in the line during the time
of the short circuit.
Mr. Mailloux: — I think that the customer sometimes has
to combat the zeal of the manufacturer's sales agent in such
matters. The importance of doing away with automatic con-
trol of the generators is, I think, such that it should not be
under estimated or passed over lightly. It is of great importance
in central stations, and it is even of greater importance in
relatively large isolated plants. Perhaps the first attempt made
to dispense with it in a large isolated plant was in connection
with the Astoria Hotel nearly nine years ago. In laying out the
plant there I foresaw that it would not do at all to have the
machines become disconnected just as soon as we happened to
have a little overload, and that it was necessary to resort to some
other means of dealing with overloads. We first tried to raise the
limit by putting on larger fuses, and we foresaw that cases might
occur even where that would not do. We finally resorted to the
expedient of putting in an overload-relay, which operated, not
to cut out the dynamo but to put on a red light and ring a big
bell, the effect being to call attention of all the attendants to the
fact that there was danger, while the red light would show the
particular dynamo that was overloaded. It was found in prac-
tice, however, that even that was not a desirable thing to do,
because it might excite a panic. The apparatus is there, but it
was never used and they now depend on the operators entirely.
There is a man whose duty it is to stand by all the tim^ and see
to it that no panic occurs. If there is any overload it is better to
let the machine run up to 100 per cent, overload, if necessary,
rather than take chances of having a machine become cut out and
198 HIGH-TENSION TRANSMISSION.
cause a serious panic. You understand that in a place like the
Waldorf-Astoria, where the load is comparable to that of a small
town, with from 20,000 to 30,000 incandescent lamps and a motor
load varying from 500 to 1,000 h.p., it is a serious matter. I am
pleased to say that in something like eight or nine years only one
or two interruptions have occurred, and one of those was due to
the breaking of a steam pipe.
Mr. Mershon: — I would like to hear further from Mr. Torchio
or his representative, Mr. Wells, in regard to a number of points.
One is in reference to his statement at the bottom of page 18.5,
that only four cable breakdowns out of 18 faults in high tension
cables could possibly have been due to defective installation. As
far as anything in the table itself is concerned, it seems to me that
nine of the faults there mentioned might have been shown by a
voltage test. I should like to ask also whether it is the practice
of the Edison Company to install cables and put them into ser-
vice without giving them any more of a voltage test than one at
normal voltage. In regard to the method, mentioned by Mr.
Torchio, of keeping each set of apparatus consisting of cables,
transformers, and converters separate and distinct until the
direct current bus-bars were reached, it seems to me that con-
dition is undesirable because of the fact that you do not get the
benefit of your copper on low loads. Under such conditions
you must, as your load diminishes and you cut out rotaries, and
transformers, cut out also the cables to them so that you keep
up to a certain point, a constant load loss on the cables that
remain in service. I suppose that if it were possible to obtain a
reverse circuit-breaker that could be depended upon to cut out a
damaged cable, which would operate under very low voltage or
at no voltage — it would be desirable to multiply the cables. I
would like to ask Mr. Stott at this point whether he has gotten on
the track of any such reverse relay, and whether he thinks there
is any chance to have one in the future? His reply will, I hope,
bring Mr. Gerry into the discussion, as Mr. Gerry expressed him-
self a while ago as confident that such device was obtainable.
If there is such device I would like to know about it.
I would like to ask Mr. Fisher whether he has made any inves-
tigation of the rise in the temperature of cables due to the diffi-
culty of getting the heat from the cable out into the ground ; that
is to say, as to the fall in temperature that is necessary to force a
watt across a given amount of duct and into the ground ; whether
he has gotten any results which would enable one to calculate, in
a duct system, what with a given distribution of load in the
cables, the temperature would be of, say, a cable in middle duct.
I tried to get some information of that sort a while ago, and went
just far enough to get the information that would answer for the
particular installation I was about to make. The results were
not very full and referred to a conduit consisting of a very few
ducts. I should also like to know whether Mr. Fisher has any
definite figures on the actual temperature at the conductor which
large paper cables will stand continuously without injury?
UNDERGROUND SYSTEMS. 199
Mr. Mailloux: — I think that the maximum voltage limit
of cables is one of the important questions. I meet with that
question constantly in my practice, in cases where one wishes to
run overhead but comes to pieces of property where we cannot
possibly get the right to run overhead. I have had such cases in
districts where rich men live, who seriously object to having
overhead wires of any kind pass by or near their properties. In
one case it happened that my clients themselves are the people
who most objected. They were stockholders of the company,
and owned it, and yet, though they understood fully the import-
ance of getting past, they did not want the lines run overhead.
In some cases we have had to resort to very expensive under-
ground construction in order to meet that difficulty. Now, as
the radius of activity of such a station increases — as the territory
expands on the outskirts — it becomes all the more important to
be able to raise the voltage. I had a case which was started
at 2,000 volts, which was intended to operate over a radius not
exceeding two miles. At the end of two years we raised the
potential to 6,000 volts and extended the radius to about 10 miles.
We are now desirous of extending that radius to 25 miles. I may
state incidentally that the station was designed for 500 kilowatts.
It is now being transformed into a 6,000 kilowatt station. This
gives you some idea of the growth of the system and of the diffi-
culties which are likely to come up in connection with a station
growing under those conditions. The problem with which we
are confronted is, to what voltage shall we now step up? We
shall probably operate at three voltages corresponding to three
zones, a 2,000 volt zone, a 6,000 volt zone, which we already
have, and a still higher zone. Now, shall that zone be 12,000,
15,000 or 20,000 volts? It seems to me that it is going to be
limited by the limiting voltage at which I can get underground
cables which will be reliable for good service. I have been told
by some that these cables can be operated successfully at 10,000
volts; by others, as high as 20,000. I should Uke very much to
hear from Mr. Mershon, from Mr. Fisher, and especially from
central station men who have had experience with high-voltage
cables. What is the highest voltage limit that we can now safely
depend upon in cables?
Mr. Walter F. Wells: — In reply to Mr. Mershon's question,
I would say that it is the practice of the New York Company not
to make over-voltage tests on cables ; and this also applies gen-
erally speaking to all electrical apparatus. Apparatus as well as
cables thoroughly tested before being installed. A test of a
slight over-voltage, say 20 per cent, to 30 per cent., is enough to
determine whether the work has been properly done or not.
As to the four faults referred to by Mr. Torchio, which might
have been found by an over-voltage test originally, two of them
were probably short bends in manholes. As to the other two, I
am not well enough acquainted with the records to know which
they were. They must have been some of the faults in splices.
200 HIGH-TENSION TRANSMISSION.
Those shown by low insulation test evidently were good in the
beginning and gradually deteriorated.
Mr. Mershon: — How about these faults designated as " in
splice? "
Mr. Wells: — Those evidently were all right in the beginning
and gradually deteriorated, whether due to external injury or
not, I cannot say. Several companies operate in the same man-
holes, and sometimes the cables are roughly handled by em-
ployees of other companies or by contractors working on the
Rapid Transit Subway excavations.
Mr. Stott: — In reference to the absence of tests on cables, I
would say it is the practice of the company with which I am
connected to make a 30 minute test of 100 per cent, over-voltage.
That is to say, on the 11,000 volt cables which we operate, we
would make a 30 minute test at 22,000 volts on the insulation
between the three conductors and between the conductors and
the ground. We find that a joint which is comparatively poor
will stand up as long as 18 minutes and then break down, and in
every case where we have broken down cables, with the 30 minute
test, the result has been fully justified by what we found in the
joints. Incidentally, I can perhaps throw a little light on Mr.
Mailloux's question as to the reliability of cables. We have in
operation on 11,000 volts, three-phase, over 120 miles of under-
ground cable. Out of that 120 miles we have had only one fault
in the cable itself. All the rest were due to inferior work in the
joints; and I would say that since they went into operation 20
months ago, we have had a total of four breakdowns while
operating. All the rest were taken care of in the over-potential
tests. Out of the entire 120 miles there has only been one spot
of weak cable. I think that is a very remarkable record and one
that shows that 11,000 volts is an absolutely safe voltage. We
have the feeling that 11,000 volts is a great deal easier to handle
underground than 650 on a grounded return circuit, because you
are very liable to get a very large current coming back through
the lead covering.
On the grounded system, such as we operate, no matter how
much copper you put in to bring back the current to the negative
bus-bar, it is almost a physical impossibility to get enough copper
in the street to reduce the drop below, say, 10 volts. The lead
sheet of a cable 2f" diameter has a resistance of approximately
1/10 of an ohm per thousand feet, so tnat a length of 500 feet sub-
jected to 10 volts will give you something like 200 amperes in the
lead sheath. We found by actual test that the lead sheet of such
a cable, 2f" external diameter, and the sheath itself being 9/64th
inches thick, would only stand 400 amperes continuously until it
reaches 100° C. rise. That of course was too high. I think that
a great deal of the underground trouble has been due, not to
faults in the insulation but to faults in the lead sheath. That is
to say, stray currents from other properties have got back into
that lead sheath and melted off the lead in spots where it touches
UNDERGROUND SYSTEMS. 201
the hanger in the man hole. Of course, that admits moisture,
and the insulation gradually deteriorates and breaks down.
Incidentally, I do not think it is worth while considering or dis-
cussing rubber-insulated cables at the present time, because the
cost of a rubber cable is approximately 100 per cent, greater than
that of a paper cable.
We have installed reverse-current relays in our substation
feeders, but owing, as I said, to the fall in potential affecting the
shunt coils, we found them entirely unreliable. That is to say,
in case of short circuit in one feeder, the other feeders will all go
out together, owing to the overload current carried by them
through the substation to the break in the cable ; so that when-
ever one feeder went up it invariably meant that the entire sub-
station was shut down for a period of from two to five minutes,
according to the number of rotaries that were running. Again,
there is always a doubt existing in the mind of the operator as to
which one of the five or six feeders was in trouble, as all the
circuit-breakers went out at the power house, and it was very
difficult for them to tell, without testing, which one was in
trouble. I do not know how Mr. Wells' people operate in that
way, but we found it absolutely impossible to determine which
feeder was in trouble, as all the overload breakers went out
simultaneously. To get around that, we simply separate the
feeders at the substation so that each feeder supplies its own
rotary. We have had short circuits on feeders since that change
was made and the automatic apparatus took care of it perfectly
without any interruption whatever to the service at the power
house or substation. In fact, no one knew anything about it
until the indicating lamps showed that the oil-switch had gone
out. I believe a new device has been gotten up by one of the
manufacturing companies which is really not a reverse current
relay, but a system they have of causing one relay to lock the
others. Suppose there are three or four feeders in multiple — the
one which has the short circuit on it will evidently receive the
greater amount of current. Therefore its solenoid will move up
faster than the others, which are merely carrying the overload.
As that one reaches the limiting point it closes a contact which
locks all the other feeder relays in that substation. As soon as it
breaks it trips its own circuit-breaker; then it releases all the
other relays again. It is simply a little solenoid at right angles
to the core of the primary solenoid, and it drags over the core so
hard that it cannot move vertically. That has been laid out and
is going to be installed on the underground division of the
Interborough Rapid Transit Company, but I do not think it has
been put into actual use up to date.
Mr. H. W. Fisher: — I will commence by answering Mr.
Mershon's first question.
About two months ago I spent nearly five weeks with the
Niagara Falls Power Company conducting experiments to deter-
mine the rise of temperature due to different currents on cables
202 HIGH-TENSION TRANSMISSION.
laid in ducts. We experimented on different single conductor
cables ranging from 3/0 to 1,250,000 cm., and also on two and
three conductor cables. The temperatures of the ducts at differ-
ent points were determined by means of thermo-couples, consist-
ing of rubber covered iron and German silver wires, all of which
had previously been compared with a thermo-couple which we
used as a kind of standard and the terminals of which we kept
daily at the temperatures of ice and of boiling water. We also
used resistance coils which had previously been calibrated to give
the variation of resistance with temperature. Our experiments
revealed the fact that there was a great deal .of difference in the
radiating power of different ducts; that the corner ducts radiate
best, and the middle and top ducts become the hottest. Some
tests made by the Niagara Falls Power Company revealed the
fact that the top ducts were the hottest ; an explanation of this
is that there were openings here and there at points where the
terra-cotta ducts were joined together, through "P'hich the heated
air circulated in an upward direction.
Tests of different numbers of 1,250,000 c. m. cables showed
that the rise in temperature of the duct when four cables were
employed was 85 per cent, of what it was when eight cables were
employed; and when two cables were employed the rise was 74
per cent, of what it was for eight cables.
The Niagara Falls Power Company is in some cases using
water circulation in iron pipes to reduce the temperature of the
ducts, and by so doing a reduction of 20° Centigrade was ob-
tained in one case.
Mr. Mershon: — ^What is the maximum temperature that a
cable will stand continually without injury to the insulation?
Mr. Fisher: — I can say that 100° Centigrade continually
applied to a paper cable will eventually deteriorate the paper,
making it quite brittle.
I am conducting experiments along this line now to find out the
maximum temperature which will not injure paper-covered
cables.
With reference to Mr. Mailloux's question as to whether cables
sold for a certain voltage could not be subjected to twice that
voltage when it is desirable to raise the voltage in the generator
plant, I would say that it is hardly fair to subject cables to a
working pressure much in excess of what they are designed for.
Whether this could be done or not would depend largely on the
kind of cable and the voltage at which it was normally designed
to work.
Mr. Mailloux: — ^What is the highest voltage you have made
them for?
Mr. Fisher: — Cables are working now at about 22,000 volts.
Mr. Mailloux: — Are they to be obtained under guarantee for
that amount?
Mr. Fisher: — Yes. By experience and experiment we are
continually learning improved methods of manufacture and dis..
UNDERGROUND SYSTEMS. 203
covering better insulating compounds, and for some time at
least I think we will be able to supply what is likely to be re-
quired in the line of h'igh-voltage cables.
Mr. Mailloux: — You say 22,000 volt cables are commer-
cially obtainable to-day?
Mr. Fisher: — Yes.
Mr. Mailloux: — That is what I wanted to know.
[Communicated after Adjournment by Mr. W. L. Waters.]
Electric Cables for High-Voltage Service.
I think the question of rubber vs. paper for high-tension cables
is a commercial rather than an engineering question. Paper
cables are simpler to manufacture, and hence are usually more
reliable in practice, but I think there is nothing to choose as
regards reliabihty between well-made rubber and well-made
paper cables, provided they are lead covered.
I used to be connected with a firm which has probably had
more experience than any other in the manufacture of rubber
insulated cables, and we found that the chief points for reliability
in rubber cables were good vulcanizing and keeping the rubber
from contact with the air. No amount of text-book science
will teach a man how to vulcanize a cable ; it is an operation that
can only be learned by experience. And if the men making the
cables have not had this experience, the cables turned out by any
firm will in all probability not be very reliable.
The rubber on a cable which is poorly vulcanized becomes rot-
ten after being in service for a certain length of time, and it
cracks and crumbles, especially when subjected to mechanical
stress. When rubber is exposed to the air for any length of time,
the sulphur apparently works out to the surface and oxidizes,
forming sulphuric acid. This effect is more pronounced when
the insulation is under electric stress on account of the formation
of ozone, and is also more marked in a cable which is poorly
vulcanized. The result in any case is the same, that the cable
breaks down sooner or later.
In rubber cables, as in most other questions regarding the
permanence of insulation, the purchaser is more or less at the
mercy of the manufacturer, and I think that the cable manu-
facturer should receive his due share of the credit for a number
of the mysterious breakdowns that we hear of on high-tension
rubber cables.
Discussion on " Use of Automatic Means for Disconnecting
Disabled Apparatus."
Mr. R. S. Kelsch: — A plant operated by the writer for five
years, was equipped with expulsion type fuse blocks using
aluminum fuses, on the eight 750 k.w. generators, and the same
type of fuse on the eight 5000 volt transmission lines at both the
receiving and the generating ends, and gave excellent results.
On one occasion the collector rings for the field leads of one
of the generators short-circuited when the eight machines
were operating in multiple. The disabled generator was dis-
204 HIGH-TENSION TRANSMISSION.
connected from the system without the trouble being recorded
on the recording voltmeter in the city substation.
On several occasions one or more of the lines were short-
circuited by wire thrown on the transmission line, and on each
occasion the disabled line was disconnected without interrupting
the service. During the past year, relays have been employed
and the fuses removed, and we have not had as good results.
Recently a dead short-circuit on one of the secondary circuits
protected by a time-limit overload relay set for three seconds
caused the potential of the system to fall so low that all power
service was interrupted.
Reverse-current relays should be set to operate at five per cent,
reverse current. Reverse current should not occur except under
abnormal conditions and under these conditions, the apparatus
protected by reverse-current relay, should be disconnected
instantaneously, and should not have a time element attachment.
A reverse-current relay so constructed would operate before the
potential lowered sufficiently to make the reiay inoperative.
The only objection to setting a reverse-current relay to operate
at five per cent, is the difficulty m synchronizing. This, however,
can be obviated by synchronizing with the incoming generator
pressure slightly above the bus pressure and the synchronizer
indicating that the speed of the incoming generator is a trifle
higher than the general system, which will insure the incoming
machine acting as a generator the instant the switch is closed.
Dr. F. a. C. Perrine: — One question which has been touched
on by a number of papers in this discussion, but which has not
been specifically treated, is that of the proper subdivision of the
lines for their protection from interference. The apparatus for
line switching and line insulation has been treated for protec-
tion against lightning and the subdivision of the circuits has
been considered, but it seems necessary to call attention to the
fact that we have not, as yet, treated the question of dividing
the line up into sections so that in case of accident the interfer-
ence with the proper maintenance of supply by reason of the use
of multiple lines shall not become excessive.
The importance of this was recently called to my attention by
some calculations I have been making on a line 350 miles long,
for which figures have been requested. If two lines were in-
stalled for this transmission, using such a size of copper as the
question of economy would best warrant, the regulation, when
only one of the two lines was in service, would be too bad for the
proper supply of energy to the service. In consequence it was
necessary to consider whether the size of line wire be increased
or the line divided up in sections, which would permit cutting out
only a short section in case of accident anywhere along the line.
In lines approaching 100 miles in length, the capital invested in
each pole line is very considerable and in addition to the loss of
energy which must be excessive if but one of the lines is in opera-
tion, there is a heavy capital charge during such times which
must be carefully considered.
DISABLED APPARATUS. 205
On most long-distance lines there are points of distribution
along the line which naturally cut such a line up into sections and
if switching stations are installed at these distribution points,
permitting the transposition of the circuits, the effect desired
can be accomplished but it is not always possible to rely on the
fortuitous arrangement of switching stations. With increased
length of line, there may be great distance between these switch-
ing stations, and furthermore the change-over switches operate
under much more serious conditions when the sections they are
controlling are long than when they are short.
It is true that up to the present time there has been a 'general
tendency to avoid multiplying switching stations on account of
the imperfection of high potential switching apparatus and the
increased danger induced will be somewhat above the necessary
imperfection of insulation in the switching apparatus itself.
Such imperfection, however, is not a necessity and is one of the
questions which must be solved in order to obtain satisfactory
long distance transmission. This problem solved, the multipli-
cation of switching points is feasible and this implies that with
long lines, where two or three duplicate transmission circuits are
established, it will become necessary to establish switching sub-
stations for no other purpose than the cutting out of sections in
the line when repairs become necessary, thus obtaining satis-
factory regulation, the efficient employment of the large amount
of chemical which is necessarily employed in the transmission
for great distances.
Such switching stations have been proposed as frequently as
ten miles apart. The ordinary practice is not to install them
more frequently than fifty miles apart. It is the writer's opinion
that they should not be more distant than twenty-five miles,
and their location at fifteen or twenty mile points would be
more practical. Handling circuits at this short distance will be
easier on the switching apparatus itself. Where switching sta-
tions are installed fifty or seventy-five miles apart, the high
capacity of the line between switching stations increases the
difficulty of switching, but even at the highest voltages, trans-
position switches can be installed with comparative ease, pro-
vided only, as I have already said, their insulation be sufficient
to prevent concern for the safety of the circtiit from this cause.
In connection with this question comes in the important
problem of the use of automatic switching apparatus for such
switching, and while the writer believes that the use of auto-
matic switching apparatus be very advisable, at the same time
we must recognize that at the present time the main problem of
switching has not been so satisfactorily solved as to permit our
consideration of automatic apparatus, however desirable it may
be.
President Scott: — We have had to-day, according to a little
account I have been keeping here, something like 75 contribu-
tions to the discussions on the papers which have been presented.
206 HIGH-TENSION TRANSMISSION.
You will notice that the papers which have been presented,
eight in number, are all by recognized experts in their several
lines of work, and the discussions are from equally well-known
men. Our Committee on High-Tension Transmission is to be
very highly congratulated on what they have given us, and the
response they have obtained.
A paper preser.ted at the ISbth Meeting of the
American Institute of Electrical Engineers,
New York, March 25,1904.
Copyright 1904. by A. I. E. E.
THE RELATIVE FIRE-RISK OF OIL AND AIR-BLAST
TRANSFORMERS.
BY E. W. RICE, JR.
Two types of transformers have been extensively used in
electrical installations up to date, distinguished by the method of
insulation and cooling employed. The " oil transformer "
relies upon oil as the cooling and insulating fluid. The " air-
blast transformer " contains insulation material mainly of cloth,
paper, and wood impregnated with oil or varnish, and is cooled
by the circulation of a blast of air. In both types the insulating
material is of an inflammable nature, and under certain abnormal
conditions may take fire with more or less serious consequences.
The electrical engineer must, therefore, consider carefully
not only the relative but the actual fire-hazard which exists, and
by proper and common-sense methods minimize such danger.
Both types can be made entirely safe by correct methods of
design and installation.
I think it will be admitted that in general that type
which contains the greater quantity of inflammable material will
occasion the greater fire-hazard. The inflammable material in
an air-blast transformer of say 1000-kw. capacity will amount
to about 800 lb.; in an oil-cooled transformer of the same ca-
pacity the amount will be about 7300 lb. While this compari-
son cannot be taken as a measure of the relative fire-risk, it is an
indication to be considered, especially in view of the fluidity, the
low temperature of ignition, and high calorific value of oil.
While the quantity of inflammable material in an air-blast
transfoirmer is, as stated, relatively small, it has an extended
surface exposed to a large volume of air, and therefore, if a fire
207
208 HIGH-TENSION TRyiNSMISSION.
starts from internal causes, such as short circuit or extreme over-
load, is capable of rapid combustion. This combustion could
be checked by shutting off the flow of air to a transformer by
means of a diaphragm automatically closed by the melting of a
fusible link, the fusible link so located as to be melted by the
first contact with flame ; a method similar to that employed for
closing fire-doors in buildings.
An oil transformer properly cooled is probably not particu-
larly subject to ignition of the oil from internal burn-outs or arcs.
It is well known that oil is an excellent medium for the smother-
ing of alternating arcs, and this principle is utilized in connection
with oil-switches. The vapor above the oil, may however, be
ignited by electrical discharges. Even in this case, while the quan-
tity of combustible material is enormous, the surface exposed
is relatively small. The principle fire-hazard in an oil trans-
former is due to the large mass of inflammable liquid material
which under certain conditions may become totally consumed . 1 1
becomes a special hazard in the case of fire from sources exter-
nal to itself.
Considerations of first cost, economy of space, simplicity,
operating costs, etc., have resulted in placing transformers in the
same room with switchboards and other apparatus, such as
synchronous converters, motor-generators, etc. Under such con-
ditions, it would seem that the air-blast transformer constituted
the lesser fire-risk than the oil transformer, and would therefore
be generally employed if the fire-risk were the only consideration.
The air-blast type, however, is limited in practice to pressures of
about 30 000 to 35 000, as the static discharge which occurs at
much higher pressures would in time break down the insulation.
It is therefore necessary to employ oil insulation on the higher
pressures now common.
The fire-risk can be practically eliminated by placing such
transformers in a room or rooms separated by suitable fire walls
from the other part of the plant. This plan has already been
proposed and introduced. An entirely separate building, sub-
divided again into suitable rooms, may be employed where the
maximum of safety is demanded. Much may be done to limit
the risk, even when the transformers are placed in the same room
with other apparatus, by proper systems of piping for draining
the oil away from the building, by placing the transformers in a
depressed area of concrete arranged for rapid drainage, etc. Of
course any of the methods commonly employed for preventing,
FIRE-RISK OF TRANSFORMERS. 209
limiting, or extinguishing oil fires may properly be employed.
In closing I wish to state that I consider a discussion of this
subject both timely and important. It is well for engineers to
consider carefully the dangers of all kinds, both to life and to
property, that may exist in connection with the use of electrical
appliances. The art is not advanced by ignoring or belittling
the existence of real difficulties, but rather by intelligently facing
the problems which occur and seeking a proper solution. Elec-
trical energy is capable of being produced, handled, and trans-
mitted more safely than any other form of energy, and such
dangers as exist usually can be foreseen and safe remedies can
be applied. On the other hand, we must not exaggerate the
danger of fire from the use of transformers of either the oil or air-
blast type. I believe the fire-hazard is extremely small, and can
be and is being reduced to a negligible quantity by the adoption
of methods similar to those I have outlined here.
210 HIGH-TENSION TRANSMISSION.
Discussion on " The Relative Fire-Risk of Oil- and Air-
Blast Transformers."
F. A. C. Perrine: — As regards the question of the relative
fire-risk of oil- and air-blast transformers, the speaker disagrees
materially from the conclusions and from some of the premises
that Mr. Rice has laid down. The experience of the Fire
Underwriters and particularly the practice of Mutual Fire
Insurance Companies shows that: " In general that type
which contains the greater quantity of inflammable material
will occasion the greater fire-hazard" is not generally admitted.
On the contrary, the question which is most important is not
of the quantity of inflammable material, but of its disposition.
Modern mill construction is one which shows a very large
quantity of inflamniable material, but its disposition is such that
the relative exposed surface is small, and this is the most im-
portant point. One question relating to the disposition of
inflammable material is the presence of dust, not only in con-
nection with the apparatus in question, but throughout
the building. In the most important fires — of six or
seven — ^the disastrous consequences have been due to the
accumulation of dust. A small fire, where there is dust ac-
cumulated, will distribute that fire very widely. In conse-
quence, it seems to me that the fusible link is a very poor
protection against fire, because if flame occurs we have the con-
sequent danger from dust. In one instance of a wooden shop
a single flame shot out, followed along dust-covered wires,
and set fire to all parts of the building, so that the operatives
had barely time to escape, although there were doors at both
ends and in the centre of the building. This shows the im-
portance in all fire-risks of avoiding the first evidence of flame.
The writer also speaks of the protection that can be obtained
by means of systems of piping for draining the oil away from
the building and by placing the transformers in a depressed area
of concrete arranged for rapid draining. In the speaker's
experience there have been three very serious fires in which
the transformers have suffered. In one case four 500-kw.
transformers were installed on a wooden platform, each trans-
former containing 14 barrels of oil. The fire occurred by
reason of a small arc at the failure of an unimportant low-
pressure switch. The fire, by dust and varnish, was immedi-
ately conveyed to the woodwork supporting the switchboard
and the transformers. When the woodwork burned away the
transformers dumped over, the oil spread on the floor, and
there was little left of the building or the transformers. A
careful investigation was made at the time to ascertain whether
the fire had been due at all to the transformers. Every foot
of wire in the transformers was gone over by hand to find out
whether there was the least evidence of an electric arc. Not
only was there no evidence of arcing, but markings on the case
were found indicating that so long as the transformers were in
FIRE-RISK OF TRANSFORMERS. 211
place and the water circulated in the transformer coils, the oil
had not even evaporated. There were markings on the cases
which showed plainly the level of the oil, and the markings
opposite the water-coils showed that the transformers had been
sufficiently hot to char the oil opposite the coils inside the
transformer, but not to evaporate any considerable quantity of
the oil. In the second instance where transformers were in-
volved, the fire was occasioned by reason of a severe short
circuit, distributing a flame to the insulation of the wiring in
the station and to certain woodwork supports of the switches
and other apparatus. The transformers were standing on a
smooth cement floor and were not disturbed. All combustible
material in the entire plant was destroyed, but on account of
the continuous circulation of water in the transformers during
the entire fire the only combustibles in the building which did
not burn were the oil-transformers, and to-day every coil in
every transformer is in operation. The wires were led into the
transformers through porcelain bushings, surrounded by wooden
bushings simply for the mechanical protection of the porcelain.
The wooden bushings were burned out, but the oil was not
materially evaporated in the transformers. In one or two of
the transformers about one quarter of the oil was evaporated
and in these the transformer coils were covered with a black
sediment, but on clearing this off the transformers were put
into and are still in service, the coils not having been injured.
In another instance a short circuit occurring inside of a
500-kw. transformer, the station attendant maintained the
short circuit until he could telephone to the superintendent and
have him come to the station. For about 20 minutes black
smoke was coming out through the insulation bushings on the
case by reason of the actual fire and short circuit which was
occurring under the oil in the transformers ; there was no flame
and no conflagration due to anything inside of the transformers.
The oil was simply boiled away.
In a recent instance where a transformer house was destroyed
by reason of an extensive wooden framework for wires above
the transformers, the latter were also destroyed because the
cases were made of thin metal soldered together, and the heat
was great enough to unsolder the cases and spread the oil over
the floor.
The conclusion to which the speaker arrived from these facts
is that the safest transformer, as regards fire-risk, is the one in
which the combustible material is so disposed as to present the
least surface to fire, and that is the oil-filled transformer. As re-
gards further protection, he believes it is an error to provide means
for draining away the oil. On the contrary, for absolute safety
the transformer should be installed in a cement pit which can
be filled with water, but not above the level of the transformer,
because if the water is flowed into the transformer the oil will
run out and even oil on the surface of water will catch fire ; but
212 HIGH-TENSION TRANSMISSION.
if the transformers are installed in a pit, which can be filled
with water from an outside source, the pit can be filled with
water and automatically drained away without' topping the
transformer. The latter is so connected by pipes that no
falling part of the bmlding can destroy the water connection of
the pipe-coils in the transformer. In this way there is secured
the safest possible installation of the transformer. Further-
more in ordinary cases the pit arrangement is entirely unneces-
sary, if only the water connection be arranged outside of the
building so that falling parts of the building cannot destroy the
piping. A number of years ago at a meeting of the Pacific
Coast Transmission Association, Mr. George P. Low, who is per-
haps the best electrical insurance expert on the coast, called
attention to the great danger in transformers which have thin
cases and particularly those in which the cases are soldered
together, because oil can be heated to the temperature which
will melt solder without setting the oil on fire. Mr. Low re-
commended at that time to the insurance authorities that they
prohibit the installation, where the building was insured, of a
transformer in a case of thin metal, or where a part of a falling
building could punch a hole in the metal of the soldered case,
or where the soldered metal would melt. This is a wise position
which he has taken, and as a consequence that transformer is
safest against fire-risk which is an oil-filled transformer, T/ater-
cooled, and arranged so that the water can be kept in circulation
no matter what happens to the building, and the case of the
transformer is strong enough so that falling parts of the building
will not puncture it. What the speaker refers to particularly
is that when you have a fire which is not complete, and objects
weighing 50 or 100 lb. may be falling, the case should be strong
enough to withstand such impact and especially should be of
such character and strong enough that the fire itself, from the
outside, cannot, by melting the case or melting the solder, allow
the oil to run out. With these provisions, the oil transformer
is by far the safest transformer to install.
J. S. Peck: — ^The introduction to the discussion on this sub-
ject covers the matter in a brief but comprehensive manner,
and the speaker is in substantial agreement with all of the
statements made therein.
It has been the speaker's experience that the air-blast trans-
former is more much susceptible to damage by fire which may
be caused by static discharges, arcs, bad contacts, etc., than is
the oil-insulated transformer, but on account of the relatively
small amount of combustible material in the former, and further
as it is in solid and not in liquid form, it is possible to have
such material entirely destroyed with comparatively little fire-
risk to neighboring apparatus or buildings.
In the oil-insulated transformer there is a very much greater
amount of combustible material, which, while less likely to take
fire, increases the fire-risk to neighboring apparatus or buildings.
FIRE-RISK OF TRANSFORMERS. 213
Under certain abnormal conditions, it is possible that the oil
in a transformer may take fire, consequently it is essential that
proper means be adopted for extinguishing the fire and for pre-
venting damage to other apparatus.
There are two sources of danger from the use of oil in a trans-
former. First, the oil itself may take fire; secondly, a vapor is
given off from hot oil, which when mixed with the proper pro-
portion of air gives a highly explosive mixture. This may be
ignited by a spark and cause serious damage to the apparatus,
and even to the building in which it is contained. The first
danger, that of ordinary burning, is fairly well understood: the
oil being raised to a high temperature, takes fire, and so long
as it can obtain a supply of oxygen, burns with an intense heat
and gives off a very dense, black smoke.
The oil used in transformers has a comparatively high burning
point (a fire-test of approximately 400° fahr.), and it is. necess-
ary that the oil be raised to this temperature before it can be
ignited. On account of the large amount of oil in a transformer,
it would be necessary to supply a great amount of heat and for
some considerable length of time in order to raise the entire body
of oil to the burning point, — a condition which rarely or never
occurs. It is possible, however, to have local heating in the oil
so that a very small portion of it may be raised to a dangerous
temperature and this may then be ignited. This local burning,
if not stopped, will gradually heat the neighboring portions and
result in a general conflagration. Such local heating may be pro-
duced, for example, by an arc drawn just below the surface of
the oil.
The nature of the second danger; that is, explosions, is not
so generally understood. It has been found that with the best
proportions of illuminating gas and air underatmospheric pres-
sure the greatest pressure which can be obtained from an explosion
is somewhat less than 100 lb. per square inch, and it is probable
that with the best mixture of oil-vapor and air at atmospheric
pressure, a force of more than 100 lb. per square inch cannot be
obtained.
The speaker has made a number of tests on transformer cases
with the view of determining the conditions under which com-
bustion of the oil, and explosions of mixtures of oil-vapor and
air may be obtained, also to determine the best methods of
extinguishing the flames.
A sheet-iron case provided with a tight cover was used; the
oil was brought to a burning temperature by ineans of an elec-
tric heater and then ignited by an arc at the surface of the oil.
As long as the cover was removed from the case so that a fresh
supply of air could be obtained, the oil would burn fiercely,
giving off a dense, black smoke. Placing the cover on the case
would almost instantly extinguish the flames. It was also found
that a hqtiid chemical fire-extinguisher was very effective but
did not act so qtiickly as the method of excluding the air.
214 HIGH-TENSION TRANSMISSION.
As long as the oil was maintained at a temperature slightly
above the fire-point no explosion was obtained, but when the
oil was raised 30° to 50° above the fire-point, so that fumes
were given ofE at a very rapid rate, it was possible to obtain an
explosion which would lift the light sheet-iron cover several
inches ofE the case. If it settled back over the case the flames
would be immediately extinguished. This explosion could be
obtained with almost every trial, but not unless the cover was
first removed and a supply of air permitted to mix with the
oil-vapor. From the nature of these explosions it was evident
that the pressure per square inch at the time of the explosion
was very small. The test was of a qualitative instead of a
quantitative nature, and no attempt was made to find definitely
the exact pressure generated.
In this connection, another instance is worth citing. A trans-
former which had been removed from the oil, and therefore
thoroughly oil-soaked, took fire from a torch used for unsolder-
ing a connection. In a few seconds the insulation was burning
fiercely ; the transformer was quickly replaced in the tank of oil,
and the flames were immediately extinguished.
From these tests it is apparent that if a transformer case can
be made reasonably air-tight, combustion of the oil cannot con-
tinue. Where it is possible to use a riveted boiler-iron case
with cast-iron cover, it may be constructed so that it will readily
withstand a pressure of 100 lb. per square inch, and if it is
properly vented a pressure above atmospheric cannot be ob-
tained before the explosion unless vapor should be given off
from the oil at such a rate that its escape is throttled by the
vent-pipe, an almost impossible condition with a vent-pipe of
sxiitable size. Even if vapor is given off at such an enormous
rate, it seems likely that the supply of air would be driven out
from the case, so that the mixture left would have little or no
explosive force. Where this type of construction can be used,
it seems desirable to make the case of sufficient strength to
withstand an internal pressure of 100 lb. per square inch with
a reasonable factor of safety, and to provide a vent-pipe of
suitable size. In such a case oil cannot burn, and should an
explosion occur it can do no harm.
Where a self-cooling sheet -iron case is used, it is impossible
to make it sufficiently strong to withstand an internal pressure
of 100 lb. per square inch, and for such construction it seems
best to make the case practically air-tight so that oil cannot
burn in it, and to provide a large safety-valve which will be
lifted in case of an explosion and will then automatically close,
thus extinguishing the flames.
It is well to consider carefully all dangers, no matter how
remote they may be. How remote is the danger from the oil-
insulated transformer is shown by the fact that, although there
are several thousands of them operating to-day, many of an
old type and often installed without apparent thought of the
FIRE-RISK OF TRANSFORMERS. 215
fire-risk, it is probable that the number of cases of serious trouble
resulting from oil fires may be counted upon the fingers of one
hand, and in the majority of these cases the trouble has started
outside the transformer. In fact, the speaker knows of but one
instance where the transformer was directly responsible for the
trouble. This was the recent fire at Snoqualmie Falls, Wash-
ington, and as it bears directly on the matter under discussion,
the following facts will be of interest:
The water-wheels and generators at Snoqualmie are located
in a pit ^out 250 feet below the top of the falls. The raising
transformers are located in a building at the top of the pit.
There were twelve 550-kw. self-cooling transformers located in
the same room.
The first indication of trouble was the melting of the insula-
tion from the conductors leading to the transformers. When
an attendant reached the transformer house one transformer
was found to be on fire; this was extinguished by means of a
Babcock extinguisher. It was then discovered that another
transformer was on fire, but as the contents of the extinguisher
had been exhausted and as there were no other means of extin-
guishing the flames, they soon burned through the wooden top
coT»ring the case, then melted the solder in the side of the case,
thus permitting the burning oil to flow out upon the floor. The
burning oil melted the solder in the seams of the other cases
and permitted the additional oil to flow out. The conduits for
the low-tension leads acted as a drain and carried the burning
oil down into the wheel-pit, and for a time the whole plant was
threatened with destruction. Fortunately the flames were ex-
tinguished without other loss than the transformer house, part
of the transformers, and the low-pressure cables. This trouble
at Snoqualmie Falls, taken in connection with other informa-
tion concerning oil transformers, leads to certain conclusions:
1. Where practicable, the transformers should be placed in
a boiler-iron case, capable of withstanding an internal pressure
of 100 lb. per square inch, the case to be suitably vented.
2. Where a sheet-iron construction is necessary, the case
should be made practically air-tight and provided with a very
large safety-valve, so that an internal explosion cannot burst
the case.
3. Provision should be made for rapidly drawing ofE the oil
in case it becomes necessary to do so.
4. Individual transformer units, or groups of units should be
located in fire-proof compartments, such compartments to be
suitably drained so that in case the oil escapes from the cases
it can flow out where it can do no harm.
5. Adequate means should be provided for extinguishing fire,
and the station attendants should be trained to know what to
do in case of emergency.
With such reasonable precautions the fire-risk to other appar-
atus from oil-insulated transformers will be no greater than
216 HIGH-TENSION TRANSMISSION.
from air-blast transformers; with either type the fire-risk is
practically negligible.
Dr Perrine has referred to the fire-risk of transformers
mounted in cases made of sheet-metal, having seams riveted
and soldered, and has pointed out the greater safety of the water-
cooled transformer mounted in a boiler-iron case with seams
riveted and caulked. Unfortunately this latter construction
cannot be used on cases for large transformers of the self-cooling
type; and as there is and will continue to be a great demand
for self-cooling transformers it will be necessary to take such
precautions in the installation as will reduce to a minimum the
fire-risk resulting from cases of this type. It is, of course, recog-
nized that a self-cooling case made without rivets and solder
is to be greatly desired. It is hoped that a case of such con-
struction may at some time be devised.
Calvert To wnley : — Strongly emphasized the fact that neither
type of transformer constitutes a serious fire-hazard. He stated
that such fire hazard as does exist should be divided into two
classes; first, a source internal; secondly, a source external to
the transformers themselves. The papers and most of the pre-
vious discussion has had to do with the internal source of fires,
but if transformers themselves constitute a low fire-hazard the
internal source is of minor importance. The chief danger from
internal fire is perhaps the blast of air in an air-cooled trans-
former, which may carry internal fire to adjacent apparatus or
to inflammable parts of the building. It is sometimes but not
always possible or easy to place transformers so that the exhaust
air will impinge only on non-combustible materials. An auto-
matic device for shutting off the air, which may not be operated
for several years, is not likely to work when it is necessary.
For a fire external to transformers the air-blast type is more
subject to attack:
First, from flames, because it has no protecting case.
Secondly, from water, which, while it will not destroy, may
put the transformer out of service for many days.
In a large installation, where both air-blast and oil-cooled
transformers are installed in about equal capacities in the same
transformer house, a somewhat severe fire occurred external to
the transformers. The fire was extinguished after burning
furiously for a time without damage to either type, but water
completely soaked the air-blast transformers, which were out
of service several days or until they became thoroughly dry,
while the oil-cooled transformers were in use as soon as the con-
nections could be re-established; that is, in a few hours.
Many people are misled as to the risk from oil-insulated
transformers by the word " oil." That word suggests kerosene
and the idea of very inflammable material, whereas oil of 400°
fire test, such as is used for oil transformers, is far from an in-
flammable material at any but very high temperatures. A
burning brand may be plunged into it and the fire will be ex-
tinguished.
FIRE-RISK OF TRANSFORMERS.
217
Both types of transformer can be constructed and installed
so that the fire-risk will be very small, and .there is no reason
why engineers or manufacturers should particularly favor the
use of either type against the other.-
Ralph D. Mershon : — The speaker must differ from Mr. Town-
ley in regard to one statement and that is that the fire-risk due
to high pressures is greater than with lower pressures; if any-
thing, the contrary is true. The speaker agrees with Dr. Perrine
in regard to the relative fire-hazard, that it is not entirely de-
218 HIGH-TENSION TRANSMISSION.
pendent on the amount of inflammable material, but is dependent
more on the location and distribution of material. It also de-
pends on the relative effectiveness of the provisions that can be
taken for coping with fire. The scheme of installing oil trans-
formers in separate rooms is not the best practice. In the case
of high-pressure transformers it involves complications in wiring
which are not advisable to use. The speaker is in favor of bare
wiring for high pressures, and the moment you put these trans-
formers in separate rooms you get into trouble with the high-
pressure wiring. If the rooms are to be a thorough protection
against fire they must be in the nature of vaults, which makes
the wiring still more difficult. If the transformers are surrounded
with fire-walls in a building of ordinary construction, and a
transformer gets on fire, the transformer goes, and the oil may
get away from you by the melting of the case.
In the case of an emergency such as might call for getting rid
of the oil in the transformers, it seems a dangerous proceeding
to draw the oil out of the case, when drawn out of the bottom,
because in so doing air must get in at the top and there is a
chance of an explosion, and that chance becomes greater as
more oil is taken out of the case. This question of protection
against fire has been carefully considered in the case of oil
transformers, with reference to a plant of 50 000 volts and over,
where the ultimate installation will mean transformers contain-
ing a good many hundred gallons of oil. The different methods
of protection against fire were carefully considered and the
scheme shown in the diagram finally adopted. The transformer
case is built so that it will stand the maximum pressure which
an explosion would cause, and all leads brought out through
stuffing-boxes which will stand that pressure. To the middle
of the top of the tank is brought a pipe running to the sewer
and at the bottom of the transformer case is brought a water-
pipe which has two valves in series, and between the two valves
a drip cock to avoid any possibility of water leaking into the
transformer through a leaky valve; the idea being in case of a
fire emergency the water will be turned into the bottom of the
transformer and drive the oil out at the top. No fire-walls have
been installed in that plant although there will probably be
some such walls between groups of transformers as an addi-
tional protection. As a last resort such an arrangement is about
as safe as anything that can be thought of. Another advantage
of this arrangement is that it leaves the whole space between
the transformer free for a high-pifessure wire, which can prefer-
ably be a bare one.
C. E. Skinner: — An element to be considered in the oil
transformer is the quality of the oil itself. It is extremely
important that an oil be selected which has a flash-test con-
siderably above the temperature at which the transformer will
run in normal operation, including overload. At the present
time a mineral oil is almost always used and can be obtained
FIRE-RISK OF TRANSFORMERS. 219
with a great range of flash-tests. One having a flash-test not
greatly above the normal operating temperature of the trans-
former will begin to give off fumes before the flash-point is
reached, and these being explosive when mixed with air form
a source of danger. An oil should be selected which has a flash-
point not lower than, say 175° cent. Such an 9!!, if properly
made, will have practically no evaporation whatever at
100°cent., this being higher than will be found except under the
most extreme conditions of temporary overload. Too high a
flash-test oil is undesirable on account of the viscosity being so
great that the power to carry heat from the transformer to the
cooler case is greatly reduced, and on account of its being un-
pleasant to handle.
Oil as a body cannot be set on fire easily; in fact a torch
held to the surface of a body of oil will not set it on fire until
the oil itself has reached the flashing temperature, or slightly
higher. It is well known in the operation of oil-switches that
an arc may be drawn under the surface of the oil and no fire
results. This is true even though the temperature of the oil is
above the flashing-point when such an arc is drawn, as air is
absolutely necessary to the continued combustion of the oil.
It is also true that an oil fire may be smothered with compara-
tively little difficulty, provided the oil is not allowed to spread.
It is therefore obvious that a well-constructed fire-proof case
with a cover which can be made practically air-tight, placed in
a fire-proof compartment with means for draining, as mentioned
by Mr. Rice, will reduce the fire-risk of oil-insulated transformers
to a minimum. The great advantages of oil in insulating and
cooling make it inadvisable on account of fire-risk to attempt
to discard oil-insulated transformers, but to provide the neces-
sary precautions to reduce this risk to the smallest possible
amount.
H. G. Stott: — He thoroughly agrees with the view taken by
Mr. Rice, that the fire-risk is absolutely proportional to the
amount of inflammable material contained in a transformer.
When the insurance inspector makes an inspection of the build-
ing upon which he is about to issue a policy, he does not merely
look at the outside walls of the building but makes a most careful
examination of the contents — and the rate depends greatly upon
these contents — so that no matter what arguments may be used
as to the method of quickly getting rid of the oil and preventing
it from flowing out of the case, thus spreading the fire, it should
be treated as an extra risk as compared to an air-cooled trans-
former. A number of instances of serious fires due to oil-cooled
transformers have been mentioned to-night, but nothing what-
soever has been said of a fire due to an air-cooled transformer,
and the speaker cannot recall ever having heard of such a case
where damage was done externally to the transformer through
fire communicated by it.
Referring to the general subject of fire-risks and efficiency
220 HIGH-TENSION TRANSMISSION.
of apparatus, he desired to call attention to the importance of
having skilled attendants in all power-plants and sub-stations.
The difference in paying the men $2 00 a day or $3 00 a day is
very small at the end of a year, but the skilled attendant at
the higher price will invariably save many times the extra cost
of his salary. It seems the height of folly to expend hundreds
of thousands of dollars on the very best apparatus which can
be bought and then, for the sake of saving a few hundred dol-
lars a year, turn it over to be operated by men of no technical
education or special training.
The very best automatic apparatus will soon become inop-
erative if not given the proper amount of skilled attention. In
at least two cases mentioned to-night of fires by transformers
due to melting of the solder on the cases, it is quite evident that
had there been an attendant present with the requisite amount
of knowledge the fire would certainly have been limited to the
transformer which was in trouble, instead of destroying the
whole station. When anything happens to electrical apparatus
there is no time to telephone to any one for information as to
what to do; the man on duty must be competent to take care
of any emergency which may arise.
P. N. Nunn: — The fire-risk due to the oil transformer is not
negligible. In a large, modern power-house filled with expen-
sive apparatus the large amount of oil contained in a full
equipment of oil transformers is a constant menace to the entire
pb.nt. This is shown by the present record of fires and by
the average station record of accidents which might have caused
fires. The risk to each transformer, due to accidents within
itself, may not be serious, but the combined risk due to many
such transformers is very serious, because it applies to the
whole investment in the plant. While compelled for the present
to use oil transformers, the conservative engineer, in designing
high-pressure work, cannot afford to neglect or underestimate
their danger, or fail to employ every reasonable precaution,
even perhaps some extreme measures, for protection. On this
account exception is taken to the spirit of some remarks made
this evening. Their effect has been to discredit the importance
of this risk, and the protective measures suggested.
Within a few years the Telluride Power Company has lost
tv/o complete sub-stations; and while the fares may not have
orirjinated in the transformers themselves, the loss suffered, of
which the transformers were but a small part, was chiefly due
to the oil. It is this danger, to which all surrounding apparatus
is subjected by the oil transformer, which constitutes the chief
argument against it in favor of the air-blast transformer.
It might be possible to use some highly insulating gas inca-
pable of supporting combustion, which might be circulated,
perhaps under pressure, through both transformer and cooling
coil.
P. M. Lincoln: — To start and sustain a fire two distinct ele-
FIRE-RISK OF TRANSFORMERS. 221
ments are necessary; first, a combustible, and secondly, a sup-
porter of combustion. Bearing this in mind, suppose we analyze
the relative fire-risks of air-blast and oil-insulated transformers.
In the air-blast transformer we have present constantly and
unavoidably both the essentials necessary to start and maintain
a fire, the insulation of the transformer being the combustible
and the cooling air the supporter of combustion. The only
thing needful, therefore, to start a fire in the air-blast trans-
former is simply a sufficient amount of heat at any point. In
this respect, however, the air-blast transformer does not differ
from any other combustible structure, except that under nor-
mal conditions the supply of air is by forced draught.
On the other hand, when we come to examine the oil-insulated
transformer we find a structure in which the combustible and
the supporter of combustion are capable of being easily segre-
gated by a fire-proof wall. Relative fire-risk is not simply a
question of the relative amount of inflammable material as
Mr. Rice intimates, but it must also involve the question of
the probability of a fire being started. The oil transformer,
although it contains a considerably larger amount of inflam-
mable material, has the advantage of segregating this inflam-
mable material so that it can be made almost impossible for a
fire to start within the transformer, and can also be shielded
from a fire outside of the transformer.
The speaker's only personal experience with a transformer fire
has been with the air-blast type. This leads him to doubt the
practicability of Mr. Rice's suggestion of a fusible link in con-
nection with a damper to shut off the air. In the instance
mentioned not only was it necessary to close the damper in
the transformer but also to shut off the air and finally to turn
the hose on the burning transformer.
In the speaker's opinion the greatest danger in the use of
oil-insulated transformers comes from improper installation and
consequent probability of the floor becoming oil-soaked. When
properly installed, neither the air-blast nor the oil-insulated
transformer involves a serious fire-hazard; but if compelled to
choose between the two types the speaker would, for reasons set
forth above, be inclined to choose the oil-insulated transformer.
C. L. DE MuRALT : — He does not agree with Mr Rice that the
greater quantity of combustible in tlie oil transformers neces-
sarily makes it a greater fire-risk. Transformers as a whole are
not by any means the greatest fire-risk in any central station.
In Europe, at least in Switzerland and France, the air-blast
transformer is considered a considerably higher fire-
risk than the oil transformer, and possibly for the
following reasons: when air-blast transformers are
overloaded, the insulation gets very much heated, and
it is just possible that it breaks down somewhere, and takes
fire either through the arc or through the heating of the insu-
lation. In the oil transformer the oil forms, so to speak, a sort
222 HIGH-TENSION TRANSMISSION.
of safety-valve, in that an overload will make itself felt only-
after a much longer time, when the other safety devices will
probably have had time to come into play and cut the trans-
former out. This may be one of the reasons why air-cooled
transformers in Europe are generally not used for sizes larger
than about 150 kw. Oil transformers can be made almost fire-
proof, and it is a good plan to put them in separate buildings.
This necessarily does not mean complication in the wiring. In
the case of hydro-electric plants, which will mostly have to do
with high pressures, the building is generally pretty long and
narrow, with the units placed on one of the long sides. If the
switchboard is placed in the centre of the other long side, it is
easily possible to place the transformers in a room right back
of that switchboard; similarly, if it is placed along one of the
short sides; and in both cases the transformer room will prob-
ably not be much longer than the width of the main part of
the central station. In both cases the leads from the generators
will go to the switchboard, from the switchboard to the trans-
formers, and as there need not be any switches in the high-
pressure side of the transformers, they may go straight out. If
the need for switches in the high-pressure side is felt, they can
as well be placed in the transformer room and actuated mechan-
ically from the switchboard. Thus, the line equipment will be,
if anything, simpler than in the arrangement with the trans-
formers in the central station itself.
In looking at the design which Mr. Mershon shows to-night,
it would appear that when there is a necessity for flooding the
transformers in order to bring the oil out, there is evidently a
large fire, and every reason to suppose that the roof will come
down and possibly break the oil piping which connects the
transformers with the sewer. If this takes place, there may be
serious danger of the oil doing more damage than if it had re-
mained in the case. If transformers are located in a separate
building, as just described, and placed in strong cast-iron boxes,
or else in casings made of boiler-iron, riveted and caulked, and
strengthened by angle-irons, and if these cases are well covered
by a tight-fitting cast-iron cover, there is absolutely no fire-risk,
either from the inside or from the outside, and such a trans-
former installation may be called as fire- proof as a brick wall.
0. S. Lyford, Jr.: — -Before this discussion is closed more
emphasis should be laid on a point raised by Mr. Townley.
The title of the paper on transformers has naturally led to a
discussion which gives the impression that these transformers
constitute a very serious fire-risk. The fact cannot be em-
phasized too strongly, that although transformers are fire-risks
these are not risks which cannot be successfully coped with.
The speaker does not agree with Mr. Nunn as to the seriousness
of the risk of the oil. This transformer subject ought to be
separated into three heads instead of two; namely, the oil-
insulated, water-cooled transformer; the oil-insulated, air-cooled
FIRE-RISK OF TRANSFORMERS. 223
transformer; and the air-blast transformer. That they are all
good should be emphasized. There is, however, a place for
each type, as is usually the case with a number of good things
of a similar character. Where water is available for cooling
purposes, there is little question that the oil-insulated, water-
cooled transformer is the type to be used. Where water is not
available, the choice lies between the other two; but there is a
distinct field for each. For instance, in a small sub-station, as
in the case of an interurban railroad, there may perhaps be a
couple of 250-kw. synchronous converters and an equipment
of from three to six transformers of moderate size. In such a
case the blower equipment is an unnecessary nuisance and the
oil-insulated, self-cooling type has the advantage. On the
other hand, in a large sub-station, such as one of those on Man-
hattan Island, there may be 20 transformers or more, and there is
a gain by placing the transformers close to the synchronous con-
verters and consequently distributing them throughout the
building. Moreover with such a number of transformers the
blower equipment is relatively a simple proposition, and all
things considered, the advantages are in favor of the air-blast
type. Therefore it seems to the speaker that a type of trans-
former for each specific service should be selected, and having
done so it is perfectly possible so to design the plant that the
risk of fire is extremely remote. In this day and generation
it is seldom that we cannot afford to make a fire-proof building ;
many things besides transformers justify this precaution. The
advantage of a' fire-proof building was clearly demonstrated at
Baltimore when practically the only two buildings left intact
were the new power-station and the sub-station of the electric
company, which were fire-proof, the fire could not get into
the buildings. An electric plant costs so much money that the
percentage added to make the building fire-proof is extremely
small. With the surroundings fire-proof and the transformers
properly located, the risk, as before stated, is extremely remote.
[Communicated by Letter.]
Howard Bayne: — Mr. Rice's paper refers briefly to the neces-
sity of employing proper means of preventing or extinguishing
oil'fires. In this connection the writer suggests the consideration of
the use of steam as a means of putting out such fires. When prop-
erly applied, this has been found by those experienced in the
oil business to be the best method of extinguishing an oil fire,
particularly when the fire is serious.
Proper arrangements should be carefully planned and must
be permanently installed. The transformers should be placed
in a separate vault and in case of a large number they might
be distributed among several vaults. Suppose each vault was
equipped with one or more permanent two-inch steam lines, ac-
cording to the amount of space in the vault. In case of fire,
all outlets, such as doors and ventilators, should be closed and
224 HIGH-TENSION TRANSMISSION.
the steam turned on. Both or either of these operations could
be arranged to work automatically. The fire would be smothered
in a very few minutes or possibly in less than a minute. The
prime reqviisite is to have a large volume of stearii turned into
the vault quickly. If the fire is confined to the surface of the
oil and the core and windings remain covered with oil, the trans-
former could be used again with very little, if any, delay.
The efficiency of steam in fighting oil fires is surprising. To
illustrate: the company which the writer represents owned an
large earthen storage tank at Gladys, Texas. It covered
five acres and contained 200 000 bbl. of crude oil which was
most inflammable since it gave off naptha vapors and hydrogen
sulphide. On August 11, 1903, lightning struck the point of
the conical roof. The small hatch at the apex was blown off
and a tremendous blaze started. After several minutes the
men got the hatch on again and turned steam into the tank.
The blaze grew perceptibly less almost immediately, diminished
rapidly, and finally went out.
The writer mentions this incident to show what can be done
by smothering an oil fire with steam in a case where the fire
has most favorable conditions for persisting. Compared to
these conditions, those existing when oil in transformers catches
fire would render the fire easy to extinguish. With oil-cooled
transformers in " fire smothering " vaults the writer thinks
the fire-risk would be almost nothing.
[Communicated by Letter.]
W. L. Waters : — ^The question of the relative fire-risk of oil-
cooled and air-blast transformers can be best decided by con-
sidering the different cases of transformers in stations with at-
tendants, and transformers in stations without attendants.
And also by considering fires due to internal causes and fires
due to external causes.
Considering first fires due to internal causes. In an oil-cool-
ed transformer it is almost impossible to start a fire due to a
short circuit or a bum-out in the transformer itself, unless there
is nearly unlimited power back of the short circuit. The oil
will smother the fire so effectually that usually the mains will
go before the transformer catches fire.
On the other hand, in an air-blast transformer a short circuit
will turn the interior of the transformer into a blazing furnace,
and even though the air supply is automatically cut off the
transformer will certainly be totally destroyed unless it is cut
out of the circuit. Whether the burning of the transformer
itself starts a general fire depends, of course, on the arrange-
ment of the building. If there are attendants present they
can take care of the bum-out and can cut out the transformers
before the situation gets serious.
In the case of an ordinary fire due to external causes the oil-
cooled transformer will be completely protected from damage
FIRE-RISK OF TRANSFORMERS. 225
by the oil, as the latter will not be heated to ignition point
and will prevent the heat from reaching the transformer itself.
An air-blast transformer in a similar case would probably be
ruined, though it might not add much fuel to the conflagration.
In the case of a large fire, the oil in an oil-cooled transformer
would be ignited, and on account of the large quantity of in-
flammable material the results would be disastrous. This might
be prevented if attendants were present to draw off the oil, or
if automatic arrangements were employed for draining the oil
in case of fire. But, in any case an oil-cooled transformer is a
very serious risk in a large fire.
Speaking generally, then, an air-blast transformer is at the
mercy of almost every fire, no matter how started; and though
a single transformer may not add much to the conflagration it
will almost always be seriously damaged itself. On the other
hand, an oil-cooled transformer is in practically no danger except
in a large fire, and then the risk is serious. Generally a set of
oil-insulated transformers will be a much safer installation than
a corresponding set of air-blast transformers.
[Communicated by Letter.]
Irving A. Taylor : — It appears to be generally conceded that
oil transformers are a greater fire-hazard than the air-blast type.
Fire is not liable to start inside them, but in the case of an ex-
ternal fire the oil is liable to catch and produce a very hot fire.
Internal short circuits are not likely to start a blaze, provided
they are well under the surface of the oil, but if the latter is
low, or the design is such that the coils are normally near the
surface, an arc is liable to reach the surface, produce gas, and
so set the oil on fire. The oil level should therefore be well
above the coils.
In transformers which are sealed air-tight, a short circuit is
likely to set up a sufficient explosive force to blow the cover off
or to crack the case, the oil either running out or being thrown
out — ^possibly on fire. Covers should therefore not be air-tight,
but should prevent a circulation of the air. One of the greatest
dangers from oil transformers is the fact that they are likely to
leak under ordinary or extraordinary conditions. In the first
instance, surrounding floors, whether of wood or concrete, be-
come impregnated with oil and are very dangerous in the event
of fire. Where cases are made of sheet-iron, or jointed with
lead, an external fire is likely to open up the seams and let the
oil out, with disastrous effect. All cases should positively be
made of substantial cast-iron, without joints if possible.
Where leaded joints are necessary, the lead should not be de-
pended upon for holding the case together, and the latter should
be fairly oil-tight without the lead.
Where oil transformers are used in large quantities- they
should, where possible, be installed in a thoroughly fire-proof
building used exclusively for the purpose and isolated from other
226 HIGH-TENSION TRANSMISSION.
buildings. They should not be placed in buildings like hotels,
or in any room not thoroughly and heavily fireproofed.
It is sometimes desirable to install oil transformers where
artificial cooling is not commercially feasible, or where water-
cooling is more convenient than air-blast. Otherwise, where
the pressure will permit, air-blast transformers are always
cleaner in operation as well as safer, and their use is therefore
more satisfactory.
Mr. Rice's proposal to use fusible links in air-blast trans-
formers is highly practicable. They should be combined with
air-tight dampers, and should be hooked in place so that the
dampers may be worked periodically for inspection purposes.
While such links would naturally be placed in the draught at
the top of the transformer, it would seem that the dampers
should be placed at the bottom so as to prevent burning material
being dropped into the air chamber and in that way carried to
the other transformers.
There should be no inflammable material, either in the path
of the air-blast above the transformers or in the ducts, and the
wiring should preferably be by lead cables enclosed in tile right
up to the transformer. Where it is necessary to use rubber-
covered wires at the cable heads in the ducts, they should be
thoroughly fireproofed.
[Communicated by Letter.]
Norman T. Wilcox: — He believes that where properly in-
stalled, the fire-risk with oil transformers is not so great as
many imagine. In two cases of fire started by lightning in the
step-up transformers in the Canyon station of the Colorado Elec-
tric Power Co., he found that they were caused by an arc,
which would not have occurred if the oil had been kept to its
proper height in the transformer. There was some trouble in
putting out the fire, especially on account of the gauze ventilators
in the top of these transformers. In one case these spaces were
blocked up with waste, which had been soaked in water,
thereby choking off the air supply and smothering the flame.
In the first case, the engineer of the station threw off the cover
to the transformer, which resulted in a lively blaze. This was
carried up the wires to the wooden framework almost directly
over the transformers suplporting the high-pressure circuit-
breakers.
He would not use an air-blast transformer on high-pressure
work if he could avoid it, as he believes that not only is the insu-
lation better with oil, but the oil prevents the insulating material
from baking, drying out, and cracking, and insures a longer life
to the apparatus.
[Communicated by Letter.]
A. C. Pratt: — For maximum safety, oil-cooled transformers
should be placed in a strong boiler-steel case, with the cover
FIRE-RISK OF TRANSFORMERS. 227
well bolted on. The latter should have a relatively large flap
opening to act as a safety-valve, so arranged that it will not
of itself remain in the open position.
There seems to be no doubt that inflammable and explosive
mixtures accumulate above the oil in transformers; but the
self-closing cover will promptly smother any fire which might
be started from this cause. These gaseous mixtures seem to be
formed, at least in part, by minute brush discharges in the oil,
which break up the mineral oil into light volatile constituents
and heavy asphalt-like residue. These effects may be readily
produced experimentally, even at pressures below 10 000 volts.
There should also be a considerable air-space to allow for a
possible boiling of the oil without boiling over. Such a trans-
former will most naturallly be of the water-cooled variety, and
will always be mounted on a fire-proof foundation. Risk from
external fire should be small. A large body of oil in a substan-
tial case, with relatively small exposed surface, will pass through
a fire, such as would make scrap of an air-cooled transformer,
and be ready for service in a day or two, upon renewal of leads
and bushings. Incidentally the transformer cover should be
water-proof to such an extent that water from a hose will not
fall into the hot oil. As a final precaution, arrangements should
be made to drain spilled oil away from the building.
[Communicated by Letter.]
H. A. Lardner: — In the discussion as to the relative fire-risk
of oil- and air-blast transformers, the opinion developed that
large oil-cooled transformers in boiler-iron cases with suitable
covers and vents were practically fire-proof, provided they could
be suitably protected from intense heat from the outside. A
suggestion was made that this class of transformers be installed
in a pit which could be flooded to within a few inches of the
top. While this gives the needed protection, it is an extremely
inconvenient method of installation, owing to the necessity of
occasionally moving the transformers. On account of the high-
pressure connections overhead it is usually undesirable to have
a crane in the transformer room, and the most common method
is to mount the transformer on trucks so that they can be
drawn out of their position and under a suitable lifting device
in another part of the transformer house when repairs are
necessary.
Naturally the installation of transformers in a pit will neces-
sitate the use of a crane and is therefore objectionable. It
occurs to the writer that, as transformers are usually arranged
along one side of a room, they might be mounted on trucks as
usual and a comparatively light boiler-iron tank installed around
them. The back and possibly the two ends would be supported
by the walls of the building while the front could easily be
held in place by tie-rods. The tank should be provided with
an overflow of ample capacity to prevent the water reaching
228 HIGH-TENSION TRANSMISSION.
the leads, bushings, or running into the transformer case. The
front of this tank should be made in sections so that a section
could be removed and a transformer wheeled out to the repair
room when desirable.
It would not be a serious fault if this tank were not entirely
water-tight, as water would only be turned into it during a fire,
and some leaking would not be objectionable.
The method of protecting transformers by submerging theni
in cooling water is believed to be good, as there can be no ob-
jection to turning water into the tank immediately upon an
alarm of fire and the protection need not be left until a last
resort. It also seems to be well established that, if the attend-
ants will promptly disconnect a transformer on fire from in-
ternal causes and cooling water be applied externally to a suit-
able air-tight case, the internal fire will generally extingtiish
itself.
[Communicated by Letter.]
H. F. Parshall: — The experience gained in England would
indicate that there is no great risk from either type of trans-
former so long as it is intelligently installed. It has been pretty
fairly proved that the oil transformer is more reliable over a
wide range of conditions. The principal advantage of the air
transformer is in installations like the Central London Railway
where an accident to an air transformer brings no risk to the
working staff, whereas an accident to an oil transformer might
bring about serious consequences. Where, however, the trans-
formers can be installed so that no matter what, the occurrence
there is no danger to life, the oil transformer is, in the writer's
judgment, to be preferred
[Communicated by Letter.]
R. S. Kelsch: — As regards the relative danger or risk in the
use of oil- and air-blast transformers, the writer considers the
use of oil transformers extremely dangerous, unless they are
installed in isolated buildings. And even then, he would hesi-
tate a long time before being responsible for the installation
of several banks of transformers, with each transformer con-
taining from five to thirty barrels of oil.
The writer has as yet been unable to obtain an oil transformer
where the case was oil-tight, notwithstanding the fact that the
contract specifically stated that in order to be accepted it must
be oil-tight. The writer has visited many plants and has not
seen an oil transformer that was free from leakage. As a rule,
a large drip-pan was placed under the transformers, to catch the
leaking oil.
In one instance three 70-kw. transformers for supplying power
to induction motors were installed in a building, and during a
thunder storm at 2 a.m. one of the transformers failed. After
the fire the evidence showed that a short circuit had occurred
at a point near the top of the transformer coils, burning a large
FIRE-RISK OF TRANSFORMERS. 229
hole in one of the cases and allowing the oil to escape, catch on
fire, and destroy all three transformers as well as the building.
In another instance, a plant in Montreal was supplied with
5000-volt, three-phase power from a water-power plant. There
we.t three 150-kw. transformers for reducing the pressure to
2000 volts. The bmlding and contents were of a temporary
nature. A short circuit ignited the oil that had previously
leaked from these transformer cases, and that which had been
forced out of the cases by the heat and the entrance of water
into the transformers. The entire contents of the building were
destroyed, only the walls remaining standing. In this same
building, having wooden floors and temporary switchboards,
an air-blast transformer of 250-kw. connected solid to the bus-
bars, fed by eight 750-kw. generators was completely destroyed.
It burned for fully four minutes before the current was cut off,
but did no damage outside of the transformer itself.
In another instance in Montreal, two 2000-kw. 25 000-volt,
air-blast transformers failed. There were no automatic switches
and in order to get the current off it was necessary to telephone
the power-house to shut down. This required nearly two
minutes, which would be time enough to burn a hole through
an iron tank filled with oil and allow the oil, already ignited,
to run over the floor; but in the case of these 2000-kw., air-blast
transformers, there was absolutely no damage, except to the
transformer itself.
From his experience with both types of large capacity, the
writer would not use oil-filled transformers, unless compelled
to do so. He does not imply, however, that an air-blast trans-
former in a frame building with a 12-ft. ceiling would be consid-
ered safe, but in making the comparison, he refers to the installa-
tion of transformers of large capacities in a modern fire-proof
station. The danger in one case arising from the possibility
of the flames due to the air-blast reaching inflammable mate-
rial, as against oil escaping from the tank becoming ignited and
covering the floor of the station with a sheet of fire. While
the oil used in transformers does not ignite readily, and will
permit a red-hot iron to be plunged into it without danger, a
heavy short circuit will ignite the oil, and in these circum-
stances becomes a dangerous piece of apparatus.
The writer suggests that air-blast transformers be equipped
with a positively air-tight damper to shut off the air. The
damper generally furnished is practically useless in the event
of the transformer failing, but he has had transformers equipped
with dampers which were practically air-tight. The parts were,
however, not rough casting^,' but consisted of a cast-iron frame
with brass gates machinedJ;Bo as to make a perfect fit. They
are operated by a key hung in a convenient place on the trans-
former. It may be argued that this introduces a possibility
of damaging the transformer, but not to any greater degree than
the use of a valve to let water into the transformer or to allow
the oil to escape.
230 HIGH-TENSION TRANSMISSION.
[Communicated by Letter.]
H. W. Tobey: — Many engineers contend that air-blast trans-
formers are the safer of the two types. The preference being
due, the writer thinks, to two reasons: first, because the con-
taining tanks of oil-insulated transformers have been made
extremely light and constantly leak oil, and in case of fire will
often open and allow the entire contents to escape; secondly,
because of the use of a poor grade of oil. With substantial
tanks and an oil having a high flashing-point, these two draw-
backs are entirely removed.
The oil-insulated transformer is capable of withstanding severe
and long-continued overloads without injury, while in the case
of a short circuit within the winding it is entirely under oil
and the arc will be extinguished before injuring more than a
single coil. Leads coming from the various coils are always
a source of danger unless carefully insulated and surrounded by
oil.
Relatively to the ability of oil-insulated transformers to with-
stand fires due to external causes, the writer can instance an
interesting experience of a large power company in the West.
At the time of the accident, the transformer equipment con-
sisted principally of a large number of 840-kw. units, all oil-
insulated and water-cooled. These were arranged in groups of
three each for stepping up from 2300 to 50 000 volts. A fire
starting from some external cause spread to the transformer
room where it burned for three-quarters of an hour. At the end
of this time a pipe line above the power-plant was opened and
the place was deluged with water for over eight hours. It
would seem after treatment of this kind that little would be
left of the transformers except scrap-iron and copper. On the
contrary four transformers (which were somewhat beyond the
hottest part of the fire) were put back into service without re-
pairs. Others were dried out with current for a few hours and
after being filled with new oil were also ready for service. There
were only four which actually required repairing. On these the
porcelain insulators had been entirely destroyed and the covers
were badly cracked. The inside surface of the tanks, together
with the coils and cores, were covered with a thick deposit of
carbonized oil. A large amount of water had also gotten into
the tanks.
The cores were taken down, the coils cleaned, and the outer
layer of tape replaced with new. The parts were then reassem-
bled and the transformers put back into service where they are
still in successful operation. It is not difficult to imagine what
would have become of this apparatus if it had not been immersed
in oil.
This brings up an interesting question. Is it good practice,
as many maintain, to empty oil-insulated transformers in case
of fire?
FIRE-RISK OF TRANSFORMERS. 231
[Communicated by Letter.]
Wm. J. Hazard: — In an oil-cooled transformer, seal ttie space
above the oil as thoroughly as possible and provide an adjust-
able vent. Fill this air-space with some inert gas such as carbon
dioxide, supplied by a gas generator which will automatically
maintain a slight pressure, just sufficient to prevent the entrance
of air to the case. The writer believes this would effectually
prevent the ignition of the oil gases, and hence add to the safety
of the apparatus. The extra complication and the cost of
maintenance would be insignificant. The amount of gas neces-
sary would of course depend on the rate of leakage.
[Communicated by Letter.]
E. P. Roberts: — In the matter of oil transformers, the prac-
tice of the firm with which the writer is connected has been for
some time to place such transformers in a fire-proof room, be-
lieving that the fire-risk justified the slight additional expense.
Our practice has been somewhat of an evolution. The Dayton
& Northern power-house, designed in 1900, had a separate room
built on the outside of the building and to one side of the gen-
erator room. This additional room was fire-proof construction
with fire-door between same and the engine-room, with the floor
on the same level as the latter. The one sub-station of this
road had a fire-proof room built into the balance of the building,
which consisted of a synchronous converter room, the fire-proof
static transformer room, a storage-battery room, freight and
passenger offices, and, above the latter, living rooms for the
attendant. The floor of the static room was on the same level
as the floor of the synchronous converter room.
In each static transformer room the high-pressure lightning
arresters and switches were placed. Since then this has been
modified, and for the Dayton & Muncie Traction Co., now
under construction, the design is as follows:
For the power-house there is an addition to the building
immediately in the rear of the switchboard. The addition has
two floors and the whole is of fire-proof construction, using steel,
brick, and concrete. The upper floor is on a level with the
engine-floor level and herein are placed the high-pressure light-
ning arresters and switches, while there is a fire-proof door into
the engine-room. The lower floor is below the level of the
engine-room basement and has a fire-proof door from such base-
ment. In this room are placed the static transformers. The
floor is of concrete, with drains, and in case a transformer should
catch fire and the oil escape, it will run into the drains and be
smothered. But even if the drain should not take it off with
sufficient rapidity, it could not run into any other room.
The additional cost of the building is slight, as, in any case,
room must be provided for the transformers and high-pressure
switches and arresters, and placing these immediately behind
the board is convenient, and does not necessitate complication
in wiring or in mechanism for controlling the switches.
232 HIGH-TENSION TRANSMISSION.
The sub-stations, of which there are three, are two new build-
ings and one old one. The new buildings have fire-pfoof static-
transformer rooms with wire towers; the floor is drained and
is below the level of the other rooms, and a fire-proof door con-
nects to the synchronous converter room.
The old building is a remodeled warehouse in the center of
the town. The static transformers are placed in a fire-proof
room in the basement and a tight brick shaft runs from this
room to the third floor. The high-pressure wires entering the
shaft through large tile ducts, which together with, the shaft
act as ventilators for the room in the basement, pass fi:oni the
pole line down the shaft to the transformer room.- Gold air is
taken from an area way under the sidewalk.
The synchronous converters are placed on the first floor, on
foundations extending into the basement and adjacent to the
static room. The high-pressure lightning arresters and switches
are placed in the static room, the switches being controlled
from the switchboard in the synchronous converter room.
This is not quite so convenient an arrangement for attention as
the other sub-stations, but it is expected that it will prove sat-
isfactory; it was necessitated by the local conditions and the
decision of the engineers relative to placing the static trans-
formers in independent fire-proof quarters.
[Communicated after Adjournment]
W. S. Moody: — Some of the gentlemen who have discussed
Mr. Rice's paper seemed to have missed the real point which
he brought out in this paper. He refers, not to the relative
liability of fire orginating in the two types of transformers, nor
even the question of relative damage which the transformer is
likely to experience should fire develop in it, but the relative
" fire-risk " of a. station equipped with one or the other type of
transformer. It is not necessary in considering this point to
assume that one or the other type of transformer is inherently
the safer or even that fire originates in the transformer at all.
The simple question is, how much does the addition to a certain
building of a certain small amount of inflammable material such
as is contained in the air-blast transformers, increase the fire-
risk on the building and contents as compared with the
addition to the same building of transformers containing
several hundred barrels of oil.-
The question seems hardly to admit of discussion. The
chances of a fire external to the transformer communicating
itself to the interior is also slight. But granted a fire can
originate somewhere and that it may set the insulating material
on fire beyond control, then will not a few pounds of varnished
wrappings constitute a perfectly negligible risk as compared
with many barrels of oil?
[For further discussion on this paper see pages 269 and 279-]
A paper presented at the 185(ft Meeting of the
American Institute of Electrical Engineers,
New York, March 25th, 1904.
Copyright 1904 by A. I. E.E.
THE USE OF GROUP-SWITCHES IN LARGE POWER-
PLANTS.
BY L. B. STILLWELL.
In a number Oi. large electric generating plants recently de-
signed in America, the feeder circuits are divided into a plurality
of groups, and a switch designated a " group-switch " is con-
nected into the circuit between the main bus-bars and each
group of feeders. Obviously, no switch should be added to an
organization of switch gear already very complicated and expen-
sive, unless practical usefulness fully justifies its adoption.
As this subject has never been discussed by the Institute,
the writer avails himself of the opportunity presented by the
invitation of the Chairman of your Transmission Committee to
introduce it.
In considering a subject such as this, accurate generalization
is difficult if not impossible. Probably no one who knows what
engineering means would affirm without qualification either that
he approves the use of group-switches or that he does not approve
their use. There are few hard and fast rules in engineering. If
such matters as the use or non-use of group-switches could be
settled once for all, and for all plants regardless of size, function,
or attendant conditions, the purchasing agent would soon suc-
ceed the engineer, the pharmacist would take the place of the
physician, and the capitalist investing his money in electric
power development and use would have no occasion to seek
among technical advisers for sound judgment resting upon broad
experience, and exercised in full knowledge of the existing state
of the art, as well as recognition of its general direction and
233
234 HIGH-TENSION TRANSMISSION.
tendency. Instead of attempting a generalization, therefore, we
may consider more profitably the arguments for and against the
group-switch in the case of a typical plant, and then glance at
some of the modifications of function and circumstance which
in the case of other plants would affect our conclusions. The
group-switch first appeared in the plant of the New York
Street Railway Company at 96th Street, but as the writer
had nothing whatever to do with the design of that plant, he
selects for consideration the plant of the Manhattan Railway
Company.
In this plant two complete sets of main bus-bars are used.
Switches are provided by means of which each of these
sets may be divided into two independent sets of bus-bars to each
of which four alternators and four groups of feeders may be con-
nected. Eight group-switches are provided, through' each of
which current is supplied to a set of auxiliary bus-bars, to which
in turn the individual feeders are connected through their respec-
tive switches. One of the eight feeder-groups is used to supply
power to auxiliaries in the power-house. The other seven groups
supply power, respectively, to the seven sub-stations which re-
ceive power from this central source. All switches in the high-
pressure alternating-current circuits are of the motor-operated
oil type.
The arguments in favor of the group-switch as used in the
plant of the Manhattan Railway Company are:
1 — It affords an additional means of opening a feeder-switch
that may fail to open its circuit, when operated for that purpose.
The advantages of the group-switch in respect to this function
to-day appear materially less than they did five years ago, for
the reason that the power-operated oil-switch within the period
named has demonstrated a high degree of reliability. However,
it cannot be assumed that the feeder-switch is invariably re-
liable, and, therefore, judgment of the weight of the argument
in favor of the group-switch, based upon its use as a reserve
for the feeder-switch, becomes a question of judgment of the
chances of failure of the feeder-switch on the one hand and the
seriousness of total interruption of power supply on the other.
2 — It affords means of reducing aggregate load upon the
power-house in case of necessity, more rapidly and otherwise less
objectionably than the usual method of cutting off individual
feeders. It will sometimes happen in the operation of a power-
plant that it becomes necessary suddenly to shut down one of
the generating units. If the load carried at the time be such
USE OF GROUP-SWITCHES. 235
that the shutting down of the generator implies reduction of the
external load, this can be accomplished most conveniently by
operating one or two group-switches.
3 — ^Where duplicate main bus-bars are used it facilitates
transfer of load from one set to the other, in case it becomes
necessary suddenly in operation to make such transfer. As bus-
bars and connections are now installed in our best plants, this
necessity does not arise frequently; nevertheless it is liable to
occur, and obviously half a dozen group -switches may be used to
effect the transfer in much less time than would be required were
five or six times that number of individual feeder-switches used.
4 — The grouping of the external feeder-circuits in group units
bearing a simple fixed relation to the generator units establishes a
symmetry and proportion most useful to the operator, particu-
larly in times of emergency. In the case of the plant under con-
sideration, at times of full load, the power passing through each
group-switch is substantially equal to the output of one generat-
ing unit. This relation of course does not exist under partial
loads, but under such loads it is not difficult usually to keep in ser-
vice generating capacity exceeding the load by a margin sufficient
to make it possible to shut down one generator without cutting
off feeders ; and in cases where this margin of capacity is not kept
in service it is, nevertheless, a more speedy and certain operation
to cut off the necessary number of groups of feeders than it would
be to cut off a proportionate number of individual feeders.
The arguments against the group-switch are:
1 — It introduces additional apparatus and, therefore, in itself
increases the risk of interruption due to failure in switch insulation ,
etc. The successful operation of many plants, particularly in
America, has been interfered with by the introduction of too
much switch gear and too many safety devices, automatic and
other; these additions in themselves being responsible in some
cases for more trouble than they prevent ; and it is to be noted
that the group-switch implies the auxiliary bus-bar. Here again
it is unwise to dogmatize, for as the result of additional ex-
perience the judgment of to-day may be reversed five years
from now. As an expression of personal opinion, however, I
may say that if the group-switch and the auxiliary bus-bars be
reasonably well insulat.ed and installed, the interruptions or-
iginating in this additional apparatus should be almost ne-
gligible in the case of such a plant as that which we are con-
sidering.
236 HIGH-TENSION TRANSMISSION.
2 — The group-switch and its bus-bars imply, of course, an
increase in cost of the plant. In case of the Manhattan plant
this increase is about 10% of the cost of the switch gear
and measuring apparatus, and about four-tenths of one per cent
of the cost of the plant. To put it another way, the cost of the
group-switches and bus-bars for the plant approximates $20 000,
and the annual cost, assuming this to be 10% of the invest-
ment cost, is $2000, which is about two-tenths of one per cent of
the annual cost of operating the entire plant, including sub-
stations.
In the plants in which the feeder unit equals or exceeds the
dynamo unit of power, the group-switch, of course, disappears.
In this case, however, it may still be advisable to use two feeder-
switches in series in order to avoid the necessity of shutting down
the entire plant in case of the failure of a single feeder-switch.
Obviously, also, there is no reason for attempting to use group-
switches in cases where the total number of feeders is small.
For plants comparable in magnitude to the plant of the Man-
hattan Railway Company, using a very considerable number of
feeders, the group-switch is important and its use generally
advisable.
USE OF GROUP-SWITCHES. 237
Discussion on the Use of Group-Switches in Large Power-
Plants.
Alex Dow : — As to group-switches ; the speaker considers that
the separation of not only the feeders but generators into groups
is now accepted as good practice. The drawing illustrating
Mr. Stillwell's paper showed a condition normal in some plants
but not representative of general practice. The accepted
practice is, according to the speaker's observation, not to
operate all the high-pressure generators in multiple . but to
separate the generators either individually or into groups and
to give to each generator or group of generators its own group
of feeders. The plant operated in multiple but only through
the low-pressure distribution system — not on the high-pressure
bus-bars; excepting, of course, that generators were put in mul-
tiple for the purpose of transferring load or taking machines
in and out of circuit. The separation of generators and feeders
into groups is indicated as advisable excepting where the trans-
mission system has considerable resistance and inductance. A
most notable exception which — ^like the tied-up air-switches —
has also come recently under the speaker's observation is the
Pacific Coast practice of running not merely several generators
and feeders but several power-houses in multiple. The feeders
and the tie-lines between power-houses are overhead and have
high inductance, either natural or artificial. The frequency
is high. Such a Pacific Coast system always " hangs on " to a
short circuit. In one of these systems the established rule for
dealing with a short circuit is to pull the field-switches of all
synchronous apparatus — generators, synchronous converters,
and motor-generators — excepting at one generating station.
None of the apparatus is cut off from the system. The obvious
result is that the remaining power-station has to supply a very
large lagging current; the e.m.f. falls, and the short circuit
breaks; whereupon the operators at the other power-stations
and at the sub-stations re-excite the fields of their machines
and normal conditions are re-established. A high-pressure sys-
tem which can be dealt with in this manner has no occasion
for group -switches. When, however, the conditions permit the
concentration of a tremendous amount of energy on one fault,
the group method is indicated and is already accepted as stan-
dard.
Ralph D. Mershon: — The reasons given by Mr. Stillwell
for the use of group -switches undoubtedly had great weight at
the time the plants referred to were designed. That was when
the oil-switch had not demonstrated its reliability, so thor-
oughly as it has now. In the present state of the art some of
the reasons do not seem to stand very well. The oil-switches
for pressures up to 10 000 which are constructed to-day seem at
least as reliable, if not more so, than the apparatus which they
control. If that is the case, it would seem that one is not justi-
fied in putting a number of switches in series. As regards the
238 HIGH-TENSION TRANSMISSION.
ease with which the load can be thrown off the power-house,
that can be taken care of by having tripping arrangements
which will operate a group of switches which can be tripped
at once. As regards the transferring from one set of bus-bars
to another, there is a great advantage for the group-switch if
the transferrence must be made quickly. If time can be taken
to do it, a selector-switch might be used instead of two oil-
switches.
H. G. Stott: — Referring to Mr. Stillwell's paper upon group-
switches, the speaker considers the group-switch as a species of
insurance. The more valuable the contents of a house, the
more insurance a man wants upon it and its contents; and in
the same way the more expensive a plant is and the more im-
portant the service supplied by it, the more important it be-
comes to take every possible insurance against a shut-down
due to any cause, as a shut-down of no matter how short a
duration has a most disastrous moral effect upon the entire
business connected with it. As a matter of actual experience
of more than two years with over 160 oil-switches, the speaker
has never yet had a single case where they failed to open the
circuit when required. In some short circuits over 100 000 kw.
were concentrated, so that certainly they have had a severe
enough test to prove their reliability under all conditions.
However, it would reqture a great deal of courage to advise
leaving out group-switches in plants above 35 000-kw. capacity
of generating apparatus.
In regard to Mr. Dow's statement as to the operation of
plants without generators being in multiple or upon groups of
feeders, the speaker does not know of any plant of any size
that is operated in this way. In all large plants in New York
City with the exception of the New York Edison Co., everything
is operated in multiple. He believes the New York Edison Co.
operates its station in two sections, but in each of these sections
several generators are operated in multiple.
Lewis B. Stillwell: — In the discussion, two things had par-
ticularly attracted the speaker's attention. One was the re-
markable short circuit Mr. Scott developed when he endeavored
to induce Mr. Nunn to open an air-switch; the other was the
interesting and original design which Mr. Mershon had adopted
in the important plant at Montreal. This design the speaker
considered well worthy of careful study, although he had not
definitely formed his opinion in respect to it; it impressed him
as being a substantial addition to engineering practice in the
matter of oil-insulated transformers.
So far as the subject of group -switches was concerned, he
was glad to know that Mr. Stott, who is now in responsible
charge of the operation of the Manhattan plant, agreed with
him in beUeving their use to be advisable. Obviously, their
use or non-use depended primarily upon the degree of import-
ance attached to an interruption of service and there was one
USE OF GROUP-SWITCHES. 239
way to state the case in respect to the particular plant to which
he had referred in his introduction which was perhaps stronger
than any which he had used; viz., by comparing the annual
cost of the auxiliary group -switches and their bus-bars with the
revenue earned by the system in a short interval of time. As
he had stated in the introduction, the cost of the group-switches
with bus-bars is not over $2000 a year, allowing 5% for interest
and 5% for maintenance, while the gross receipts of the system
in rush hours often exceeds $5000 an hour. When the subject
is looked at in this way, it is evident that the additional pre-
caution is well taken. The speaker did not agree with Mr.
Mershon in regard to the use of group-switches. The speaker
understood Mr. Mershon to say that if by using a single switch
for each feeder the risk of interruption of service by reason of
switch failure was reduced to a point where it did not exceed
the risk of interruption due to failure of the apparatus con-
trolled, it would be unwise to double the switches. The speaker
felt that this view was not correct and pointed out, for exam-
ple, that if in a given plant using no group-switches six inter-
ruptions of service should occur in the course of a period of
five years by reason of dynamo failures and six interruptions
by reason of switch failures , it would be wise to use group-switches
which might be reasonably expected to reduce the interruptions
due to switch failure and so reduce the total interruptions of
service.
[Communicated by Letter.]
William B. Jackson: — In determining the best arrangement
of the switching equipment for a power-plant, two prime con-
siderations and one of lesser importance must be the deciding
factors. These are in order of importance: the reliability of
service that may be expected from the system under considera-
tion ; the convenience and flexibility of operation ; and the cost
and depreciation of the equipment.
The use of duplicate bus-bars throughout electric power-
plants as well as two single-throw selector-switches for trans-
ferring from one set of bus-bars to the other in place of one
double-throw switch, has come to be recognized as standard
construction.
No single arrangement of switching devices can be laid down
as the perfect one for all plants. In general, however, the most
reliable service is attained by bringing directly to the main
bus-bars all of the generator and feeder circuits. Each circuit
in this case should be supplied with a master-switch by which
it can be disconnected independently of its two selector-switches.
With such an arrangement of circuits no local accident which
may occur beyond the main bus-bars and their connections can
interfere with more than one circuit. Also no switch need be of
greater capacity than that of its circuit. As the quantity of
energy which must be handled by a switch has much to do with
the reliability of its operation, this latter consideration is of im-
240 HIGH-TENSION TRANSMISSION.
portance; especially as the individual circuits of large power-
plants usually transmit as much power as can be conveniently
handled by one switch.
In a group-switch arrangement as described by Mr. Stillwell
the reliability of service is not so great as in the arrangement
above described, since it introduces auxiliary bus-bars and
associated connections, an accident to which will disturb the
operation of all of the circuits in the group ; also by the addition
of currents of several circuits at the group-switch a troublesome
switching problem is engendered.
By carrying each of the circuits directly to the bus-bars a
more convenient and flexible system of switching can be ar-
ranged. The individual circuit, which is the natural unit of
distribution, is duly recognized in this arrangement. By this
system each circuit, whether it be a generator circuit or feeder
circuit, has its own individual group of switches the operation
of which will effect its connections alone, and it may be con-
nected to either or both sets of bus-bars or disconnected there-
from with complete independence.
Although more switches are required for a reliable system
for individual circiiit control, yet the fact that each switch has
to do with its own circuit alone permits of a switching system
of great simplicity, and of perfect flexibility. The controlhng
table and instrument board can be arranged so that each circuit
may have its own individual sections upon which all controlling
levers, or switches, and all indicating instruments may be ar-
ranged so that the exact condition of the circuit can be instantly
seen, from the observation of a single section.
It is entirely unnecessary to use a group-switch system to
permit of simultaneously disconnecting or transferring groups
of circuits. With most of the methods of switch control,
whether they be mechanical, electrical, or pneumatic, master-
control can readily be arranged for operating the switches of
two or more circuits simultaneously, while the several circuits
still retain their individual control.
In the element of cost the use of a group-switch arrangement
will usually reduce the actual first cost of the switching equip-
ment as compared with a thoroughly reliable system where each
feeder is brought to the bus-bars, owing to the greater number
of switches that must be installed for the latter case. For
instance in the arrangement described and illustrated by Mr.
Stillwell, six circuits are handled by use of six single-throw
circuit switches and two group-switches. To control six cir-
cuits where each circviit is brought to the bus-bars, twelve
selector-switches and six master-switches would be used.
The matter of depreciation will also favor the group-switch
arrangement owing to the less number of moving parts therein
contained though this will not be so great as might be supposed,
since it is necessary to introduce the higher-capacity switches
in the group system as already referred to.
USE OF GROUP-SWITCHES.
241
The cost of the switching devices required for any power-
plant is exceedingly small as compared with the total cost of
the plant, and a slight gain in reliability, ease and flexibility
of operation will more than compensate for any added cost
and depreciation that may be occasioned by the bringing of
each circtiit to the main bus-bars.
The plant referred to by Mr. Stillwell is an unusual case in
which each set of feeders that are controlled by the group-
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switches may apparently be considered, under ordinary circum-
stances, as a multiple-feeder carrying current to the same set
of sub-station bus-bars. Under such conditions it would always
be necessary to transfer all of these circuits simultaneously. It
would seem that a more perfect result might be attained by
arranging the system throughout so that all of these feeders
would not of necessity be operated from the same set of main
bus-bars.
242 HIGH-TENSION TRANSMISSION.
In power-transmission plants, where step-up transformers are
employed, a use of switches is made that may properly be con-
sidered in this discussion, but which is somewhat different from
the group-switch arrangement described by Mr. Stillwell. In
all plants where A-connected single-phase transformers are used
it is desirable to be able to disconnect any one transformer
without disturbing the others. Also, it is quite important that
in changing from one set of bus-bars to another all of the trans-
formers be transferred simultaneously. It is therefore quite
desirable that the individual transformer circuits should be
provided with their own disconnecting devices while transformer
group-switches be arranged for transferring the A from one
set of bus-bars to another. The arrangement is shown in the
accompanying sketch.
Taking everything into consideration, it is the opinion of the
writer that the arrangement of group-switches as described by
Mr. Stillwell is one of limited usefulness, and that an arrange-
ment wherein the individual circuits are brought directly to the
main bus-bars is usually to be preferred.
[Communicated by Letter.]
Irving A. Taylor: — Mr. Stillwell has enumerated, in very
concise form, the several advantages in favor of group-switches.
No. 1 is that they provide an additional means of breaking the
circuit in case of failure in the feeder-switches. Nos. 2, 3, and
4 cover advantages of group operation.
It seems as though the latter class of advantages might be
obtained as readily and more simply and cheaply by the use
of multi -point control -switches, used in parallel with the ordinary
ones ; as group operation could be easily obtained in this way.
Advantage No. 1 was certainly very strong at the time the
plants in question were designed, but, as Mr. Stillwell says, is
not so important to-day, on account of the reliability of the
oil-switch, but yet has some weight.
There are few plants, even of great magnitude, where a com-
plete shut-down for five minutes (sufficient to clear a defective
switch), once a year or two, is of sufficient importance to warrant
the expenditure of several thousand dollars to prevent it. Prob-
ably large lighting companies, having a low-pressure network,
are an exception to this, on account of the difficulty of starting
up after a shut-down. With this exception, it looks very diffi-
cult to decide in favor of group -switching at this point of time,
and this applies particularly, as inferred by Mr. Stillwell, aa
plants are smaller.
Another point that has to be considered in arranging feeder-
or generator-switches is that few men of sound judgment would
allow a man to touch lines, or even the coils of a generator, if
an open oil-switch were the only thing between the man and
death. The risk is not much ; but life is too important to assume
it. An oil-switch handle may be open, but one line may be
USE OF GROUP-SWITCHES. 243
short-circuited in the switch, or the latter may be broken.
Therefore, some kind of an air-switch should be provided in
series with each feeder or generator oil-switch, for use on such
occasions. An ordinary air-switch having short break, but pro-
vided with barriers, seems to be very proper for the generator
circuit. On feeders, it seems as though a fuse-block could be
used to advantage, as it will not cost materially more than
the air-switches and will give additional means of automatically
disconnecting the circuit, as well as fulfilling the above functions.
In any case such switches or fuses should be installed between
the bus-bars and the oil-switch.
Expulsion fuse-blocks with spring tension have proved to be
very reliable on ordinary power and lighting circuits, provided
they are occasionally inspected. It would be interesting to
know whether such fuses are really reliable for breaking high
currents to synchronous apparatus, as this is the worst possible
condition. The writer understands that this fuse-block has not
the same vital objection as the air-switch, in causing an ab-
normal rise of pressure or breaking the circuit. It may seem
like a step backward to propose fuses, but if the objections
noted are set aside, it would seem as if this were their proper
field.
[Communicated by Letter.]
Gilbert Wright: — ^The writer suggests that in place of
the arrangement of group-switches, selector-switches, and bus-
bars shown on the plan submitted by Mr. Stillwell, one set
of main bus-bars be used instead of two, and that the feeders be
tapped directly from this one set of bus-bars, the feeders to
be controlled electrically, singly, and in groups. This method
of control; that is, single and group, is very readily accom-
plished by installing one control-switch for each feeder and one
master-switch for each group. This reduces the total number
of switches by 32, eliminates one set of main bus-bars, eight sets
of group bus-bars, with the necessary wiring between the switches
and bus-bars.
Mr. Stillwell says that the group -switches and the group bus-
bars in this station cost $20 000. Estimating the cost of the
16 selector-switches for the generators and the extra set of main
bus-bars, with the necessary wiring, to cost another $20 000,
would make a total saving of $40 000. By spending, say,
$10 000 of this in improving the feeder-switches and in addi-
tional insulation and fireproofing of the main bus-bars and wiring,
and on the additional control-wiring necessary to_ control the
feeders singly and in groups, it is the writer's opinion that a
greater factor of safety on the whole plant would result and that
the same facility of handUng changes in load would be obtained
as by the plans described in Mr. Stillwell's paper.
The writer looks upon group -switches, duplicate bus-bars,
and the necessarily complicated wiring for connecting same in
the power-house, as so much insurance on the continuous opera-
244 HIGH-TENSION TRANSMISSION.
tion of the plant; this insurance placed in small amounts, in a
great many places and at a cost much too large in proportion
to the results obtained. It will be seen that a possible saving
of $30 000 could be made on this plant by the method described
above.
The writer would suggest for general station practice to use
as few switches, bus-bars, and as little wiring as possible, and make
switches larger, more rugged, and with capacity to handle not
once but many times the maximum load that they may under
any conditions of service be called upon to handle.
[Communicated by Letter.]
John B. Taylor: — ^The writer agrees entirely with the author
of the paper, that no hard and fast rules can be laid down as to
the conditions under which the use of the group-switch is, or
is not, advisable. Apart from the question of mere additional
cost, the following features in connection with the plant have
some bearing on the matter:
(a) Pressure of the system.
(b) Number of cables or independent circuits supplying energy
to each of the sub-stations.
(c) Liability of trouble occurring on any of the conductors
or cables, requiring disconnection from the network.
(d) Reliability in operation of the high-pressure switching
apparatus used, as shown by behavior of a number of switches
in practical service.
(e) System of connection of low-pressure distribution; that is,
with one sub-station out of service can cars be kept in operation
adjacent to this sub-station, through power supplied by other
sub-station ?
(f) Character of service, — whether city work or interurban.
Taking up in order the various arguments given in the paper:
L " Additional means of opening a feeder-switch that fails
to open its circuit when operated for that purpose." The need
of two switches in series for all circuits, both generators and
feeders, connecting to the main bus-bars, must finally be largely
a matter of personal opinion, based mainly on what the designer
of a new system has observed or can learn from others regarding
the behavior of the high-pressure switch it is proposed to use,
under severe service conditions.
IL " It affords means of reducing aggregate load upon the
power-house in case of necessity, more rapidly and otherwise
less objectionably than the usual method of cutting off individual
feeders." It is evidently advantageous to cut off all energy
supply to a single sub-station without the necessity of locating
and individually operating five or six controlling switches located
at a greater or less distance from each other. While the use of
the group-switch and the bus-bar gives the complete control of
power supply to each sub-station through an individual switch,
it should be noted that this same control could be obtained at
USE OF GROUP-SWITCHES. 245
an expense extremely small, compared to the cost of a group-
switch and additional bus-bar, by bringing to a central point
the wires which control the opening of the feeder-switches. A
single motion of a gang-switch would simultaneously open all of
the four or five or more feeders supplying the sub-station to
be cut out.
III. " Where duplicate main bus-bars are used, it facilitates
transfer of load from one set to the other ..." Obviously
for the Manhattan station, fewer switches are necessary with
the group bus-bar than would be required if two switches (one for
each bus-bar) were supplied for each of the feeders. He thinks
that in many plants the extra expense and complication of a dupli-
cate bus is unnecessary and undesirable. In most cases, a single
set of bus-bars, properly installed, with knife-blade disconnecting-
switches, will be found cheaper, simpler, and quite as reliable.
With very few exceptions, a spare bus-bar when installed is made
use of only to allow men to work safely upon, or near, the regular
bus-bar. The disconnecting-switches above referred to need
occupy no additional space, and a judicious placing of same,
to suit number of generators, number of feeders, character of
load, etc., will permit cutting out a portion of the bus-bar, so
that same may be handled with safety.
IV. " The grouping of the external feeder circuits in group
units bearing a simple fixed relation to the generator units
establishes a symmetry and proportion most useful to the oper-
ator, particularly in times of emergency." This symmetrical
relation between number of generators and groups of feeders,
is obviously not necessarily a general case, and while the pro-
portion will hold more or less closely in most cases of city work,
the relation between the number of generating units and outgoing
feeders in a power-plant supplying an interurban system or a
portion of a main trunk-line will be quite different. In the
case of the city system, each sub-station is supplied by a number
of independent cables, while in the general case of the inter-
urban system or trunk-line, there are relatively very few feeders,
which may supply several sub-stations, passing in and out of
the stations intermediate between the generaing stations and
the most distant sub-station. For service of this character,
there could in many cases be but two groups, each consisting
of the line either way from the power-plant. In the latter case,
a group-switch is likely to be of very little benefit.
Regarding the two arguments cited by Mr. Stillwell against
the use of the group -switch ; that is, additional apparatus which
m.ay of itself increase the risk of interruption of service and the cost
of installation and maintenance, the writer comments as follows:
The advantages to be gained through a complicated system
of connections and switches equipped with all the various
automatic and protective devices for overload and reversal in
direction of energy transfer, with arrangements for instantaneous
operation and adjustable time-limit, are always more plainly
246
HIGH-TENSION TRANSMISSION.
evident on paper than in a plant in practical operation. It is
better to err on the side of simplicity, giving the reduced amount
of apparatus rigid inspection and attention, than to go to the
other extreme of constructing a cumbersome switching arrange-
ment, which is flexible only in theory, and confuses the operators
in times of emergency by offering a number of possible combi-
nations, each of which may be right, but no one of which is the
only thing to be done, and that in a hurry.
Referring to the diagram of bus-bars and switches in the 74th
Street station of the Manhattan Railway Company, it will be
noted that each of the group bus-bars is fed at a single point and
has no sectionalizing .switches. Now this means that no work
can be done on a group bus-bar without entirely shutting down a
sub-station, and any trouble occurring on this bus-bar or on the
connections between it and the switches, will cause a complete
J'eedei's to
Sub-station
1 2
© © © O
COJfNBCTIONS OF SWITCHES AND BUS-BABS
■FOKA
^ XABGE.EOWBK'ELAN'T
^^ Knife disconnecting switcb »T/\>iie.. . . ■, » . .-
1^ Hisb-prcMure oU-swltcll ^°™' '^='»S'«°"'&«'«':ot Itr'e-ploM .jatem l.iliown in diagrao
shut-down of a sub-station, until the trouble can be repaired
or cleared. This criticism could easily be avoided by feeding
the auxiliary bus-bar at the middle instead of at one end, and in-
serting knife-blade sectionalizing switches either side of the
feeding point. Such an arrangement would permit the opera-
tion of the sub-station with half of the feeders, while work might
be done on the other half of the group bus-bar. A still better ar-
rangement would be to tap one of the group-switches at each
end of the group bus-bar, knife disconnecting-switches being in-
serted in the middle of the group bus-bar.
In the accompanying sketch, the writer has dra,wn up an arrange-
ment of switches and bus-bars which is essentially a single main
bus-barandaseriesof group bus-bars, which, however, may be in-
terconnected to form a reserve main bus-bar in case of trouble or
to facilitate work upon the main bus-bar, It will be noted that this
USE OF GROUP-SWITCHES. 247
arrangement in its normal connection retains the group switch
and also provides two switches in series between each generator and
the bus-bar. The writer has shown the same number of generators
and groups as are shown in the Manhattan diagram, and it will
be noted that sixteen less high-pressure oil-switches are re-
quired. Oil-switches might be substituted for the knife-switches
connecting the different group bus-bars and also in place of
the knife sectionalizing-switches in the main bus-bar, but the
writer considers the use of oil-switches at these points unneces-
sary.
[Communicated by Letter.]
H. F. Parshall: — So far as the writer is aware the only in-
stallation in Great Britain using group-switches is that of the
Glasgow Corporation Tramways Department, the sole reason
at the time being to safeguard against the failure of individual
switches. With absolutely reliable switches there would be no
possible advantage in such an arrangement. Granted that
each switch safely and reliably controls its own circuit a duplica-
tion of switches is unnecessary and undesirable.
[For further discussion on this paper see pages 271, 280.
A paper presented at the 185//» Meeting of the
American Institute of Electrical Engineers^
New York, March 25, 1904.
Copyright 1904, by A. I. E. E.
OIL-SWITCHES FOR HIGH PRESSURES.
BY E. M. HEWLETT.
This paper naturally compares the oil-break switch with
the air-break switch. In treating this subject the following
points appear to be the main points for consideration:
1 — Abnormal Rise in Pressure: owing to the fact that in
oil-switches the circuit is opened at the zero point of the wave,
the rise of pressure found in the air-break switch is not experi-
enced. This point is of particular importance in high-pressure,
long-distance lines, and in cables carrying considerable energy.
2 — Capacity: experience has proved that oil-switches may
be designed to break circuits of practically unlimited capacity.
3 — Length of Arc : owing to the smothering action of the
oil on the arc the length of arc under oil is only a fraction of its
length in air.
4 — Insulation: the insulating qualities of the oil decrease
the distance required to prevent leakage and arcing.
5 — Size of Switch: owing to the fact that the arc length is
materially decreased and the value of the oil as an insulation
reduces the creeping surface, an oil-switch can be made very
much more compact than an air-switch.
6 — Remote Control: the design of the oil-switch lends itself
readil)'' to operation by control from a distance.
7 — Arc Confined: the fact that the arc is ruptured under
the oil within the switch has two advantages; 1st. switches can
be placed close together without danger of short circuit ; 2d. in
case of emergency, confusion is avoided as there is no visible arc
to disconcert the attendant.
248
OIL-SWITCHES FOR HIGH PRESSURES. 249
S — Station Arrangement: the flexibility of the oil-switch
places no limitations on the station arrangement, permitting
the circuits and bus-bars to be arranged in the most advantage-
ous manner.
9 — Isolation of Phases: the possibility of complete isolation
of the phases in a reasonable space is easily secured by the use of
oil-switches
250 HIGH-TENSION TRANSMISSION.
Discussion on " Oil-Switches for High Pressures."
C. C. Chesney :^A) It is quite apparent that in the rapid evo-
lution and in the perfecting of electrical machinery for power-
stations, switch and switch-control design have been more or
less neglected. On account of the great importance to all
power stations of good switching mechanism, the reason for
this neglect is rather difficult at this date to understand, although
it is evidently more or less due to the apparent simplicity of a
rather difficult problem. While dynamo, engine, and wheel de-
sign have been reduced to an almost exact science by the best
talent of the engineering profession, the switch and the control-
ling mechanism have been refused the attention they deserve,
although it may be safely stated that in power-stations of this
country there are more shut-downs due to defective and inad-
equate switching mechanism than to any other one cause. Mr.
E. W. Rice, several years ago in his paper on " High-Potential
Control " pointed out the inadequate means at hand at that
time for controlling and switching currents of large volume and
pressure. In the same paper he described certain switches
designed by the General Electric Co., which from extensive tests
were believed would meet any and all requirements of heavy
station-service. Since then these switches in actual service have
fulfilled the designers' expectations. During the same period,
the other manufacturing companies specially interested in high-
pressure alternating-current machinery have developed high-
pressure switches, on more or less different lines, which are
believed to be equally good. However this may be, it can
hardly be expected that the design of any of these switches is
final and that there is no room for further improvement. The
following notes are therefore offered in order to outline the more
important features and essential elements which have made
some of the later switches successful, but without any attempt
to describe any particular make of switch or describe any par-
ticular switch design.
(B) Types: on American high-pressure transmission lines there
are four general types of switches now in use:
1 Switches designed to break the circuit in the open air.
2 Switches designed to break the circuit in an enclosed air-
space.
3 Switches designed to break the circuit with the aid of an
enclosed metal fuse.
4 Switches designed to break the circuit under oil.
Type No. 1. The large amount of space required by this
switch in order to be certain that the arc will be broken makes
its use impossible except in rare instances and then it can be
used with safety only when the line pressure is comparatively
low, for the reason that a circuit containing inductance and
capacity may have very high-pressure oscillations set up in it
by an open air arc, unless the current is broken at zero value.
The result of the increased pressure is likely to be the destruc-
OIL-SWITCHES FOR HIGH PRESSURES. 251
tion of the insulation on some part of the system, probably
that of the transformers.
Type No. 2. This switch is a decided improvement over
Type No. 1, as far as the amount of space occupied is concerned,
but its effect on circuits containing inductance and capacity is
very little different from Type l,so that there will be the same
oscillatory rises of pressure and the same destruction of the
insulation on opening the circuit. In addition, the explosion
on opening heavy currents with this switch is at times so terrific
as to endanger not only the switch itself, but all delicate in-
struments in the immediate neighborhood.
Type No. 3. Two forms of this switch has been more or less
used. In the first form the fuse is connected in parallel, and in
the second in series with the current carrying parts of the switch.
The first form is limited to low-pressure circuits, because of the
total unreliability of the enclosed fuse on comparatively high
pressures when the circuit is fed from large central stations.
The second form operates through the severing of a metal fuse
within an enclosing tube filled with powdered carbonate of
lime, or some other non-conducting powder. The end of the
fuse is drawn through the tube by the moving arm of the switch
and the circuit is opened without serious commotion if the
switch has been well designed and care has been taken properly
to fill the tube. The switch will open safely almost any circuit
at almost any pressure, but like the open air-switch is limited
by the amount of space required, while the powder set flying
by the explosion of the arc is a decided objection if there is any
moving machinery in the same room.
Type No. 4. This type of switch has within the past year
been almost universally recognized as the only switch to be
used for high-pressure work, for the reason that it can be made
in compact form at reasonable cost and when properly built
will disconnect from the generating system with certainty and
safety any circuit under any condition of load, even a low re-
sistance short circuit. Contrary to general expectations, it has
been shown by a number of experiments that the opening of a
circuit by an oil-switch is not a quick break; the oscillograph
shows that the effect of the oil is to allow the arc to continue
for several periods and then, as a rule, to break the current at the
zero point of the wave. As a consequence, the opening of any
circtiit with oil-switches is rarely accompanied by destructive
rises of pressure. The true reason for this fortunate action of
the oil-switch is rather difficult to see. One prominent ex-
perimenter has attributed it to the " practical incompressibility
of the oil, and, in consequence, the gas bubble which is formed
at the terminals of the switch is under an enormous pressure
and holds the arc up to the next zero value of the current. At
the next zero value of current the Uquid pressure blows out
the arc." Another holds that by the breaking up of particles
of oil by the arc, a high resistance conducting strata is formed
252 HIGH-TENSION TRANSMISSION.
between the terminals of the switch, which allows the circuit
gradually to discharge itself. It is probable that both of these
phenomena may simultaneously enter into the action, because
it is true that an oil-switch creates less fuss in the oil if it is
opened slowly ; but it is also true that an oil-switch for 40 000
or 50 000 volts must have a depth of oil over the terminals of
at least four or five inches. If less depth of oil is used, the oil
is likely to be thrown out of the oil pots, on the opening of the
circuit, although the arc will be broken.
Of the two types of oil switches, used on 20 000,- 30 000-and
40 000-volt circuits, one, the plunger type, breaks the arc in a
vertical plane, while the other breaks the arc in a horizontal
plane. The plunger type has been used quite extensively in
the larger power-stations of the East. The other form has been
used more particularly by one or two of the larger Pacific Coast
long-distance power-transmission companies. Some time ago
the writer had an opportunity to test thoroughly a switch of
the latter type on the circuits of the Bay Counties Power Com-
pany.
The switch was of the three-pole type and was arranged to
break simultaneously the three legs of the three-phase circuit.
During the regular running of the plant it had given satisfactory
results under rather trying conditions. In order more thor-
oughly to test the arc-breaking qualities of the switch, one pole
was connected across the main transmission line and the line
was short-circuited at the full line pressure. The short circuit
was then opened by one pole of this switch. As the switch
was hand operated, there was no record of the exact time length
of the short circuit, but it was not over one second. These
experiments were repeated a number of times at both ends of
the 150-mile line of the Bay Counties Power Company. Each
time the circuit was opened without disturbance of any kind,
and, as far as it could be determined, the short circuit was
opened equally as well at either end of the line. During these
experiments the Bay Counties Company were supplying their
regular customers, and were operating at a line pressure be-
tween 45 000 and 46 000 volts. All of the alternating current
generators at both power-houses were in operation and the output
amounted to about 11 000 kw.
Fig. 1 shows one pole of this switch and gives the approximate
dimensions. The mechanical construction of the switch is ex-
tremely simple. The contact-arm is mounted on an insulator
at the end of the vertical operating rod. The outer ends of
the contact arm carry fingers, which make contact with ter-
minal-blocks on the ends of the studs which pass through the
porcelain insulators to the line. It will be noted that each pole
has two breaks in series, each about nine inches long. The switch
was operated by rotating the operating rod which moved the
contact arm through an angle about 90°. The oil-tank was 28
inches in diameter and there were about five inches of oil over the
OIL-SWITCHES FOR HIGH PRESSURES.
253
contacts. During the test the cover of the switch was off so that
the breaking of the arc could be observed. At each break
there was a small arc formed at the terminal-blocks, but there
was only a very slight elevation of the surface of oil immediately
over the arc.
SuSUX ^eyation, Section of Tank
aoo^lab OB Jjne.A-B
Fig. 1.
(C) On the assumption that the oil-switch, in the present
state of the art, is the only switch to be used for high-pressure
work, the following points of construction will bear consideration
after the particular form of oil-switch has been selected:
254 HIGH-TENSION TRANSMISSION.
1 Rating: The performance of the switch under abnormal
conditions of a low resistance short circuit should be considered
as well as the capacity of the switch under normal operating
conditions.
2 Oil: Any good paraffine oil will answer, but it should have
about the following characteristics:
Flashing point 215° cent.
Fire Test 250° cent.
Specific gravity 0.865
Viscosity —
Acid None.
AlkaH None.
Evaporation Negligible.
3 Insulation: The insulators and insulating bushings should
be either glass or porcelain. The switch should stand a break-
down test between the I've parts and the metal case and frame-
work of at least twice the working pressure. The external
terminals should be far enough apart, or sufficiently well in-
sulated, so that there can be no possibility of the current striking
across through the air from terminal to terminal.
4 Location: Oil-switches should be placed away from the
switchboard as well as the generating and transforming ap-
paratus. Each pole should be placed in a separate fire-proof
cell, so that by no possibility can an arc or explosion in one cell
be communicated to another or to the neighboring machinery.
5 Method of Operation: All switches should be either mag-
netically or electrically controlled from a central switchboard,
and all the poles of a switch should be operated simultaneously.
It is also desirable to equip each switch, especially if it is auto-
matic, with a time-element attachment, so that the circuit
cannot be opened for at least a second after the operating
mechanism is set in motion.
F. A. C. Perrine: — ^The speaker wishes to describe some ex-
periments tried last fall with three oil-switches operating on the
same principles as the one Mr. Chesney describes. The three
switches were connected up at Mission San Jose in California,
98 miles from the power-plant of the Standard Electric Com-
pany, and the experiments were carried on during the night so
that command of the entire generating station could be had.
This station contained four 2000-kw. machines. A single handle
controlled all three switches so that they opened simultaneously.
The three-phase line was first connected through the switches, and
the three phases short-circuited at the other side of the switches,
thus putting a switch in series with each break. The line pressure
was 40 000 volts. The switches were opened and closed about six or
eight times that night. Then the work was shut down until
the next night, when the switches operating as a short circuit
between the wires of each phase could be connected, so that
each switch formed a short circuit on a phase, the three
OIL-SWITCHES FOR HIGH PRESSURES. 255
switches short circuiting the entire line, which is very much
more severe service than in the former connection. The
line was short-circtdted and the switches were opened several
times, first opening the switches quickly after they had been
closed, and afterward holding them in short circtiit. The
switch operated successfully, the machines held the speed and
the voltmeter showed the pressure was held up. The ammeters
went off the scale at 12 500 kw. Finally the experiments were
discontinued because at the power-house end of the line the
lightning-arresters arced over. These were a series of the so-
called Dutch-horn lightning-arresters which, especially for the
experiments, were set 4.5 in., so that from line to line the gap
was nine inches. The arc in almost every instance when we open-
ed the switch went across these lightning-arresters and finally they
were destroyed, the pole head was destroyed, and the No.
ground wire was entirely fused. The superintendent said that
the appearance at the station was as though the sun had come
down in the back yard. The interesting thing was that those
switches did not fail to open the circuit on any one of the ex-
periments, and the experiments were only discontinued on
account of the danger to the generating and transformer ap-
paratus due to the apparently high-pressure as shown by the
current jumping across nine inches of open air space.
Alex Dow: — In his opinion the oil-switch had definitely
arrived — ^it was not merely coming. In Pacific Coast installa-
tions visited within the past thirty days he had found the air-
break switches carefully tied up so they could not be operated;
and in series with them, oil-break switches which were regularly
used. This substitution of a nine-inch oil-break for a six-foot
air-break was general on the Pacific Coast.
Ralph D. Mershon: — Referring to Mr. Hewlett's paper, the
speaker did not agree with Mr. Dow that the oil-switch has
necessarily come. It has come for some pressures, but not
necessarily as yet for 30 000, 40 000, or 50 000 volts, as any con-
struction which in the present state of the art means going into
cables with high pressures is objectionable. With such oil-switches
as the speaker is familiar with, this is necessary or else a
large amount of space for their wiring and installation becomes
necessary. If an oil-switch could be put up in the roof truss of
the building, being made as it were a part of the high-
pressure conductors, — ^then it seems that the oil-switch would
be a very advantageous piece of mechanism to use in connection
with high-pressure plants, but until that is done it does not
appear attractive.
C. F. Scott: — So much has been said about the oil-switch and
so little that was favorable about the air-switch that the speaker
thought of asking Mr. Nunn to say a few words on the subject.
The air-switch a few years ago was introduced in high-pressure
work when there was no oil-switch for that work, and it seems
it still has a large field of its own in places where the
256 HIGH-TENSION TRANSMISSION.
pressures are high and the amount of power, as for instance in
small sub-stations, is small; where the oil-switch, as developed
now, will be too expensive to install. In the first high-pressure
plant of 40 000 volts, installed at Provo, Mr. Nunn had certain
air-switches which it is understood rendered excellent service.
P. N. Nunn: — The impression is conveyed by Mr. Scott that
a defence of the air-switch may be expected. The high-pressure
air-switches at Provo are rapidly being replaced by oil-switches.
This is in order to avoid the line disturbances caused by air-
switches, and also in order to substitute the automatic feature
of the oil-switch for the fuses necessary with air-switches. It
is true that oil-switches are very expensive, but, while a reduc-
tion in cost will be most welcome, even at present prices, they
will undoubtedly be used in all future high-pressure work.
C. L. DE Muralt: — The speaker's firm uses both oil-type and
air-type switches, the former in preference in all important in-
stallations, at least in the main leads. But there are cases
where it would be very expensive to have oil-switches in every
single place where the current may have to be interrupted at
some time or other. Therefore, in places where such interrup-
tions occur only once in a great while, or only in cases of an
emergency, he sometimes, when economy is necessary, employs
switches which resemble somewhat the horn-type of lightning-
arrester. The main part is in fact btiilt exactly like one of these
lightning-arresters, the air-gap being bridged by a terminal
part which, when the switch is actuated, is drawn away. The
arc then breaks itself by drawing toward the upper ends of the
horns, which are wider apart. The current of a 1500-kw. gen-
erator at 26 000 volts has been ruptured in this way, which is
a fairly severe test. For oil-type switches he uses a switch
which can either be manipulated manually or mechanically or
automatically as a time-Hmit overload switch. The latter ar-
rangement is as follows: the switch is held in position by a trip-
ping device. If the latter is tripped a spring will open the
switch. That tripping can be done either manually or by means
of a magnet. The magnet in its turn can be energized either
by directly closing a switch in the circuit providing it with
current, or by a relay, the latter being actuated by overload
currents. These currents set up in the relay a magnetic field
which tends to turn an aluminum disc and the turning of this
disc winds up a weight. As soon as the weight comes to its
top position it closes the relay circuit. If the overload is very
heavy the disc will revolve very fast, and thus the switch will
be quickly released. If the overload is light, it may happen
that it ceases before the weight reaches the top position and
it will then re-descend and the switch will not be tripped. This
constitutes an absolute time element overload relay, and makes
out of the switch an ideal automatic circuit-breaker.
OIL-SWITCHES FOR HIGH PRESSURES. 257
[Communicated by Letter.]
H. F. Parshall: — Before the perfection of the oil-switch, the
air-switch with long break and large clearance for flaming was
the most reliable device and many of the early installations owe
their success to the use of the air-switch. Subsequent experi-
ence gained is that oil-break switches can be installed in a
great deal less space and can be depended upon to open the
circuit with much less damage to the switches. The one con-
dition which his experience would lead him to impose in connec-
tion with oil-switches is that there must be absolutely no in-
flammable material in the switch other than the oil; that is to
say, the use of wood and such like materials for sepaTrators and
insulators is to be avoided.
In a brief written communication, A. R. Henry described a
switchboard of the Canadian Electric Light Company's power-
house, Chaudiere Falls, Quebec,
[For further discussion on thxs paper.see page 275.
A paptr presented at the 185th Meeting of the
American Institute of Electrical Engineers,
New York, March 25th, 1904.
Copyright, 1904. by A. I. E. E.
TERMINALS AND BUSHINGS FOR HIGH-PRESSURE
TRANSFORMERS.
BY WALTER S. MOODY.
This subject will include cables, straps, connectors, etc., for
both high- and low-pressure side, designed both for terminal
connections and for changes in the ratio of transformation, to-
gether with their insulation. In transformers for moderate
pressure and having but two high- and low-pressure terminals,
the problem of terminals is a simple one; with higher pressures
and numerous changes in the ratio, however, the design of these
parts of the transformer often becomes a most difficult problem,
upon the proper solution of which depends, to no small extent,
the reliability of the transformer.
Location of Terminals on Coils.
It is much better to have the high- and low-pressure terminals
at opposite ends of the structure, for it is almost impossible to
keep safe distances between the terminal and connecting coil
leads when all are at one end. In a shell-type structure, having
its coils in a vertical position, this requires one set of coil terminals
to be at the bottom of the case, but to bring these safely to the
top is not as difficult as to separate high- and low-pressure con-
ductors that are at the same end of the windings.
Insulation of Terminals on Coils.
In an oil-immersed transformer, this presents little difficulty,
as it is simply necessary to have all leads rigidly spaced a safe
distance from each other and from the coils, and covered with
sufficient waterproof insulation to prevent any moisture pene-
trating the coil around the terminals before the oil is put in.
258
TERMINALS AND BUSHINGS. 259
In air-blast transformers, however, the case is different; here
all terminals must be covered with an insulation integral with
that on the coil itself, to a distance from the coil ,that provides
sufficient surface insulation, even when the lead is well covered
with dust and dirt.
Often the dielectric strength of a transformer is materially
lowered by allowing the coil-terminals or taps to project beyond
the sides of the coils, thus shortening the distance between
primary and secondary. " Spreading " the exposed ends of the
windings removes this difficulty, except when the terminal
comes from a point well within the coil, but introduces a more
serious defect, lack of rigidity to withstand the strains of short
circuits. Usually the problem can be solved by so winding coils
as to have only outside terminals and locating such coils as have
taps on the outside of the coil structure.
Location of Main Terminals.
The best location for these naturally varies with the type of
transformer and its pressure; for the air-blast type, the air-
chamber forms a convenient and natural location for the low-
pressure wiring, and the terminals of these are therefore usually
located in the base of such transformers and made accessible by
doors in the side of the base. For pressures not exceeding 25 000
volts, the high -pressure wiring can also be placed in the air-
chamber, without making the air-chamber of excessive cross-
section, so that all transformer terminals are in the base and
exposed wiring is avoided. Heavy rubber-insulated cable is to
be avoided in such construction, however, for should the rubber
take fire from short circtdt or other causes a draft of air will
carry the fire rapidly along the duct and into the transformers.
In oil-filled transformers the terminals are, of necessity,
located at or near the top of the case. Often for convenience in
external wiring, projecting pockets are provided through which
terminal-leads may leave the case in a downward direction.
With such construction, it is necessary to have a solid section in
the cable, just above the oil line, and to have this section insu-
lated or covered with an insulation impervious to oil, otherwise
the cable and insulation will act as a siphon and discharge oil.
Insulation of Main High-Pressure Terminals.
Below 40 000 volts, the insulation of terminals offers no
special difficulty; porcelain or glass bushings can readily be
obtained that are safe for this pressure, even if the conductor
260 HIGH-TENSION TRANSMISSION.
has no insulating covering. For higher pressures, the problem
is more difficult. If no insulation is used on conductor, the bush-
ings become expensive and so large that there is scarcely room on
top of a moderate size transformer for as many terminals as are
often required. The following are some of the more common
forms of bushings that have been used:
Wooden tubes ;
Hard-rubber tubes ;
Glass and porcelain tubes, both single and concentric ;
Numerous forms of molded porcelain bushings.
Wooden tubes of the necessary size cannot be thoroughly
dried and filled. Hard rubber is so apt to contain impurities
that it is unsatisfactory; moreover, it deteriorates rapidly if
ozone is generated near it. Glass is fragile and must be pro-
tected with other semi-insulators. Porcelain, or any smooth
tube, must be very long if it have sufficient leakage surface to be
safe when dirty, and even the best shapes of corrugated bushings
are large and expensive when capable of withstanding a test of
from 75 000 to 160 000 volts. All things considered, the writer
has found the following practice quite satisfactory for test-
pressures not exceeding 160 000 volts.
Insulate the lead with varnished wrappings that will safely
withstand for one minute about half of the test-pressure to be
applied, bringing out this lead through a porcelain bushing having
the same strength as the insulation of the lead, and sufficient
surface to prevent leakage at this pressure when dirty ; in other
words, let the insulation of the leads be sufficient for the working
pressure, and the porcelain be of such strength as to give the
factor of safety desired. This combination forms a far safer
insulation than a bare conductor and a larger bushing which
would stand the same puncture test as the combination, from the
well-known fact that oxidized linseed oil is an insulation that
will momentarily stand several times as much as it will for any
considerable length of time, while porcelain, glass, etc., have no
such time-factor.
In leads requiring a test of 100 000 volts or more, and insulated
in this manner, an additional difficulty is met in the induced
charge on the outer surface of the insulation ; at this pressure the
surface is covered with a heavy brush discharge that so reduces
the surface resistance to leakage that 100 000 volts will travel
along several feet. It is usually impracticable to make the
insulated lead long enough to withstand the pressure under
TERMINALS AND BUSHINGS. 261
these conditions, but the discharge may be broken up, so
that it will not appreciably reduce the surface resistance, by bell-
shaped pieces of rubber, porcelain, or other insulation slipped over
the lead before all the varnished wrappings are put on, and
having its small end so shaped as to allow of its being buried in
the outer wrappings.
In transformers designed for Y-connection and grounded
neutral, some transformer builders, in order to save expense on
high-pressure bushings, have grounded one terminal on the case
and insulated only such leads as are to be connected to the line ;
this prevents operation with A-connections, but otherwise seems
unobjectionable. In similar manner, the use of three-phase
transformers with the inter-connecting between the phases made
within the case reduces the expense and possibility of trouble
with bushings.
Eighty thousand volts is the highest pressure that is now
practicable for transmission work, but transformers and insu-
lators must be tested, consequently there is some demand for
transformers working up to 200 000 volts. The insulation of
the terminals of such transformers is the most formidable part of
their design. As yet, I know of no satisfactory solution of the
problem except to use oil-filled tubes as terminals. A terminal
that has withstood 375 000 volts without any indication of
weakness is constructed as follows:
The tube was the shape of two truncated cones, bases together ;
about 12 inches in diameter at the centre, and four inches at
either end; it was built up of thin wooden rings, telescoped a
short distance into each other, and held together by the con-
ductor which, for mechanical purposes, was made quite heavy,
and which was located in the axis of the cones and supported
by washers at either end of the tube ; between each section of the
tube were collars of insulating material, some three inches larger
in diameter than the tube, which served the purpose of greatly
increasing the leakage surface. After the sections were drawn
tightly together by nuts at each end of the conductor, the whole
structure was repeatedly dipped in varnish and dried, thus
sealing all joints. The terminal was mounted with the lower end
several inches under- the oil in the transformer and with its
largest diameter on a level with the cover; the lower end of the
tube was tightly sealed, making the tube perfectly oil-tight.
Internal Terminals.
At- present we are passing through a perioa of development in
262 HIGH-TENSION TRANSMISSION.
line construction. Each engineer of a new transmission system
of considerable length desires to use as high pressure as possible
with a line construction of reasonable cost, but few are sure
whether 50, 60, 70, or 80 thousand volts is the safe maximum for
their conditions. It is common, therefore, for the manufacturers
to be asked to make transformers that can be operated at several
voltages on the high-pressure side. The result, whether accom-
plished with series-multiple connection, changing from A to Y,
or simply by taps, usually requires so many terminals, that it
becomes quite impracticable to place all the necessary leads
outside of the case, even were it desirable to do so ; consequently,
accessible terminals inside the case must be provided. Again,
at these and lower pressures also, it is usually desirable to pro-
vide for limited range of adjustment in the ratio, say by 2% steps,
with a total of 10%; such changes are usually too small
to be made except by means of taps on the high-pressure wind-
ings. Except in transformers of very large capacity, there would
be no room safely to insulate so numerous terminals above the
surface of the oil; the practice is therefore to locate such ter-
minals just under the oil and make them as accessible as possible,
either by the removal of the transformer top, or through an
auxiliary cover on the top of the case. It is better that each of
these terminals be separately supported by glass or porcelain
insulators; for a single support, such as a slab of marble, is
almost sure to collect sufficient semi-conducting material to
cause trouble sooner or later. Such terminals being, at best,
rather inaccessible there is danger that a wrong or imperfect
connection will be made when changes are desired. The following
method of mounting transformers in the tank greatly simplifies
the problem of getting at such terminals, especially when trans-
formers are installed -under a crane: instead of supporting the
transformer proper on the base of the case as usual, it is hung
from a strong cover; the interior terminals are placed in about
the usual position, but are supported by the bolts carrying the
transformer. To get at these terminals it is then simply neces-
sary to raise the cover with the transformer, until the terminals
are on a level with top of case; connections may then be made
with convenience and safety and the transformer returned to its
position in the tank.
Low-Pressure Terminals.
Usually these present no special difficulties; when trans-
formers are connected in multiple and deliver 500 amperes or
TERMINALS AND BUSHINGS. 263
more, special caution should be taken that all joints are soldered
or that terminals are of such construction as to have extremely
low contact resistances. Taper plugs and receptacles are per-
haps the most reliable form of contact for the purpose.
Current in excess of 500 amperes should never be brought out
through separate openings in the case, otherwise there will be
local heating around the terminal and needless reactance intro-
duced into the circuit. Currents over 2500 amperes should be
brought out by means of intermixed bus-bars for the same
reason.
264 HIGH-TENSION TRANSMISSION.
Discussion on "Terminals and Bushings forTransformers."
Ralph D. Mershon: — In Mr. Moody's paper there is one
point in regard to the terminals for high-pressure transformers
with which the speaker thoroughly agrees. The speaker con-
siders that the marble terminal board has no place in high-pres-
sure transformers. The leads should be brought out to por-
celain insulators located underneath the oil, each to its separate
insulator. In a number of cases troubles have occurred on marble
terminal boards, at times too difficult to remedy. A marble ter-
minal board scored by a discharge and afterward apparently
made perfectly clean by scrubbing, will not stand the normal
pressure when again put into service, and the only way in
which it can be made to stand is to chip out the marble where
the discharge occurred. Instead of using rubber-covered cables
in air-blast transformers for high-pressure terminals, as Mr.
Moody suggests, the speaker prefers to have these terminals
come out into the air and remain bare during the rest of their
course to the sub-station or the next bank of transformers.
C. E. Skinner: — Every transformer designer who has had to
do with pressures of 20 000 volts or over appreciates the diffi-
culty of bringing out the high-pressure terminals from such
transformers. It not infrequently happens in extra high-
pressure work that the size of the transformer, and particularly
the containing case, is materially modified by the reqiiirements
for bringing out the terminals. In the case of air-blast trans-
formers pressures are limited by the tap to an amount which
makes the problem comparatively simple, provided a large num-
ber of ratios have not been required to increase the flexibility
of the system.
In the case of oil-insulated transformers the pressures have
already gone as high as 55 000 volts in actual service, and higher
pressures are now being seriously considered. As stated by
Mr. Moody in his introduction to the discussion on this subject,
these higher pressures present a very formidable problem to the
designer, and this difficulty is sometimes still farther increased
by the requirements for the transformer case to be able to with-
stand considerable mechanical pressure. Mr. Moody has men-
tioned some common forms of bushings, which have been used
for the purpose of insulating the main high-pressure terminals.
Wooden tubes alone are not satisfactory for pressures, which
at the present time may be considered as high. Hard-rubber
tubes deteriorate rapidly. Glass and porcelain are mechan-
ically fragile, and it seems next to impossible to get a moulded
porcelain of sufficient dimensions for some of the higher pressure
now being required.
As a general proposition it is necessary for the higher pressures
that the distance between the high-pressure conductor and the
metai of the case, where the conductor passes through, must be
of such a value and the material of such quality that there
will be no apprecial^on brush discharge at this point. Where
TERMINALS AND BUSHINGS. 265
the transformer tanks are not required to withstand heavy pres-
sures a satisfactory construction consists in fastening a slab of
insulating material, such as marble, in the top of the cast-iron
cover into which are placed heavy tubes for the conductors
with sufficient extension to give the necessary surface insulation.
Tubes made up from alternate layers of varnished paper and
mica have proved very effective. In one instance where the
line voltage was 50 000 the transformer case was required to
withstand a pressure of approximately 100 pounds per square
inch. In this instance the marble slab mentioned above was
not allowable on account of the mechanical pressure require-
ments and the problem was solved by making extra heavy bush-
ings, which passed through stuffing-boxes arranged to clamp
the tube very tightly. This has given excellent service.
An interesting example of bushing trouble occurred on a
55 000-volt line where the bushing consisted of a glass tube with
0.625 -in. wall incased in a heavy wooden bushing for mechan-
ical protection, the combination being set in a wooden cover.
The static discharge over the surface of the glass tube scored
the tube to a depth of 0.0312 in. to 0.0625 in., making the
surface rough and finally a breakdown occurred directly through
the tube, shattering it into many pieces. This shows that glass
has a time-factor at extra-high pressures.
Mr. Moody mentions the complication frequently imposed in
the construction of the transformer itself by requiring combina-
tions for various pressures and for a slight amount of regulation
by bringing out taps from the high-pressure windings. From the
designer's standpoint the speaker wishes to protest against this
practice of requiring almost universal flexibility. After the trans-
formers are in service the operating man considers that the
paramount idea is continuity of service. Every extra lead and
tap complicates the design and makes the construction more
expensive and difficult. It is possible, of course, to secure great
flexibihty by such means, but the chances of trouble from those
leads and taps which are not in service, and the possibility of
making a wrong connection, greatly increase, and it is the speaker's
experience that in many cases where such elaborate systems are
required they are never used.
[Communicated by Letter.]
Irving A. Taylor: — Instances have been noticed in air trans-
formers where an uninsulated or lightly insulated tap is brought
out through the external coil insulation and a lead soldered
on and the joint insulated. This leaves a weak spot on the
lead insulation just where it enters the coil insulation. Leads
should be heavily insulated to a point well within the coil-jacket
and should pass through the latter in a slanting rather than a
straight direction, so as not to leave a vulnerable point in it at
the point of entrance.
In some cases internal leads are brought up through the top
266 HIGH-TENSION TRANSMISSION.
layers. This is a grave source of weakness as it gives a creeping
surface through the inter-layer insulation. It also makes it
necessary to wind the upper layers around it, and these are
therefore liable to be crushed together. Taps from inner layers
should always be brought out from the end of the layer, and
in such a manner as not to cut the inter-layer insulation.
Where main terminals are located in the path of the air-blast,
a great deal of surface dirt and consequently a long, creeping
surface should be reckoned on. Terminal boards in air-blast
transformers for this reason appear to be a source of danger,
and where there are not many terrainals it would seem best to
use cables with heavy caps, the joints being made inside the
case and above the fire-damper, if such is used. Fire-proof
cables should be used in or near the air chamber.
Leads from oil transformers give a great deal of trouble by
syphoning oil, and it is not at all easy to suggest a certain
way of stopping it. Mr. Moody's remark that a solid section
in the lead is necessary is correct; but it is difficult to insulate
this section in practice so that the oil will not creep between
the layers of insulation and on to the stranded cable. After a
good deal of experimenting, the writer used a porcelain tube
(filled with sulphur) over this solid section, and found it to be
about the only successful method of stopping creepage. Bush-
ings through the case should be extended well above the iron
and the cable should be sealed in with non-solvent, insulating
compound (sulphur may be used) , so arranged as not to pocket
any oil, but to drain it off. It is best not to have the braided
covering of the lead extend inside the case as it is liable to carry
oil out.
Where transformers are connected to outdoor leads they
should have a solid section, well covered with water-proof mate-
rial, in the external lead, as water will follow through a stranded
cable for a long distance and in large quantities. This is a fre-
quent source of burn-out in cable heads, etc.
All transformer cases should be grounded to prevent fire and
make them safe to handle. Attention should be given to the
fact that the ground wire should be heavy in proportion to the
circuit protecting devices used. Thus, a No. 8 wire should not
be used on transformers protected by 300-ampere fuses on the
secondary side. The ground connection should be electrically
sufficient and its resistance should be tested to determine this,
a moderate pressure being used.
Where rubber-covered leads are used, the rubber should be
heavy (not less than 0.25-in. wall per 10 000 volts) and of high
quality, and fire-proof covering should also be employed. Extra
flexible cable is usually preferable.
While taps allow one of the greatest advantages of the trans-
former to be utilized — ^that of obtaining different pressures from
the same apparatus — it seems as though many specifications re-
quire more taps than are actually necessary. Taps cost money
TERMINALS AND BUSHINGS.
267
on account ot the necessary space, and besides are nearly always
a source of weakness. They should therefore be avoided unless
their use is absolutely justified. Except where transformers are
to be used partly as pressure regulators, one 5% or 10% tap
should give sufficient adjustment of ratio to meet lighting or
railway conditions. Mr. Moody's remarks regarding the use of
separate porcelain insulators instead of terminal boards are
entirely correct. The writer thinks that the necessity of using
a crane and taking a transformer apart to change or make in-
ternal connections, is hardly justified. Transformers should
always be tested before connecting to their bank to discover
wrong connections.
[Communicated by Letter.]
N. M.Snyder: — The writer suggests that the design of the
high-pressure insulator be drawn on — for meeting the conditions —
without resorting to the oil-filled tubes for high-pressure ter-
minals. First by making a suitable insulator for the glazed
porcelain bushing, e.g., to fit inside, having the conductor pass-
ing through its centre.
The insulator being double petticoated as the cut shows, gives
a much greater resistance path than the straight bushing.
Side elevation cross-section showing insulator and bushing.
In bringing out heavy currents from transformers in multiple
he concurs with the idea of sub-division of terminals, while it
may introduce the necessity of more openings it has the advan-
tage of distributing the load more evenly on the windings,
assures less local heating and greater terminal surface for cool-
ing.
[Communicated by Letter.]
A. C. Pratt: — In considering the location of internal ter-
minals in transformers one point might well be brought to the
attention of the designer of relatively high-pressure apparatus.
Many transformers for power transmission are provided for
adjustment of pressure with taps on the high-pressure winding
for cutting out perhaps 10% to 15% of the winding. These
2G8 HIGH-TENSION TRANSMISSION.
adjustment taps are usually either in whole or in part located
on the outer coils nearest the line terminals. If the line ter-
minals be connected to a pair of these taps, cutting out say 5%
on either end of the coils, then the maximum pressure to ground
within the transformer becomes 10% more than from either line
wire to ground. This material increase of insulation strains is
especially undesirable in high-pressure transformers, where
small brush discharges become troublesome, not only in air-
cooled but also in oil-cooled transformers. Moreover the outer
turns near these taps must be heavily insulated from one an-
other to withstand lightning and other static strains.
If all these taps be made on adjacent ends of coils nearest the
middle of the total winding, then the internal pressure in the
transformer never exceeds line pressure; lightning strains are
confined to the outer ends of the end coils, and when the taps
are connected to cut out, say 10% of the total turns, the effect
is merely an electrical over-lapping of the turns which are cut
out, and the latter, if of equal number on the two adjacent
coils, might even be connected in parallel, saving, in this assumed
case, 7.5% of the P R loss in the high-pressure winding.
As to iDushings, glass is being rightfully tabooed; it is fragile
and necessarily of too small a diameter, thus naturally carrying
too dense a charge on its surface, as noted in the paper. The
tube is a condenser, the entire bore being at the pressure of the
wire, and some other pressure, usually ground, applied near
the middle of the outside of the tube. Charging current flows
to and from the ground, along the tube, held close to the
smooth surface of the glass, thus breaking down a thin film of
air. The thinness of the film may be illustrated by wrapping
strips of tape around the tube, when, upon applying test-pressure,
the breakdown discharge will pass between the glass and the
tape.
The remedy is, first, to increase the thickness of the tube
wall thus decreasing the capacity (which is also affected by the
kind of dielectric employed) and at the same time increasing
the surface along which the charging current will fiow, thus in
two ways decreasing the current density on the surface of the
bushing ; secondly, further to break up and dissipate the surface-
charging current by insulating rings set approximately at right
angles to the axis of the bushing, as suggested in the paper.
It is essential that the wall of the tube be so made as to avoid
long, thin air spaces extending along the axis of the tube, as
these will be the seat of local currents, which may lead to the
failure of the whole bushing.
[For further discussion on this paper see page 276 .]
FIRE-RISK OF TRANSFORMERS. 269
MEETING AT CHICAGO, MARCH 29, 1904.
Discussion on " The Relative Fire-Risk of Oil- and Air-
Blast Transformers."
James Lyman: — ^The following features should determine the
selection of transformers, as well as other electric apparatus:
1. Reliability of service, including capacity for all probable
overload conditions of practice.
2. Efficiency, regulation, the low rise in temperature under
the various operating conditions.
3. Safety against personal danger to operators and safety
against fire-risk, either from internal or external cause.
4. Compactness, simplicity of design, easy access to parts, and
general cleanliness.
In small sizes the external surface of well-designed trans-
formers is ample to radiate the heat due to copper and iron
losses. The radiating surface per kilowatt, however, rapidly
diminishes as the capacity increases, and in large sizes, from
1000 kw. up, it becomes absolutely necessary to carry off the
heat by some circulating fluid, such as air, blown directly
through the coils and the iron core, or water circulating in a coil
of pipes suspended in the oil. While in transformers from 50
to 300-kw. capacity, it is perfectly practicable to design them
of the self-cooling oil type, it is frequently more desirable to
have them cooled from some entirely external source, such as
by air-blast or water, as they can then be installed in a limited
space where proper surface radiation cannot normally be ob-
tained. The air-blast transformer has the advantage over the
oil- or water-cooled type in being pretty nearly fire-proof. The
insulation on the winding is the only combustible material in
its construction, and this amount is comparatively small.
Bum-outs in properly designed air-blast transformers are ex-
ceedingly rare, due to the fact that a comparatively low tem-
perature can be maintained even under heavy overloads by
varying the air-blast. The power required for driving the
blowers is generally from 0.1 to 0.3% of the rating of the
transformers, according to their sizes, so that the power re-
quired need not be considered in the efficiency of the trans-
formers. In cases where bum-outs have occurred in air-blast
transformers the writer does not know of an instance where the
fire has extended beyond the damaged transformer, the shell
of the air-blast transformer acting as a good fire-proof casing,
and in case of external fire the air-blast transformer is seldom
seriously damaged. When properly designed for thorough cir-
culation of oil through the core and around the coils, and with
properly-designed tanks, oil-cooled and water-cooled trans-
formers should not offer serious fire-risks. The speaker be-
lieves that within the limiting pressure for which air-blast trans-
formers can be used they are decidedly preferable to the oil
270 HIGH-TENSION TRANSMISSION.
cooled. They are clean, compact, thoroughly reliable, and fully
equal in efficiency and other characteristics, and, if anything,
capable of greater overload abuse than the oil type. Above
30 000 volts the oil-cooled and water oil-cooled transformers
must be used.
W. A. Blanck: — In regard to the two types of transformers
for transmission plants mentioned in Mr. Rice's paper, it is the
speaker's opinion that a pressure of 30 000 volts forms the
upper limit for the air-blast and the lower limit for the water-
cooled oil transformer.
If the transformers be installed in the power-house and not
separated from the engine-room by a fire-proof wall, the speaker
is in favor of air-blast transformers on account of smaller first
cost, convenience in securing proper attendance, and the con-
siderably smaller fire-risk due to the small quantity of inflam-
mable material.
If conditions call for a separate transformer house without
special attendance, the speaker is in favor of water-cooled oil-
immersed transformers set over suitable trenches so that any
overflowing oil would be properly discharged outside of the
building. The principal trouble encountered so far in oil trans-
formers seems to arise from external sources, such as arcing
switches and lightning-arresters mounted on wooden frames near
the transformers. To overcome these fire-risks it will be neces-
sary to use oil switches in brick compartments and to install all
wiring on insulators carried by iron supports. Moreover the
most essential requirement is to make the transformer house
completely fire-proof.
If for any reason self -cooled oil transformers are installed,
the cases, if made of corrugated iron, should be strong enough
to withstand external heat and should also be set over a suit-
able trench to discharge any overflowing oil. A fireproof
housing is also greatly to be desired.
P. Junkersfeld: — One advantage of the oil-cooled type
would appear particularly in those instances where large cur-
rents are taken from transformers for synchronous converters,
at comparatively low pressure. Connections of sufficient cur-
rent carrying capacity for 1000 kw. at 160 volts, would be
difficult to bring into the top of an oil-cooled transformer.
Under such circumstances the air-blast type would have the
advantage of making possible a shorter and more satisfactory
heavy copper connection between transformer and synchronous
converter.
G. N. Eastman: — He asks if any one has ever seen an oil-
cooled transformer bum up; that is, the oil actually take fire
and burn.
D. W. Roper: — A case of that kind occurred in the East
some time ago. A large single-phase, low-pressure trans-
former had the two sides of the secondary circuit brought out
through different holes in the iron case. The hysteresis loss
USE OF GROUP-SWITCHES. 271
in the iron produced enough heat to start a flame at one
end, but the transfornier did not burn up. The circuit was
opened and the blaze was smothered.
In another case at the same plant an oil-cooled transformer
of an early type was cooled by means of a water coil, in a tank
removed from the transformer. An electric arc in the chamber
in which the transformer piping was located burnt a hole in
the pipe, which led from the transformer to the oil-tank. There
was no check-valve in the pipe, and the arc set fire to the oil.
The blaze continued until all the oil in the tank was consumed.
. This took some time, and in the meantime the switchboard
operator tried to pull switches in the endeavor to put out the
arc. Long before the fire stopped every switch in the plant was
open. Those are two cases wliere fire occurred without destruc-
tion to the transformers.
G. H. Lukes: — If a device for smothering a fire in air-blast
transformers is desired, use might be made of carbonic acid
gas, which is easy to obtain. In case of a fire in an air-blast
transformer, the air could be shut off and the carbonic acid gas
turned on, when the fire would be quickly put out.
Discussion on " Group-Switches in Large Power-Plants."
W. G. Carlton: — In laying out a distributing system for
high-pressure work, simplicity should be aimed at in the switch-
ing arrangements at both the generating and receiving ends of
the lines, and also in the way of avoiding taps on the lines as
far as possible. If the system is of any size, conveniences for
testing should be provided so that no unnecessary time will
be lost in starting up the system after a shutdown, and also
so that in case of trouble on a line the latter can be easily and
quickly tested without interfering with the operation of the
rest of the system and without danger to the persons making
the test. This matter is frequently lost sight of in the design
of a station, and the men who must operate it are placed at a
disadvantage.
Oil-switches on high-pressure lines are commonly provided
either with a straight overload tripping attachment, with an
overload time-limit element or with no overload at all. If it
is necessary to use any overload device, and it frequently is,
it should have a time element depending on the load.
To illustrate: if the normal maximum is 300 amperes, the
overload should be set so that it would hold 450 amperes for
three seconds, but would open instantly on 700 amperes.
These figures are used for illustration and would vary with
conditions.
The straight time-limit device is all right in case of an over-
load, but if this overload approaches short-circuit conditions,
the switch will not open before the overload has dropped the
pressure on the system sufficiently to cause synchronous ap-
paratus to drop out of step. This has caused the abandonment
272
HIGH-TENSION TRANSMISSION.
of straight time-element overload devices in the care of one
station.
Underground high-pressure transmission lines should be care-
fully protected in manholes, both to provide against fire
spreading from one cable to another and also to confine the
arc in case a cable burns out. In the case of an unconfined
arc if the system is of any size, excessive pressures are likely
to be set up due to resonance, and the insulation of other
cables and apparatus is Ukely to be broken down. Various
forms of protection have been used. One of the best is split
vitrified clay tile, using 45- degree elbows for the bends in the
cable. When carefully installed, this gives practically a con-
tinuous conduit line through the manhole. On long lines the
lead sheaths of transmission lines should be broken at suit-
able intervals to prevent the flow of stray currents.
P. Junkersfeld: — In connection with Mr. Stillwell's paper,
he would like to emphasize the fact that it is difficult to dis-
cuss this problem without referring to a particular case. Mr.
OJitg))ing ffino
Sectional dae Biu4tu
KtG. 1
HJGH-PBESSDEB
OOHNEOTIQNS
"H&niaOD SU Station
GhicB^o Edison Co.
6 6
Oenerator OlbSvEltob
6
Generators
Stillwell selected the case of a large power-house for street-
railway systems. The conditions were known; that is, the
load was pretty well known in advance, and the location of
the sub-stations and the arrangement of the system could be
figured out quite closely in advance. It was a conversion
from steam to electric motors in the case of the Manhattan
system and with the road in operation they could determine
readily the load on transmission system. Likewise with the
Metropolitan.
In a central-station system engaged in the lighting and
power business for instance, the conditions are somewhat
different. It is not only a problem of designing the switch-
ing apparatus for conditions as they then appear, but also of
meeting the conditions that arise in a rapidly-growing system.
USE OF GROUP-SWITCHES.
273
Due consideration must be given to the percentage of total
investment involved in different parts of the system. For
instance, an additional investment in switches would often
be small compared to an additional investment in lines. There-
fore, while the number of long lines and the number of gen-
erating units are comparatively few, it will very often pay to
introduce more flexibility in oil-switches and bus-bars.
To illustrate, in one of the Chicago stations, which is de-
veloped to its ultimate capacity, the high -pressure switching
apparatus was entirely rearranged and overhauled during this
last year. In that case the problem was not difficult and
somewhat similar to that cited by Mr. Stillwell. The solution,
however, was slightly different. Instead of the group-switch
arrangement, a sectionalized bus-bar scheme was used as shown
in Fig. 1. This line bus-bar is sectionalized in such a way
that each generator may be made to supply its own section
independently if desired. The transfer bus-bar can be divided
into two sections only. Each generator has two selector-
switches by means of which it can be connected either to its
300000 civ. MUb. 3 Conductor Cable 250000 Clr..M!ls. 3-CoQductor CaSle 0000^ Conduotor Cable.
._.
i-t-o-i
LI
-Outeolng Line
^■111 I -I I I I i •
r^nf??? - rfvirirf L ine on-switch
I I I r I^M I I I Sectional Line Bus-bar
6
I ' ' — *--*] — I ' ' ' '^ — , ' ' — ' — ^ — I ' ' — ' — ^ Auiillarj Bufl-bar
^ I I 1 1 I I I T riinftfer Bua-bai
Q M " m jT] w
6
FIG. 2
HIGH-PRESSURE
CONNECTIONS
Fisk St. StatiOQ
CommoQw.ealth
Electl-ic Co.
6
m
6
Generator
Selector-B witch
OoneratoT BuB-baV
- Generator Oil-Bwitch
■-— Exolwr Oll-Bwitch
o
50 kw. Induction
Motor Generator
Exoltei Set
500 kw. Turbo-
alternator
own section of the line bus-bar or to the auxiliary bus-bar.
With the generator-switch open and the two generator selector-
switches closed, we also have a tie between a section of the
line bus-bar and the auxiliary bus-bar. While each line has
only one switch, there would, in case of trouble on line, always
be two switches in series as the tie-switch would be used to
cut off the section having trouble, in case the Hne-switch failed.
This case is the Harrison Street Station of the Chicago Edison
Company. The conditions were fairly well known when the
overhauUng was done, and the general design was, therefore,
a comparatively simple matter.
In another case, the Fisk Street Station of the Common-
wealth Electric Company, it was somewhat different. The
scheme adopted is a little more complicated, at least it will
be during the earlier development of the station. As the
station grows larger, any one generator or Une going out of
service is a smaller percentage of the total and will not cripple
27-1 HIGH-TENSION TRANSMISSION.
the system so seriously as in the first few years. The scheme
is similar to the one previously outlined and shown in Fig. 1,
except that there is an additional bus-bar introduced.
As shown in Fig. 2, there is a sectionalized line bus-bar, a
transfer bus-bar and a third bus-bar known as an auxiliary
bus-bar. In this case, there are three instead of two gener-
ator selector switches, and two instead of one line switch.
One or more lines can be connected to the transfer bus-bar
only through the medium of the generator selector switches,
which under that condition perform the function of so-
called group-switches. The installation of selector switches on
each line and of the auxiliary bus-bar introduces a little mofe
complication than the scheme shown previously, but the total
number of switches is not greater than used in most high-
pressure stations, having same size of generators and number
of lines. Ultimately it is hoped to have simply the section-
alized line bus-bar and the one transfer bus-bar similar to the
scheme shown in Fig. 1.
W. A. Blanck: — Mr. Carlton's remarks in regard to time-
limit devices in connection with high-pressure oil switches are
very interesting, but disappointing to learn that these devices
in which so much hope h^s been placed for the satisfactory
operation of a high-pressure distributing system have been
discarded. Why has this been done?
W. G. Carlton: — In regard to the straight time-limit switch,
a number of cases of trouble occurred, such as a short circtiit
on an underground line. If there is a time-limit switch on
that line and the time limit is held on and will not allow the
switch to open, the short circuit will work back and affect the
whole bus-bar with which the line is connected, and, as a rule,
will shut down everything running on that bus-bar. There
have been a few cases of trouble on underground lines, not ex-
actly in the nature of short circuits, possibly a ground, or
something which would cause a good heavy overload and when
the time limit has not been on, the switch has opened and cut
out the line; when it has been, it has shut down everything on
the bus-bar.
W. A. Blanck: — Could not that difficulty be overcome by
the proper setting of the time-limit devices, for instance the
feeder-switches for two seconds and the generator-switches
for four or six seconds?
G. N. Eastman: — The trouble with setting the time-limit
switch for any given predetermined time is increased by the ■
size of the system and the manner in which the lines are run.
Conditions will arise in almost any system where there will be
time-limit devices on lines which normally are not in series
but under conditions of short circiiit will be fed in series.
The result is that other circuits are interrupted whicTi have
time-limit devices on them and always will be interrupted
unless on that circuit on which the short circuit occurs, the
time limit is set so that it operates before all others. One
OIL-SWITCHES. 275
can readily conceive how impossible it will be in a large sys-
tem to vary the time so that these difEerent time-element de-
vices would be caused to operate for the location at which
there is a short circuit.
P. Junkersfeld: — It seems that the original time-limit
device was developed when the high-pressure system on which
it was used was comparatively small and had comparatively
few lines or branches. As the systems grow much larger,
particularly in the cases cited by Mr. Carlton and Mr. Eastman,
the straight time-limit relay is satisfactory for overload, but
it is unsatisfactory for serious trouble on cables. Before such
a time limit operates a good many things happen and it is
necessary to have a device which will open very quickly and
positively.
W. G. Carlton: — In the matter of the time limit, if the time
is at all appreciable, before that time has elapsed with a heavy
short circuit, unless there is a very large amount of power on
the bus-bar, the pressure on that bus-bar will drop sufficiently
so that synchronous apparatus will all be stopped. That is
one of the serious objections to a time-limit device.
m
Discussion on " Oil-Switches for High Pressures."
W. A. Blanck: — ^The superiority of oil switches over air-
break switches for high-pressure work, in so far as it relates
to reliability of operation and line disturbance, is very well
recognized, but still there are many cases where the much-
abused air circuit-breaker in the form of a fuse breaking under
oil or a lead fuse in connection with a spring-operated lever is
the only device suitable to be installed.
In the case of a high-pressure transmission line passing a
mining district, where the customers are usually widely scat-
tered over the territory, and sub-stations with static trans-
formers of less than 100 kw. capacity are often required, it
is evident that an automatic oil circuit-breaker in a brick
compartment would involve nearly double the investment of
the transformer.
But as a matter of fact the high-pressure tap to the trans-
mission line will- be interrupted only in case of a breakdown
of the transformers, since all secondary shorts or overloads are
limited by properly dimensioned secondary fuses, so that the
action of the air circuit-breaker, installed in connection with
a set of disconnecting switches, is only called for in utmost
emergency.
James Lyman: — In most cases the source of current supply
for operating oil switches is a storage-battery, and wherever
it is used it has proved a very reliable source. It is very sel-
dom that an automatically operated oil-switch fails.
P. Junkersfeld: — He believes that although switches are
carefully built and located in the station, but little thought is
given to the arrangement of the connections. This should not
be the case.
276 HIGH-TENSION TRANSMISSION.
Discussion on " Terminals and Bushings for, High-Pres-
sure Transformers."
W. G. Carlton: — The speaker desired to know if any one
present could state whether or not there are any 80 000-volt Unes
in operation.
E. O. Sessions: — In California the lines are operated from
45 000 to 60 000 volts, depending upon the reactance in the
line.
P. JuNKERSFELD : — In a very large proportion of high-pressure
work oil-switches play rather an important part. One question
of importance is the building of suitable doors for oil-switches.
The question has been discussed in difEerent parts of the coun-
try as to what is the best and most satisfactory door for an oil-
switch compartment. The glass door and wire glass door can
readily be seen through for inspection purposes. While with
the iron door or with the Alberene or slate slab you cannot readily
inspect, and are liable to use the switch when it is not in order.
Alberene slabs and iron doors can not be so easily and safely
removed as glass ones and consequently the switches are not
so frequently inspected as they should be.
G. N. Eastman: — One instance might be cited where a com-
pany operating in Chicago had a solid door and for some reason
the oil suddenly disappeared from the oil wells. There was
only a slight indication of this from the oil on the floor outside.
The switch, however, operated satisfactorily on closing, but
not so well on opening the circuit. When the doors were re-
moved it was seen that there was considerable oil inside the
switch.
W. G. Carlton: — ^The speaker thinks the amount of wood in
the frame of the door is not enough to cause much fire. There is
practically an equal amount of inflammable material close to the
switch in the insulation of the leads. In operating a number
of lines on one bus-bar, when several switches open up due to
trouble, it is not always possible to tell on which line the
trouble is. If the oil-switch opens up a line on which there is
a short circuit, some oil will generally be thrown from the
switch. With a glass door the attendant can see where oil
has been thrown out of the switch and thus save time in lo-
cating the trouble, as has been proved by experience in a number
of cases. There is the possible objection of breaking the glass,
but there is not much fire-risk with the amount of wood avail-
able.
I. E. Brooke: — In the construction of some oil-switches it
seems as if an iron door comes rather close to the live copper,
and that the liability of grounding on the iron door would more
than overbalance the objection to the fire element on a wooden
door.
Mr. Thomas : — ^The speaker believes it has been the practice
to ground the framework of the oil-switch as well as the door.
He approves of it and considers that everything in the shape of
framework on a switchboard should be grounded.
TERMINALS AND BUSHINGS. 277
P. Junkersfeld: — One point particularly has been brought
out in connection with oil switches, and that is that they need
a great deal of attention. A switch is looked upon as some-
thing which can be operated occasionally and then left alone;
but that is not the case with an oil-switch. It must have fre-
quent and good inspection, and in order to get good inspection
it must be arranged so that the operator may easily see its
condition. One of the speakers has made the suggestion to
have an iron door which would open outward and downward.
Why does he say you get better inspection when a man opens
an iron door than when he looks through a glass door?
E. 0. Sessions : — The speaker has used wooden doors with glass
windows for the switch-cells, but they were replaced by iron
doors, about eight and a half inches away from switch-tank
with a two-inch air-space all around the door, on account of the
destruction of the wooden ones.
P. Junkersfeld : — Glass doors of heavy plateg-lass in three sec-
tions, which will enable every part of the switch from the bot-
tom terminal to be seen, have been in service for some time.
W. G. Carlton: — In the case Mr. Sessions mentioned of the
glass door being blown off, why would not the same thing
happen to an iron door? also trouble has been caused by
switches grounding to an iron door.
E. O. Sessions: — ^With wooden doors the case was fitted
tight, while about the iron doors there was left a two-inch space.
With glass doors after one blowout of the switch, the glass
would be so obscured that it would be impossible to note what hap-
pened without opening the door, but arranging the iron door
so that it lacks two inches of closing will permit the inspection
of the switch.
R. F. Schuchardt: — To illustrate the point brought out by
Mr. Brooke, the speaker cited the following case: An oil-switch
had opened on a very heavy overload and some of the porcelain
posts were so badly broken that one of the oil-wells fell for-
ward. After the switch was opened the lower part connected
to the oil-wells was still alive and if this well had fallen against
an iron door thoroughly grounded, the resultant short circuit
would certainly have caused great damage. With a wooden
door with a glass front no live parts could come in contact
with metal.
E. O. Sessions: — In the Waterside Edison station in New
York all the doors are made of soapstone, or Alberene, as it is
called, and are fitted in close against the brickwork.
Edw. Schildhauer: — If Mr. Session's advice is followed to
erect the door two inches from the brickwork, the fire-proof
advantage of the iron door is nil. It would look rather odd
to see a brick switch compartment lined with Alberene stone
on three sides and equipped with an iron door on the fourth
or front side, while the distance from the oil vessel to the door
is the same as to the Alberene. If an oil vessel bursts with
278 HIGH-TENSION TRANSMISSION.
enough generator capacity back of it, the speaker believes
that there will be in most cases very little left of the iron door.
P. Junkersfeld: — The large companies in Chicago have
had some oil-switches in operation for a number of years; in
fact, some of the first hundred switches that were made for
the Metropolitan station in New York, which was the first
extensive installation of the compartment -type of switch, were
shipped to Chicago. The first had the asbestos and iron doors,
then followed Alberene doors, and more recently the advan-
tages of the glass door appeared. One or two experiences
brought out very forcibly that it was desirable to have a glass
door and at the same time a fire-proof door. That, of course,
meant a metal casing. After that, however, it was realized,
as Mr. Carlton pointed out, that what little wood is introduced
does not seriously diminish the fire-proof character of the door
and does not increase the danger. The fire-proof barriers be-
tween the phases are really depended upon to prevent trouble.
It is not often that the switches are gotten close enough so
that anything thrown out at the front would be a serious matter.
G. N. Eastman: — Some five years ago, when the question
first came up about using oil-switches in preference to air-
switches, he made some tests to determine what the relative
rise in pressure in the cable would be upon opening the circuit.
He found that in a three conductor No. 00 cable three miles
in length, the changing current was great enough so that upon
opening the circuit with an air-switch, the arc could be grad-
ually drawn up, and an increase in pressure of 50% " noted
by a static voltmeter " could be obtained. If the switch was
opened quickly, using a single break in the oil, no increase in
pressure could be noted. Drawing the arc out in the oil a rise
of from 10 to 15% was obtained. By connecting four breaks
in series in oil it was practically impossible, under any condi-
tions, to obtain a rise in pressure.
The speaker believes that upon opening a short cir-
cmt the tendency of the arc to hold would be reduced by
having breaks in series. With some conditions, it is only by
holding the arc — " the arc acting as an interrupter " — ^that
you obtain a rise in pressure. The rise will be more severe with
a short circuit under certain conditions than with only the
charging current.
FIRE-RISK OF TRANSFORMERS. 279
MEETING AT PITTSBURG, APRIL 7, 1904.
Discussion on "The Relative Fire-Risks of Oil- and Air-
Blast Transformers."
J. W. Farley: — For fires inside of transformers themselves,
a chemical extinguisher can be used to good advantage. If a
flash should occur inside the transformer, and ignite the oil
which has soaked up on the insulation on the leads, the fire can
be put out with ease by means of an extinguisher, which will
be very effective even if the surface of the oil is actually burning.
Light brick walls may be built between the different trans-
formers and low deflecting walls may also be arranged so that
in the event of an accident to the transformer case, due perhaps
to the falling of a beam or tile from the roof at the time of a
fire, the escaping oil would be prevented from spreading over
the premises and would be diverted either into a sewer or out
of the building at some point where it would do the least
damage. It is always a good plan to pipe from the transformer
cases to a storage-tank or to a pit or sink-hole located in the
most advantageous place, in order that in time of emergency
the oil may be withdrawn from the transformers.
One field for the air-switch is its use for high pressures,
where the amount of power is not very great. Under these
conditions the air-switch will act just as satisfactorily as an oil-
switch and often is very much cheaper than the latter. This
is particularly true for pressures between 20 000 and 40 000
volts, and where the amount of power available on short cir-
cuit is comparatively small, as at the end of a transmission
line at a sub-station with an output of 600 or 800-kw. Air-
switches can easily be installed and at a cost probably not one
half that of installing oil-switches.
Regarding the relative amoun^t of space required by air-
switches and oil-switches, in a complete layout for a typical
transformer station for a single-phase railway plant it was found
that the use of air-switches made just as compact, if not a more
compact, plant thah could be secured with the oil-switches, as
the latter needed disconnecting switches and series transformers
for their operation.
N. J. Neall: — ^The speaker has noticed that in the West so
much more account is taken of the ability of electrical apparatus
as to afford continuous service than of its efficiency. One in-
stance of what is now considered an old station has the high-
pressure transformers in the main power-house only a slight
distance from the generator. During an accident to the switch-
ing apparatus considerable burning oil was thrown out on the
floor of the power-house; this heated up the transformer cases
but did not injure the transformers.
Another plant visited had placed each transformer in a com-
plete building by itself, the idea being that if one transformer
280 HIGH-TENSION TRANSMISSION.
went out it would not communicate fire to the adjacent trans-
formers.
A. B. Bond: — There is one point in connection with air-break
switches which has not been brought out to-night and that is
the question of thoroughly drying out the switch before its
installation. Conditions sometimes arise under which the
wooden parts of the conventional fuse-switch may become
damp and thus introduce an element of danger to the attendants.
In a prominent Western plant considerable trouble was ex-
perienced with fires in the oil-filled transformers. The cases
were perforated at the top, and it was found that by thoroughly
caulking up all openings, the trouble from fire was eliminated.
In this plant it was customary to use sand for fires in trans-
formers. A patent extinguisher was also employed in which
the novel feature of an interrupted stream was incorporated.
With this extinguisher it was impossible for an attendant to
receive a serious shock in consequence of directing the stream on
live high-pressure wiring — a danger that exists where a con-
tinuous stream is used.
Discussion on " The Use of Group-Switches in Large
Power-Plants."
B. P. Rowe: — It appears that the use or disuse of group-
switches is one which will be mainly decided from the station
operator's standpoint. The fact that the Metropolitan Street
Railway Company in their 96th Street and Kingsbridge stations
and the Manhattan Railway Company in its 74th Street station
are both in favor of using group-switches seems to indicate that
there must be enough good reasons for using the system to
overbalance the objections Mr. Stillwell mentions, and any
others he has not mentioned. The speaker has noticed that
other large stations beside those of the Metropolitan and Man-
hattan companies are being laid out with group -switches, and
for large stations of this class, with a large number of feeders,
there seems to be a decided sentiment in favor of using this type
of switch.
In the first place, if a power station is a large one no one
questions the advisability of using two sets of bus-bars. If
every feeder must be capable of being thrown to either of the
two sets of bus-bars, there are required three oil-switches to
each feeder. If the feeders are grouped as Mr. Stillwell has
described, the two switches which act as selector-switches for
one feeder will, if large enough, be suitable to transfer a whole
group of feeders ; so that with a double-throw system, the group-
switches, acting as selector-switches, are rather a saving in ap-
paratus than otherwise.
But when a single set of bus-bars is used, with the ring system
USE OF GROUP-SWITCHES. 281
and junction-switches, the group-switch is undoubtedly an extra
to be considered, just as Mr. Stillwell has considered it. Such
a case as this is the Kingsbridge power-station, where the group-
switches were installed by the Mecropolitan Street Railway
Company, who already had had the experience of operating the
96th Street station to guide them, and considered them necessary.
Under such conditions, an arrangement of feeders is made, so
that the opening of a group circuit-breaker does not shut down
an entire sub-station. Mr. Stillwell presents a diagram which
indicates that if the operator suddenly opens a group-switch
in an emergency, to cut out a bank of six feeders, he thereby
shuts down an entire sub-station. The arrangement the writer
has in mind is to have one or two feeders from a group carried
to one sub-station and the balance distributed to other sub-
stations, so that each sub-station draws its supply of current
through two or more group-switches. Thus the liability of
shutting down sub-stations is not so great. The writer under-
stands that the Kingsbridge and 96th Street feeders are con-
nected in this way.
A point not brought out by Mr. Stillwell is that when a group-
breaker is installed it must have a capacity sufficient to carry
all of the feeders in the group and to open the total load under
the worst conditions. Now if the feeders in the group are carry-
ing large amounts of energy it is manifestly a more difficult thing
to open it all on one switch than to divide the load and open vit
instead on the several feeder switches. In some cases it means
a large switch and the amount of energy to be handled intro-
duces an element which can hardly be neglected. There is
obviously more liability that the large switch will cause trouble
than any one of the smaller ones. In such a case a station operator
would probably rather consider the group-switch an emergency-
switch than to be habitually breaking large amounts of current
on it to save time in transferring feeders or cutting them out
of circuit.
This would seem to indicate that where feeders are of very
heavy capacity so as to require large group-switches, they might
be a source of trouble rather than a benefit unless they are reli-
able. Reliability is demanded because the group-switches are
connected directly to the bus-bars. In the Kingsbridge power-
station the opening of the group-switch automatically opens all
the feeder-switches connected to it. This insures that there
shall be two breaks in the circuit and might help out the group-
switch.
A paper presented at the 188th Meeting of
the American Institute of Electrical Engineers,
Chicago, June 21-22, 1904.
Copyright 1904 by A. I. E. E.
PROTECTION OF CABLES FROM ARCS DUE TO THE
FAILURE OF ADJACENT CABLES.
BY W. G. CARLTON.
The matter of the protection of cables depends largely on
the number of cables and amount of room available. This
protection is needed in stations and sub-stations, also in man-
holes on underground work; on inside work there is generally
available room for separating the cables, and for this reason it
is easier to take care of them than in underground work. In
'general, similar protection can be used in either place, except
that in underground work material must be used which will not
be affected by water, as manholes are liable to be flooded. Pro-
tection of cables in manholes will be considered particularly.
In old conduit systems where a large number of ducts have
been installed and no attempt made at separating them as
they enter manholes, it is a difficult matter to protect cables.
If, however, the work has been carefully laid out, plenty of room
taken in manholes and the ducts spread so that there is a vertical
space of from 8 to 12 inches between the two halves of the conduit
line, it is much easier to ensure satisfactory protection. It
should be borne in mind that a conduit line of a large number
of ducts is not a desirable thing. Two independent lines will
cost considerably more than a single line of the same capacity,
but this extra cost is an insurance against future trouble.
On account of the large amount of energy carried by high-
pressure cables their protection is of the utmost importance.
High-pressure transmission cables operate usually at from 5000
to 15 000 volts and are nearly always three-conductor cables.
It is to the protection of such cables that this paper refers par-
ticularly, although it will generally be found that protection
282
PROTECTION OF CABLES. 283
is needed more from bum-outs on low-pressure cables than from
those on high-pressure ones. High-pressure cables are usually
protected by automatic overload devices and, if these are sat-
isfactory they will disconnect the cable before any large amount
of damage is done. On the other hand, low-pressure cables
may continue to bum without drawing enough current to cause
them to be cut off. Cables generally break down in manholes
due to poor work in jointing or to careless handling during in-
stallation. Various methods are in use for fireproofing and
isolating them from one another.
A method employed in a number of places is to wrap the
cables with asbestos paper or tape about 1/8 in. thick, using
two layers and binding the asbestos on by means of steel or
brass tape. The metal tape is wrapped either in an open spiral
leaving an inch or more between turns, or with the edges touch-
ing leaving no open space. With the metal tape wrapped close
there is less danger of the asbestos disintegrating on account
of water in manholes or of other causes. The asbestos wrapping
should be carried well into the duct. This protection has been
found adequate by several large companies. Its life, however,
is uncertain, particularly on underground work. One disad-
vantage is that in the case of loaded cables the heat is less
easily radiated on account of the asbestos covering. Asbestos
paper soaked in silicate of soda has been used for wrapping
cables; this has the advantage of not requiring any metal tape
for a binder, as the paper treated in this manner is cemented
to the cable. It is doubtful if the silicate of soda treatment
will be satisfactory for use in manholes that are likely to be
flooded, although it should be in dry places.
A second method of isolating and protecting cables consists
in providing separate chases or runways for them. Sometimes
this is done by building special long and thin bricks into the
wall of the manhole leaving them projecting so as to form a
shelf. Soapstone slabs are also laid in the wall forming shelves
or boxes for the cables. The cables may be further protected
with asbestos if desired. It is difficult with this method of
protection to make a satisfactory job where the cables enter
the ducts unless there has been a very elaborate spreading of
the ducts.
The third method of protection, which is very satisfactory
when the cables run fairly straight through the manholes, con-
sists of a covering of vitrified-clay tile. Ordinary single-duct
284 HIGH-TENSION TRANSMISSION.
clay tile in 18 in. lengths is used, the tile being cut nearly
through befere baking so that it is easily broken in halves.
The tile on the lower layer of cables is supported by means of light
galvanized angle-irons run longitudinally through the manholes.
The upper layers are supported on the lower ones. For the
bends in the cables 45 degree curves with a 12 in. radius are
used. These curves being laid in reverse similar to the letter " S ''
near the end of the manholes where the cable enters the duct.
The tiles are laid in cement mortar forming a good mechan-
ical piece of work and giving practically a conduit line through
the manhole. One or two of the lower ducts should be left
open at each end of the manhole for a space of about one-hali
inch so that water will drain from the conduit line. The prin-
cipal objection to the use of tiling is, that in the case of trouble.,
making it necessary to remove a cable, the tiling must be brokec
out. Iron brackets are avoided by the use of tiling and there
is no chance for current to flow from the lead sheath of oe/?
cable to that of another except such leakage as may occur du?
to moisture in the ducts. Personally, the writer is in favor of
using the split -clay tile covering where possible, and asbeste?
paper and brass tape in other places.
High-pressure cables should be covered, not only to protec*
them from the failure of adjacent cables but also on acount
of the dangers which may arise from an unconfined arc. Oscilla-
tions may be set up which will produce pressures many times ir
excess of that at which the cable is working, and these high-
pressures are liable to break down the insulation on the cables
or on the switchboard apparatus, transformers, or generators,
which may be connected to the cables. For this reason one
large company in New York has installed on all cables within
a mile of the power-house, in addition to the regular asbestos
-covering, a sheet -iron armor 1/16 in. thick. This armor being
rolled and especially prepared to meet curves or bends in the
cable, each section lapping the next one. This sheet-iron
is clamped together so as to make a strong mechanical covering.
A manhole fire causes more trouble at the top of the hole
than lower down, and for this reason the most important cables
should be kept towards the bottom of the manhole. In the
case of large manholes it will often be found desirable to build
a partition wall longitudinally through the hole, making prac-
tically two manholes.
While burn-outs in cables are bound to occur — ^and for this
PROTECTION OF CABLES. 285
reason, fireproofing cables, particularly important ones, is neces-
sary — at the same time, the number of burn-outs can be kept
to a minimum by careful work. Only experienced and careful
men should be allowed to train cables. The manhole should
be built so that it is not necessary, or even possible, to make a
short bend in the cable in taking it from the duct to the side
of the hole. The jointing should be done by thoroughly reliable
men and they should be given to understand that it is not
speed which is wanted but first-class work. If it is not desir-
able to do the jointing as soon as the cables are pulled in, the
ends should be sealed, first cutting them back far enough to
be positive that there is no moisture present. Tests for
moisture should be made if there is any reason to suspect its
presence.
The experience of one company in Chicago has bee^ that
nearly all trouble that has occurred on three-conductor high-
pressure cables has been due to defective joints, to moisture in
the cables near the joints, or to sharp bends in the cable. Some
bum-outs have occurred due to the lead sheathing of the cables
being damaged by electrolysis. This can be prevented by
grounding the lead of the cables at suitable intervals or by in-
sulating them if possible. Frequent inspection should be made
to determine whether the lead sheaths of the cables are carrying
ciirrent, a recording voltmeter having a total range of from three
to five volts will be found convenient for this work and a chart
covering the entire day will be found much more valuable than
a few single readings.
286 HIGH-TENSION TRANSMISSION.
Discussion on " Protection of Cables from Arcs Due to
Failure of Adjacent Cables."
Ralph D. Mershon: In addition to the protection of cables
in manholes, there is also the question of the protection of
cables in power-stations. It is not always easy to install cables
in such a way that they will be protected from each other, es-
pecially if the power-house has not been laid out with reference to
them. The question of protecting cables by means of asbestos and
similar wrappings has for its chief objection that there is no
chance to get rid of the heat in the cable. For that reason,
and for the greater one of reliability, the speaker very much
prefers either tile or brick protection to asbestos.
Mr. Carlton speaks of using a voltmeter for determining the
current being carried by the cable sheath. Will Mr. Carlton
please explain a little more fully the method of using the volt-
meter, and also the method he prefers for permanent grounding of
metal sheaths ?
W. F. Wells: Mr. Carlton refers to two independent
lines of subway as being an insurance against trouble
on a high-pressure cable system. In New York this practice
has been carried a little further, and four separate and inde-
pendent trunk subways have been installed, leading from the
generating station along four different routes. From these
trunk subways run branches arranged so as to give each sub-
station two or more feeders, following entirely different subway
routes. In case of a manhole caving in, or general trouble on
any subway line, not more than one quarter of the high-pres-
sure cable system can be affected.
Regarding the injury to high-pressure cables by the burning
out of low-pressure cables; this has occurred, but burn-outs
have also originated in the high-pressure cables. Some of these
troubles were due to defective joints and some to short bends
in the cable where it leaves the duct. In order to obviate this
latter cause, the cable is now run straight out of the duct 12 in.
before bending it over to the side of the manhole, thus pre-
venting the edge of the duct from cutting into the sheath of the
cable.
For the past two or three years the high-pressure cables in
manholes have been wrapped with asbestos bound on by galvan-
ized-steel tape, as described by Mr. Carlton, and the results
have been very satisfactory. No trouble has been experienced
from the heating of the cables where covered with this asbestos
wrapping. In the stations, clay ducts or iron pipes are used
wherever possible, to protect the lead-covered cables, and,
when there is sufficient space, braided cables are carried on
insulators through runways oi^brick 12-in. square.
H. C. Wirt: Will Mr. Carlton state whether he considers
an underground line more reliable than overhead line as re-
gards interruption of service?
Ralph D. Mershon: Mr. Carlton speaks of the extra ex-
PROTECTION OF CABLES. 287
pense of separating ducts. It seems that in some cases sep-
aration may not in the end be an extra expense. The capacity
of the subway ^s not necessarily proportionate to the number
of ducts in it. Allow a certain limiting value to the tempera-
ture of the cable, then the ducts near the center of the conduit
will not be as effective as those outside, no matter how they
are arranged; if they are separated, it might be cheaper in the
end because of the greater capacity the two subways would
have over the single. So far as the speaker knows there are no
accurate data in regard to this matter. The speaker has done
a little work himself in special cases, and some work was done
at Niagara some time ago. Perhaps Mr. Carlton and Mr. Wells
have some information on this subject.
W. G. Carlton: In regard to the capacity of the cable
being lessened in a larger conduit line; the speaker has no
accurate information on that subject. Where cables are run
at extremely heavy loads the gas generated inside of the cable
will puncture the lead sheath, and this is one of the limiting
features. The permissible watt consumption per linear foot
of cable depends on the number of cables in one conduit line.
With a single cable 20 watts per foot would probably be safe;
with a larger number of cables, three or four might be the limit.
It is a good plan to treat the cables in the power-house — if
they are lead-covered ones — practically the same as you would
for underground construction. A conduit line can either be
built, or when the cables are in place they can be covered with
split clay tile. The ends of the cables need special care. Three-
conductor cables must have some sort of terminal bell which
allows spreading out the conductors for connection to the single-
conductor cable, this bell to be filled with an insulating com-
pound.
In regard to detecting possible stray currents on the lead
sheaths of cables; a Bristol recording meter with a five-volt
scale has been used; this is fairly satisfactory. A meter with
the zero line in the middle of the chart and giving readings
each side of this line 'would be much better. The voltmeter
is connected between the lead sheath of the cable and a good
ground. In our stations we connect with the ground plate;
we have a ground bus-bar in our stations connected to several
ground plates. In a manhole it would be connected to a water-
pipe or sometimes to the cast-iron frame of the manhole or to a
rod driven in the ground. The grounding of the cable sheaths
is done ordinarily in the power-house, on the brass bell on the
end of the cable.
Answering Mr. Wirt's question in regard to overhead and
underground lines; in the case of one company operating pos-
sibly 75 miles of 9000-volt Hnes, 65 of which is underground,
possibly 90% of the trouble on the lines is on the 10 miles of
overhead line. This has been caused generally by boys throw-
ing wires over the line, or by kite-strings.
288
HIGH-TENSION TRANSMISSION.
H. B. Alverson: When the asbestos covering a cable is
saturated with sihcate of soda, the wrapping will harden and
become nearly as good a conductor of heat as the lead jacket;
this overcomes the objection that asbestos covering confines the
heat within the cable.
W. G. Carlton: How does that stand in a wet manhole?
H. B. Alverson: We have had no experience of -that sort.
E. M. Lake (by letter): In visiting some of the larger East-
em stations, about three years ago, it was observed that very
little attention had been given at that time to the protection
of outgoing cables. The bus-bars and immediate connections
were protected by a hiost elaborate scheme of barriers built up
of brick and concrete and of soapstone. The outgoing feeder
Unes, however, and in one or two places the main leads from
the generators, were laid side by side upon cast-iron racks or
upon thin sheet-steel shelves.
When this question came up in connection with the design
of certain Chicago sub-stations several methods were consid-
ered for protecting and isolating the whole cable equipment
so as to reduce to a minimum the liability that a burn-out '
would spread to adjacent cables. The plan of using thin slabs
of slate or vitrified clay was not found feasible because of the
difficulty of applying in places where the ' structural work and
cables were already in place. Then, too, this plan did not
afford a simple and ready method of completely enclosing the
cables where there were several in one run. Steel shelving and
partitions when used alone were open to the same objections,
besides being still further objectionable on account of the very
small resisting power when subjected to the intense heat of an
electrical bum-out. The proposition then narrowed down to
some form of vitrified clay conduit because of the convenience
of form, good mechanical strength, and high arc-resisting
powers. Since the application must very often be made to
cables in place, a split or divided form was necessary. There
were found two forms of split conduit. One was divided in a
straight line upon the diameter of the bore (Fig. 1). The other
PROTECTION OF CABLES.
289
was divided at an angle to the diameter, the two parts not
being symmetrical (Fig. 2). These conduits were each applicable
to certain conditions and locations, but a form was desired
that would adapt itself readily to any and all places where
protection of this kind was required. The style designed for
this purpose was divided on lines parallel to the diameter of
the bore but offset about an inch with reference to the diam-
^^'>-^M^^i^M^^^i^^^i^M$i¥^M^
Fta. Z.
eter (Fig. 3). This gave two symmetrical sections which were
interchangeable and possessed several distinct advantages over
the existing forms.
It will be observed that in this form of conduit the joints
in two adjacent ducts are not directly opposite. This of course
insures a much more effective barrier between the cables en-
closed by the conduit. For horizontal runs in walls the form
. <.■-■:.;•■>•
'^^>^^'~r^t'^i^?i'ii^Tx^^ru^4''
of the half-section is such that when laid it forms a convenient
bed for the cable. Then when the cable is in place it does not
form an obstruction to the laying of the remaining half of the
conduit. Elbows on a safe radius for large cables and in an
arc of 45 degrees were provided. Short straight lengths of
4i in. and 9 in. were also ordered. With these forms and the
standard 18-in. lengths it was comparatively easy to follow
290 HIGH-TENSION TRANSMISSION.
the curves of any run of cables in a station or manhole, provided
the cables had not been laid on less than a 12-in. radius.
A. M. Hunt (by letter): A covering for leaded cables where
exposed in manholes can be made as follows : mix a stiff mortar
using calcined magnesite (finely ground) and a saturated solu-
tion of magnesium chlorid; this combination hardens to stone
in a few hours, and is heat-resistant and water-proof. Coat
the lead of cable with oil, and wind it spirally with strips of
canvas, putting the mortar on the inside of strip as the winding
progresses. Any thickness of coating may be built up in this
way. An outside finish of the mortar should be used. If the
lead is not oiled, the mortar will adhere to it strongly, and be
difficult to remove. The materials can be bought at prices
which do not make the cost of such work heavy, and the cov-
ering is solid and effective.
As a protection against electrolytic action on the lead sheath
of cables in an extensive network, the writer has tried operating
a direct-current machine of low pressure with the negative ter-
minal solidly connected to the lead sheathing and the positive
strongly bonded to rails. The sphere of influence of this ma-
chine was much more extensive than might be imagined, and
the application is worthy of consideration in cases where elec-
trolytic action is severe. In the case noted the energy con-
sumed was quite small.
J. W. F. Blizard (by letter): The writer suggests wrap-
ping the cable in manholes with tape or thin asbestos, and then
spreading a layer of about one-eighth inch of litharge on the
cable. This will harden quickly and form a perfect protection
from arcs, and may with ease be extended into the ducts for
an inch or two. Ground mica and varnish would probably
prove equally satisfactory, and cost considerably less. The
asbestos or tape covering would prevent the compound used
from adhering to the cable sheath, thus making the cable access-
ible in case of trouble, by simply breaking the protecting shell.
In addition to the dangers arising from the unconfined arc
mentioned by Mr. Carlton, there is the often very serious one
of gas explosions. No good ventilating system for under-
ground conduits having yet been devised, this danger is an
ever present one, and its importance should not be underrated.
A paper presented at the 188th Meeting of the
American Institute of Electrical Engineers,
Chicago, June 21-22, 1904.
Copyright 1904, by A. I. £. £.
SYNCHRONOUS MOTORS FOR REGULATION OF POWER-
FACTOR AND LINE PRESSURE.
BY B. G. LAMME
General Discussion.
It is well known that the synchronous motor, running with-
out load on an alternating-current circuit, for instance, can
have its armature current varied by varying its field strength.
A certain adjustment of field strength will give a minimum
armature current. Either stronger or weaker fields will give
increased current. These increased currents are to a great ex-
tent wattless. If the field is weaker than the normal {i.e. the field
for minimum armature current), the increased armature cur-
rent is leading with respect to the e.m.f. waves in the motor
and lagging with respect to the line e.m.f. The current in the
motor is therefore corrective in its nature. For stronger than
the normal field, the current is to a great extent lagging and
tends to lessen the flux in the motor and the current is leading
with respect to the line e.m.f. A synchronous motor therefore
has an inherent tendency to correct conditions set up by im-
proper adjustment of its field strength. The correcting current
in the motor is drawn from the supply system and this current
also has a correcting effect on the supply system, tending to
produce equalization between generated pressures in the motor
and the supply pressure. This characteristic of the synchronous
motor can readily be utilized for two purposes; namely, for
varying the amount of leading or lagging current in a system
for producing changes in the power-factor of the system (in-
cluding transmission line, transformers, and generators), or a
synchronous motor can be utilized for pressure regulation in
a system,
291
292 HIGH-TENSION TRANSMISSION.
As the synchronous motor can be made to impress a leading
current upon the system, and as the amount of this leading
current will depend upon the field adjustment of the synchronous
motor, it is evident that this property can be used for neutral-
izing the effects of lagging current due to other apparatus on
the system. The resultant leading or lagging current can be
varied and the power-factor of the system can be controlled over a
fairly wide range, depending upon the location of the synchronous
motor or motors and upon the current capacity of the motor, etc.
As the wattless current in the motor is primarily a corrective
current, it is evident that for most effective purposes for ad-
justing power-factor on the system the corrective action of
this current on the motor itself should not be too great. When
used for such purpose the synchronous motor should therefore
be one which would give a comparatively large current if short-
circuited as a generator. Also the motor should preferably be
one in which the magnetic circuit is not highly saturated, for
in the saturated machine the limits of adjustment in the field
strength are rather narrow.
As has been noted above, if the field strength of the motor
be varied, a leading or lagging current can be made to flow in
its armature circuit, this current being one which tends to
adjust the pressure of the armature and that of the supply
system. It is evident that if the armature pressure is held con-
stant and the supply pressure varied, a leading or lagging
current would also flow. If for instance the line pressure were
dropped below that of the motor, then a lagging current would
flow in the motor tending to weaken its field, and a leading
current would flow in the line, tending to raise the pressure on
the line. If the line pressure should be higher than that generated
by the synchronous motor, then the current in the motor would
be leading, tending to raise its pressure; while it would be lag-
ging with respect to the line, tending to lower its pressure.
The resultant effect would be to equalize the pressures of the
line and motor, and there would thus be a tendency to regulate
the line pressure to a more nearly constant value. It is evident
that the less the synchronous motor is affected by the correc-
tive current and the more sensitive the line is to such corrective
action, the greater the tendency will be toward constant pres-
sure on the line. It is therefore evident that the synchronous
motor which gives the largest current on short circuit as a gen-
erator would be the one which gives the greatest corrective
action as regards pressure regulation of the system.
POWER-FACTOR AND LINE PRESSURE. 293
For such regulation, the synchronous motor which gives a com-
paratively large leading or lagging current with small change to
the pressure of the system is the most suitable one. Or, the
motor which gives the greatest change in the leading or lagging
current is the one which gives best regulation. It is the change
in the amount of wattless current which produces the regulation.
This current could vary from zero to 100 leading, for example,
or could change from 50 leading to 50 lagging, or could change
from 100 lagging to zero lagging. Any of these conditions
could produce the desired regulating tendency, but all would
not be equally good as regards the synchronous motor capacity.
If in addition to the regulating tendency it is desired to correct
for lower power-factor due to other apparatus on the circuit,
it would probably be advisable to run a comparatively large
leading current on the line due to the synchronous motor, and
the regulating tendency would be in the variations in the
amount of leading current, and not from leading to lagging,
or mce versa. A larger synchronous motor for the same regu-
lating range would be required than if the motor were used
for pressure regulation alone. It is evident that the current
capacity of a motor regulating from 50 leading to 50 lagging
need be much less than for current regulating from 100 leading ^
to zero. It is evident therefore that if there is to be compensa-
tion for power-factor as well as regulation of pressure, that
additional normal current capacity is required.
Regulating Characteristics as Fixed by Speed, Fre-
quency, Etc.
In case such synchronous motors are required for regulation
purely, it may be suggested that such machines be operated
at very high speeds compared with ordinary practice. At first
glance it would appear that such a synchronous motor could
be operated at the highest speed that mechanical conditions
would allow, but there are other conditions than mechanical
ones which enter into this problem. For instance, it is now
possible to build machines of relatively large capacity for two
poles for 60-cycle circuits, and for Vfery large capacities — say
1500 kilowatts — having four poles. Therefore mechanical con-
ditions permit the high speeds, and the electrical conditions
should be looked into carefully to see whether they are suitable
for such service. As such synchronous motors should give rela-
tively large currents on short circuit the effect of high speeds
and a small number of poles on short-circuit current should be
considered.
294 HIGH-TENSION TRANSMISSION.
In order to give full-load current on short circuit, the field
ampere-turns of such a machine should be practically equal to
the armature ampere-turns, taking the distribution of windings
etc., into account. By armature turns in this case is not meant
the ampere wires on the armature, but the magnetizing effect
due to these wires. Therefore to give, for instance, five or six
times full-load current on short circuit, the field ampere-turns
should be relatively high compared with the armature.
This means that the field ampere-turns per pole should be very
high, or the armature ampere-turns per pole very low. Ex-
perience shows that for very high speed machines, such as used
for turbo-generators, there is considerable difficulty in finding
room for a large number of field ampere-turns, and therefore
in such machines it is necessary to reduce the armature ampere-
turns very considerably for good inherent regulating charac-
teristics. This in turn means rather massive construction, as
the magnetic circuit in both the armature and field must have
comparatively large section and the inductions must be rather
high. This in turn means high iron losses in a relatively small
amount of material compared with an ordinary low-speed ma-
chine, and abnormal designs are required for ventilation, etc.,
and for mechanical strength.
An increase in the number of poles usually allows increased
number of field ampere-turns without a proportionate increase
in the number of armature ampere-turns. This condition is
true until a large number of poles is obtained, when the leakage
between poles may become so high that the effective induction
per pole is decreased so that there is no further gain by increas-
ing the number of poles, unless the machine is made of abnormal
dimensions as regards diameter, etc. Experience has indi-
cated that in the case of very high-speed and very low-speed
alternators, it is more difficult to obtain a large current on short
circuit than with machines with an intermediate number of
poles. For example, it is rather difficult to make a 600 kilovolt-
ampere, 3600 rev. per min., two-pole machine which will give
three times full-load current on short circuit. A 4-pole, 1800
rev. per min. machine can more easily be made to give three
times full-load current on short circuit and with comparatively
small additional weight of material. The material in the ro-
tating part of the four-pole machine, while of greater weight,
may be of considerably lower cost per pound. The stationary
part of the four-pole machine may have a somewhat larger in-
ternal diameter, but the radial depth of sheet-steel will be less
POWER-FACTOR AND LINE PRESSURE. 295
than in a two-pole machine. The total weight of material in
the armature of a four-pole machine may be practically no
greater than in a two-pole machine. Therefore a two-pole
machine of this capacity should cost more than a four-pole
machine, if designed to give the same current on short circuit.
A six-pole machine would show possibly a slight gain over the
one with four poles, but not nearly as much as the four-pole
machine would over the one with two poles. The real gain of
the six-pole over the four-pole construction would be in ob-
taining a machine which would give more than three times
full-load current on short circuit. It would possibly be as
easy to obtain four times full load current on short circuit
with a six-pole machine as to obtain three times full load cur-
rent on four-pole machine. An eight-pole machine would be
in the same way somewhat better than the six-pole machine.
Therefore if a 600 kilovolt-ampere machine giving six times
full-load current on short circuit is desired, it would be advan-
tageous to make the machine with possibly eight to twelve
poles. The question of which would be the cheaper would de-
pend upon a number of features in design.
If very large short-circuit currents are desired, then, as in-
dicated above, the number of poles for a given capacity should
be increased, or the normal rating of the high-speed machine
should be decreased. If, for example, the 600 kilovolt-ampere,
3600 rev. per min. machine, mentioned above, should be rated
at 200 kilovolt-amperes, then it could give nine times full-load
current on short circuit; but such a method of rating is merely
dodging the question.
In general, the following approximate limits for speeds and
short circuit currents for 60-cycle apparatus can be given.
These limits are necessarily arbitrary, and are intended to rep-
resent machines which could probably be made without using
too abnormal dimensions;
600 kilovolt-amperes, 3600 rev. per min., two to three times
full-load current on short circuit.
1000 kilovolt-amperes, 1800 rev. per min., three to four
times full-load current on short circuit.
1500 kilovolt-amperes, 1200 rev. per min., four to five times
full-load current on short circuit.
2500 kilovolt-amperes, 900 rev. per min., four to five times
full-load current on short circuit.
For 25 cycles it is more difficult to give limiting conditions.
296 HIGH-TENSION TRANSMISSION.
as the choice of speeds is very narrow. If, for example, a 1500
kilo volt-ampere, 2-pole, 1500 rev. per min. machine can be
made to give three times full-load current on short circuit,
then as machines of smaller rating cannot run at higher speed,
the limiting condition of such machines must be the amount
of current which they will give on short circuit. In the same
way a 4-pole machine running at 750 rev. per min. may be
made for 6000 kilovolt-amperes for three times full-load current
as the Hmiting rating, and there is no choice of speeds for
ratings between 1500 kilovolt-amperes and 5000 kilovolt-amperes.
It should be noted that the above speeds are very high com-
pared with ordinary alternator practice and are up to high-
speed turbo-generator practice, but machines with the above
short-circuit ratings and speeds are probably more costly to
btiild than machines of corresponding ratings at somewhat
lower speeds. It will probably be found therefore that for
the above maximum current on short circuit the cheapest
synchronous motors for the given ratings will have somewhat
lower speeds than those indicated above. It is certain that
the lower-speed machines will be easier to design and will be
slightly quieter in operation. Probably best all-round condi-
tions will be found at about half the above speeds.
The above limiting conditions are given as only approxi-
mate and are based upon machines having ventiliation as is
usually found on rotating-field generators for high speed. Arti-
ficial cooling, such as obtained with an air-blast or blowers,
could modify the above figures somewhat; but in general it
has been found that high-speed alternators can be worked up
to the limit imposed by saturation before the limit imposed
by temperature is attained. Therefore if higher saturation is
not permissible, then there may be relatively small gain by
using artificial cooling.
Synchronous Motors on Long Transmission Lines.
One of the principal applications of such regulating syn-
chronous motors would be for controlling or regulating the
pressure at the end of a long transmission line for maintaining
constant pressure at the end of the line, independent of fluc-
tuations of load or change of power-factor. In this case, in-
creased output of the transmission line may more than con-
pensate for the cost of the regulating synchronous motor. In
such a case the synchronous motor not only acts as a regulator
on the system but costs nothing in the end. In general, the
more current that such a synchronous motor will give on short-
POWER-FACTOR AND LINE PRESSURE. 297
circuit, the better suited it will be for its purpose at the end
of a long transmission line.
Where a number of such synchronous motors are installed
in the same station, the field adjustment must be rather care-
fully made, to avoid cross-currents between machines; and the
saturation characteristics of the various machines should be
very similar. The better such machines are for regulating
purposes, the poorer they are for equalizing each other by
means of cross-currents.
As to the use of dampers with such synchronous motors,
it is difficult to say just what is required. A synchronous
Kiotor on a line with considerable ohmic drop is liable to hunt
to some extent, especially if the prime mover driving the gen-
erator has periodic variations in speed. If the synchronous
motor gives very large current on short circuit, then its syn-
chronizing power is high ; this will tend to steady the operation
of the motor and decrease the hunting. The writer believes
that such motors in practice will be found to operate better
and have better regulating power for constant pressure if pro-
vided with rather heavy copper dampers effectively placed on
the field poles. With such heavy dampers reaction of the
armature on the field is retarded, and therefore the armature
may give a larger momentary current than would flow if there
were no damping effect; in other words, the motor is more
sluggish than one without dampers. Therefore the addition
of heavy dampers on such a machine may produce the same
regulating effect which would be obtained by a machine without
dampers which gives a larger cu-rrent on short circtdt. Also
a machine with heavy dampers will usually be the one with
the least hunting tendency and therefore will have the least
e-Sect on the transmission line due to hunting currents.
A Synchronous Machine as Regulator and Motor.
In the above, the synchronous motor has been considered
o.nly as a regulator and not as a motor. It may be worth
considering what would be the effect if the synchronous motor
can do useful work at the same time that it regulates the
system. In this case, with a given rated output, one com-
ponent of the input will be wattless, and the other part will
be energy. The ratio of these two components could be varied
as desired. For example, considering the input as 100, the
wattless component could be 60 when the energy component
is 80; or the synchronous motor could carry a load of 80%
of its rated capacity, this load including its ownJosses, and could
298 HIGH-TENSION TRANSMISSION.
have a regulating component of 60% of its rated capacity.
If the motor is used as a regulating machine only, then its
wattless component can be practically 100. It appears there-
fore that the machine could be used more economically as both
motor and regulator than as a regulator alone, but in such case
it would probably be advisable to run the motor at somewhat
lower speed than if operated entirely as a regulator. This
reduction in speed may practically offset the gain in apparent
capacity by using the machine for a double purpose. Also
there is comparatively Umited use for large synchronous motors
for power purposes, as better results are usually obtained by
subdividing the units and locating each unit nearest to its
load. If a load could be provided which would permit very
high-speed driving, then it would probably be of advantage
to utilize the synchronous motor for driving.
Synchronous Converters as Regulators.
As the synchronous converter is one form of synchronous
motor, the question of utilizing such machines for regulators
should be mentioned. Upon looking into the question of dis-
tribution of losses in the converter, it will be noted that the
losses in the armature winding are not uniform. Investigations
show that at 100% power-factor the lowest heating in copper
is obtained, and that any departure from this power-factor
shows considerably increased loss in the copper, such loss being
very high in certain portions of the winding. Next to the
taps which lead to the collector there are strips of winding
which at times are worked at a very high loss. Experience
shows that it is not advantageous to operate converters at a
low power-factor, and that if so operated continuously, or
for any considerable periods, the winding should be made much
heavier than for higher power-factors. Also in the usual de-
sign of converters the field is not made as strong compared
with the armature as in alternator practice, and therefore the
regulating tendency of the converter compared with a generator
or ordinary synchronous motor, is low. Synchronous con-
verters can and do act as regulators of pressure for sudden
changes of the supply pressure, but such correcting or regu-
lating action should not be continual; that is, the pressure
suppUed to a converter from a line should nominally be that
required by the converter for best operation as a synchronous
converter. Unless designed for the purpose, a synchronous
converter should not be used to correct low power-factors
due to other apparatus on the circuit.
POWER-FACTOR AND LINE PRESSURE. 299
Relative Costs of Synchronous Motors as Regulators.
In the above considerations only general reference has been
made to the cost of synchronous motors for regulating pres-
sure and power-factors. It is difficult to give even approxi-
mate fig;ures for relative costs of such apparatus. As inti-
mated before, there is some mean speed or number of poles
which will be the most suitable for giving a certain maximum
current on short circuit. For speeds slightly above or below
such mean speed, the cost of the synchronous motor should
vary almost in proportion to the speed, provided the maximum
short-circuit current can be diminished somewhat at the same
time. If the speed is further increased or further decreased,
the cost will tend to approach a constant figure. As the ex-
treme conditions are approached, the cost will begin to rise.
The above assumptions are on the basis of continuous opera-
tion at a given current capacity, this being the same in all cases.
The above asstunption is on the basis of decrease in the max-
imum short-circuit current, as the machine departs from the
mean, or best speed. If the same maximum current is re-
qiured, then the lowest cost should be at the mean or best
speed, while at either side the cost should rise.
It is evident that it would be difficult to give any figures on
relative costs of such apparatus. The machine for the best
or mean condition, should cost practically the same as an alter-
nating-current generator of the same speed, output, and short-
circuit characteristics. As this speed would probably be some-
what higher than usual generator speeds, the cost of such
machine would therefore be somewhat lower. This cost would
be to a considerable extent, a function of the current on short
circuit for a given rated capacity of machine. As mentioned
before, in giving a table of limiting speeds and short circuits,
it is probable that one-half this Umiting speed would be near
the best condition. .Such machines would probably cost from
60% to 80% as much as similar machines for usual commercial
high-speed conditions, neglecting turbo-generator practice. The
frequency has considerable effect on this, as, for example, there
is small choice of speed as regards high-speed 25-cycle machines.
Taking very general figures only, it is probable that in the
case of a given capacity of machine for say three or four times
full-load current on short circuit the cost cannot be ex.pected
to be lower than one-half that of machines of similar rating at
ordinary commercial speeds, turbo-generator practice being ex-
cluded. The costs in general should approximate more nearly
300 HIGH-TENSION TRANSMISSION.
those of turbo-generators; but again, an exact comparison
cannot be made because in usual practice the turbo-generators
do not give three to four times full-load current on short circuit.
Some Other Elements in the General Problem.
There are a number of other conditions in this general problem,
such as the advantage or disadvantage of placing synchronous
motors in the main power-house, or distributing them in a
number of sub-stations. Also there is the question of the effect
of the cost on the generating plant when used with such regu-
lating synchronous motors. If higher power-factors are main-
tained on the transmission system and generator, a cheaper
form of generator can probably be used. The high power-
factor permits a larger output from the transmission system
and thus represents a gain. If the synchronous motor can be
operated at its best speed and also do work, then there is a
further gain. If the synchronous motor should be located at
the center of power distribution, and the power is distributed
throughinductionmotors, then there is a possibility of reducing
the cost of such motors by designing them for a lower power-factor,
this being compensated for by the synchronous motor deliver-
ing leading currents. As the cost per horse power of small
motors will be much greater than the cost per horse power of
a large regulating motor, there is a possibility of gain from this
source. If the induction motors are distributed over wide
territory, this gain would be lessened and might disappear.
It should be mentioned that the power-factor of a system
as influenced by difference in wave form has not been con-
sidered in the preceding discussion. It is obviously impracticable
to neutralize by a synchronous motor the effect of currents
in a system due to difference in wave form. Such currents will
in general be of higher frequency than the fundamental wave
of the system, and the synchronous motor obviously could not
correct for them, unless it impressed upon the system opposite
waves of the same frequency. This would mean a synchronous
motor with a different wave form from that of the system.
The power-factor of a system will also be affected by any
hunting of the apparatus on the system. It is evident that
the synchronous motor could not correct or neutralize such
effects, except through exerting a damping effect on the system
and other apparatus on the system. A synchronous motor
with heavy dampers can reduce the hunting in a system, but
such hunting can also be damped by induction motors with
low-resistance secondaries, especially if of the cage type. This
POWER-FACTOR AND LINE PRESSURE. 301
correcting effect should therefore be credited to the damper
rather than to synchronous-motor action. There are a number
of other questions which arise in connection with this regu-
lating feature of the synchronous motor, but the subject is too
broad to permit even mention of them.
Summary.
The substance of the preceding statements can be summarized
as follows:
1. A synchronous motor can be used to establish leading or
lagging currents in its supply system by suitable field adjust-
ment, and can thus affect or control power-factor or phase
relations of the current in the alternating-current system.
2. A synchronous motor will set up leading or lagging cur-
rents in its supply system if its field strength is held constant,
and the pressure of the supply system is varied above or below
that generated by the synchronous motor. Such leading or
lagging currents in the supply system will tend to vary the
pressure of the system. A synchronous motor can thus act
as a regulator of the pressure of its supply system.
3. This regulating action is greatest with synchronous motors
which have the closest true inherent regulation (as indicated by
high field magnetomotive force compared with the armature
magnetomotive force) in distinction from machines which have
close apparent regulation obtained by saturation of the mag-
netic circuit.
4. If the synchronous motor is used both for regulating the
power-factor for neutralizing the effect of other apparatus on
the circuit, and for regulating or steadying the pressure of
the supply system, its normal capacity for regulating will be
diminished.
5. The most suitable speeds for best electrical conditions
will in general be considerably below highest possible speeds
as limited by mechanical conditions.
6. Heavy dampers will increase the effectiveness of the reg-
ulating tendency.
7. If the synchronous motor can be used for power purposes
as well as for regulation, its apparent capacity is increased.
This is due to the fact that the regulation is obtained by means
of a wattless component and the power from the energy com-
ponent, and the arithmetical sum of these two is greater than
their resultant which fixes the current capacity of the machine.
8. Synchronous converters in general are not suited for reg-
302 HIGH-TENSION TRANSMISSION.
ulating the pressure or controlling the power-factor of an alter-
nating-current system.
9. The costs of synchronous motors for regulating purposes
will in general be lower than for alternating-current motors
or generators of customary speeds, and will approach more
nearly to turbo-generator practice.
POWER-FACTOR AND LINE PRESSURE. 303
Discussion on " Synchronous Motors for the Regulation
OF Power-Factor and Line Voltage."
P. O. Blackwell: In a large plant it is an unnecessary ex-
travagance to figure the copper for a low power-factor when
the power-factor can be made 100% by adding leading current
to the lagging current caused by induction motors. Even a
small lagging power-factor increases the amount of copper
very greatly for any assumed regulation.
Rotary condensers are also of great advantage in permitting
the pressure of a power transmission system to be regulated
at the centre of distribution. It would be perfectly possible
to run a power transmission system with rotary condensers
in the sub-station without any communication between the
sub-station and the distant power-house. The first case of
the use of a rotary condenser that the speaker knows of was
in a Southern cotton-mill which was equipped with about
4000 h.p. of induction motors and 3000 h.p. of generators.
The pressure and the current at the generators was excessive
on account of the low power-factor of the load and something
had to be done to relieve the apparatus. By installing a
rotary condenser of 500 apparent kilowatts capacity in the
mill the pressure at the generator, if the speaker remembers
correctly, was cut down about 15% and the current was re-
duced about 20%." The rotary condenser also greatly improved
the regulation of the system and avoided the installation of a
new generator in the power-house, which would have other-
wise been necessary and would have cost several times as
much as the rotary condenser.
A 6000 h.p. plant in India, which transmitted power
90 miles, reached the limit of its capacity. The owners de-
cided to increase its capacity by installing a 1000-kw. rotary
condenser, and they have been enabled to transmit 50% more
power over their existing line, with the same regulation as
they had originally with the smaller amount of power. If it
had not been for the rotary condenser they would have had
to construct an entirely new transmission pole-line.
It is possible not only to maintain 100% power-factor in a
transmission system, but also a leading current which will
boost the pressure over the reactance of the line and step-up
and step-down transformers, so that you can have as high a
pressure at the sub-station as at the power-house, or even a
higher pressure.
Of course, if a synchronous motor can be used to do useful
work it is more economical than a rotary condenser. The
most efficient power-factor would be 70% leading, at which
point the energy and wattless components of the current are
equal. You would then get 70% of the rated capacity of the
motor for work and 70% for rotary condenser action.
As Mr. Lamme has pointed out, the high-speed, steam-
turbine alternator is not the cheapest machine that can be de-
304 HIGH-TENSION TRANSMISSION.
signed. A speed of about one half that used in turbo-alter-
nators avoids all extreme strains which require special mate-
rials and methods of construction and is therefore more eco-
nomical in design.
W. L. Waters: This paper is a suitable sequel to the paper
which Mr. Lincoln read last year on the " Choice of Frequency
for Transmission Lines." Mr. Lincoln showed that if the
power-factor on a transmission line was low, the amount of
power which could be transmitted over that line, with reason-
able regulation, was surprisingly small, and it followed from
this that the power-factor should be kept as near as possible
to unity.
Mr. Lamme is not quite clear when he describes the effect
on the regulation of an over-excited synchronous motor. The
beneficial effect of a synchronous motor is' entirely due to the
leading current, which it takes from the line. The amount
of leading current which a motor can take from the line is
decided by two things: 1. the margin in ampere-tums, which
we have on the magnets. 2. the current in amperes, which
the armature can carry.
Both of these are limited by the heating of the magnets
and armature, so that, if we are manufacturing a synchronous
motor for regulating the pressure on the transmission line,
the correct rating of that machine should be the amperes of
leading current which it can take when running at a given
pressure without the temperature rise of the magnets or arma-
ture exceeding 40° cent. The normal rating of the machine
and the short-circuit current tell you very little as regards
the value of the machine for producing leading currents. We
might have a large motor capable of giving a large short-circuit
current, which, at the same time, was valueless for pressure
regulation on account of the fact that we could not over-excite
the magnets because their temperature rise was already high.
As the rating of the motor, as above suggested, is entirely
limited by temperature, the force of Mr. Lamme's remark
that turbo-alternators are unsmtable for this work becomes
very plain. Those who have had experience with these very
high-speed machines know that the great difficulty in designing
them is to obtain low temperature rises, especially on the
field magnets. The other objection to high-speed machines,
that they are less reliable in operation, is not of much im-
portance in the case where these motors are used exclusively
for regulation of the power-factor. So considering only the
question of temperature rise, probably the most economical
machine would be one in which the output was about 250 kw.
per pole in a 25-cycle machine and about 125 kw. per pole, in
the 60 cycle.
Mr. Lamme calls attention to the inherent regulating power
of a synchronous motor. This effect certainly exists, but
under ordinary conditions it is unimportant, and the main
POWER-FACTOR AND LINE PRESSURE. 305
use for the synchronous motor as a pressure regulator would
^be as a hand-operated regulator. In this respect, Mr. Lamme's
statement that " the motor should preferably be one in which
the magnetic circuit is not highly saturated," is incorrect,
because a motor which had saturated magnets would have a
much greater inherent regulating capacity than one in which
the magnets were unsaturated; if the motor were infinitely
large and perfectly saturated its inherent regulating capacity
would be perfect. This statement, as regards unsaturated
field magnets, is also incorrect if we consider the motor as
being hand regulated, because the effect is one of ampere-
turns and not of magnetic flux; that is, assuming the magnetic
leakage is not excessive.
The effect of copper dampers on the pole pieces is only a
time effect. They slightly delay the effect of a sudden rush of
leading or lagging current, but in any case this effect only
applies to the inherent regulating automatic action of the
machine, so that for all practical purposes the effect of dampers
on the pole pieces can be neglected, except as regards their
effect on the hunting of the system. In regard to this hunting,
Mr. Lamme's statement that squirrel-cage induction motors
are more powerful as dampers than motors with coil-wound
secondaries and collector rings, is not correct. The damping
effect of an induction motor is greater the lower the resist-
ance of the secondary. If we consider modem commercial
induction motors, that is, motors capable of starting under
full load without taking excessive current, then the resistance
of a squirrel-cage secondary is about five or six times that
of a coil-wound secondary with short-circuiting device, and
in consequence the damping effect of the squirrel-cage arma-
ture would be proportionately less.
The question of the use of a synchronous motor running
light as a pressure regulator is entirely a commercial question,
and the advisability of its use in any particular case must
be decided by the question whether the cost of this motor is
more than compensated for by the increased output obtained
from the line.
H. B. Gear: This question has been discussed thus far
with reference to the compensation of systems where the low
power-factor was due to lagging current.
In a system operating at 40 000 volts with 200 miles of
line the conditions may be reversed, the low power-factor
being due to the component of leading current caused by the
charging of the line. In such a system the kilovolt-amperes
required to charge the lines amount to about 1800. It there-
fore requires a load of 3000 kilovolt-amperes at 80% lagging
to bring the power-factor of this system up to 100%.
The use of a synchronous motor in compensating for a low
power-factor on such a system would therefore be limited
to the compensation of leading current up to the point where
306 HIGH-TENSION TRANSMISSION.
the loaa of induction motors reached 3000 kilovolt-amperes.
Under certain conditions it might therefore be possible to in-
stall a synchronous motor of relatively small capacity, using
it during the light-load period to compensate for leading cur-
rent and during the heavy-load period to compensate for lag-
ging current.
W. B. Jackson: All of us must appreciate that this paper
upon synchronous motors is an excellent and timely one. Al-
though the question as to the proper use of synchronous ap-
paratus has been recognized as quite important for a number
of years, yet it is assuming much greater importance as the
great transmission systems are becoming more common.
One phase of the use of synchronous motors has not been
touched upon in the paper. In the construction of our power
transmission plants receiving their power from water, it is not
unusual for the hydroelectric portion of the plant to be devel-
oped to a point far beyond the minimum capacity of the water.
Consequently an auxiliary steam plant is installed to assist
during low-water periods. Under such conditions there is
often an excellent possibility for the plant to be so designed
that the generators in the steam department may be used for
balancing motors during the time of heavy load upon the
hydraulic plant. It is readily appreciated that at times of
low water or of serious back-water conditions the transmission
department of the system will be lightly loaded and that,
therefore, ample electrical capacity will be at hand to take
care of a lower power-factor without difficulty so far as the
transmission department is concerned, and at the same time
we have the steam auxiliary in operation which will act as the bal-
ancing factor upon the system.
Why should not any such plant be so arranged that the
engines and generators can be readily disconnected during
the times when balancing by synchronous motors is desirable?
In other words, when we have the transmission side of the
system loaded to its utmost capacity? There is no reason
why the possibilities of our auxiliary generator as a balancing
motor should be lost sight of simply because it is normally
connected to an engine. It is not at all difficult to arrange
to disconnect these alternators from the engines and use them
for balancing machines, thus making a double use of the ap-
paratus that is installed for the auxiliary plant.
The reversible use of alternating-current generators in trans-
mission plants, either as generators or motors, as the occasion
may require, is not uncommon, but the reversible use of the
machines as generator or balancing device is quite a different
question.
Reference is made in the paper to the possibility of so in-
stalling synchronous motors upon the circuit that they may be
caused to hold the pressure at the end of the line as high or
even higher than that of the generators. There are several
POWER-FACTOR AND LINE PRESSURE. 307
plants where such use has been made of synchronous motors
for years past; in fact, there are two plants that the speaker
knows of where it has been customary to. operate generators
at approximately the same pressure as at the distributing end
of the line, these being plants where a large part of the capacity
of the plant was supplied to synchronous motors, and where
it was possible to get into communication with the several
synchronous motor installations without difficulty from the
power-house. It would probably not be difficult to find plants
where it would be practically impossible to operate at all were
the synchronous motors now installed replaced by induction
motors.
F. A. C. Perrine: The suggestion Mr. Jackson has just made
is a very important one, and we all would perhaps be inter-
ested to learn that it has been quite extensively used in some
Western plants, and in connection with reserve steam ma-
chinery for compensating for large leading current on the
line, and also automatic compounding of the synchronous
motors. For example, in the steam station of the Oakland
Transit Company, Oakland, California, supplied by the Old
Bay Counties system, transmission of 140 miles, they were
compelled to have a steam reserve, on account of fluctuations
in pressure. F. H. Baum, one of our members, was called on
to determine what could be done, as on account of the very
heavy leading current when the load wac light the pressure
went up, and when the load was heavy the pressure went down.
The fluctuations of the pressure were of a serious nature.
Mr. Baum compounded the exciter for the synchronous
motors by the direct current, using an extra winding on the ex-
citer, and he arranged this compounding so as to maintain
a constant pressure on the system and almost a constant power-
factor automatically without any hand regulation of the ma-
chine or the synchronous motors. He found, furthermore, by
examination with an oscillograph, that Mr. Lamme has ap-
parently not made himself understood on page 300, as he
says it is not possible by means of the synchronous motor to
correct errors in wave form. In the latter part he says;
" such currents will in general be of higher frequency than the
fundamental wave of the system, and the synchronous motor
obviously could not correct for them, unless it impressed upon
the system opposite waves of the same frequency. This would
mean a synchronous motor with a different wave form from
that of the system." That is exactly what the synchronous
motor does at the end of a long line ; at the end of a long line
the initial wave form is very seriously distorted, and the syn-
chronous motor having a wave form similar to the generator
corrects for the variation induced at end of the line.
Again, in some of the mining plants supplied from long-
distance transmission lines where the charge has been made on
the basis of the maximum current, they have found it advan-
308 HIGH-TENSION TRANSMISSION.
tageous to install synchronous condensers for maintaining high
power-factor, the plant being operated by induction motors,
the synchronous condenser being used as a reserve steam gen-
erator when, by reason of any accident, the power from the
transmission line was interrupted.
As regards small plants where it is necessary to maintain
a constant power-factor — and the power-factor is already rea-
sonably high, due to the use of lighting load entirely — the
synchronous motor as a regulator can be conveniently used,
especially where a combined railroad and lighting load are
operated from the same generator, and this again, by com-
pounding the synchronous motor through its exciter from the
direct-current end of the system. And again, this is used in
connection with the steam-driven alternator atixiliary ; that is,
where a large alternating-current generator is employed during
periods of light load, that load can be carried from a separate
steam-engine of lower capacity driving an alternating-current
generator. When the load rises beyond the capacity of the
small engine the latter can be cut off and the load carried from
the large alternator through the synchronous motor, the latter
being compounded through the direct-current side and thus
the power-factor maintained. This does away with the greatest
objection to the installation of synchronous motors; the use
of the synchronous motor gives the operator control of the
whole system.
The matter of cost as presented by Mr. Lamme is surprising ;
not because he states there is a certain speed at which we find
a minimum cost, but due to his statement that the cost of
the synchronous converter will be from 60 to 80 per cent, of
the cost of an ordinary-speed generator. If we take a gen-
erator having about 100 revolutions per minute, cost will be
about ten dollars a kilowatt, while high-speed machines recently
sold for four dollars a kilowatt. And this shows, furthermore,
that the use of the synchronous motor as a condenser is about
as cheap a regulating machine as can very well be obtained.
It is a question whether in large sizes there can be built any
hand-regulating induction regulators that will cost much less
than four dollars a kilowatt, at which to-day these large high-
speed machines are actually being sold, and that makes a mini-
naum cost of a high-speed machine about 40 per cent, of the
cost of the ordinary-type machine, rather than 60 per cent.
The general question is an exceedingly important one, taken in
conjunction with the fact that it is possible by the use of these
synchronous condensers, especially when connected with direct-
current machines, to automatically compound; the same auto-
matic compound may be produced through the exciter by
means of the Tirrell regulator or some other regulator cf
this form. And when we get away from the difficulty and
the inaccuracy of hand regulation, we have overcome the
most serious objection that has been raised in any of the dis-
cussions on the employment of the synchronous condenser.
A paper presented at the iSSth Meeting of the
American Institute of Electrical Engineers^
Chicago^ June 21-23^ iqo4.
Copyright, 1904, by A. I. E. E.
LONG SPANS FOR TRANSMISSION LINES.
BY F. O. BLACKWELL.
Many cities to-day are dependent for their lighting, trans-
portation, water supply, and the operation of their industries
upon electric power transmitted over considerable distances.
Unfortunately interruptions of the power service do occui
not infrequently and when they do happen they so inconven-
ience the public as to be most conspicuous. The impression
that long-distance power transmissions are unreliable has some
basis of fact that seriously interferes with their development.
Although absolutely continuous service may not be possible,
many of the troubles now experienced can be either altogether
eliminated or greatly reduced. Among the. principal causes
of interruption, so far as the line is concerned, may be men-
tioned :
Short circuiting of lines by branches of trees, wires, or by
large birds getting across them.
Burning of wooden pins, cross-arms, and pole-tops by leakage
or electrostatic discharges from the conductors.
Burning of wooden poles at the ground from forest or prairie
fires.
Failure of insulators from puncture by the current, or their
destruction by missiles, discharged maliciously.
Lightning damaging the apparatus connected to the circuits
and sometimes destroying poles.
Accidents due to heavy winds overturning the poles or to
floods washing them out.
The deterioration of a line requires its replacement in from
five to twenty years, depending on climatic conditions and
the material which is used in its construction. This replace-
309
310 HIGH-TENSION TRANSMISSION.
ment of the poles with new ones can only be done by shutting
ofE the current or at the risk of accidental interruptions.
Let us see what can be gained by substituting a steel
tower construction with long spans for a wooden pole line.
Short circuits are by far the most common difi&culty, the only
remedy for which is to put the wires so far apart that they are
unlikely to be bridged across. This can readily be done even
with more than one circuit when a steel cross-arm is employed.
Burning is of course entirely done away with where metal
construction is used.
Failure of insulators from electrical causes can be obviated by
getting larger and better insulators; this is practicable where
the spans are long and the number of insulators is small. In-
sulators on high towers are much poorer targets than when
they are near the ground and so are less liable to be broken.
Each metal tower is a lightning-arrester and as they are the
highest points in the line they materially assist in its discharge ;
the tower itself, being a conductor, cannot be injured by light-
ning. Steel structures can be exactly figured to meet safely
any strains that can come upon them and can generally be
located only at safe places where there is no danger of washouts.
The deterioration of a properly constructed and well-galvanized
steel tower is very slight, as is proved by marine and windmill
experience, and is practically negligible so far as the pins and
cross-arms are concerned. Any part of a steel tower can be
readily removed and replaced without interrupting the service.
By far the greatest gain obtained from long spans is in the
reduction of the number of parts. If one insulating support
takes the place of four or five, line troubles will be reduced
nearly in direct proportion ; the inspection and repair of the line
will be much simplified and its cost of maintenance corre-
spondingly diminished.
Cost of Towers.
The cost of a tower construction as compared with wooden
poles depends on the locality. Where the right kind of tim-
ber exists, it is of course cheaper; but in tropical countries
where wooden poles would have to be transported long dis-
tances the towers are much less expensive. In addition, to
obtain long life a creosoted wood only could be employed and
this still further increases the expense. The fewer insulators
and pins and the ease of transportation and erection are in
favor of towers. They can be packed in light bundles suitable
LONG SPANS. 311
for mule-back transportation and quickly put together even in
the most inaccessible places. Even where the cost of the
tower construction is more it is often justified by the greater
certainty of operation which it insures and the lower cost of
maintenance.
Strength of Conductor.
The first and most important consideration for long spans
is the material of the conductor. Copper, aluminum, and
iron are availiable for this purpose. Various alloys of copper
have great strength, but their conductivity is too low and
their cost too high to compare favorably with the more common
metals. Copper wire varies widely in its characteristics, de-
pending on the methods used in its manufacture. The copper
is received at the wire-mill in the form of cast-wire bars weighing
300 to 350 lb. It is then rolled into rods and the rods are
drawn into wire of the required size. The temperature at
which the metal is rolled, the reduction of area both in rolling
and drawing, and the amount of annealing which the wire is
given — all have an important bearing on its characteristics. As
the size of the original wire bar is limited, the smaller the wire
the more it is worked and in general the better the result.
Cable made up of several strands has the advantage of using
smaller wires than a solid conductor, and also permits of longer
lengths of conductor without splices. Assuming a 300-lb. wire bar,
a 19-strand cable, for example, can be made up weighing 5700 lb.
while if solid wire were used the weight of one piece would be
300 lb. In other words, there would be 19 times as
many joints with the sohd wire as with the 19-strand
cable. The smaller the wire and the greater the strength, the
more brittle it becomes. This is partly compensated for by
the greater flexibility of a cable and the fact that a strand can
break without the whole conductor parting.
Each strand should be a continuous wire without joints.
Joints in the cable should be as few as possible and made by
means of sleeves, as brazing or soldering anneals the wire and
much reduces its strength. The permissible tension in the
cable must not exceed the elastic limit, by which is meant the
point at which the material will continue to elongate and will
eventually break, and not the usually accepted meaning of elastic
limit as that point at which the strain ceases to be proportional
to the stress. Copper cable recently made for a transmission
plant with spans of 500 feet had an elastic limit of 40 000 lb.
312 HIGH-TENSION TRANSMISSION.
per square inch; similar aluminum cable had an elastic limit
of 12 000 to 14 000 lb. per square inch; galvanized-iron tele-
graph wire has an elastic limit of 35 000 lb. The ultimate tensile
strengths of these wires were 60 000 lb. for copper, 24 000 lb. for
alumintim, and 55 000 lb. for iron.
The advantage of aluminum is that it weighs less than copper
for the same conductivity, but for long spans its lesser strength,
greater diameter, and higher coefficient of expansion are against
it. Steel wire has about nine times and iron wire or cable
about six times the resistance of copper so that they are more
expensive as a conductor than copper. In order to avoid
oxidization it is necessary to galvanize iron or steel wire; which
partly anneals it and reduces its strength. There are cases
where the size of high-pressure line conductors is determined
not by resistance but by mechanical strength, and in such
cases iron or steel wire can be used to advantage.
Elasticity.
The elasticity of the conductor is of considerable value in
reducing the sag when the stress is removed, as will be shown
later. The elongation of the wire under stress is less after it
has once been stretched. The elasticity of cable is greater than
that of solid wire, but both wire and cable take a set under any
stress to which they may be subjected. In the following table
is given the modulus of elasticity of copper, aluminum and iron
wire.
Copper hard-drawn wire 19 500 000
Aluminum hard-drawn wire 10 200 000
Iron telegraph wire 24 000 000
Copper hard-drawn cable wire 16 300 000
Each sample was stretched to a point somewhat below its
elastic limit before testing. It will be noted that the copper
cable is considerably more elastic than the solid copper wire,
the latter being a strand of the cable. The aluminum wire
was of nearly the same conductivity as the copper-wire strand
and presumably would have had a lower modulus of elasticity
if made up into cable. Aluminum is considerably more eaastic
and has a decided advantage over copper in this respect.
Coefficient of Expansion.
The coefficients of expansion for Fahrenheit degrees are as
follows:
Copper 0.0000096
Aluminum 0.0000130
Steel 0.0000064
LONG SPANS. 313
As the worst condition so far as sag is* concerned is readied
when the conductor is hot, a low temperature expansion is
most desirable for long spans, and steel is fti this respect better
than either copper or aluminum.
Strains in Conductors.
The strains upon the conductor are those due to its own
weight and the wind acting upon its surface. In a cold climate
in addition sleet may form upon the wire, increasing the weight
and the surface exposed to the wind. On a line carrying any
considerable amount of power it is improbable that sleet will
ever form, the formation being prevented by heat due to losses in
the conductor. In order to be on the safe side, however, it is best
to assume in the North a coating of ice one inch thick all around
the conductor. The wind velocity could never exceed 100 miles
an hour which would give a pressure of 40 lb. per square foot
on a fiat surface, or 20 lb. on a cylindrical surface such as that
of a wire. The weight is of course a vertical stress and the
wind a horizontal one at right angles to the wire. The greatest
strain is caused by the resultant of these two. The worst con-
ceivable condition is sleet on the wire, followed by extreme
cold weather with high winds. Under such conditions the
probabilities are that the ice on the conductor would break
off, but without some data on the subject it is hardly safe-
to assume that this would be the case. In warm climates the
absence of sleet and the lesser range of temperature make
permissible longer spans than in cold climates.
Sag of Wire.
The maximum sag may be due to the conductor being loaded
with sleet or to heating of the wire in a hot sun. The latter will
generally be found to give the greater sag. Owing to the con-
ductor being elastic it is not necessary to consider the greatest
deflection from a horizontal line between supports as the ver-
tical sag of the wire. The wind pressure causes the wire to
swing to one side and it is elongated by the combined strain of
wind and weight, but as soon as it is relieved of the wind pressure
it swings back to a vertical position and contracts to the length
required to carry its weight alone. The sag due to heating
of the wire is also somewhat less than it otherwise would be,
because when expanded the strain is less and the wire contracts.
The extreme variation of the temperature of the air in cold cli-
mates is about 150° fahr., while farther south it does not exceed
100° fahr. ■ To this must be added something for a metal con-
314
HIGH-TENSION TRANSMISSION.
ductor exposed to a hot sun. There are no data upon this but
a total variation in the temperature of the conductor of 175°
fahr. should be sufficient in any country.
Span and Sag Curves.
The attached curves of span and sag are based on the fol-
lowing data:
Aluminum Copper
Area 6-strand cable 0.21 sq. in. 0. 132 sq. in. i
Diameter 6-strand cable . 59 in. 0.51 in.
Weight per foot 0.240 1b. 0.509 1b.
Elastic limit. 12 000 lb. 40 000 lb.
100
Span
md Maxlni|uin Sag of
3opr«
r
/
/
90
1
Jpper
jower
Curve
Curvt
isbas
isbaf
edon
ttaxim
Maxiil
umSt
um S
resso
resBD
20C00
1 10001)
lbs, pe
Jbs.p
rsq. :
srsq.
u.
/
80
/
70
/
60
/
/^
/
60
/
y"
y
40
ffl
A
^
^
30
a
bn
A
y
^-
20
^
^
' 1
^
^
10
2
U
^■^
6
Sl
an in
S
feet
10
00
12
10
y-
)0
Fig. 1.
Stress at 1/2 elastic limit 1267 lb. 2640 lb.
Stress at elastic limit 2534 lb. 5280 lb.
Wind pressure per sq. ft 40 lb. 40 lb.
Wind pressure per ft. cable . 98 lb. . 84 lb.
Coefficient of expansion 0.000013 0.0000096
Variation in temperature 150° fahr. 150° fahr.
Modulus of elasticity 8 000 000 16 000 000
The equations from which the curves were calculated are given
below and alongside of them is an example of a 1000-ft. copper
span.
5^XW 1000^x0.98
^ 8 7 8x2640 ~ *''-^"-
LONG SPANS.
315
In which D = deflection in ft. "^
S = span in ft.
W = resultant of weight and wind in lb. per ft. of cable
and
T = stress allowed in cable in lb.
L ^ S +
8D^
1000 +
8x46.4'
3S ^ ' 3x1000
In which L = length of cable, cold.
L 1005.74
= 1005.74 ft.
Lo =
1 +
E
1 +
20 000
16 000 000
= 1004.38 ft.
i'oo
Spai
and.
Maxil
lum Sag of| Alun
liBun
/
/
90
trpp(
Lowf
rCur
r-Our:
60001
leisb
42000
isedo
38. pe:
ised.o
bs.-pi
a Miaximuui
scj.in.
aMamnum
stress
itreaa
/
/
r —
80
r Bq. .1
X.
/
/
/
70
/
/
/
60
/
/
/
50
/
/
/
40
f
/
/
/
30
4
/
/
y
^
20
y
^
y
10
2
tr^
i
6
ipan
8
Q tee
10
)0
12
)0
1'
00
Fig. 2.
In which Lj, = length of cable without stress
F = lb. per sq. in. permitted in cable
and £ = modulus of elasticity
Lh = Lo(l + C"S) = 1004.38 (1 + 0.000009 x 150). = 1005.81 ft.
In which Lh = length of cable, hot (150° fahr. rise in temperature)
C = coefficient of expansion
and B = maximum degrees F. rise in temperature
D^ + ^iS-U)D= 64EA
D» +
3x1000
8
(1000 - 1005.81) D
D^ - 2178.7 D
^ 3x1000^x1005.81 W
64x16 000 000x0.132
22323 W
31G HIGH-TENSION TRANSMISSION.
In which A = area of cable.
From this equation any deflection of the cable can be assumed
and the corresponding weight calculated. For instance, in
the example if D = 48.8 ft., W= 0.51 lb.; that is, the sag hot
without wind is 48.8 ft., and this is the maximum vertical de-
flection under the conditions assumed.
If D = 51.1 ft., W = 0.98 lb. which is the maximum deflec-
tion with wind but this is at an angle of 31° from the horizontal
and the vertical sag is only 26.6 ft.
The curves (Figs, land 2) give the maximum sag for copper and
aluminum cables at different spans with an increase of temperature
of 150° fahr. above the minimum temperature. The stresses at
the minimum temperature due to wind and weight are limited
to half the elastic limit in the upper curves and to the elastic
limit in the lower curves. The modulus of elasticity of the
copper cable was obtained by experiment, but that of the
aluminum cable was assumed by considering its elasticity to
increase as much as copper cable compared with solid copper
wire.
Height of Towers.
The height of towers is determined by the vertical sag and
the clearance required above the ground. If a telephone cir-
cuit is below the transmission wires the distance between the
telephone and power wires must be added. For instance, if
the maximum sag is 12 ft. the telephone 6 ft. below the power
wire and the clearance above the ground 20 ft., the tower must
evidently support the wires 38 ft. from the ground.
Insulators and Pins.
The insulators and pins must have sufficient mechanical
strength to bear the strain transmitted to them from the cable.
For example, in the 1000-ft. span just figured on the strain
would be 980 lb. per insulator 31° from the horizontal. A
properly-designed porcelain insulator will stand any strain that
the pin will bear without bending. A rigid cast-iron or steel
pin is therefore essential and can readily be obtained.
The Cross-Arms.
The cross-arm is of course subjected as a beam to the weight
and wind strains transferred to it from the cable, but in addition
there is a torsional strain due to the breaking of a conductor
that can best be borne by a pipe. The length of the cross-arm
should be sufficient to space the wires well apart and prevent
LONG SPANS.
317
short circuits either from objects thrown over the line or from
the wires swinging together. The former is the more important
and if a safe distance apart, say six feet, is chosen it will be
sufficient to guard against the latter, as on short spans with
relatively less distance between wires they invariably swing
together and never touch each other.
Construction of Towers.
The most economical tower construction is one in which the
— 8-£t. 4 I * 8-ft^--
Fig . 3 — Single circuit tower used with 448 ft. spans for the Guanajuato
Power and Electric Co . of Mexico .
spread of the legs at the ground is about one quarter to one
third the height of the tower. If a less spread is used, the
318
HIGH-TENSION TRANSMISSION.
weight of the legs becomes excessive and with a greater spread
the cross-bracing must be much increased in size. For a single
circuit the common windmill tower construction in which the
legs are locked together at the top has the advantage of reducing
the strains to a simple compression of the legs on one side and
Fig . 4 — Double circuit tower used with 440 ft. spans for the Guanajuato
Power and Electric Co. of Mexico.
tension on the other, the only function of the cross-bracing being
to prevent the legs buckling when in compression.
Where there are two or more circuits the length of the cross-
arm is so great as to require two points of support. The tower
LONG SPANS. 319
can then be made with a width at the top approximating that
at the bottom and the cross-bracing has to bear its full share of
the lateral strains. A truss construction with the fewest num-
ber of parts and opportunities for slack motion and racking of
the tower is preferable. Spreading the legs far apart obviates
the necessity for expensive concrete foundations, as the strains
can be made well within the limits which earth will stand in
compression and the weight of earth above the foot of the tower
is sufficient to prevent its pulling out of the ground. A heavy
galvanizing coating on the tower appears to be an effective
protection against rusting and avoids the expense of painting.
Fig. 3 shows the construction employed in the transmission
of 101 miles from Zamora to Guanajuato, Mexico, which was
the first transmission employing steel towers exclusively. The
towers were spaced 440 ft. apart and are designed for a single
circtiit.
Fig. 4 shows the tower which will be used for the transmission
of 90 miles from Necaxa to the City of Mexico, and 170 miles
from Necaxa to El Oro, Mexico. These towers will be spaced
500 ft. apart with occasional spans running up to 1000 ft.
The same tower will be used for the transmission of 90 miles
from Niagara Falls to Toronto but the distance apart will in the
latter case be 400 ft. on account of the possibility of sleet ac-
cumulating on the conduotors. There will be two circuits or six
wires on each tower and in both the Necaxa and Niagara Falls
transmissions noted above there will be two lines of towers
making four parallel circuits altogether.
This paper has been intentionally confined to the mechanical
construction of transmission lines which the writer believes is
more important now than the electrical side. To-day the
highest pressure employed is 60 000 volts and the longest trans-
mission 150 miles. There is nothing to prevent the use of
higher pressures and longer transmissions, provided reliability
can be obtained by a more permanent, substantial, and simpler
construction even if the expense is greater. The use of long
spans and metal construction is a most important step in the
right direction.
■620 HIGH-TENSION TRANSMISSION.
Discussion on " Long Spans for Transmission Lines. "
Ralph D. Mershon: At the bottom of page 309 Mr Black-
well says: " The deterioration of a line requires its replacement
in from five to twenty years." Presumably Mr. Blackwell
refers only to the structure supporting the line. His statement
would not hold true regarding the conductors. Of course the
whole line does not deteriorate in any such short length of
time. On the next page he speaks of the steel tower acting
as a lightning-arrester. A few days ago the speaker heard of
one line which had been in operation for some time, the con-
struction of this line being similar to that described by Mr.
Blackwell. Iron rods were attached to the tower and bent up
around the insulator in order to protect it from a stroke by
lightning. Has Mr. Blackwell ever seen a similar construction?
Mr. Blackwell also says: " If one insulating support takes
the place of four or five, line troubles will be reduced nearly
in direct proportion; the inspection and repair of the line will
be much simplified and its cost of maintenance correspondingly
diminished."
The speaker's experience with line , troubles has been that
of having less trouble from insulators than from any other
part of the construction. Most of the trouble has been caused
by forest fires burning the poles; trouble has also been caused
by short-circuits due either to wire thrown over the line ma-
liciously or by carelessness in the construction work for exten-
sions, etc.
When a line is first put up, it is almost always the case that
a number of the insulators are broken maliciously ; after a little
while, the insulators are let alone, even in the West. One
transmission line with which the speaker was associated crossed
a cattle ranch; the cowboys used the insulators for targets,
shooting off as many of them as they could. In a short time,
however, that practice was stopped, for that class of men, if
you appeal to them in the right way, can be easily approached
and reasoned with. One of the line inspectors brought the
matter home to them by saying that the breaking of one of
the insulators might mean the killing of a man at another
place, a man who, after touching off a blast, was endeavoring
to reach the surface by means of an electric hoist. In that
particular case, where trouble of this kind was the worst that
the speaker has ever known, it was stopped almost entirely.
On page 311 Mr. Blackwell says: " Permissible tension in
the cable must not exceed the elastic limit, by which is meant
the point at which the material will continue to elongate and
will eventually break, and not the usually accepted meaning cf
elastic limit." Now what is the difference between what Mr.
Blackwell defines there and the ultimate tensile strength which
he speaks of on the next page?
There is another matter of importance mentioned by Mr.
Blackwell; that is, if a line carries a considerable amount cf
LONG SPANS. ■ 321
power, sleet is not so likely to form on the wire. This is es-
pecially true of high-pressure lines. With a given loss, the
higher the pressure the smaller the conductor and consequently
the greater the loss per unit of radiating surface of conductor,
and, so far as the speaker has been able to observe, a small
variation in temperature from that at which sleet forms will
prevent its formation.
F. 0. Blackwell: Answering Mr. Mershon's question; of
course the deterioration on a line is confined to the wooden
parts. Poles, under unfavorable conditions, may rot out in
two years. In some places, as in India, ants eat up the poles.
In dry ground, with the right kind of wood, the life of a pole
may be 20 years. Mr. Mershon also refers to some trouble
experienced at Guanajuato which was attributed to lightning.
They have had some insulators break there, but, as the speaker
understands it, they do not feel certain that the breakage was
due to lightning. They are experimenting, however, with an
extension of the tower to form a lightning-rod which they will
place at exposed points on their transmission system.
Regarding the elastic limit of materials used for conductors,
our experiments show that all of them, including copper, alumir
num and iron, take a considerable set when subjected to any
strain, and that the amount of this set depends on the time
during which it is subjected to the strain. The cable is a sort
of spiral spring. It is more elastic than a solid wire and its
elasticity depends a great deal on the number of twists in the
cable, the size of the hemp centre, and other conditions. We
used a hemp centre because we found by experiment that a
metallic core took the strain to which the cable was subjected
before the outer strands and broke first. This made the cable
with a conducting core weaker than one made with a hemp core.
Regarding sleet, it is probable that the only time when
trouble would be experienced on a transmission of any size
is when the power is off the line. At other times there will
be sufficient heat generated in the wire to keep it above freezing
point. In the case of this Guanajuata construction the in-
sulators were cracked and split open. There was nothing in
particular to indicate lightning ; they were not burned except so
far as they would be by short circuit from the line current.
A. S. Hatch: Possibly the experience of 20 years may be
of interest in tower construction. In May, 1884, a windmill
tower was erected for lighting a section of Detroit; it was tri-
angular in cross-section, 22 feet on a side at the base and taper-
ing to a point. There are nine 18-ft. gas-pipe sections, the
first three being of 2.5 in., the middle three of 2 in. and the
top three of 1.5 in., making the total height 161 feet. Weak-
ness has been found to be buckling of the pipe standards, due
principally to wind-strains. The towers have not been good
lightning-arresters since switch-cases have been punctured after
a storm. At the base of the towers are switches to control
322 HIGH-TENSION TRANSMISSION.
the wiring, the cases of which were connected to the tower;
and after a severe storm, a switch would be found punctured,
showing the hghtning had either left the line, jumping to the
case of the switch and thence to ground, in case the ground
is moist, or, as commonly the case, the lightning leaving the
tower for the grounded line. The most common class of tower
in use is also triangular but of uniform cross-section, and is
built of 2-in. and 1.5-in. pipe, a section being 8 ft. high and
6 ft. on a side. The girts are 1-in. pipe and braced with f-in.
diagonal stay-reds. The base of the tower is a single pipe
15 ft. high on which is a fitting to which both the horizontal
and brace supports are fastened. The towers are guyed in
four directions by two sets of guy-ropes consisting of 0.5-in.
steel strand fastened to wooden stubs. These towers vary
from 150 to 175 feet high, and on account of being used in a
city are preferable, but the taper tower is better for trans-
mission purposes on account of avoiding the use of stubs. There
is no side-strain except that due to the line-wires fastened to
the tower and sometimes having a span of 250 feet from a pole.
Chas. F. Scott: The subject covered by Mr. Blackwell is
a most timely and important one. It is notable that this
paper deals mainly with mechanical problems, and that those
which are particularly electrical in their, bearing are minor in
number. In fact, after the electrical engineer specifies a few
general conditions as to conductivity and gives his attention
particularly to insulators, the rest consists of matters which
pertain to mechanical and economical problems.
Mr. Blackwell has pointed out the principal causes of the
interruption of lines as they are now constructed. The new
type of construction moreover apparently removes in a large
measure all the principal causes of interruption to service in
present lines; this is a very strong argument for the tower con-
struction.
The discussion in the paper with regard to the character-
istics of conductors and making comparison between copper,
aluminum, and iron are of much interest, particularly the data
upon copper cable. The difference between the elasticity of
the wire and the cable, the latter being, as Mr. Blackwell ex-
pressed it, in the nature of a spiral spring, is noteworthy. One
of the elements in this type of construction is the probable
change in length of the conductor due to temperature variation.
-If the conductor could be made a spiral spring or if the twisting
.of the cable could even be carried to a greater extent than
it is in the ordinary cable, then the conductor might be given
a great elasticity and the limitations which are reached due
^o the variable sag of the cable might, in a measure, be elimi-
'nated.
Mr. Blackwell did not state specifically the pressure which is
used on the line to which he refers. The inference is, however,
that it is 60 000 volts.
LONG SPANS. 323
N. J. Neall: Has Mr. Blackwell any data to show the
value of steel towers as lightning-arresters compared with
standard lightning-arresters? and does he know of any case
where steel towers were struck directly by lightning and what
happened ?
F. O. Blackwell : The speaker knows of a number of trans-
missions using pipe poles. In general it would appear that
there is less trouble from lightning with an iron than with a
wooden construction. Should lightning actually strike the line
it would naturally go down the first pole. It would do no
damage to a mAal pole but would shatter a wooden one. With
wooden poles there was always evidence left in the burning of
or splinters from the pole, but with an iron pole you might
have a stroke of lightning and never know it, except for a
short circuit on the line, or unless an insulator were broken,
which is rather improbable.
N. J. Neall: Let us assume a case of a 60 000-volt trans-
mission line in a mountainous country, such, for example, as
in the far West. How would the cost of steel towers compare
with the best present wood pole construction?
F. O. Blackwell: The comparative cost of steel towers
and wooden poles can hardly be definitely stated, as it varies
with the locality and the conditions. In this country, a wooden
construction would almost invariably be cheaper as the tower
system would be about equivalent to a cost of, say $10.00 per
wooden pole. The steel tower in the tropics, where wood will
not last any length of time, is essential; in this country, the
speaker considers the use of a metal construction preferable on
account of its more permanent character. The use of steel
for long-distance transmission will probably supplant wood in
order to get a more permanent and reliable construction. Where
there is more than one circuit on a pole the necessary distance
between conductors — ^to avoid the danger of short-circtiiting —
requires such a long cross-arm that it is essential to use two
wooden poles in order properly to support the cross-arm. This,
of course, doubles the cost of a wooden pole-line but makes
practically no difference in the cost of a steel-tower construc-
tion.
A cable is preferable to a solid wire because it is more reli-
able and more elastic. The cable is flexible, which makes it
less liable to damage during construction and from the swinging
of the conductor in the wind. Should one strand of a cable
break the whole conductor will not come down and the broken
strand can be repaired at any convenient time. With a cable
we can use a more brittle wire which has a much greater strength
per square inch than would be possible safely to employ were
a solid conductor used.
Regarding telephone circuits, it does not appear to the
speaker that there is any disadvantage in the use of a metal
structure; in fact, there is an advantage in that it is impossible
324 HIGH-TENSION TRANSMISSION.
for high-pressure current to leak from the tower wires to the
telephone circuit as it could on a wet wooden pole, which is
a conductor of high resistance, whereas the tower is always
grounded. It is most undesirable to do any work on a high-
pressure circuit when it is alive. Wherever possible, multiple
circuits should be employed so that one of them can be cut out
for repairs without interrupting the tower service.
Wm. Hoopes: a few words may be devoted to the aspect
of this paper towards the comparison drawn between aluminum
and copper for work of this character. By inspection of page
314. of the paper, it would appear that a sag of aluminum of
53 feet may be expected in a 100-ft. span.
Two and one-half years ago, the Pittsburg Reduction Com-
pany erected on a blufE 300 feet high, on the Allegheny River,
in one of the most exposed situations in Western Pennsylvania,
four 1000-ft. spans of No. 0000 aluminum wire, for the purpose
of determining what might be expected from such a span.
Observations taken on these spans on June 17, with a tem-
perature of 80° fahr., showed a sag of 22 feet. As the sun
was shining at the time the observation was taken, the tem-
perature of the wire should be taken as 105°, using the figure
assumed in the paper as being correct ; i.e. , that the wire would
be 25° hotter than the air, due to the sunshine. The mini-
mum temperature since the spans were erected was -14°, making
a total range of temperature between the minimum and the
time of observation of 119°. The paper assumes that a further
rise of temperature of 56° may occur; if it does, the sag of
the wire will be 27 feet. There is therefore considerable dis-
crepancy between what actually has happened in such a span
(which is about representative of what is likely to occur) and
the 53-ft. sag which the paper says may be expected.
The reason for this discrepancy is the difference between the
conditions which have actually occurred and the conditions
which the paper contemplates as possible. The conditions con-
templated by the paper are:
1. That the wind will blow with an actual velocity of 100
miles per hour.
2. That such a wind velocity will be coincident with mini-
mum temperature.
3. That the direction of the wind will be at right angles to
the line.
If any section 100 miles squaje were selected and a pole
line built across it, by assembling what data is available from
the U. S. Weather Bureau and applying the theory of proba-
bilities, we would find that a combination of these conditions
is not likely to occur oftener than about once in 20 000 years.
The Government reports give the velocities as actually indi-
cated by the standard anemometer. These figures require a
considerable change to convert them to true velocities. One
hundred miles actual velocity would be reported as 135 miles
LONG SPANS. 325
per' hour. Such a velocity is almost unknown in thfe annals oif the
Weather Bureau. A search of the Bureau reports for six years
shows for 28 widely scattered stations a maximunl indicated
velocity of 86 miles, or an actual velocity of 68 miles per hour.
None of the maximum velocities have occurred coincidently
with low temperatures and it does not seem within the range
of probability that they will so occur. The maximum velocity
occurring in Chicago last winter when the thermometer was
below zero was 38 miles per hour indicated.
The only wind which actually seems likely to do harm to a
line of this character is a tornado, and which it is impossible
to erect any line to withstand, since the effects of tornadoes
have been observed which must have been due to an actual
velocity of 300 miles per hour, or a pressure of 360 pounds
per square foot. Provision against this would involve a cost
of construction absolutely prohibitory. Aside from the tornado
the most severe condition a long span line is likely to be called
upon to withstand, so far as wind strain is concerned, is ia
wind velocity of 40 miles per hour, occurring at from 20 to 30
degrees above the minimum temperature.
Although the conditions assumed in the paper seem un-
likely to occur, it is worth while to consider what would take
place with a line not designed to meet these conditions but
to meet those which actually seem probable. Such a line using
aluminum of the size referred to in the paper would be
erected to have a sag, at minimum temperature, of 13.25 feet,
and a tension of 11 000 pounds per square inch, the elastic
limit being 14 000 pounds per square inch. If in that condition
it were subjected to a 100 mile wind, at right angles, the
effect would be to stretch the wire, not to break it, so that a
sag of 42 feet would take place, which upon cessation of the
wind would become 38 feet.
The effect upon the wire would be permanently to stretch
it about four feet. It will withstand an elongation of 16 feet
before rupture, and there really exists, therefore, a factor of
safety of four, against breakage, even when the improbable
conditions here chosen are used as the basis of calculation.
It is to be noted that in the case of spans of wire, the real
factor of safety is not the ratio between the strength and the
strain, which is the usual definition, but the ratio between the
elongation at rupture and the possible elongation.
With regard to the strains due to sleet, there seems to be
no limit to the amount of sleet which may gather on wire and
it is very doubtful if the assumption of a depth of &ne inch for
the deposit provides for the probabilities. If it is to be con-
sidered at all, a greater thickness should be considered as pos-
sible. However, the opinion of most practical transmission en-
gineers, based on experience, seems to be, that sleet does -not
form on high-tension wires, and that its consideration does
riot therefore constitute an element of the problem.
326 HIGH-TENSION TRANSMISSION.
With regard to the necessary Strength of supports, and
therefore their cost, the most seVere requirement is most hghtly
touched on in the paper. This condition will be when, for
any reason, all three conductors part in the same span, leaving
the unbalanced strain to be taken care of by the supports,
which supports must be strong enough to withstand this strain,
as in the event of such an occurrence several miles of the line
might go down, if they are not so constructed. If the sup-
ports are made strong enough to meet this condition, they
will be amply strong enough to meet the wind strains calcu-
lated, since the side strains due to the wind are less than
one-fifth the longitudinal strains produced by this condition.
It also becomes apparent in this connection that, if a maxi-
mum strain per conductor of 5000 pounds for copper and 2500
pounds for alimiinum is allowed, the towers will have to be
twice as strong for copper as for aluminum. If, on the other
hand, the strain per conductor is to be kept down to 2500
pounds, the maximum sag of the copper will be about the same
as that of the aluminum, instead of about one-half as much,
as shown in the paper. The expediency of allowing the amount
of sag designated appears very doubtful, since, if the improbable
conditions assumed do occur, the only effect will be, not to
break the wires and interrupt service, but to introduce a sag,
which can be removed at leisure. To allow the amount of sag
calculated, if not necessary, forfeits considerable advantage,
because if such a line were constructed on 75-ft. towers, for
instance, and a sag of 50 feet allowed, the wires at the center
of the span, being only 25 feet from the ground, could easily
be short circuited by malicious persons. On the contrary, if a
sag of 30 feet only be allowed, (which is all that is probably
necessary), a clearance of 45 feet is obtained, and malicious
interference becomes very difficult, and, therefore, improbable.
It would appear to be the best practice on a line of this sort,
to erect the conductors so that they would reach a maximum
tension at a minimtun temperature of about 80% of their
elastic limit, without considering the wind as a strain producer.
If this is done, it will be only on very rare occasions that
the wind or other causes will permanently stretch the wires
and produce a greater sag than is contemplated, and this, when
it does happen, will be on short stretches of the line only, making
repairs a matter to be done at a convenient time and at very
slight expense.
One result of following the method of calculation in the
paper is that the sag to be allowed for every different size of
wire would be different, although the wire is of the same ma-
terial. This is because the wind pressure varies directly as the
diameter of the wire, while the strength to resist the wind
pressure varies as the square of the diameter. If the calculations
on which the paper is based had been made for No. 1 copper,
instead of No. 000 copper, the results would have been entirely
LONG SPANS. 327
different and the maximum sags to be provided for very much
greater.
F. O. Blackwell (by letter) : Referring to Mr. Hoopes' com-
ments, the writer affirms that it was not his intention to lay
down any rules for the sag employed in long spans but to
give the data and formulas which can be used in figuring upon
them.
The maximum strain in the conductor and the wind pressure
which should be assumed are matters of engineering judgment.
A wind pressure of 40 lb. per sq. ft. is that commonly em-
ployed in making the calculations upon practically all engineer-
ing structures, and, therefore, the writer would not take any less
pressure without further data on the subject. A long-distance
transmission line may cover a great deal of territory and if
there is any high wind it is most likely to be interrupted by
it. The fact that an isolated span with much less sag has
been up for two or three years does not necessarily prove any-
thing. The probabilities are that at the particular point at
which the experimental span was erected no high winds have
been experienced.
It does not impress the writer as being good engineering to put
up a long span and then let it take its own sag by stretching
the wire as Mr. Hoopes suggests, any more than it would be
advisable to do the same thing in a suspension bridge.
The writer does not agree with Mr. Hoopes regarding the
strains to which towers are subjected lengthwise of the line. The
ordinary tie-wire which attaches the conductor to the insulator
will not bear any considerable strain. If a conductor breaks it
always slips over the insulators for a considerable distance on
both sides of the break and distributes the strain, due to the
tension in the conductor, over a number of insulators and
towers. As Mr. Hoopes states, the amount of sag to be allowed
varies with different sizes of wires. Each transmission must
therefore be calculated separately and no tables or curves can
be given which will cover all conditions.
Eugene Clark: The speaker is particularly interested in the
paper by Mr. Blackwell, because he argues for better mechanical
strength in the pole line, which is generally conceded to be the
weakest point in an electrical system. The speaker thinks it
possible, however, that Mr. Blackwell might have left the
impression that line construction with steel poles would be
just as cheap as similar construction with wooden poles, and
if this were true, he wishes to offer a correction to that im-
pression. The speaker objects to the figure of $10.00 a pole which
Mr. Blackwell has submitted as the equivalent in wood, of steel
construction, The speaker knows that steel poles have long been
in use in many steel plants of the country, not for the purpose
of securing longer spans for light wires, but for the purpose of
sectiring better mechanical construction for the exceedingly
heavy lines necessitated by the large amounts of power carried
at low pressures in such plants, " '
328 HIGH-TENSION TRANSMISSION.
That the cost of such poles, which are quite heavy, varies
from $60.00 to $120.00 each, erected, including cross-arms,
concrete foundations, etc. One steel company has recently had
occasion to cross a navigable river, and to do so found it
necessary to put up very high steel towers. In this case, the
total cost of each tower amounted to more than $1500.00.
The speaker believes thoroughly ,however , in the advisability of
the superior mechanical construction made possible by the use of
steel poles, calling attention to the fact that moving machinery,
such as cranes and hoists, is commonly designed with factors
of safety of from 5 to 8; whereas, the factor of safety on
pole lines, as frequently constructed, scarcely amounts to
2 or 3 for ordinary service. The factor of safety should
be at least as high on a pole line as on moving machinery.
President Arnold: The New Yotk Central engineers also
investigated pretty thoroughly the matter of steel poles. They
began with steel poles that cost approximately $200 each;
by dint of much effort they were finally estimated to cost about
$80 each. The argument in favor of steel poles is strongest
for the long-distance transmission lines running across country
where the poles can be spread as far apart as will be justified
by mechanical consideration. In cities the poles must be placed
close together, necessitating the use of a larger number of steel
poles per mile of line than would obtain in the country; this
increases materially the cost of the line as obviously steel poles
cost more than wooden ones. As Mr. Blackwell says, where
the wooden poles are expensive, as in Mexico, the transportation
of wooden poles is likely to make them cost as much or more
than the steel towers. On the Guanajuato plant the cost was
much less with five steel poles to the mile than it would have
been with wooden poles spaced the ordinary distance apart.
So the question is always one of the relative cost of wood versus
steel in position. In the speaker's opinion there is no doubt
about the desirability of steel poles; the question is rather one
of getting sufficient poles to carry the line at a price that will
justify their use.
The engineers of the New York Central road have decided
upon overhead transmission for most of the line and for these
two reasons: first, less first cost; secondly, the likelihood of
less trouble with overhead lines than with underground cable — ■
all this notwithstanding Mr. Carlton's statement. His state-
ment is undoubtedly correct, but it seems that he refers to a
specific case. The evidence in the New York Central case
showed that they might expect less trouble with overhead
transmission lines running across country than with an under-
ground cable. For these reasons cable is being installed only
in New York and its vicinity, where the use of cables is prac-
tically compulsory. A pressure of 11 000 volts will be used
on this system. There will be six wires, two circuits, and the
spans will be made as long as the conditions will admit. There
LONG SPANS. 329
is quite a number of curves in the track which necessitates
putting the poles closer together than in an ordinary con-
struction. The bridge engineers of the company are figuring
the relative cost of poles; the poles are approximately between
16 and 18 inches at the base and 45 ft. high.
In further explanation of why the engineers of the New
York Central adopted the overhead plan it might be said that
the possibility of trouble on the line was taken into considera-
tion ; for with overhead construction trouble can be located and
remedied quickly and easily, much more so than would be
the case with an underground cable. The objection to cable
seems to be that when anything happens the trouble can be
neither located nor repaired promptly.
Eugene Clark: It does not make so mucn difference about
the angle-iron, if the rails are good in the first place, but the
construction of the pole must be rather unusual. The common
poles that the speaker referred to as costing $60 and $120,
consist of four irons latticed together, on the other side with
rounds to form the ladder. The speaker does not see how
you can get that amount of steel in for $15, if it is steel.
W. D. Ball: The South Side Suburban Railway Company
of Chicago has ordered a few poles on trial, and information
regarding their cost and weight may be of interest. The poles
in question were 30 ft. high, weighing 616 lb. each, and the
price f.o.b. cars Chicago or vicinity was a little less than three
cents a lb. The actual cost of the pole is considerably less
than any other type on the market, as it weighs less for any
given strength and the cost per lb. is a trifle less, as tubular
poles were quoted from three to three and a half cents. The
construction consists of three U-section steel uprights tied to-
gether with special malleable castings every two feet or 30
inches. The poles in question were six inches, at the top and
thirteen inches at base.
Ralph D. Mershon: There are two matters in connection
with steel towers which have not been referred to ; one of them
is the amount of torsion that the steel tower shown by Mr.
Blackwell can resist in case one or more of the conductors
should break. The speaker knows of one instance where a
latticed steel pole was erected, where no allowance was made
for torsional stresses with the result that every time a wire
broke there was considerable trouble.
Another matter in connection with steel supporting struc-
tures with long spans is the question of repairs. A span of
say 150 feet is easier to repair than a much longer span; this
means that in case of a break in the line the power service
will be interrupted for only a comparatively short time. In
comparing this type of construction with other types the first
cost alone should not be considered; we should consider every-
thing which goes to make up the total cost; first cost, main-
tenance, etc.
330 HIGH-TENSION TRANSMISSION.
It seems to the speaker that there is one point in which the
steel tower construction falls short of what is claimed for it.
Although it is true that the conductor will, for the greater
part of its length, be higher than an ordinary pole-line, still
with the construction described by Mr. Blackwell, the con-
ductor is only about 25 feet from the ground, making it easy
to short circuit the line at this point with a bale wire as in the
case of a shorter span and lower pole.
N. J. Neall: The following facts should be borne in mind
with respect to the development of steel towers; some of the
more recent wooden pole constructions are very stable; a num-
ber of lines have been built with a great deal of attention to
the mechanical features, heavier poles and greater strength
throughout, and the maintenance of an almost continuous line
service for a year or more would indicate that the wooden pole
line has been developed very materially. When you have such
a construction near the base of supplies, it may require more
than the arguments brought out to-day to substitute steel
towers for wood. In the case cited by Mr. Blackwell where
wood is as difficult to obtain as steel, it is perhaps more eco-
nomical to make use of the steel tower. In cities and their
outlying districts still other conditions enter, and it might be
easily advisable that the tower construction, even though more
expensive, should be employed.
In addition to the emphasis given the advantages pointed
out by Mr. Blackwell for metal towers, it does not appear from
the discussion that the cost of such a tower construction is,
broadly speaking, prohibitive. The advantages of the metal
tower as a lightning-arrester seem to be unduly emphasized.
The metal tower might be considered as having approximately
the same discharge value as an overhead grounded wire on a
wooden pole-line, and it is obvious that in view of the frac-
tional value of such protection we are in no degree relieved
from having protective apparatus in the stations. The dis-
charge value of the metal tower seems only incidental to its
other advantages.
Chas. F. Scott: We are getting on the wrong line of dis-
cussion with reference to Mr. Blackwell's paper. While the
cost, the relative cost, of the two different types of construction
is an important thing to consider, it is not the only thing. Mr.
Blackwell does not begin his paper with the consideration of
cost or to find something that is cheaper. He begins it: " Un-
fortunately interruptions of the power service occur not in-
frequently and when they do happen they so inconvenience
the public as to be most conspicuous."
It is a better kind of service, a different order of construction
that he is seeking for; he finds out how that construction will
overcome present difficulties. Sometimes cost is important;
sometimes it is relatively unimportant. A few years ago an
engineer who was making a prehminary layout of a trans-
LONG SPANS. 331
mission plant asked the speaker what he thought of the en-
gineer's transmission system; it was 20 miles in length, and
he proposed to use one pole line and two circuits of 30 000 volts.
The engineer was told that his pressure was very high and
he was putting a good deal on a one-pole line, and as he wanted
reliability he would better consider lower pressure and two
separate pole lines. The cost of the line complete, conductors,
poles, insulators — the whole cost as the speaker remembers — ^was
something like four per cent, of the total investment. Here,
then, was the element in the system upon which the continuity
and reliability of service depended — the most vital element in
the whole system, and he had gotten it down to four per cent.
of the whole investment. By increasing that element, say
doubling its cost, and running two pole lines say of 20 000
volts each, he would increase his total cost only a few per cent.
and he would increase his coefficient of reliability by a very
much greater per cent. So in the general question now under
discussion, we have to consider, first the general engineering
condition, which would be the best plan and would give the
most reliable service; and then determine as to the cost. This
paper should be considered on its general engineering merits,
and it seems to the speaker that Mr. Blackwell's points are
pretty well taken.
Another thing: we have been comparing a new type of con-
struction with certain lines and poles now used. We are com-
ing into a different order of conditions in power transmission —
the circiiits are of greater output, higher pressure, and greater
importance. Where there are many circuits, with large and
heavy wire, where continuity of service is of the utmost im-
portance, where the cost of the line could often be consider-
ably increased in order to increase the coefficient of reliability,
then we must consider the problem from an entirely new stand-
point. In these respects the lines laid down in this paper are
very promising.
F. A. C. Perrine: While agreeing entirely with Mr. Black-
well and Mr. Scott in the statement that reliability is more
important than cost in long distance transmission, the speaker
believes that a number of points raised by Mr. Blackwell re-
qtiire consideration.
As regards the limit of transmission with any particular
size wire it may be noted that up to 40 000 volts no wire of
sufficient strength to be employed in a transmission line is
small enough to allow- discharge through the air, consequently
allowing the rule that the practice in transmission pressure is
to employ about 1000 volts per mile. The question of limiting
size of wire is not of importance until the distance exceeds 30 or 35
miles. For longer lines where the pressure is between 40 000
and 60 000 volts no wire smaller than f in. in diameter may be
used; since Mr. Scott has already shown in the paper referred
to that at such pressures a wire i in. in diameter will discharge
332 HIGH-TENSION TRANSMISSION.
a large amount of energy. This necessity for the use of a
large wire on long lines is one of the advantages in the use of
aluminum, an advantage not noticed by Mr. Blackwell in his
paper. This is particularly an advantage of aluminum, since
where small amounts of energy must be transmitted over a
wire of a definite size the loss is not important, and the alumi-
num wire is very much cheaper than the copper wire of the same
size. These large wires are invariably made stranded, as in
this form they are more reliable than any solid wire of the
same area, on account of the fact that the smaller wire has a
high tensile strength and by reason of the fact that the weak
places are distributed along its length. The writer believes
that Mr. Blackwell is in error when he states on page 557 strands
are made of tinjointed wire. The practice amongst manufac-
.turers being to joint reel after reel in their machine, cutting
off the completed strand in the lequired lengths without refer-
ence to the lengths of wire on the spools of the machine which
are jointed as required. Experience has shown that the large
strand which must be employed in very long lines gives no
trouble in breaking.
The speaker knows of very few instances where strands of
over 0.5 inch in diameter have been burned off; the few cases
occurring have been due to a solid short circuit where the
station fuses did not operate, but it is generally the case that
the station fuses operate before the line wire is fused.
Attention must be called to an additional advantage of tower
construction, that it permits the use of large cross-arms sup-
porting the very heavy insulators which must be used in the
higher pressure construction. Insulators at present weighing
from 30 to 50 pounds are common, and with electrical pressures
increasing the present tendency is toward larger insulators weigh-
ing as much as 100 pounds. Some insulators now in use cannot
be installed on a wooden cross-arm less than 6 by 6 inches,
which arm cannot be securely supported on a wooden pole
with a 9-inch top. In consequence the steel tower, whether
the cross-arm be of steel or wood, is probably capable of fui:-
nishing the more reliable type of construction, since in long-
distance transmission lines we must decrease the number of
insulators by lengthening the spans and correspondingly in-
crease the size of the insulator. This can only be accomplished
by the use of the steel tower.
The value of the steel tower as a lightning-arrester the speaker
considers very important. He believes that to-day the advan-
tage from the use of a grounded wire for protecting the long-
distance transmission lines is unquestioned, though there is de-
cided difference of opinion concerning its permanence; but with
the steel-tower construction a sufficient number of grounded
points are brought close to the wire without the use of an extra
wire. On one transmission line with which the speaker is
familiar there is a section 37 miles in length where the average
LONG SPANS. 333
span is 300 feet ; this section is one-third of the line and extends
over a series of low hills. Such lines can undoubtedly be made
more permanent if steel towers are used in place of the wooden
poles. While not an advocate of the steel-tower construction
for short lines and low pressures, the speaker strongly believes
in the steel-tower construction for long lines and high pres-
sures; first, because of the increased value of insulation by
reason of a lesser number of insulators; secondly, because of
the lightning protection afforded; thirdly, because of the per--
manence of the towers themselves, and because of the fact
that they allow the use of a cross-arm which will support a larger
insulator and a larger wire.
Finally the speaker would call attention to what he believes
to be an error in Mr. Blackwell's Introduction, pages 314 to
316, where he inakes use of the standard coefficient of linear
expansion in calculating the temperature changes. This is not
correct unless the modulus of elasticity is introduced into the
equation, which then becomes too complicated for solution. If
a fictive coefficient of expansion based on experiments .at different
temperatures with actual spans, then the form can be considered
correct.
The equivalent cross-section of a solid wire will have a lower
tensile strength than a strand, because the wires of a strand
have been subjected to an increased amount of working and
are consequently harder. Furthermore the weak places in a
strand are distributed. In consequence the strength of a strand
is proportionally more than one would expect from the de-
creased size of the wire.
Ralph D. Mershon: Does Dr. Perrine mean that the ulti-
mate strength of the cable will be greater than the sum of the
ultimate strengths of the individual wires?
F. A. C. Perrine: Yes; so far as the speaker knows, with
copper, with soft strands. That is absoultely untrue with steel,
with metal that will not crush.
Eugene Clark: The speaker calls attention, as being of in-
terest in this connection, to the fact that hoisting ropes used on
cranes built to handle molten metal have been made with cores
of soft iron wire, or of asbestos, it being necessary to use a fire-
proof material. In practice, it is found that the strain on the
ropes acts to extend the helices formed by the outside strands
of the rope. In the case of asbestos-cored rope, the core would
break at various points throughout the length of the rope and
separate, so that sometimes 18-in. or 24-in. space intervenes
between, the two broken ends of the core. The result would be
to allow the rope to flatten at that point. In the case of the
soft iron-cored ropes, the iron core was cut out of the rope at
each end. When the rope stretched, the iron core was stretched
enough to pull through and leave the open space at each end
of the rope, where it caused no damage. In view of these facts,
t&e. speaker feels convinced that a central straight strand for a
334 HIGH-TENSION TRANSMISSION.
transmission cable would certainly receive more strain than the
outside strands.
Ralph D. Mershon: It seems to the speaker that Dr.
Perrine overrates the question of lightning protection from
steel towers. The speaker does not see how a steel tower can
be the equivalent of a ground-wire, nor how a steel tower can
ward off electrostatic induction. The tower might take a light-
ning stroke, but it does not seem that it could be of any pro-
tection from effects due to electrostatic induction or from light-
ning strokes which might get into the line-wire. In the latter
case the charge will probably jump to a pole, but in doing so
will probably shatter an insulator. The speaker does not recall
any case where a wooden pole has been shattered by lightning
where the insulators on that pole have not, one or more of
them, been shattered. It isn't a case of simply flashing-over
the insulator, nor is it a case of flashing-round or yet a case
of puncture. In most cases the insulators go all to pieces;
the speaker knows of one case where a pole on a high-pressure
line was struck by lightning and an insulator smashed to pieces ;
the French Canadian patrolman who reported upon this occur-
rence said in his report: " I found pieces of her over in the field;
if she had been hit by a stone she would not have gone so far."
Dr. Perrine and Mr. Scott have both said the cost is not the
important question. This the speaker cannot agree with, for
he believes that cost is the only question; not necessarily first
cost but the total cost, including interest, depreciation, etc.
Into this cost must enter and be considered the question of
reliability, a question which cannot easily be evaluated in dollars
and cents. Its weight and valuation must enter into the cal-
culation through the meditun of the engineer's judgment. It
is easy to imagine a situation where, with a type of construction
subject to mishaps resulting in interruption to service, a plant
might be a commercial success in spite of occasional interrup-
tions, but where the cost of absolutely reliable service would
swamp the enterprise; on the other hand, there are situations
where anything less than the very best and most reliable con-
struction would swamp it. It is all a question of cost, and of
cost proportional to the conditions to be met.
W. B. Jackson: The speaker fully agrees with the state-
ments that the iron tower would seem to be excellent as a light-
ning protection.
The speaker does not agree with Mr. Mershon that the light-
ning in jumping around the insulators as a rule breaks them.
For instance, in a 20 000-volt transmission line, with which
the speaker is familiar, the lightning has struck the line a num-
ber of times and smashed one or more poles at or near the
point of striking and has then run along the line each way
jumping around the insulators for several poles consecutively,
slightly splintering the poles. It was seldom the case that the
insulators were broken in the discharge of the current ovei
LONO SPANS. 335
them. It was usually possible to replace the broken poles by
setting a new pole immediately alongside of the broken one
and transferring, the cross-arm and the pole-top insulator with-
out further repairs. In the case of the steel towers there would
apparently bfe little tendency toward the destruction of the
tower, and should the lightning strike the line it would have
a tendency to run along the line and relieve itself over the
insulators at the adjacent towers.
Referring again to the line mentioned before; it was not
infrequently struck at points between the lightning-arrester
stations, and sometimes struck hard without any indication
■whatsoever of the discharge getting as far as the lightning-
a;rrester stations, though indications of its leaving the line over
the insulators was amply abundant.
As already indicated it is entirely possible that the lightning
might strike between the supports in the case of iron towers
and run either way along the line, dissipating itself through
induction and by discharge to the towers. Of course the exact
action under these conditions cannot be predicted with any
certainty, especially as with the steel -tow«r construction we
generally associate the higher pressures such as 60 000 to 80 000
volts, and so must solve the problem according to our best
judgment considering that we have no operating data to work
upon — ^but we must always remember that lightning works
according to ways other than our own.
There is another feature in connection with the tower con-
struction that has been brought out a very little this morning,
that would seem to warrant further consideration. It has not
been uncommon on 20 000-volt transmission lines and even
30 000- and 35 000-volt lines that a wire of the transmission
circuit has dropped on to the cross-arm carrying wires and no
one has been the wiser for the fact until the line inspector
discovered it. In the case of the steel tower, the dropping of
one of the wires upon the support might be indeed serious,
owing to the fact that the wire would probably be burned off
at the point of contact, with disastrous results; thus the problem
of the mechanical strength of the insulator and the attach-
ment of the cable thereto is of paramount importance. As
Dr. Perrine has pointed out, there is extremely little chance
of a properly constructed cable breaking except under abnormal
conditions, therefore, the absolute certainty of support of the
cable is of the greatest importance, for if there is danger of
the insulator breaking, or the attachment of the wire to the
insulator giving way, the possibility of the wire being burned
off would be considerable. With the long spans and heavy
cables that would usually be contemplated in connection with
steel towers, the breaking of the wire might be a catastrophe
of real magnitude.
Except in extraordinary situations, the speaker's feeling is
that a well-constructed pole line using wooden poles and wooden
336 HIGH-TENSION TRANSMISSION.
cross-arms must continue to be the most satisfactory construc-
tion for transmission lines, so far as general practice is con-
cerned in this country.
A conversation which the speaker had with Mr. Blathy of
Ganz & Company at Budapest may be interesting : he remarked
that it would be unwise to attempt to employ 35 000 or 40 000
volts in accordance with the usual European practice in trans-
mission work considering the status of the insulator at that
time, and asked: " What do you think would be the best to do
under the circumstances? " My reply was, to use the usual iron
poles but attach wooden cross-arms to them. He replied that
they would not permit such unsightly construction as this would
necessitate, though he felt that the wooden cross-arm was a
material advantage.
H. B. Alverson: In regard to lightning on lines of 11 000
volts and 22 000 volts, our experience has been that where it
struck, the insulators would be shattered. Either way from this
point the insulator would usually be punctured, while slightly
farther away no damage would be done. At the time when
the lightning struck the line, the circuit would be short cir-
cuited, undoubtedly at the point where it struck. In the case
of a steel tower line this would probably cause the shutting
off of current before enough time has elapsed to bum off the
cables.
Peter Junkersfeld: Mr. Mershon's statement that cost of
the transmission line is everything, cannot, it seems, be gen-
erally accepted without some qualification. If the owners or
managers of the line are interested simply in receiving and
delivering power without much restriction .or responsibility,
the statement might hold. In that case, however, it is only
a temporary or perhaps expedient commercial organization, be-
cause for ultimate and permanent success we must consider
everything all along the various steps from prime mover to
the individual consumer.
" Reliability of service " is a term that must be used rela-
tively and usually should be the first consideration, the second
being the securing of such reliability for the lowest permanent
annual expenditure. This reliability of service is always ex-
tremely important. In large cities even with the principal
high -pressure transmission underground, this represents a com-
paratively small part of the total investment in the central
station system, and it would seem unwise even for some con-
siderable difference in total cost of high-pressure transmission
to take chances with the particular part of the central station
system which represents perhaps the greatest responsibility and
least annual expenditure per unit of output.
Similarly in the New York Central's present undertaking,
the cost of high pressure transmission must be small compared
to the total when we consider car equipment, track construc-
tion, power and substations, and so on. For reliability let us
LONG SPANS. 337
compare a duplicate overhead line, six wires on the same set
of poles, with a duplicate underground line both in same group
of conduit, assuming best construction in each case. In both
cases the conductors are heavy enough so that loss of one line
will not interrupt the service. Assume now that probability
of breakdown in insulation of conductors is nearly equal in
the overhead and underground construction, the probability
of external injury of all possible kinds is very much greater
with the overhead lines. In event of serious short circuit on
one line, the probability of both lines being disabled, resulting
in a total shut-down of lines, would seem greater with over-
head construction, as the two overhead lines on same pole cannot
be isolated, while the underground lines can. Experience and
observation would ^indicate that ordinarily with transmission at
11 000 volts, good underground construction would be much
more reliable.
In the question of overhead and underground transmission
for the particular case of the New York Central, it is probable
that there were a number of unusual conditions not generally
known. The estimated cost of underground being seven or
eight times that of overhead construction, indicates at least one
very unusual condition. The annual expenditures, however,
on account of transmission lines operation and maintenance,
would not be in the same proportion.
President Arnold: Mr. Benezett Williams has requested
that the speaker ask this question:
" What would be the effect on the permissible voltage by
the protection of the insulators and cross-arms from rain,'
snow and sleet; that is, how much above 60 000 volts could the
pressure be carried? "
The general question is, what kind of protection should the
insulators and cross-arms have from rain, snow, and sleet?
F. A. C. Perrine: The speaker wishes to present a pro-
posed construction for discussion; this construction is designed
for a 350-mile, 80 000-volt line. On investigating it was found
that a 14 by 14 insulator was small enough for 60 000 volts,
but it was a question whether any reasonable-sized insulators
for use out of doors could be made for 80 000 volts. Further-
more, it was found that with a duplicate three-phase line, if
one line was out of service for repair the regulation of a single
line would be so bad that the service could not be maintained.
In other words, in trying to get along with half the copper
the regulation would be too bad to give any kind of service.
Consequently a system was proposed involving the erection on
a tower of a house about ten feet square with four wires on
insulators in separate compartments each being five feet square
and ten feet long, the idea being to put the insulators in an
enclosed house having four wires all told; three wires being in
service at any one time, the other wire being out of service for
cleaning insulators and for repair. In that way enough metal
338 HIGH-TENSION TRANSMISSION.
could be concentrated on three wires to ensure regulation.
In addition the tower was to be provided every 10 miles with
a switching station, so the service of any one wire could be
switched on any of the four.
In regard to the covering of insulators, the Kontenric
Company in British Columbia has built a line with a pent-
house over each insulator but from this they have not derived
any very great advantage, for while the pent-house protects
the insulators against rain or snow it does not protect them
against dust and fog; the combination of dust and fog makes
mud, producing the worst possible conditions. In estimating
this line, 18 000 volts were figured on.
H. C. Wirt: Will President Arnold say whether the New
York Central lines are to be operated with the Y connection
grounded? There seems to be a difference of opinion in refer-
ence to the advantage of operating in this manner.
President Arnold: No; it is not intended to run it under
abnormal conditions; provision is made in- the power-houses
and sub-stations for grounding whenever the engineers see fit
to use the ground wire.
N. J. Neall: Dr. Perrine has brought out very justly the
advantages shown by Mr. Blckwell's paper, and moreover
the discussion has brought out the fact of a cost that is pro-
hibitive; but it seems that in addition to what has been said
as to the advantages electrically, it is not out of the question
from a financial standpoint. One matter seems to have been
given undue emphasis; that is, the lightning protection. Last
year at Niagara we were discussing the advantage the barbed-
wire or the ground -wire had over the transmission, that it was
a good thing to take off some of the static discharges. You
must remember that when you have a climatic disturbance
you have an electrostatic disturbance, and an electromagnetic
disturbance. The steel tower, and for that matter the barbed-
wire protector, does not in any degree relieve us from having
protection in the stations. And the electrostatic can be taken
to some extent by the entire line, but only incidentally. The
best protective apparatus to-day provides for the discharge of
this disturbance as well as the electromagnetic. We cannot con-
sider the steel tower as having anything more than an inci-
dental advantage, but they are better than wooden poles be-
cause they will absorb from the atmosphere some of the static
disturbance.
F. O. Blackwell: There is another thing in connection
with steel-tower construction. The towers can generally be
located on high ground, so that the maximum sag will occur
over the low ground between towers. A tower would iiaturally
be located at the highest point — on every hill which is passed
over — these are the points which would naturally be struck
by lightning, and the towers, if especially provided with points
projecting above the line, will take a lightning charge without
LONG SPANS. 339
affecting the system. Wherever there is a sudden change in
altitude, or other conditions which cause lightning phenomena
at certain points, there should be lightning-arresters connected
to the circuits which will discharge them to ground.
N. J. Neall: In consideration of the relatively great dis-
tance between cloud and line, the addition of lightning-rods
to metal towers would probably not be as efEective as Mr.
Blackwell suggests, and hence for any direct strokes the metal
towers should be able to attract and discharge these disturbances
as well as if equipped with lightning-rods.
H. C. Wirt: Reports received from a few plants where
ground-wires are used indicate that such wires prevent the
shattering of the wooden poles and they also assist to protect
the apparatus at stations and sub-stations. If the interruptions
due to shattering of poles are frequent, it may be necessary
to use ground- wires.
N. J. Neall: Is the case referred to by Mr. Wirt regarded
by him as general or special, because there have been plants
where transmission lines have had their poles shattered and
the contintiity of service not disturbed. Any questions regard-
ing overhead grounded wires are meant solely to bring out
their value, not to disparage their use. If lightning has shat-
tered poles and disturbed the service then any protection of
the pole to eliminate this is indeed valuable. It seems too
early to decide the worth of overhead grounded wires, and
we must certainly wait until those who have had the courage
to install this system and investigate its behavior report their
observations; and even then to be of permanent value these
observations must cover a wide geographical area and have
lasted for more than one lightning season. So far these ob-
servations have been special. If we should take up the metal
tower, then overhead grounded wires would probably not be
used.
S. B. Storer: One of the speakers said in referring to the
use of barbed-wire that he frequently obtained an extra
high pressure between any two transmission lines. Now if
a barbed-wire is added to the transmission line it seems to the
speaker that the trouble is increased about one-third, because
the same pressure might obtain between the grounded wire
or between the barbed wire and the transmission wires that
would obtain between any of the transmission wires.
H. C. Wirt: — ^Theory or laboratory tests should not be relied
upon wholly in the design of lightning-arresters. We will have
to work with the lines themselves and make extensive trials
on any protective device that may be proposed. Recent ex-
amination of transformers that have burned out has shown
that a very high pressure has existed from line to line. At-
tention is called to a photograph of a connection board printed
in the speaker's paper. The tension necessary to make an arc
go across the terminals was 42 000 volts, and the working
340 HIGH-TENSION TRANSMISSION.
pressure was 2000 volts. Too much attention has been given
in the design of lightning-arresters to provide an easy path to
ground and too little to prevent a rise of pressure between line
and line.
In low-pressure work we started with transformers using
insulation between primary and secondary that would with-
stand two or three times the working pressure. We now
have to insulate our transformers to withstand five times
the working pressure of 2000 volts. With these modern trans-
formers we find that the bum-outs due to lightning effects
are from line to line and rarely from line to ground. With
high-pressure transmission lines it would seem to be necessary
to provide a path from line to line as well as from line to ground
so as to prevent the lightning current making its own path
through expensive apparatus.
In many cases reactive coils were used for protection. It
is possible to have an electromagnetic effect in the line wires;
that is, upon a heavy stroke of lightning passing to ground
high-pressure currents are created in the transmission system.
R. F. Hayward {by letter): Since the commencement of
transmission work in Utah the writer has maintained the opinion
that structural strength and stability are the first requisites for
transmission lines. Every year's experience has strengthened
this opinion. There are now 500 miles of transmission pole-
line in Utah, and experience has abundantly proved that the
line which is mechanically strongest gives the best service.
Glass insulators are not mechanically strong enough, nor will
they stand the continued stress of heat and cold. Wooden
pins should not form part of a strong line. Iron pins have
been used on all the comers of the Pioneer line between Ogden
and Salt Lake, and there has been no failure on their account
in seven years. Porcelain insulators have stood the test of
strength thoroughly well. Where properly designed and made,
they do not check or break except when shot, and then they
only chip instead of flying to pieces like glass. In only two
or three instances have short circuits been caused in the Ogden-
Salt Lake line by insulators broken by a rifle shot, out of thou-
sands which have been chipped by bullets.
On a transmission line, the failure of one pole or one in-
sulator may cause an interruption of service and therefore the
factor of safety should be very large. A line designed for
50 000 volts can be depended upon for 30 000 volts. If a trans-
mission line cannot stand the cost of an expensive porcelain
insulator there can be no profit in building it. There is little
excuse for interference from trees, but it is more difficult than
might be supposed to get rid of trees in settled districts. In
eight years' service on the Ogden line the greatest amount of
trouble has been caused by burning of poles from brush fires.
Careful patrolling has kept the interruptions from this cause
down to a very small amount, but on one occasion 15 poles
LONG SPANS. 341
were burnt off in a sage-brush fire. In a few cases poles have
been splintered and insulators shattered by direct Hghtning
strokes. Except in these instances no breakdown of the line
itself can be directly traced to hghtning.
There have been many interruptions caused by wires or
sticks thrown over the lines; a few by birds, and one by a wild-
cat. Once only has a pole been blown down, while once the
whole superstructure of a box car was blown from a train into
the wires.
In the inter-mountain region wooden poles have a life of
not more than ten years; many last only five years. It has
been found that salt is the best preservative for the butts of
poles, but if the butt is made to last ten years the upper part
of a cedar pole will check and become so brittle that its useful
life is gone in that time.
The writer in 1903 constructed a pole-line for the Utah
Sugar Co. from their power-house on the Bear River to the
Utah Light and Railway Company's power-house at Ogden, a
distance of 45 miles. The line was designed for 40 000 volts,
and is operated at 28 000. It is located at the base of the
Wasatch range, just above cultivated ground, but within a
few hundred yards of a good county road. The location was
costly as regards pole construction, but was necessary in order
to avoid trees. The line consists of 40-foot cedar poles with
cross-arms. The wires are spaced on a six-foot triangle. The
upper cross-arm is short and the insulator is placed on alternate
sides of consecutive poles. This arrangement avoids the bad
practice of placing a pin on the top of a pole. The lower cross-
arm is heavily braced and the cross-arms are strengthened and
prevented from splitting by ^-in. steel plates held together by
carriage bolts. Poles are spaced 44 to the mile. The line
wire is No. 0, soft-drawn, solid copper. The insulators are
three-part Locke brown porcelain. The upper part is 11-in.
diameter, and was tested to 40 000 volts. The middle part
was tested to 30 000 volts, and the lower to 50 000 volts. The
pin is of cast iron with a collar S^-in. diameter and a f-in. steel
bolt cast into the shank. It is cemented into the insulator
with neat Portland cement. The pins and insulators complete
weigh 20 lb. each and cost nearly $2.00 in place on the pole.
They are heavy and expensive, but they are strong and make
a splendid insulator for a heavy line.
In stringing wires half a mile of wire was stretched at a
time, and the writer has repeatedly seen a single insulator
stand the whole strain without any trouble. There are three
long spans on this line, two of 250 feet and one of 450 feet.
Solid No. was used for these spans, and 15 feet sag allowed.
The wires were supported by three insulators at each end, set
in a special iron fixture. The whole strain of the span is taken
by these insulators. All corner strains are taken by single
insulators and they are strong enough to stand them. The
342 HIGH-TENSION TRANSMISSION.
whole line was built for mechanical strength and so far it has
given no trouble. Some 30 or 40 of these insulators have been
in use through the past winter on outdoor 40 000-volt air-
switches and have shown no sign of failure. The insulators
are not expensive to repair, as the upper part when broken can
be cracked off and a new part cemented in its place ; the pin
and the rest of the insulator are used over again.
This pole-line cost $2000 per mile, and has probably as much
steel and iron in its construction as can be used on any wooden
line. The next important Hne in Utah will undoubtedly be
entirely steel supported, for a careful comparison of costs shows
that the Bear River line, just described, could have been built
just as cheaply with steel towers as with poles.
The writer believes that a single line of steel towers set 500
feet apart carrying two circuits of copper wire, spaced on six-'^
foot triangles, will be much cheaper, both in first cost and
maintenance, and freer from interruption and safer for repair
work than two separate wooden pole lines.
It may be argued that if a wire from any cause drops on
the structure it will make a dead short circuit. It will, but
the wire will be burnt off in an instant and in a properly laid
out and operated plant the trouble will be located and the
section isolated without delay.
It would be interesting to get figures on the cost of erection
of the steel towers, assuming labor at $1.50 per day, teams
at $3.50 per day, and average length of haul four miles. The
writer is not in favor of using aluminum cable. It is cheaper,
and lighter than copper, but it lacks the strength and may be
worth very much less per pound in a few years, whereas copper
is not liable to depreciate much in value.
A. S. Hatch (by letter): On page 310 it is assumed that
the steel towers act as Ughtning-arresters. The writer cannot
agree with the statement unless the tower is grounded in per-
manently moist earth. In testing the street lighting circuits
for grounds or opens, it is found that the towers are not gen-
erally grounded in dry weather, being grounded but a few days
after a storm. As a storm usually follows dry weather, at
least before the rain has had time to penetrate any distance
into the ground, .the towers may be fairly well insulated by
the dry earth. There have been several instances where light-
ning has struck a tower and, following a guy -wire to the wooden
stub, has splintered it in passing to earth rather than follow
the tower. In one case, lightning struck a tower and puncturing
the lamp insulator discharged through the circuit which was
grounded in the station. This experience, together with the
statement made during discussion that the steel towers were
usually located on high points of ground, emphasize the im-
portance of grounding the towers thoroughly,
A paper presented at the ISSth Meeting of the
American Institute of Electrical Engineers,
Chicago, June 21-22, 1904.
Copyright 1904, by A. I. E. E.
CONDITIONS FOR CONTINUOUS SERVICE OVER LINES
OPERATED IN PARALLEL.
BY M. H. GERRY, JR.
In order to maintain a continuous service, nearly all of the
more important transmission systems have installed two or
more pole lines, each carrying one or more circuits. As a
rule the circuits are operated in parallel but are so arranged
that at least one of them may be entirely disconnected without
interrupting the delivery of energy.
Two sets of conditions are met with in practice: first, normal
operating conditions; secondly, accidental conditions. It is pos-
sible by design to provide for the first, and, in the main, for
the second. The normal operating conditions include inspection,
repairs, and additions to the circuits. But little work can be
done on high-pressure circuits while in service, and it follows
that adequate switching devices must be provided such that
any circuit may be disconnected without an interruption of
the service.
Both the air-break type of switch and the oil-switch are
now available for pressures to 60 000 volts, and may be in-
stalled in various ways to obtain the desired results. They
may be operated either automatically or manually. There are
in use several systems of switching transmission circuits in
parallel. Some arrangements provide for connecting only the
low-pressure side of the transformers; others only the high-
pressure side, and still others provide for the connecting of both
the high- and the low-pressure sides in multiple. An arrangement
of connections for two transmission circuits in parallel is shown
in the accompanying diagram.
343
344
HIGH-TENSION TRANSMISSION.
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CONTINUOUS SERVICE. 345
This system may be elaborated by adding group -switches on
one or both sides of the transformers. If more than two cir-
cuits, or more than two banks of transformers be employed,
various devices are resorted to for providing the required flex-
ibility. Practice in this last connection has taken the direction
of sectionalized bus-bars, with some form of group switching.
In addition to the switching devices at either end, it is desirable
on long lines to install sectionalizing and paralleling switches
so arranged that a section of a transmission circuit may be en-
tirely isolated and the remainder continue in parallel with the
other circuits. The switches for this purpose are usually
mounted on the poles and are operated manually. It is prob-
able that the practice of sectionalizing long transmission lines
will be extended in future and that improved switching appar-
atus will be employed for this purpose.
In addition to normal operation, the accidental conditions
which may arise and affect the continuity of the service should
be anticipated and provided for. These conditions, whatever
may be their primary cause, usually result in an open circuit,
a short circuit, or a grounding of the conductors. Whenever
one of these occurs it is essential that the entire circuit, or at
least the defective section, be immediately isolated from the
other circuits of the system. This may be accomplished either
by automatic devices or by the attendants. The automatic
methods, on account of the time-element involved, are undoubt-
edly superior, but the apparatus should be of thoroughly reliable
construction and should be tested frequently if the best results
are to be obtained. The best practice calls for circuit switches
controlled automatically by means of time-limit overload relays
at the generating end, and similar switches controlled by time-
limit reverse-current relays at the receiving end. These de-
vices properly installed will effectually isolate a transmission
circuit in case of trouble, but other conditions must also be
considered if the service is to be uninterrupted. Whenever a
parallel circuit is disconnected it disturbs the entire system
and especially affects the electrical pressure. A long trans-
mission circuit represents a considerable capacity, inductance,
and resistance, and when this is removed or placed in parallel
to other circuits, it becomes necessary to readjust the pressure.
This is usually done by the attendants at the generating station
but a reUable automatic device would be of value for this pur-
pose if designed to meet all the requirements of transmission
service.
346 HIGH-TENSION TRANSMISSION.
A considerable change in pressure at the receiving end of
the Une may result in an interruption if induction motors or
synchronous apparatus be operated by the current. The greater
the number of circuits in parallel, the smaller the amount of
disturbance produced by removing a single circuit. Many of
the better high-pressure transmissions depend, however, upon
two lines of one circuit each, and in case of accidental difHculty
with one of the circuits the entire load is carried temporarily
on the other line. By a proper design this may be successfully
accomplished, and even in the case where one of the circuits is
suddenly isolated by automatic devices the variation of pres-
sure may be kept within such limits that there will be no
interference with the service.
The reliability of high-pressure and long-distance transmis-
sion has been thoroughly demonstrated, and it has been shown
by actual results that a continuous service can be maintained
for indefinite periods by the use of multiple lines and proper
appliances.
CONTINUOUS SERVICE. 347
Discussion on " Conditions for Continuous Service over
Lines Operated in Parallel."
Ralph D. Mershon: There is one point which the speaker
would like to have taken up, because of its bearing upon a pre-
vious discussion at Niagara Falls. The speaker refers to re-
verse-relay devices; they are interesting things to talk about,
but does anyone know of a reverse-relay device that will work
under all conditions ?
P. H. Thomas (by letter) : Absolutely continuous service may
be realized in theory and ultimately will undoubtedly be closely
approached in practice. At the present time, however, no such
perfect devices are available.
The usual arrangement of overload circuit-breakers at the
generator end of two transmission lines in parallel and reverse-
current relay circuit-breakers at the other ends does
not operate properly in all cases when there are gen-
erators at both ends of the line. A theoretically satisfactory
arrangement can be constructed, however, which will open the
right line at both ends in all cases of short circuits by operating
at all points at which the lines are paralleled, the relays con-
trolling the circuit-breakers jointly from current transformers
connected in the two lines. These currents must be so di-
rected that during an equal division of load between the lines
(or division in any desired proportion if so desired) the influence
of one line shall just neutralize the influence of the other line.
When with this arrangement current is reversed in one of the
transmission lines, the influence of two lines is in the same
direction in the relay and can be made to open the defective line.
Another method appears to the writer to have a number of
advantages. In endeavoring to maintain continuous service
with apparatus now available, the system having duplicate
parts all through may be operated as two systems entirely inde-
pendent electrically, each so arranged as to carry approximately
one-half load. Each of these systems should of course extend
into all important sub-stations. In case of trouble to one line
causing a drop of pressure, half of the load of the system will
be dropped. Immediately this should be thrown to the other
system, which must of course be able to carry the double load
for a short time. If the attendants are properly instructed this
may be done without special orders from headquarters, thus
avoiding a very important loss of time. All parts of the dead
system which are uninjured may then be immediately paralleled
with the live svstem, enabling it to carry the full load easily.
A paper presented at the li&th Meeting of the
American Institute of Electrical Engineers,
Chicago, June 21-22. 1904.
Copyright 1904, by A. I. E. E.
THE USE OF GROUND-SHIELDS IN TRANSFORMERS.
BY J. S. PECK.
In any transformer there is a possibility that the high-pres-
sure winding may become metallically connected to the low-
pressure winding through failure of the insulation between these
windings, so that if the low-pressure winding is not connected
to ground it may be raised to a high potential above the earth.
Under these conditions a person coming in contact with the
low-pressure circuit may receive a dangerous shock, while the
apparatus connected to this circuit is subjected to undue strains.
If, however, the low-pressure winding is connected to ground,
the maximum difference of potential which can exist between
any part of it and ground is that which is established between
the grounded point and that portion of the winding farthest
removed, electrically, from the ground.
The ground-shield is a metallic sheet so placed between the
high- and low-pressure windings of a transformer that the high
pressure cannot break through to the low pressure without
first going to ground. The ground-shield should be made pre-
ferably of copper, of a thickness of approximately 1/32 in.,
though it may be of any conducting material, and of practically
any thickness desired. A convenient arrangement is to connect
the ground-shield to the core of the transformer, which is
grounded directly, or through the case. It is obvious that since
the ground-shield surrounds the magnetic circuit it must not
form a complete turn, and for this reason it is cut through
in one place and the joint insulated.
While upon first thought the use of a ground-shield would
appear to eliminate entirely the possibility of an abnormal
pressure existing between low-pressure winding and ground,
348
GROUND-SHIELDS. 349
there are, nevertheless, ways in which it may fail in accom-
plishing its purpose, and there are numerous practical difficul-
ties in its use, particularly in large high-pressure transformers.
Some of the objections to the ground-shield are:
1. It does not prevent the possibility of an abnormally high
pressure .existing between low-pressure winding and ground,
due to a connection between high- and low-pressure leads
inside the case, or in the wiring exterior to the transformer.
2. The ground-shield must be of thin material. With trans-
formers of large size where enormous current may flow in case
of a short circuit, it is possible that a portion of the shield may
be burned away or that the connection between it and the
ground connection may be burned off, thus leaving the high-
and low-pressure windings connected, but insulated from ground.
3. The introduction of the ground-shield into a transformer
increases its cost, or lowers its efficiency, or both; for the same
amount of insulation must be placed between the high-pressure
winding and the ground-shield as is ordinarily placed between
high- and low-pressure windings ; and in addition the ground-
shield must be insulated from the low-pressure winding.
4. In transformers there is a leakage magnetic field between
high- and low-pressure coils. In that portion of the coils out-
side the iron this leakage field cuts through the ground-shield,
producing eddy currents which may greatly increase the trans-
former losses. This is particularly true on high-pressure trans-
formers where it is necessary for insulation purposes to make
a difference in the lengths of the coils. On such transformers
it is necessary to use very thin sheet-metal for the shield, and
to slit it at the ends into a number of narrow strips, which are
insulated from each other, except at one point.
Conclusions. — Since the ground-shield does not afford abso-
lute protection, and as it increases the cost or reduces the effi-
ciency of the transformer, and on account of the mechanical
and electrical difficulties involved in its use, it would seem that
for large high-pressure transformers the ground-shield is a
theoretical, rather than a practical, means of protection.
It is believed that the grounding of the low-pressure winding
at the neutral point is a safer, more practical, and cheaper
method of protection than is the use of the ground-shield.
350 HIGH-TENSION TRANSMISSION.
Discussion on " The Use of Ground-Shields in Trans-
formers."
Ralph D. Mershon: Undoubtedly, if grounding the neutral
of a low-pressure winding does not protect, protection will not
be obtained by the use of ground-shields. It seems to the
speaker that it is not safe to install a high-pressure transmission
system, feeding a city distributing system, without either mak-
ing use of ground-shields or grounding the neutral of low-
pressure windings. Aside from the question of a cross between
the high- and low-pressure circuits, it is possible, with every-
thing in good condition, to have electrostatic effects of high
pressure on the low-pressure windings, high enough to damage
insulators and endanger life. It seems therefore that it is
rather unwise to install transformers feeding distributing sys-
tems without using one of these means of protection. In some
cases the expedient of using spark-gaps between the low-pres-
sure windings and ground is resorted to, and in some cases
between the neutral and the ground instead of grounding the
neutral. But these spark-gaps are generally the cause of more
or less trouble ; it is the speaker's opinion that it is much better
to ground the neutral permanently.
H. C. Wirt: Transformers having ground-shields were used
to a limited extent in this country at a time when the National
Board of Fire Underwriters would not permit grounding the
secondary. Now that grounding the secondary is permitted,
there seems to be no good reason why transfomiers with ground-
shields should be used.
C. E. Skinner (by letter): In specifying the use of ground-
shields between the high-pressure and low-pressure windings
in transformers, engineers seek to prevent any possibility of an
electrical connection between these windings. The question to
be considered is, therefore, whether or not this result can be
accomplished.
In the writer's opinion, ground-shields are very undesirable
from a constructional standpoint; they do not necessarily ac-
complish the result for which they are used, and they increase
the cost of transformers in which they are used. The writer
agrees that the grounding of the low-pressure winding at the
neutral point is a safer, more practical, and cheaper method
of protection than is the use of the ground-shield. This method
gives almost absolute safety, while the use of the ground-shield
is at best a doubtful expedient.
P. H. Thomas (by letter): Mr. Peck has hardly emphasized
sufSciently the objections to the use of ground-shields in large
high-pressure transformers. That a very efficient protection
against the raising of the pressure of the low-pressure winding
of transformers, due to a certain class of breakdown, is secured,
cannot be denied, but the incidental difficulties and opportunities
for trouble introduced through the use of ground'Shields far
GROUND-SHIELDS. 351
outweigh its advantages, when protection can be so simply
obtained otherwise.
The writer fully agrees with Mr. Peck's conclusions, but
wishes to bring out one point : when the grounding of the neutral
point of the system is relied upon for protection, there is one
weak point. From the nature of the case, the connection be-
tween high pressure and low pressure, when occurring on
wiring or at the leads of transformers, will be of the nature
of a static discharge, also the low-pressure winding of the trans-
former constitutes a choke-coil between the source of the dis-
turbance and the grounded point; as a result there will be a
short-circuit strain impressed upon it of a very severe nature,
wliich may easily cause a breakdown of insulation. This may
be avoided by using lightning-arresters as discharge gaps on
the leads of the low-pressure winding. This method will not
be effective where the connection between high-pressure and
low-pressure systems occurs at an intermediate point in the
winding of the transformer. Since in this case the trans-
former is already injured, this fact will not be of such serious
consequence.
W. L. Waters (by letter): A ground-shield undoubtedly
affords some protection, but such protection can be obtained
in a much simpler and more reliable way by grounding the
low-pressure side of the transformer, or by means of some auto-
matic grounding device, such as the Cardew. Considering the
question from all points, the writer agrees with Mr. Peck, that
the doubtful protection afforded by the ground-shield is ob-
tained at far too high a cost, and that at the present time a
ground-shield would be more suitably placed in a historical
museum than in a power transformer.
A paper presented at the 188(/i Meeting of the
American Institute of Electrical Engineers,
Chicago, June 21-22, 1904,
Copyright 1904, by A. I. E. E.
THE PROTECTION OF HIGH-PRESSURE TRANSMISSION
LINES FROM STATIC DISCHARGES.
BY H. C. WIRT.
The various devices for the protection of transmission lines
from hghtning and other static stresses, made by the leading
electric companies, are constantly modified, and it is apparent
that improvement in this class of apparatus is needed. The
best way to develop such devices is to make a careful exam-
ination of the transmission lines and of apparatus that may
have been damaged by such high-pressure discharges. It is
to be hoped that the following comments on various devices
now in use will be of interest, and will bring out discussion of
their operation.
Ground-Wires. — Overhead ground-wires have been used in
several transmission plants. It is evident that if efficient pro-
tection can be secured at the power-house and sub-stations, it
is superfluous to use such an overhead wire. If a ground-wire
be used, it must be large enough not to break and of material
that will stand corrosion; a suitable wire will cost almost as
much as an additional transmission wire.
A certain power transmission plant, having three power-
houses and seven sub-stations, operating 90 miles of overhead
transmission lines at 40 000 volts, has protected the greater
part of its transmission system by No. 4 galvanized iron wire
placed at the top of the poles, half the length being barbed wire,
the other half plain wire, — the wire being grounded at every
fifth pole. This wire was installed about 14 months ago ; before
that time many of the poles had been shattered by lightning,
but since then no pole has been damaged, but some apparatus
has suffered from lightning, the arc jumping from the trans-
352
LINE PROTECTION. 353
former lead above the oil, in all cases. If lightning-arresters
had been placed at all the stations, and no overhead wire used,
there would probably have been less damage to apparatus, but
the poles would have been shattered. It is not at present the
custom to use lightning-arresters on transmission lines, and it is
not known whether poles can be protected in any other way
than by an overhead ground-wire. It would be of interest to
have data upon the frequency of interruption of service of trans-
mission lines on account of poles being damaged by lightning.
My opinion at present is that a transmission line can be pro-
tected from lightning discharges by suitable apparatus placed
in the stations, and that it is not necessary to use ground wires;
but an exception will probably have to be made in cases where
poles are shattered with great frequency.
Another installation, operating at 25 000 volts, uses lightning-
arresters at stations and sub-stations, with reactive coils, con-
structed to break down at 50 per cent, above the working pres-
sure, and with a resistance in the ground connection. The
arresters have a series of gaps, and are equipped with the
" multiplex connection," giving a minimum breakdown distance
between line and line. Prior to the installation of this equip-
ment, there was frequent loss of apparatus at the stations, but
since, no apparatus has failed on account of lightning, although
there have been many severe storms. The management of
this plant had begun to equip the transmission lines with a
ground-wire, but has decided not to proceed with this plan.
We have in these two cases entirely opposite methods of
protecting lines. In one case, the management is so well sat-
isfied with ground-wires that lightning-arresters will not be
used; in the second case, the management is so well satisfied
with lightning-arresters that ground-wires will not be used.
These two plants are in country very similar in its physical
characteristics, and are only a few hundred miles apart.
Experience with apparatus damaged by lightning proves that
it is as important to provide an easy path for the lightning dis-
charge from line to line as from line to ground. Up to the
present, the principal idea in designing a lightning-arrester has
been to provide a good path to ground; they have frequently
required twice as great a pressure to break down the gap space
from line to line as from Hne to ground. Recently a new type
has been suggested called the " multiplex connection," in which
a shorter path is provided from hne to Hne, requiring practically
354 HIGH-TENSION TRANSMISSION.
the same breakdown pressure as from line to ground. It is
believed that this type will afford additional safety. The
photograph herewith shows a particular case in which hghtning
passing from line to line, jumped across from one terminal to
the other of a porcelain primary connection board; to jump
this space required 42 000 volts.
Reactive Coils. — Much difference of opinion has existed
among engineers on the value of reactive coils, in connection
with lightning-arresters. Some recent tests made with the
best types of lightning-arresters show that the arresters did
not protect the apparatus until reactive coils were used; it
seems now that there can be no question that reactive coils
are effective, and therefore they should always be used. Al-
though much has been written upon lightning-arresters, there
is little available information upon the relative pressure suit-
able for the spark-gap ; it is difficult to determine just how
near to the pressure of the generator a spark-gap can be ad-
justed without danger of flashing over. When apparatus has
burned out, it is possible either to increase the insulation re-
sistance or to decrease the spark-gap distance. Many arresters
are now supplied, adjusted for a breakdown pressure only 50%
greater than the generator pressure; it can be determined only
by experience whether it is feasible to set arresters nearer the
generator pressure than this ; generators are in many cases
insulated to stand only 50% increase above the working pres-
sure, and in this case there is no difference between the break-
down pressure of the insulation and the spark-gap; but the
insulation of the machine stands a one-minute test and the
static stresses exist only momentarily, which is undoubtedly
LINE PROTECTION. 355
the reason that apparatus has not burned out more frequently.
Present experience indicates that apparatus, to be safe, should
stand an insulation test of 100% greater than rated pressure
for one minute; such apparatus may have to be insulated for
higher pressure than the present Institute standard, as it is
extremely difficult to protect apparatus unless it will stand
the double-pressure test.
Experiments have shown that very high pressures exist
momentarily between the outside turns of the coils of a trans-
former at the moments when it is switched into or out of
circuit. Transformers insulated for only 1000 volts per turn
will withstand these very high pressures momentarily; as the
best modern construction of transformers provides for re-
enforcing the insulation in the outside turns, thus providing a
larger factor of safety, it is a question where the additional
protection against breakdown of the outside turns should be
provided ; a rise of temperature on switching transformers has
been noticed in some installations, which is attributed to capa-
city and reactance, producing resonance, and it has become
the practice to provide special means to obviate any rise of
pressure due to these causes; such apparatus is known as a
" static-arrester." It is necessary only to provide a circuit
having a moderate current capacity in order to relieve the line
of high pressure, due to these causes.
356 HIGH-TENSION TRANSMISSION.
Discussion on "The Protection of High-Pressure Trans-
mission Lines from Static Discharges."
J. S. Peck: Mr. Wirt says: " Many arresters now are
supplied adjusted for a breakdown pressure only 50%
greater than the generator pressure." While this adjustment
is a measure of the breakdown pressure of the arrester at the
generator frequency, it does not necessarily measure the pres-
sure at which the arrester will break down under an extremely
rapid change of potential; that is, static discharge. All high-
pressure arresters now consist of one or more air-gaps in series
with a resistance connected between the line-wire and ground.
Tests have recently been made on a number of these ar-
resters to determine the pressure at which they would break
down under two conditions: first, with a current of low fre-
quency, such as is developed by the ordinary alternating-cur-
rent generator; and secondly, by suddenly discharging a con-
denser through the arrester. It was found that in all cases
the pressure required to break down the arrester under the
condenser discharge was very much higher than was required
at the generator frequency. With the condenser discharge
the pressure was measured by means of a spark-gap shunted
around the arrester. By placing the spark-gap around dif-
ferent portions of the arrester, it was found that the greater
part of the excess pressure required to break down the arrester
under the condenser discharge, was taken up by the series re-
sistance.
It is obvious that if a highly inductive resistance were con-
nected in series with the air-gap, the discharge of a condenser
through it would be greatly impeded ; and it appears that even
the straight carbon-rod resistance offers a considerable amount
of impedance to the discharge of a condenser. For this reason
the speaker thinks that a statement regarding the breakdown
pressure of an arrester under generator frequency is of prac-
tically no value as a measure of its protective power against
lightning discharges.
Ralph D. Mershon: It is gratifying indeed to know the
result of the experiment just cited by Mr. Peck. The writer
thinks the result was probably due to the fact that the " non-
inductive resistance " was non-inductive in name only.
The question of the accurate adjustment of the striking
pressure of arresters is relatively non-important. We do not
so much care whether the arresters will discharge at 50 per
cent, above the generator pressure, or at 100 per cent, above
it, as we do that when they do discharge they will allow to pass
sufficient current to keep the pressure of the discharge down
to a safe figure and still prevent the generator current from
continuing and holding an arc after the discharge has ceased.
Another matter often overlooked in the case of metal cylin-
der lightning-arresters — a matter which sometimes gives con-
siderable trouble — is the amount of power that they take on
LINE PROTECTION. 357
discharge. A 2000-volt arrester with a given number of gaps
will take on discharge a given amount of generator current.
If on 50 000 volts the number of gaps is increased in propor-
tion to the pressure, the current will be the same on discharge,
but the power taken will be about 25 times as great; the result
is that if there is a great amount of load on the system there
is not enough power left for anything else on the circuit while
the lightning-arrester is operating. This condition is espe-
cially bad for the operation of synchronous apparatus.
N. J. Neall: The speaker wishes to take exception to the
conclusions drawn by Mr. Wirt — that experience with ap-
paratus damaged by lightning proves that it is as important
to provide an easy path for the lightning discharge from line
to line as from line to ground.
If we take into account the great distances between the
cloud and the line during a lightning disturbance, and the rela-
tively small distances between wires, then, relatively, all wires
of any transmission line receive their disturbances as if they
were formed of one wire; and it is therefore difficult to see
how any difEerence of potential from this cause could exist
between any two wires. It follows that the assumption made —
of the necessity for a discharge between wires — does not hold
theoretically.
The study and development of protective apparatus during
the last eight years emphasize very strongly that certain phe-
nomena occur repeatedly and can be overcome. Generally
speaking, if nothing is destroyed in a station equipped with
protective apparatus, or if the troubles are comparatively
few, the protective apparatus is very highly thought of, al-
though it might turn out that the arresters were really not
protecting, and other causes were accountable for relief from
lightning disturbances. An excellent plan is to have station
operators or line operators record the action of the protective
apparatus on their systems, just as they would record the
operation of their generators or transformers or any other
apparatus which can be metered. A device for this purpose
has been suggested, that of using a slip of paper in some of
the arrester gaps which would be punctured by discharges.
If these papers are removed frequently and systematically
doubtless much of the phenomena which we have been study-
ing would have further evidence to substantiate our theories.
It is also Ukely that many troubles would be brought to light
that are far more injurious to the normal operation of the Une
than are lightning disturbances.
Another difficulty is the close setting of spark-gaps to any
given pressure. Those who have worked with spark-gaps and
spark-gap material know that it is extremely difficult to make
measurements and repeat them within five per cent, of the
pressure which can be estimated by the ratio of turns. More-
over, it does not seem of such importance in lightning-ar-
358 HIGH-TENSION TRANSMISSION.
Testers that we should set our gaps so closely, because if regu-
lar apparatus must stand 50% rise certainly any spark-gap
can be set to meet such requirement.
F. O. Blackwell: Lightning occurs at irregular intervals
and in different forms. The kind of arrester which would
be best in one lightning storm might be of no value in another.
In general, the best we can do is to have a weak point in the
system which will allow the lightning to pass through without
damaging the machinery. The most primitive form of light-
ning-arrester, which consists of a grounded pail of water and a
wire from the water to the line, furnishing a constant leak to
ground, is very effective.
H. C. Wirt: A type of lightning-arrester used in Switzer-
land and Italy consists of a jet of water turned on the line,
so that the line will be discharged through the stream of water.
Neither the water-stream arrester nor the horn arrester will
take a sufficiently large discharge to relieve the line properly.
The principal difference between these arresters and those of
American design is in the number of gaps employed. The
water-stream arrester with a single gap could be used but the
water would have to be of high resistance to prevent an arc
holding.
We have not tried either of these lightning-arresters but
we intend to do so. The question of the amount of current that
an arrester should be designed to take is undetermined. If
the resistance used in the arrester is low the current that would
follow after a lightning discharge may be large enough to shut
down the plant; if the resistance is too high the lines may be
only partly relieved and the lightning may then go through
some transformer. We should of course consider the light-
ning-arrester in theory but we should also have extensive tests
of arresters under service conditions. The speaker means that
no one should decide for or against the use of a ground-wire
unless he has been at places where such wires are in use.
R. F. Hayward (by letter): The writer believes that it is
the apparatus, not the pole-line which needs protection from
lightning. If poles get shattered frequently it may, as is
pointed out, be necessary to use a grounded wire, but steel
construction would be a better remedy.
The transmission lines in Utah, consisting of 300 miles of
40 000-volt pole-line and 125 miles of 28 000-volt line are situ-
ated at the base of the Wasatch range where the thunder-
storms almost invariably break. These lines are particularly
liable to be affected by lightning, and every thunder-storm
manifests itself in some way. It is seldom, however, that
poles are struck, though there have been several cases of shat-
tered insulators and splintered poles. With duplicate lines
the striking of a pole should cause but a short interruption,
and the damage is easily repaired. But if the transformers
are damaged a whole station may be temporarily disabled,
LINE PROTECTION. 359
and the damage is costly. When a pole-line is struck a wave
is set up which finds its vent in a lightning-arrester, breaks
itself against a transformer coil or breaks down the coil. If
the insulation of the coil stands the shock and there is no light-
ning-arrester discharge, an arc may form from terminal to
case. Experience seems to show that a lightning discharge
has the greatest effect on the station nearest to it, but that
the horizontal discharge, occurring between clouds and more
or less parallel to the lines, produces some of the most severe
shocks at lightning-arresters or transformers. In the neigh-
borhood of Salt Lake City it seems that there is a greater ten-
dency to horizontal discharges between clouds than to light-
ning discharges direct to ground. This is doubtless due to
the abrupt rise of the mountains from the level of the valley.
There is no doubt that lightning can and does induce very
high pressure waves between wires, many instances having
occurred in Utah. Protection should therefore be provided
against this.
The writer is in doubt about the use of reactive coils, as there
are instances which show their value, and others which do
not. It seems that a reactive coil to be effective must be
pretty large. It has occurred in the writer's experience that
a pole has been struck with lightning and at the same instant
a discharge has occurred from transformer terminal to case,
while there was no discharge over lightning-arresters, although
a reactive coil was in circuit.
Instances showing that a transformer coil or the windings
of an armature act as a " breakwater " to the passage of high-
frequency waves are too numerous to mention. One instance
is interesting. One of the 2000-volt circuits supplying Ogden
City is lead from the power-house through booster transformers.
A severe storm occurred when the boosters were not in cir-
cuit and a discharge took place across the collector rings of
one of the armatures in the power-house. A few days later
a similar storm occurred when the boosters were in circuit
and one of them was burnt out.
The writer believes that reactive coils of comparatively
cheap construction should be put in to satisfy the conscience
of the engineer, but for real protection the money should be
spent on the transformer. An 80 000-volt transformer working
on a 40 000-volt circuit and protected by a 40 000-volt light-
ning-arrester ought not to break down. The writer's opinion
has changed somewhat during the past year in this matter
and he now believes that any reactance coil of large capacity
introduces some extra apparatus and additional wiring, whereas
the same money spent in the transformers themselves ought
to provide sufficient insulation to stand these shocks.
The writer believes that lightning-arresters should be ad-
justed so that they are near the limit of their own safety ; plenty;
of spare parts should be provided and an occasional burnout
360 HIGH-TENSION TRANSMISSION.
of the lightning-arrester resistance should be accepted as proof
that the lightning-arrester is giving some protection. Anyone
can put so many gaps and so much resistance in an arrester
that it will never bum out, but it does not follow that this
arrangement affords any protection.
P. H. Thomas (by letter): Static discharges in high-pres-
sure transmission lines arise from two causes: first, abrupt
changes of potential caused by switching or accidents in the
transmission system itself; secondly, lightning.
The best protection against the first class, which are certain
to be quite numerous, is in providing ample insulation in the
design of the plant, not so much in the heavy thicknesses of
the solid insulating material, which is exceptionally strong
to resist static strain, as in the air distances, oil distances, and
surface distances between exposed points. In the opinion
of the writer, it is extremely important that these distances
be ample. For instance, they should be laid out to stand
with certainty double the normal pressure of the system, since
probably in very few cases would static pressures exceed this
limit, except of course in case of lightning. It is true that
pressures of startling magnitude are occasionally reported
from transmission plants, but in few cases have the existence
of such been clearly proved, and in many cases the reports
have proved to be unfounded.
In laying out surface distances and air spaces, it must be
remembered that the jumping power of high pressures increases
much more rapidly than the pressure itself. Distances should
not be doubled for double pressure but a curve of actual tests
should be used. It must be remembered as well that surface
distances have their insulation strength much deteriorated
by a deposit of moisture or of conducting dust, and that some
kinds of material, notably hard rubber, may have a gradual
deterioration. It must also be noted that the jumping dis-
tance over a surface is much afEected by the presence near
that surface of another conductor at a different pressure. For
example, a wire within a bushing, and the presence of such a
conductor, in extreme cases may increase by several times
the jumping distance of a given pressure. This fact is very
well established and has been given entirely insufficient recognition
in laying out surface distances for insulation. Still another
factor weakens the insulation strength of surfaces when sub-
ject to static discharges; namely, the fact that for an abrupt
change of pressure a considerable quantity of electricity must
flow at the time of the application of strain to charge up the
surface of the insulation near the charged conductor, and this
flow of current momentarily weakens the total insulation
strength of the surface.
It appears to the writer that since a great mass of data with
regard to the effect of ground-wires or other devices on the
elimination of troubles due to lightning is required to eliminate
LINE PROTECTION. 361
the effect of conditions other than those being studied, that
little can be gained from the consideration of one or two cases
of ground-wires, and that all our accurate data furnish an in-
sufficient basis for conclusions at the present time. It seems
unlikely that even though the grounded wires may be proved
to have protective effect, as they undoubtedly do, they will
ever be of general use, in view of the mechanical and elec-
trical difficulties and expense involved. As Doctor Perrine has
stated, there is a tendency where ground-wires are brought
near to high -pressure conductors, for current to be set up in
the ground-wires, causing more or less energy loss and pos-
sibly other difficulties. Furthermore, there is an increase of
electrostatic capacity, due to the presence of ground-wires in
the neighborhood of the high-pressure conductors. These
objections may be much less critical on low pressure, short-
distance plants. In some such plants ground-wires may turn
out to be the best ultimate protection.
Experience shows that direct strokes of lightning must be
expected on transmission lines in most localities. Unless
grounded guard-wires are used, these strokes must inevitably
injure poles. Such injuries, however, often do not cause a
shutdown of the plant. It is highly desirable for these severe
discharges to get to earth as quickly as possible.
Arresters in the station constitute the most approved prac-
tice and will be relied upon in most cases. In very important
high-pressure plants, however, it would seem that where regu-
lar attendance is feasible a set of arresters at a point from
one-half a mile to two or three miles from the station would
be a very desirable precaution. In such cases where constant
attendance is not feasible, but where there is a suitable loca-
tion for arresters, the use of fuses, possibly arranged so that
when one blows another comes into service, would be satis-
factory. In such cases, should trouble occur at the arresters,
the line would clear itself immediately.
Reactive coils may serve two functions: the prevention
of short-circuit strains between the turns of windings, for
which purpose they are especially suited, and to assist the
discharge of lightning-arresters to ground by delaying the
rise of pressure of a transformer terminal at a time of static
disturbance. In either case the protection derived from the
reactive coil is a matter vf degree, depending upon the rela-
tive electrical characteristics of the transmission hne, the
windings of apparatus, the arresters, and the pressure of line.
A given coil may be very effective on one circuit at one pres-
sure, and entirely inadequate for another circuit on another
pressure. A freely-discharging arrester on a line of small
electrical capacity, protecting apparatus itself having a large
electrostatic capacity near its terminal, would require com-
paratively the smallest choke-coil for restraining the ultimate
rise of potential above ground. An arrester with a ground-
362 HIGH-TENSION TRANSMISSION.
connection on a line of large electrostatic capacity and high-
pressure, where the apparatus to be protected has a compara-
tively small electrostatic capacity near the terminal, would
require a coil very many times more powerful to obtain the
same protection to ground than the coil of the first case.
For the protection against short circuits in windings, the
choke-coil must be proportioned in its choking power to the
number of turns, etc. and the winding itself, at least approxi-
mately; and to be effective without being unduly large can
oftentimes be advantageously assisted by the use of a con-
denser connected between the terminal of transformer and
ground. It would seem evident from the above that react-
ive coils should be of a power adapted to the circuits upon
which they are to be used.
N. M. Snyder (by letter): On the assumption that the line-
wires of a transmission line have capacity, it might be said
that when we use an overhead ground-wire as suggested* the
nature of the protection afforded seems to be due to the static
charges surging from the line-wires to the ground-wire, as
evidenced by the jumping of the arc across the transformer
leads above the oil. This shows capacity in the circuit. The
writer concurs with Mr. Wirt in saying that we should be able
to protect stations and apparatus without resorting to the
use of the ground-wire. If we make the same conditions at
the station as existed when the grounded line was used, it should
be of material benefit. If we connect a plate or series of plates,
t Line Wire
nz ^zz2. —
B liw Wiu
equal in capacity to the wire to be protected, at the power-
house and sub-station and do this with all wires, arranging
them symmetrically and equidistant from a central or ground-
plate of equal area, should we not have an ideal static arrester?
As long as the wire or wires are balanced and current is flowing
equally in all, no interference should be experienced in re-
tardation by the ground-plates, nor any serious faults from
resonance. A static disturbance occurs; it surges from wire
to wire as through a condenser; the ground-plate is neutral
to the plates of the wires; so any charge of static on either
wire will promptly be communicated to the ground-plate and
relieve the strain. Of course in adjusting the plates care should
be taken to have them sufficiently separated to exceed 25
per cent, higher pressure than that of the generator. This
LINE PROTECTION. 363
will prevent the breaking down of the air-gap, the principle
being to make a static line balance normally; and when any-
excess of static occurs it is quietly induced to earth in an effi-
cient manner by making use of the condenser principle.
John Pearson (by letter) : There is one point in regard to
the grounded wire with which the writer thoroughly agrees.
The writer considers that the grounded wire cannot well be
used: first, on account of cost; secondly, because with this
wire a short circuit may easily be established; thirdly, because
it does not afford complete protection to apparatus at gen-
erating or distributing stations. For more than three years
the writer has been with a company operating a 4000-h.p.
power-plant (not using the grounded wire) located near Som-
erset, Wis. This plant transmits current to St. Paul, 28 miles
distant, at 25 000 volts pressure. During this time only three
poles were split so that they had to be removed, but not so
badly as to interfere with the operation of the plant. An-
other plant, only four miles distant, with a pole-line running
through a hilly country, and not using the grounded wire, has
not suffered at all from poles being shattered by lightning;
but it has suffered a great deal from lightning, due to ineffi-
cient lightning-arresters.
From this and other data, it seems that lightning- and static-
arresters can be arranged so as to be of more protection than
the grounded wire. Experience proves it necessary to provide:
first, an easy path from line to ground, through which the line
wires may be relieved of high pressure in respect to the ground ;
secondly, to provide choke-coils between arresters and ap-
paratus to be protected, so as to give the arresters more time
to discharge; thirdly, to provide the multiplex connection
'which Mr. Wirt suggests on the arrester side of choke-coils so
as to provide an easy path from line to line; fourthly, to pro-
vide the high-pressure winding of transformers (or generators)
with a static by-pass between sections of such windings. This
is done by bringing out a number of leads, at equidistant points,
from the high-pressure winding of a transformer or generator
to be protected, to provide metal knobs and series resistance
between these leads, so that normally this combination is a
non-conductor, but at say 50% increase in pressure across a
section this combination becomes a conductor, and relieves the
particular section which it is designed to protect.
The writer knows that when the lightning-arresters which
are connected to the line side of choke-coils discharge, great
differences of pressure are set up between wires on transformer
or generator side of choke-coils. This difference of pressure
frequently causes a flash from lead to lead in transformer top,
and sometimes will break down the insulation between
layers in transformer coils, especially the layers next
to line wires. An efficient remedy for this is to provide
an easy path for the discharge outside of the transformer top,
364
HIGH-TENSION TRANSMISSION.
by bringing out leads and joining as suggested above. One
feature about connecting a static by-pass over successive sec-
tions of the winding is that it will take no more pressure to
break down all the air-gaps across the whole transformer wind-
ing than it will take to break down the air-gap across a single
section, owing to the fact that all the gaps are not broken
down at the same instant. This idea in transformer protec-
tion has been used for over two years at St. Croix Power Co.'s
3L
WAtCfo-
if
/
Fig. 1.
plant, Somerset, Wis., and has also been installed at a new
plant in New York State.
Prior to using this form of protection for transformers, the
St. Croix Power Co. lost four transformers in one season, caused
by static jumping from lead to lead in transformer top; since
then there has been no loss from similar causes. In Fig. 1,
A represents the core of a high-pressure transformer; C the
low-pressure winding; C — C terminals of this winding. B rep-
resents the high -pressure winding; B' — B' represent the ter-
minals of this winding. Leads L-L are brought out between
LINE PROTECTION.
365
terminals of this winding, dividing it into three sections in
regard to static-arrester, and between these leads are pro-
vided non-inductive resistance, h, metal knobs, g, with their
air-gap, also wire (or conductor) d.
Fig. 2 shows this scheme connected to a high pressure gen-
erator with revolving field. The connection is. the same as in
Fig. 1. Referring to Fig. 1, it can easily be seen that there
exists great strains between B'-B', due to lightning arresters
discharging or other causes (this charge being of an oscillatory
nature) ; each one of the air-gaps is broken down successively,
one after the other, and it will take no more strain to break
down all the air-gaps than it will take to break down a single gap.
ANSWERS TO QUESTIONS RELATIVE TO HIGH.
TENSION TRANSMISSION.
The answers to questions printed in this report have been gathered from
authoritative sources. These answers indicate present electriccu engineering
practice; hut it should be understood thai the Institute merely transmits the
information contained in the answers, and that neither the Institute nor the
Committee on High-Tension Transmission assumes any responsibility
as to its correctness or its reliability as a guide to best engineering practice.
At a meeting of the Board of Directors of the American Institute op
Electrical Engineers, held September 26, 1902, it was
" Resolved, That a Committee on High-Tension Transmission, con-
sisting of five members, may be appointed for the purpose of collecting
data respecting present practice in electric transmission at high voltage
and of presenting a report which will indicate the successful methods
which are now in operation in such form as to be of immediate value
to electrical engineers. It is within the scope of the Committee to
secure data upon line construction, insulators, pins and the like, and
the conditions of operation at different voltages and under different
climatic conditions; to investigate methods of testing insulators and to
indicate the method or methods which in its judgment are superior.
Also to ascertain the methods employed for voltage regulation, the
conditions attendant upon the switching of high-tension circuits and to
collect data respecting lightning and static disturbances and the use
of grounded protective wires."
In accordance with this resolution the Transmission Committee pre-
pared a list of questions, copies of which were sent to those connected
with and operating transmission plants, with the request that the answers
to the questions be filled in and the lists returned. Although the num-
ber of replies received fell far below the number hoped for, a consid-
erable amount of information was obtained. The following matter pre-
sents in condensed form the answers received. For convenience in presen-
tation, the plants have been classified with respect to the voltage of
transmission.
Total number of plants that have filled out lists to date, 47. These
plants are classified as follows:
Class A. Plants transmitting tmder 12 500 volts.
B. Plants transmitting from 12 500 to 19 000 volts.
C. Plants transmitting from 20 000 to 24 000 volts.
D. Plants transmitting from 25 000 to 29 000 volts.
E. Plants transmitting from 30 000 to 39 000 volts.
F. Plants transmitting from 40 000 to 60 000 volts
I. LINE IN GENERAL.
3. What is the distance of transmission*
4. What is the transmission voltage at the generating end and at the re-
ceiving points?
5. Is the transmission single-phase, quarier-phase{two-phase) ,or ihree-phasef
6. What is the frequency?
7. How much power is transmitted?
8. What is the average power-factor at the generating station and at the
sub-stations?
14. What is the distance between conductors?
(For answers to these questions see Table A,)
366
REPORT.
367
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368
HIGH-TENSION TRANSMISSION.
12. How many complete circuits are there on each pole line?
13. What is the standard distance of the lowest conductors above the ground?
15. What length of span is standard?
16. What is the longest span used with standard construction or modifica-
tion of it?
24. What is the greatest deflection of line ordinarily allowed on a single
angle- pole?
25. Do angle-poles have double fixtures?
26. Are angle-poles braced or guyed? If guyed, at what point relative to
the power wires are the guys attached? {A sketch is desirable.)
27. What is the normal length of span between angle-poles?
28. // guys are used, do you use strain insulators in the guys?
32. Are the power wires transposed? If so, how many times and at what
intervals of distance?
(For answers to these questions see Table B . )
TABLE B.
6
k
o-°
■ ^
II!
•as§
a
■s
1
h
W.S
■s
c a
n! O
fto
i|
11
t3
J3S
No. of plants using
strain insulators in
guys.
■3
18
80
100
10°
15G.
50
A
9
to
40
to
125
to
240
to
90°
17
2G&B
to
130
11
8
15
80
100
10°
20
B
3
to
32
to
125
to
175
to
60°
6
7G
to
100
6
5
15
90
100
12°
3G
12
C
2
to
to
to
to
9
2B
to
4
8
27
140
300
30°
4G&B
100
25
90
125
15°
IG
60
D
2
to
to
to
to
4
2B
to
2
3
35
130
200
45°
IG&B
90
19
100
360
3G
80
E
2
to
27i
to
130
to
400
45°
3
IB
to
120
1
4
l§i
100
200
IG
F
1
to
30
to
180
to
320
10°
1
IG&B
110
4
r?
strand Buy Wire^
Wvi*
Insulatoi-s
FIG. J
Highway
t]
"9
*Ww
Main Line
FIG. I
18. What heavier construction, if any, is used on such spans?
19. What is the longest span of any kind?
20. What is the distance between wires on this span?
REPORT. 369
General Description op Construction Used in Extra-Long Spans.
Spans to 300 feet: the poles are usually double cross-armed and guyed;
in some cases double poles are also used.
Span 626 feet: double poles, double cross-arms guyed two ways, and
wires were spaced eight feet apart.
Span 800 feet: double poles and 6 by 6 in, cross-arms, poles guyed with
steel cable two ways.
Span 586 feet: six poles, two poles for each wire, a cross-arm bolted
on top of each pair of poles with four insulators in it; the six poles
are framed together and braced in all directions.
Span 1750 feet: two poles set 10 feet apart, 66 feet high, 10-in. tops, J-in.
steel cable was used on this span, it being constructed to take the place
of a pole line across a dry river bed in case of washout. Factor of
safety is only 1.6 on this span and has withstood winds of 00 miles
per hour. It is supported by compression strains on insulators whose
pins stand radially around the beam; six feet between wires.
Span 400 feet : four poles set same as a tower and held together, also
guyed; double cross-arms, wires spaced four feet apart.
34. Do you consider transposition necessary so far as the power line itselj
is concerned? If so, whyf
35. Do you consider the transposition of the power lines necessary for the
protection of adjacent telephone and telegraph wires?
Reasons for Transposing Power Line.
One company thinks transposing of power lines is not necessary for
lines up to 30 miles and voltages under 20 000, but for distances and volt-
ages in excess of these, thinks it better as power wires are more symmet-
rically located as regards the earth.
One company does not think transposing is necessary when syn-
chronous converters are used at intervals along the line.
One company thinks it is decidedly necessary to transpose power lines,
their principal reasons are; the lack of interference with telephone and
telegraph wires running parallel, and the more spiralling, the less apparent
impedance.
Another company does not think it necessary to transpose power lines
when there is only a single line on poles; they think it is advisable if
not absolutely necessary to transpose power lines as a protection to
adjacent telephone and telegraph lines.
Out of 23 companies that express opinions on the necessity of trans-
posing or not transposing the power lines so far as the power line itself
is concerned, 15 think it is not necessary, and nine of the 20 think it is
not necessary to transpose power lines as a protection to adjacent tele-
phone and telegraph lines.
29. Are braces used on the cross-arms? If so, of what material and how
constructed? {A sketch is desirable.)
30. How are the cross-arms attached to the poles, and how deep are poles
gained?
370 HIGH-TENSION TRANSMISSION.
Methods of Bracing and Fastening Cross-Arms to Poles.
Class A .
Majority of cases, strap-iron braces li by J in. are used.
In one case angle-iron braces are used.
In three cases strap-iron galvanized braces are used.
In one case no bracing is done.
In eleven cases through bolts are used to fasten cross-arm to pole.
In six cases lag-screws are used to fasten cross-arm to pole.
Through bolts average from J to } in. in diameter.
Poles are gained from J in. to 3 in. deep.
Class B.
Strap-iron braces are used in all cases.
In one case the strap-iron braces were galvanized.
In four cases through bolts were used to fasten cross-arm to pole.
In three cases lag-screws were used to fasten cross-arm to pole.
Gains J in. to 2 in. deep.
Class C.
In two cases wooden braces are used.
In three cases strap-iron braces are used.
In one case strap-iron braces were galvanized.
In two cases 1} by IJ angle-iron braces were used
In two cases no braces were used.
In seven cases bolts were used to fasten cross-arms to poles.
In one case bolts were galvanized.
In two cases lags were used, average f in, to f in. diameter.
Gains f in. to IJ in. deep.
Class D.
In two cases strap-iron braces were used.
In one case no braces were used.
In two cases through bolts were used to fasten cross-arms to poles.
In one case i in. lag screws were used to fasten cross-arms to poles
Gains } in. to 1 in. deep.
Class E.
In three cases strap-iron braces were used.
In one case only one brace used on each cross-arm.
In one case strap braces were galvanized.
In one case angle-iron brace on one side of cross-arm.
In three cases J in. through bolts were used.
In one case lags screws were used.
Gains \ in. to 2 in. deep.
Class F.
In three cases no bracing done.
In one case white oak J in. by 3 in. was used.
In one case cross-arms were mortised through pole.
In one case two f in. bdhs were used.
In one case two f in. lags screws were used.
Gains IJ in. deep.
(See sketches showing variotis arrangements of conductors on cross-
?rms, p. 396-399
REPORT. 371
37. In crossing other power lines, telegraph or telephone lines, railroads
or highways, are there any special precautions taken against the
danger of the power lines breaking and falling? If so, what?
Various Methods of Crossing Other Power Lines, Telephone or
Telegraph Lines, and Railroads and Highways.
Class A.
1. Extra cross-arms and idle wires.
2. Double pole fixtures and short spans.
3. Guard wires underneath power wires.
4. Extra-high poles.
5. A ground net of J in. steel cable suspended across railway right
of way under power wires and six feet below them.
Class B.
1. A grounded network of iron wire under power line.
2. Extra-high poles.
3. Telegraph lines put under ground.
Class C.
1 . Guard net under power wires.
2. Truss bridges built across railway track upon which power wires
are supported.
3. Guard wires placed over telegraph wires.
4. High poles.
Class D.
1. Short spans and double fixtures.
2. High poles placed eight feet apart, telephone line passes between.
3. Bronze cables used over railway crossing.
4. Telegraph wires put in cable underneath.
Class E.
Guard wires.
Class F.
1. Twelve foot span and high poles.
2. Guard wires.
3. A grounded net made of f in. steel cable suspended between poles
over railway right-of-way about six feet under power wires.
40. Are there automatic overload devices arranged for cutting off the indi-
vidual sub-stations from the power line?
The following automatic overload devices are used for cutting off the
individual sub-stations from the power line :
Class A .
Four plants use high-tension fuses.
One plant uses high-tension fuse-switch operated by hand.
Two plants use automatic oil-switch.
Class B.
One plant uses high-tension fused cut-outs.
One plant uses fuse-switch.
One plant uses air-brake circuit-breakers.
372 HIGH-TENSION TRANSMISSION.
Class C.
One plant uses fuse circuit-breaker.
One plant uses oil-switch.
One plant uses oil circuit-breaker.
One plant uses automatic circuit-breaker.
Class D.
None.
Class E.
One plant uses fuses.
Two plants use fuse-switch.
Class F.
Two plants use oil-switch.
Two plants use fuse.
41. Are the intermediate sub-stations sources of much trouble? If so,whatf
Various Sources of Trouble at Intermediate Sub-stations.
Class B. — One company had trouble with their rotaries but had cross-
circuiting rings put between each armature section. O.K. now.
Class C. — One company had endless trouble with double-current genera-
tors ; armatures burning out. One company has had trouble due
to defective switching apparatus.
43. How are the wires carried into the power house and into the sub-sta-
tions? {A sketch is desirable.)
44. How is the support arranged just outside of the building, and just inside
of the building? {Sketch.)
(See sketches showing various methods of bringing lines into power
houses and sub-stations Figs. 2-15.)
45. Do you have switches located outside to cut the wires entirely clear of
the sub-stations?
No. of plants that have switches located outside to cut the wires en-
tirely clear of sub-stations.
Class A B C D E P
8 3 11
II. CONDUCTORS.
47. Of what material are they made?
48. Are they solid or stranded? If latter, how many strands or separate
wires?
49. // of copper, are they hard drawn, medium, drawn, or soft drawn?
50. Are they bare or insulated?
Kind of Conductors.
Class A .
Six plants use solid copper hard drawn.
Seven plants use solid copper medium drawn.
Four plants use solid copper soft drawn.
One plant uses 19-strand aluminum.
One plant uses 7-strand aluminum.
Twelve plants use bare conductors.
Seven plants use waterproof insulated conductors.
REPORT.
373
3}^x3;i'x3o"oak
2 Hard Rubber Tubes
.JVaUs
Valtag«
12000
Voltage
J5000
Plate
Voltagls
. J6000
Z^x'fu'piate Glasa
Hole ^
lli'Briok WeU
FIG.fi
Votfaea
23000
lSxja"Eiate0laa»
Porcelain ICUJ
X Ji Strap Hon
'Indow iFrame
FIG, 7
374
HIGH-TENSION TRANSMISSION.
Voltage
30000
\LIne Insulator
"Wood
Clamp
REPORT.
375
376 HIGH-TENSION TRANSMISSION.
Class B.
Two plants use solid copper hard drawn.
Two plants use solid copper medium drawn.
Two plants use solid copper soft drawn.
One plant uses stranded aluminum.
Five plants use bare conductors.
Two plants use waterproof insulated conductors.
Class C.
Three plants use solid copper hard drawn.
Three plants use solid copper medium drawn.
Three plants use stranded aluminiun.
All plants use bare conductors.
Class D.
One plant uses solid copper hard drawn.
One plant uses solid copper medium drawn.
One plant uses solid copper soft drawn.
One plant uses 7-strand aluminum.
All plants use bare conductors.
Class E.
One plant uses 7-strand copper soft drawn.
One plant uses solid copper medium drawn.
Two plants use 7-strand aluminum.
All plants use bare conductors.
Class F
Two plants use solid copper medium drawn.
One plant uses solid copper hard drawn.
One plant uses solid aluminum. •
51. Have you had any serious amount of corrosion of conductors due to
any cause sf If so, what are the causes?
Only two plants have experienced trouble with conductors corroding;
viz., one company has one sub-station at a chloridizing quartz mill; the
gases corrode the copper and cover the glass line-insulators with a film.
The other company has its copper lines corroded by chemical fumes.
52. If the conductors are aluminum, have you found them, satisfactory?
If not, why?
One company experienced a great deal of trouble with their soUd
aluminum line; cause being that the aluminum crystalized due to the
continuous vibration, and used to break frequently.
53. 75 high-tension wiring inside of buildings done with hare or insulated
wire, and if the latter, what kind and thickness of insulation?
54. What kind of insulators are used for this interior wiring?
The majority of plants use rubber-insulated wire for their interior wire
(high tension) the thickness of rubber varying from -^^ in. to J in.
The balance use bare wire, with the exception of four or five plants which
use paper or rubber lead-covered cable laid in ducts. The interior wiring
in classes A and B is held on porcelain cleats and knobs in the majority
of installations. In classes C, D, E, and F the ordinary line insulator is
generally used to support the interior high-tension cond(Uctors.
REPORT.
377
III. LINE INSULATORS.
55. Are the insulators glass or porcelain?
56. What is name of maker and what is the trade name or designation for
them?
57. Have you any preference as to material and if so, why?
58. // porcelain, are they tinted, and what color?
60. Are the wires carried upon the top or the side of the insulators?
61. What tests were given the insulators before installing?
62. At what voltage will a flash occur between wire and pin when being
sprayed with water?
63. At what voltage will they puncture?
64. Have you found your insulators satisfactory, if not what has been the
trouble and to what has it been due?
TABLE C.
Material.
Color.
Method
of Tying.
Tests.
Class.
d
'3
1
(2
3
B
<« .
Ih
d
s
3
A
•o
(21
Puncture
Volts.
Spray
Volts.
Makers,
A
6
9
3
7
2
6
11
20 000
to
50 000
—
B
2
4
1
3
1
4
2
40 000
to
50 000
25 000
1
C
4
4
1
3
3
4
3
50 000
to
75 000
—
mas & Son Co.
gway Glass Co.
al Porcelain W
.nowles.
ke & Co.
1 Electric Co.
dsCo.
Italy.
D
2
2
—
1
1
2
1
80 000
to
120 000
—
E
4
4
4
60 000
to
90 000
35 000
to
55 000
F
2
1
1
1
1
1
1
120 000
saltwater
70 000
Nodes. — Prefer porcelain to glass on, account of greater mechanical
strength; greater dielectric strength; less liability to creeping of
static over siirface.
Prefer glass to porcelain on account of defects being easier de-
tected by inspection ; less tendency for dirt to hold on.
Four companies had trouble with tops breaking off glass insulators
at grooves, due to changes in weather, etc. Two companies had
trouble with glazed filled insulators, the insulator cracking at the
joints.
One company had trouble with film forming on glass insulator
from quartz mill.
378 HIGH-TENSION TRANSMISSION.
IV. CROSS-ARMS.
65. What are the dimensions of the cross-arms?
66. Of what material are they made?
Sizes vary from 2\ in. by 4i in. to 4i in. by 9 in., the average section
being 3i in. by 4i in.
The majority of plants use yellow pine, other woods used are: white
pine, yellow fir, Oregon pine, spruce, Oregon fir, peroba, and cabreura,
the last two being Brazilian woods.
67. // of wood, have they been treated in any way? If so, in what way?
The following are different methods of treating cross-arms :
(1) Painted with white lead.
(2) Painted with mineral red in oil.
(3) Painted two coats.
(4) Painted coal tar.
(5) Painted two coats metallic paint.
(6) Treated with carbolinium.
(7) Boiled in linseed oil two or three hours.
(8) Dipped in bitumen paint.
(9) Dipped in creosote.
V. POLES.
68. What kind of poles? Steel or wood? If wood, what kind?
Majority of plants use cedar poles. Other woods used are: chestnut,
jvmiper, cypress, red cedar, tamarack, Idaho cedar, spruce, and white
cedar.
71. What are the dimensions of the tops of the different lengths of poles,
also the minimum diameter of the butts?
Tops vary from 5 in. to 8 in. in diameter. ) n i i
15 ^^ r o • ... n/ • ■ J- ^ C Poles vary from
Butts vary from 9 in. to 24 in. m diameter. ^
.r. I
eter. >-
in. )
"""" '"7 "."'" ." "' 't "' "'°;r ( 25 ft. to 45 ft. long.
Average top is 7 in. ; average butt is 12 m. ^
72. How deep are the different lengths of poles set into the ground?
Poles are placed in ground from 4 ft. to 8 ft. according to their length
and condition of soil.
Poles were treated in the following ways :
74. Are the poles treated in any way? If so, how? Are they painted?
(1) Gains painted with metallic paint.
(2) Butts tarred.
(3) Poles painted.
(4) Butts painted.
(5) Tops painted.
(6) Butts treated with carbolinium.
(7) Tops painted with linseed oil.
(8) Butts burned and tarred.
(9) Butts painted with asphaltum.
75. How are the tops finished?
Majority of plants roof the tops of the poles.
A large percentage paint tops of the poles.
REPORT.
379
One plant puts cast-iron caps on poles.
One plant charapfers the pole tops to pin that is in end of pole, and
binds No. 6 galvanized-iron wire around end, and paints top with P. & B.
paint.
76. Is there a pin in the top of the pole, and if so, is there a metal band
around the top?
Four companies that have pin in top of the pole have an iron ring
around pole.
One company uses a composite pole made with a 7-in. iron pipe, socket
13 ft. long, Australian jarra wood top 7 by 7 in., 17 ft. long, pressed
into the socket; this pole is placed 6 ft. in the ground. Poles are tarred,
and a galvanized-iron cap is put on top of pole. A few companies use
octagonal and square poles.
Kind of Wood.
Location.
Life of pole in years.
Red Cedar
Ohio
20
Cedar
Oregon
10-15
■
California
10-15
Idaho
15
■
Montana
6-7
'
Washington
10-15
'
Minnesota
14-16
1 "
Pennsylvania
9
"
Canada
15
Chestnut
New York
8-14
••
Pennsylvania
8
"
Massachusetts
8-12
" (2d growth)
Pennsylvania
12-16
Juniper
Georgfa
15
Cypress
Carolina
8
Tamarack
California
5
Pine
Pennsylvania
8
69. What is the length of their life and on what peculiar conditions, if any,
does this depend?
78. Give dimension sketches of pole-head, showing cross-arms, pins, and
insulators.
See dimension sketches on pages 396-399
73. Are any of the poles set in concrete or otherwise, giving additional
solidity in the earth?
The following methods are used for poles in boggy or swamp land:
1 . Set in concrete.
2. Tamped with broken stone.
3. Protected by rock cribs.
380 HIGH-TENSION TRANSMISSION.
VI. PINS.
79. Of what material are the pins made?
80. // of wood, what kind of wood?
Classes A, B, C, and D.
In these classes the standard 1 J in. locust pin is iised in most cases;
other kinds of pins used are: black locust, oak, eucalyptvis, hickory,
iron with wooden thimbles, porcelain, and iron | in. fastened into
insulators with cement.
Classes E and F.
Following kinds of pins are used :
1. Iron pins held into insulator with Portland cement.
2. Iron pins, wooden thimble, porcelain base.
3. Locust and eucalyptus.
4. Steel pin and cast-iron bushing in cross-arm (see sketch).
81. Are they treated, and if so, how?
Pins are treated in the following ways:
1. Boiled in paraffin about 24 hours.
2. Boiled in linseed oil about two hours.
3. Painted.
4. Dipped in elastic bitumen.
In a great many cases pins were not treated in any way.
In all cases where wood pins were used they were boiled in paraffin for
24 hours.
83. Are the pins fastened in the cross-arm and pole, and if so, how?
Pins are fastened to cross-arms in the following ways:
1. Nailed (in most cases).
2. Nut and washer (when iron pins are used).
3. Wooden dowel (in one case).
4. Iron spring (in one case).
5. Driven into cross-arm tightly.
The following methods are used to hold pins in cross-arms and poles:
1. Pins screwed into top of pole.
2. Nut and washer (irpn pins).
3. Nailed through cross-arm.
4. i in. and } in. oak dowel.
82. What are the dimensions of the pin? {A sketch is desirable.)
See sketches showing various size pins. Figs. 16-21
VII. TELEPHONE LINE.
85. Have you telephone lines upon your transmission poles?
All plants with the exception of four have telephone lines on same poles
as the power lines. One plant in Class F has its telephone line on
separate poles 200 feet from the power line.
87. What kind of pins, insulators, and cross-arms or brackets are used?
Majority of plants use standard side brackets, cross-arms, pins, and
glass telephone insulators.
REPORT.
381
'T
Ql
■■;■-.
-25^-
.L
Fig.. U
-Z%r-*\
-•ax—-.
.1-.
Cemented into Insulator
n:
27000 VoItPJn
Fig. J 7
ffisp Pin CrossArmJRin
' 30000 Volt.lron Pin,
t« 2}
o
-1
^
^
w=
35 000
i
^
y
CURVES SHOWING ECONOMICAL VOLTAQE
POWER PURCHASED AT $10.90 PER KILOWATT PER ANNUM.
lOO 200 eoo 400
p=distance in miles.
Fig. 1.
eoo
600
700
for any given output and distance of transmission.
Fig. 2 shows, in a corresponding manner, the economical
drop.
Fig. 3 shows the diameter of the conductors corresponding to
the conditions of Figs. 1 and 2.
Fig. 4 shows the relation between D, the distance of trans-
mfssion, and p, the percentage net profit on the investment for
MAXIMUM TRANSMISSION DISTANCE.
415
different values of output W and for selling price of $34 per
kilowatt per annum.
Fig. 5 is similar to Fig. 4 but applies to a selling price of $20
per kilowatt per annum.
Fig. 6 shows for different selling prices the relation between
30
.18
^
14
la
10
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
' /
'
y
A
/
/
/
/
/
/
/
UJ
n-^
r
/
/
/
/
/
/
/
>
III
.
f
/
^
."^
/
/
/
/
/^
/
a
Li.
o
/
;
/,
/
/
/
z
/
/
/
.*
%
k
/
/
Q.
/,
/
/
/
f
3
0.
/
/
/
/
/
/
a
II
//
V
/
/
/
s
/.
d
y
/
//I
/ /
^
/
//
//.
'/
4
'/
CURVES SHOW.INQ ESOISIjOMICAL DROP.
POWER PUaCHASED AT $10^0 PER KILOWATT PER' ANNUM.
/
^ioo ^ _8)io aoo Joo 3oo
d=distance in miles.
Fig. 2
600
TOO
the distance of transmission and the output for a net profit of
12%. The lower curve of Fig. 6 is derived from Fig. 4 by plot-
ting the distances and outputs of Fig. 4 corresponding to a net
profit of 12%. In a similar manner the upper curve of Fig. 6
is obtained from Fig. 5. The other curves of Fig. 6 were ob-
416
HIGH-TENSION TRANSMISSION.
tained from other sets of curves (not included herein) , similar
to those of Fig. 4 and Fig. 5, and applying to the other prices
of power to which Fig. 6 applies.
In obtaining these curves the constants have all been given
1.80
1.30
1.00
0.90
0.80
0.70
0.60
0.50
0.40
0.30
\
\
.
W=5
00 000
CO
UJ
^
o
z
■
W=3
00 000
§
\
o
Q
■^
^
oo-ooo
O
o
s
CURVES SHOWING DIAMETERS OF CONDUCTORS.
POWER PURCHASED AT $10.90 PER KILOWATT PER ANNUM.
UJ
S
<
II
a
---.
^~
W=l
00 000
^
W =
50 000
""^
—
W=
3.5 000
100
soo
BOO 400 500
d=distance in miles.
Fig, 3.
600
700
values favorable to long transmission distances. The costs
have been taken lower than those ordinarily current in the
endeavor to anticipate somewhat possible future prices. Also,
the cost of power purchased at the step-up station has been fixed
MAXIMUM TRANSMISSION DISTANCE.
417
at the very low figure of $10.90 per kilowatt per annum. These
facts should be carefully borne in mind in considering the curves,
which will all be more or less modified by changes in the quan-
tities mentioned.
100
90
CURVES SHOWING NET PROFIT FOR DIFFERENT
DISTANCES OF TRANSMISSION.
POWER PURCHASED AT $10.90 PER KILOWATT
PER ANNUM.
POWER SOLD- AT $34.00 PER. KILOWATT
PER ANNUM.
Too 400 SOO
d=distance in miles.
Fig. 4.
On comparing the diameters of conductors given by Fig. 3
and the voltages to which they correspond with the values of
diameter and critical voltage given by Professor Harris J. Ryan
in his splendid paper on that subject,* it appears that the
diametersof Fig. 3 are considerably above those of, the paper men-
* See paper read by Professor Ryan before American Institute op
Electrical Engineers, February 26, 1904.
418
HIGH-TENSION TRANSMISSION.
tioned. The values of Fig. 3 are afEected by the price paid for
power at the step-up transformers, but if this be takeji even as high
as $20 per kilowatt per annum instead of $10.90, the diameters
of the conductors remain below those for the critical voltages. It
appears, therefore, in the light of present knowledge, that the
limit of voltage will come through economic conditions and
not through conditions depending upon atmospheric losses.
It is difficult to fix upon a figure for the selling price of the
delivered power which shall be representative. Power prices are
so dependent upon conditions, especially those arising from the
location and magnitude of the market and of the supply, that
any figure chosen will be objected to by some as too high and
40
io
CURVES SHOWING NET PROFIT FOR DIFFERENT
DISTANCES OF TRANSMISSION
POWER PURCHASED AT $10.90 PER KILOWATT
PER /IN NUM.
POWER SOLD AT $20.00 PER KILOWATT
PER ANNUM.
z
LU
O
cc
LlJ
\
z
\^
\
u.
o
q:
\
\^
^-
UJ
\
S
&
II
0.
V
^
^«.J
^
^^^
^0
:^
'::zz
^^
lOO SCO 300 400 SQB
d^distanoe in miles.
Fig. 5,
coo
700
by others as too low. The same statement applies to the price
assumed as that paid for power at the step-up station, but in a
lesser degree. The selling prices of $34 and $20 have been
chosen as the upper and lower limits for the price of power
in such large amounts as are under consideration.* While it is
tinquestionably true that in some parts of the country power
is worth, and will bring, much more than $34, the markets
where such prices are obtainable are not very large; in the
East, where large markets are possible, much more than $34
cannot be expected for very large amounts of power.
* The paper as originally presented contained curves applying to the
selling price of 134.00 only.
MAXIMUM TRANSMISSION DISTANCE.
419
On the other hand, $20 is believed to be as low as will obtain
under any other than the most exceptionable circumstances.
Fig. 6 covers this range of prices, giving curves for intermediate
prices as well as the limiting prices mentioned.
The voltages to which the curves apply are much higher
than those now in use commercially, but they are not beyond
the range of future possibility. Manufacturers will now under-
take commercial transformers for voltages as high as 150 000
600 000
CURVES SHOWING DISTANCES OF TRANSMISSION
FOR DIFFERENT OUTPUTS AND DIFFERENT VALUES
OF S = SELLINQ PRICE PER KILOWATT PER ANNUM.
POWER PURCHASED AT $10.90 PER KILOWATT
PER annum:
NET PR0F1T=12 PER CENT.
o
BOO 000
L
<^
;
i
/
/
1
/
/
dOO'OOO
/
1
/
/
/
>b
/
/
/
/
/
300 000
= w
MAXIMUM TRANSMISSION DISTANCE. 425
Now if the first derivative of gi with respect to E be set
equal to zero to determine the best value of E, there results a
quartic equation more interesting than valuable, so far as the
present purpose is concerned. It will greatly simplify matters
if instead of substituting the value of x in (1 + ;!;)' we substitute
ior X, x^, a fixed drop of such value as will correspond to the
average cost of insulator between the two extreme values of x
which will be met with in practice ; a.s will be shown later, the
error due to such a course will be small. Hence
2hcnWDE-' + p,K,E' (l + x^Y D + p,K,' (E+J^/)TF *
Setting the first derivative of this equation equal to zero,
^-| — Sj there results
E--
\%pJi^{\^x;fD V 2,iop^Ki {l^x^^'D-'^ Zpj<:^{\-Vx^^'
= (- 3066^* ^J 9400356 g + 3438.5 wf (3.)
This shows that the voltage may be increased with increase of
output, which was to be expected since those costs which limit the
voltage will diminish in their amount per kilowatt as the output
increases. The value of x^ used in the above equation was
determined upon as follows : The minimum percentage drop which
is ever likely to obtain is, say, 2.2; the maximum is, say, 11.5.
The reason for selecting these values will be apparent on consider-
ing the values of E calculated from the above equation, and given
below, in connection with the values of W to which they corre-
spond, and the respective distances to which in each case the
various amounts of power would probably be transmitted.
The intermediate value of drop which will give the average
insulator cost is 6.45%, and this value of x^ is taken. With
this value of x^ the maximum error in insulator cost, between
the limits assigned, will have place when x = 2.2 and x = 11.5.
The percentage error at either of these limits is about 13%. But,
as appears in the solution of the first derivative, at the point
of minimum of the variables affected by the voltage the com-
426 HIGH-TENSION TRANSMISSION.
bined values of the annual cost due to the conductors, the annual
cost of the line loss, and that portion of the annual transformer
cost due to voltage, is more than three times that due to the
insulators. The total variable quantity involved, therefore, is
more than four times the annual cost due to insulators, and
the error as a percentage of the total of values of the variables
13
involved is less than — =• 3.25, instead of 13%. As will be
seen on examining the manner in which Xi enters the equation
for E, the maximum error in E will be less than 3%, also which
will to a like extent affect the values of x. This error is negli-
gible so far as the main problem is concerned, and indeed so far
as the question of voltage itself is concerned.
In Fig. 1 are shown curves plotted from equation (3). These
curves show the kilovolts E for different distances D, and dif-
ferent outputs W. Fig. 2 gives curves plotted from equation
(2), using the values obtained from the curves of Fig. 1. The
curves of Fig. 2 show the percentage drop x for different distances
D, and different outputs W In Fig. 3 are curves showing the
diameters of the conductors for the conditions of Figs. 1 and 2.
These diameters were calculated from the formula
which gives the diameter d, in inches, of a solid conductor.
These diameters were in this case calculated for a solid con-
ductor instead of a stranded one because we have at present
available data as to the critical point in the atmospheric loss
curve for solid conductors only, and while perhaps this critical
point will come at a higher voltage in the case of the stranded
conductor with its greater diameter, there are no definite data
at present on the subject. On comparing the diameters of con-
ductors given by Fig. 3 and the voltages to which they corre-
spond with the values of diameter and critical voltage given
by Professor Ryan* we see that the diameters of Fig. 3 are con-
siderably above those of Prof. Ryan's paper. It appears, there-
fore, from the present knowledge available, that the limit of
voltage will come through economic conditions, and not through
limitations connected with atmospheric losses.
*See foot note, page 417.
MAXIMUM TRANSMISSION DISTANCE. 427
In the determination of both x and E the quantity h has
been employed. This quantity is a factor which, when multi-
plied into the cost of power at the low-tension bus-bars of the
step-up transformers, will give the cost of power at the high-
tension terminals of the transformers. That is to say, h takes
account of all charges which should be made against this power,
including interest and depreciation of the step-up station, trans-
formers, etc., and labor for operating the station, also the loss
in the transformers. Now, strictly, there should be substituted
for h, the proper functions of the quantities on which it de-
pends, but to do so would seriously complicate the equations
and would be of little utility, since h can be approximated
with sufficient accuracy in any particular case, and the manner
in which it occurs in both x and E is such as to make the error
in the quantities due to an error in h much smaller than the
error in h itself. In the specific problem herein the value c = 10.9
is taken as being the lowest which will probably ever obtain,
where large amounts of power are available within transmission
distance of a desirable market. The value taken for h in the
determination of E and ic is /f = 1.1, so that he = 12.
The next step is the determination of the forms of the several
functions indicated. In what follows the constants have been
evaluated for the specific problem herein. The costs resulting
from the use of these constants will be found to be, in general,
considerably less than present commercial costs. The con-
stants were purposely based on prices less than can be now
obtained, in the endeavor to anticipate, somewhat, possible
future prices.
From a careful consideration of transformer prices, it has
been determined that, for transformers of 1500 kw. and over,
the cost, installed, very closely follows the law,
/, (£, W) = K,' (E+K/) W^ = 13. {E+K,") W^,
.-. p, f, (E, W) = p, K,' (E+Kf) W^ = 1.625 (E+K/) W^
in which K/ is a constant and Ki" a " variable constant," a
quantity which varies slowly with the output in accordance
with the law,
K^" = ki + ki'Vi^ = 55 + 0.000227 W
Theoretically the transformer cost would vary with the
drop Xi, since the step-up transformers would have an output
and voltage greater than the step-down transformers. Prac-
428 HIGH-TENSION TRANSMISSION.
tically, however, step-up and step-down transformers are built
so nearly in the same lines that the drop would make little dif-
ference. Such difference as would exist can be taken care of
approximately by adjustment of the constants, which has been
done.
While the apparatus for the control of the high-tension side
of the transformers would theoretically vary with the voltage,
such variation for 50 000 volts and over will be small, since
in most modem plants the high-tension switching apparatus
is simple; and higher voltages are likely to cause it to remain
so. The lightning protection for the high-voltage lines might
vary with the voltage, but it is probable that for high voltages
there will soon be a reversion to much simpler and inexpensive
apparatus than we use now, so that the variation, if any, due
to higher voltages, will be negligible. The switchboard for the
lower voltage side of the transformers will vary only with the
output, since we assume the lower voltage to be the same in
all cases, say 6000 volts or thereabouts. The apparatus for
the control of transformers may, therefore, be considered as
depending only upon output. Under this assumption a con-
sideration of costs of transformer controlling apparatus and
cables, shows that we may assume, with a close degree of accu-
racy, that
/, (£, W) = K,'+K/ W = 21 OOOH-0.9 W
.-. p, U (E, W)=p, K,' + p, K," W = 2625 + 0.1125 W
The cost of buildings and the real estate for them will increase
very slowly with the output. The variation of this item due
to variation of output can be expressed closely enough by
U(W) =K/ + K,"Wi = 125 000+1251^*
•■P,h(W) = p,K,' + p,K/W» = 9375 + 9.375 Ty«
The cost of an insulator will, theoretically, vary with the
diameter of the conductor and the voltage. Practically, how-
ever, the diameter of the conductor will have nothing to do
with the cost. A consideration of insulator prices shows that
the cost of an insulator will vary as the sum of a small constant
plus the product of a constant into the cube of the voltage.
With high voltages the small constant is negligible, so that we
may write
f, (E,d,D) = Kt E^ (l+x,y D = 0.000732 (1.0645)' £'D =
0.000883 £» D.
:.pJAE,d,D) = p,K^E'il + x,yD = 0.0000883 £» D
MAXIMUM TRANSMISSION DISTANCE. 429
The cost of the pole-line material and construction will depend
somewhat upon the diameter of the conductors, since, as the
diameter of the conductors increases, the wind and sleet stresses
will increase. The increase of cost with increase in diameter of
conductors will be slow. The law followed will be that of a con-
stant plus a function of the diameter of conductors, since, no
matter how small the diameter of conductor, there will be a
certain cost representing the minimum sized pole which would
be employed. We may, with a fair degree of accuracy, write
U {d, D) = {K,'+K," d)D = U (E, W, X, D)
or, putting in the value of x = n— >
/, (£, W, X, D) = K,' D+^^' (f JD = 3000I? + 37.2(f j D
K " k fW\i
.•.p,hiE.W,x.D)=p,K,'D + p, -^' {^) D
= 375 L> + 4.65 l^j D
which answers for a stranded conductor.
Cost of right of way will be directly proportional to distance,
hence
/o (D) = K,D = 1000 D
.■.p,hiD)=P,K,D=50D
A consideration of synchronous motor prices shows that the
cost of synchronous motors may be written,
/, (W) = K/ + K/ W = 12 000 + 5.4 W
■■■P^UiW) = PtK^' + P,K,"W = 1500 + 0.675 T^
The switchboards and cables for the motors will follow the
same law as those for the transformers, hence
/, (WO = K^' + K," W = 8400 + 0.17 W
.■.p»fi (W)=psKi' + p,K/W = 1050 + 0.02125 PF
From the well known relations between the cost of con-
430 HIGH-TENSION TRANSMISSION.
ductors, and the voltage, distance, output, and drop, we may write
U (E, W, X, D) = K, -^ = 0.346
E' X ' E^ X
■ , , . D
or, putting m the value ofx = n^
, ,_ ,^. „. j^WD K,WD ^,WD
fg {E, W, X, D) = Kg -=. = — ° -=r- = 9.1 — =r-
'"^^ ^ En n E E
WD WD
.-.p, U (E, W, X, D)=p,K,^^ = 0.455 '-—
The cost of labor, for the operation of the step-up and step-
down transformer stations, and for executive and clerical pur-
poses, would probably not vary at all. We have, in each case,
the same number of units to be looked after, and the size of
these units would make little, if any, difference in the cost of
attendance upon them. Similarly, the output will make little
difference in executive and clerical costs. We should probably
be justified in making /^ (W) a constant. In order, however,
to cover such small increase in labor and salaries as there might
be with increase of output we will write
f,o (W) = K,,'+K,," Wi = 32 000 + 26 W*
It is to be noted that the labor in connection with the line
is taken care of in the depreciation and repair percentages
applicable to the supporting structure and insulators respect-
ively.
The efficiency of the whole system is , — ^-~
\-\-x
Putting in the value oix = n^=r
E
e, 0.925
e = —
1 + w^ 1+0.038^
E E
^^ W(l + ng). ^^,^^ ^^^^^^
e e^ e^ e^ E E
The various lunctions above arrived at may now be utilized
in obtaining N and M of equation (1), p = — ,
Remembering that R is the sum of the products of the
various functions by the corresponding percentages representing
interest, depreciation, and repair; that L = /^ (W), and repre-
senting the various resulting collections of constants as follows
MAXIMUM TRANSMISSION DISTANCE. 431
a = p, K," + p, K," + p, K," = 0.788
b = K,,' + p,K,' + p,K,' + p,K,' + p,K,'= 46550
m = K,o" + p3K/ = 35.38
r = p,K,' + p,K, = 425
then N^Ws- ^'^^ + '^^ -L-R
- p,KAl+x,y E' D -r D - ^' ^J ^' H^^D-b.
Representing constants as follows
a = K/ + K," + K/ = 6.47
13 = K^ + K^' + K^+Ks' =166400
r = K^'+K^ = 4000
M = a W+ — °^+i^/ Wi +K,'{E + K,") Wi
n E
^K,{l+x,rE' D + rD + ^^(^^y D + p.
These values of N and M, if substituted in equation (1) will
give, in its final form, the equation connecting distance, output,
voltage, and profit, or, in connection with equation (3), for volt-
age, the relation between distance, output, and profit. Such
substitution results in a cumbersome equation and will not be
made here. If the various numerical values, already deter-
mined for the specific problem herein treated, be substituted
in N and M, there results,
Ar=(5-12.57) T^- 0.902 ^^-35.38 W'l -1.625 (E+Ki")Wi
- 0.0000883 £» Z? - 425 Z> - 4.65 0^\ Z) - 46 550
M= 6.47 TF+9.1^ + 125W*-l-13(£;+ii:/)W^'^+0.000883£'I>
-f 4000 £> -f- 37.2 (^) D+1Q6 400.
432 HIGH-TENSION TRANSMISSION.
Putting in this equation the various values of ^ and calculat-
ing the value of p for different outputs, W, and different distances
D, the curves of Fig. 4 and Fig. 5 (and the other sets of similar
curves for other prices of power) have been obtained. These
curves show, for different values of W, the relation between
p and D. Assuming that the minimum acceptable profit is
12 per cent, and taking from Fig. 4 and Fig. 5 and the other
sets of similar curves (not included herein) the values of D and
W corresponding to this percentage profit, there has been
plotted the final curve, Fig. 6, which shows the relation be-
tween distance and output for the percentage profit assumed.
In considering these curves, the assumption made in con-
nection with them should be carefully borne in mind. A small
change in the purchase price or selling price of power will make
a great difference in the result. Smaller amounts of power will
in general be purchased at a higher price per kilowatt, but
on the other hand they would probably be transmitted to points
where the power would bring a higher price, since in general, the
larger the market the cheaper can power be produced by steam ;
this fact compensates somewhat for the error in assuming the
same purchase price for large and small amounts of power.
It would be interesting to let 5 — c/e, equal to zero and de-
termine p which would then be the cost, including interest, of
operating the plant. If curves showing the percentage of the
investment for operation were thus determined, also the total
cost of the plant, both tor various outputs, the results would
be valuable in preliminary estimates. The writer hopes to work
up such data, later.
It will be noticed on referring to the curves that some of
them reach to distances which cause the drop to exceed the
value taken for the upper limit of drop in connection with insu-
lator cost. The error due to 1 or 2% excess will not greatly
affect the final result. It would have been somewhat better
however to have chosen the limits of drop as 5% and 15% re-
spectively instead of those taken.
MAXIMUM TRANSMISSION DISTANCE. 433
Discussion on " The Maximum Distance to Which Power
Can be Economically Transmitted."
President Lieb: It is gratifying to have had another pio-
neer paper from Mr. Mershon, presenting data for the solution
of problems in the transmission of electrical energy, an im-
portant branch of electrical industry. Large parts of our
western territory are vitally interested in the solution of these
problems of transmission, notably the Pacific coast territory
and vast tracts of land in need of irrigation.
The bringing of cheap industrial power into the mining cen-
tres is doing much toward lessening the cost of handling ores,
making it possible to develop the poorer grades of ore. In the
South also the econornic conditions have been vastly improved
by the utilization of the natural sources of power.
In Switzerland and Italy, for instance, it is hardly too much
to say that the future prosperity of those countries is intimately
bound up with the utilization of the vast sources of natural
power, the " white coal " of the Alps.
While the speaker has no data at hand as to the extent to
which the coal consumption is affected by the utilization of the
water courses, the effect must be important, as industrial centres
like the plain of Lombardy (Italy) are no longer operating their
cotton mills and silk mills by steam power, but are now de-
pendent upon electric power from transmission plants. When
it is considered that almost all of the coal consumed in Italy is
brought in bottoms from England, it is evident what an eco-
nomic evolution such a change represents.
H. G. Stott: This paper is a most interesting one, not only
to the engineer, but to the capitalist; for the modern trend of
events shows that at no distant time the steam railroads in this
country will in all probability be operated electrically. That in
itself brings up the question of the maximum distance to which
power can be economically transmitted ; and the suggestion occurs
at once whether we can transmit our power any more
cheaply over wires than we can in the shape of coal in cars, and
also which is the more reliable way of doing it. After all, every
transmission scheme gets down to the question of reliability.
An electrical transmission line, as we well know, is a sensitive
piece of apparatus, subject to atmospheric disturbance, subject
to the small boy with the kite, and with the piece of wire which
he can throw over the line at any time. The freight-car is a
pretty hardy piece of apparatus and not only hardy, but it has
the possibility of a storage of power in the shape of coal at the
point where the power is to be generated. The question of re-
liability is difficult to define, as to just what we want in
the shape of reliability ; power would not be considered reliable
if the total interruptions per year exceed one hour. That
criterion in some cases may be too exacting and in other cases
not exacting enough. In large lighting plants, such as there
are in New York, an interruption of one hour, unless taken care
434 HIGH-TENSION TRANSMISSION.
of by storage-batteries, would be so serious a menace to the
interests of the company and so annoying to the public that it
would not be considered for a moment as permissible.
This paper deals with figures of 200 000 or 300 000 kw., and
with distances of 550 miles. The transmission of power from
Niagara Falls to New York would come well within the limits
defined by the author, as the distance is approximately 450 miles
and the amount of power used by the large plants in this city
approximates 175 000 kilowatts.
The author makes the recommendation: " Frequency of trans-
mission not less than 25 cycles nor more than 30 cycles as being
the limiting frequencies," and in the paragraph immediately
following is the statement: " Idle synchronous motors at step-
down station to correct for power-factor, the average power-
factor of the line being held as near unity as possible." By in-
creasing the frequency we increase the capacity current of the
line, and in that way can compensate for quite a large lagging
power-factor. If there were not so many established plants
using 25 cycles, the speaker thinks it would be profitable to
discuss the question of using this frequency, whether 25
cycles is not too low. In the west, where 60 cycles is used
almost exclusively, the power-factor is nearly always leading.
That has another bearing on the cost of copper, and also elimi-
nates the idle synchronous motors, which may be a source of
much trouble in the case of disturbances, such as short circuits,
on the line.
The principal criticism to be made is that the cost has been
worked out without consideration of the load-factor, when it
can not be expected that the load-factor will be greater than
50%, and this in turn affects the entire copper calculations.
Examination of the mathematical analysis upon which the
curves in this paper are based shows that load-factor has been
entirely ignored and that the assumption has been made that
power can be sold at a uniform price per kilowatt independent
of the load-factor. Many attempts have been made to sell
power upon this basis, but the speaker's experience is that they
have ended in a mutual recognition by the producer and the
consumer that it was not fair to the latter. $34.00 per kilowatt
would mean that the cost per kilowatt-hour (on one-hour peak
load lasting 309 days per annum) would be over 11 cents, or more
than double the cost of steam power under the same load-factor.
As a general proposition, it may be safely stated that no distant
water power transmission plant can compete with a steam plant
located near the point at which power is to be delivered, if the
load-factor is less than 40% and coal less than $3.25 per ton.
In regard to the figure given of $10.90 per annum per kilowatt
for power at the source of supply, there are few if any water-
power plants developed for less than $100 per kilowatt, and
some have gone as high as $190 per kilowatt, so that if we allow
12.5% for interest, depreciation, etc., as in the author's paper,
the minimum cost per kilowatt would vary from $12.50 to $23.75.
MAXIMUM TRANSMISSION DISTANCE. 435
Philip Torchio: Mr. Stott said he looked at this paper
from the point of view of transmitting power from Niagara
Falls to New York, or to similar large centres where there is a
great market for power. This discussion will be somewhat from
the same point of view, and not from the point of view of terri-
tories, such as exist in the West, where the cost of coal may be
a great factor in the development of long-distance power trans-
mission.
The general problem treated by the author involves the
study of the two main factors which enter into the
problem of power transmission, i.e., the transmission pres-
sure and the cross-section of the conductors. The elements
which are affected by the pressure are the cost of transformers
and insulators, which increase with the pressure, and the cost
of line conductors and line losses, which decrease with the
pressure. All the other elements are practically not influenced
by the change in pressure. The author has treated the subject
in detail, and has given a formula for the determination of the
most economical transmission pressure. In this formula there
enters the cost of line losses and interest and depreciation on
conductors, both of which are dependent upon the most econom-
ical cross-section of conductors ; therefore the dominating factor
in a study of this character is the determination of the cross-
section of conductors for the fixed conditions of each problem.
The author has adopted the Kelvin law for the determination
of the cross-section of conductors, and he has obtained the re-
sults shown in Fig. 3, giving: " The diameter of the conductors
for power purchased at $10.90 per kilowatt per annum."
The speaker has, during the last ten years, done considerable
work on problems of transmission of power for a great variety
of conditions; in all these studies he has made frequent use of
the Kelvin law, which has been of great service to him. Its
importance, however, is not generally recognized among engi-
neers, perhaps for the reason of the great care which must be
used in the selection of the factors entering into the formula,
and also on account of the mistaken interpretation of the mean-
ing of the formula which is often expected to give a general
solution of any specific problem without regard to other require-
ments not taken into consideration by the Kelvin law. This
law gives with accuracy the most economical cross-section of
the conductors of a circuit in which we want a certain current
to circulate. Other requirements, such as the safe carrying
capacity of wires, the regulation, the brush discharges of high-
pressure lines, etc., may substantially modify the conclusions
arrived at from the consideration of the theoretical conditions
of efficiency alone, and these modifying influences must be given
due weight.
The speaker wishes to make a criticism in connection with
the author's assumption of $10.90 per kilowatt per annum for
the line losses, this being the same amount as paid for the main
436 HIGH-TENSION TRANSMISSION.
bulk of current. The author, in this instance, failed to apply
the very same principle which is one of the prominent features
of the treatment of his paper, i.e., " That the greater the out-
put of a plant, the less is the cost per kilowatt of all the equip-
ment." Now if there is a case where this general principle is
unquestionably correct, it is the case of the increment cost of
station equipment for amounts not exceeding say 5% or 10%
of the total equipment; that is, if a plant of 100 000 kw.
will cost, say $10 000 000 or $100 per kilowatt, we must certainly
be able to increase the capacity of the apparatus say 10% at
an increment cost considerably less than the average of $100
per kilowatt. The fact that in the paper the power is assumed
to be purchased at a fixed rate per kilowatt will not alter con-
ditions, as the saving derived from this increment cost of gen-
erating equipment will be felt either directly or indirectly by
the transmitting company, either by lower fixed charges for
the operation of the generating plant, or lower price of power
charged by the generating company. If the transmitting
company owns and operates the generating plant as well, nobody
will question the above reasoning. The speaker does not see
any reason why the same should not hold for the two enterprises
operated independently; at least in this theoretical discussion
such assumption should be made. If this had been done, per
haps the increment cost of power for line losses and other losses
would have been $5.45 instead of $10.90 per kilowatt, while
the cost of power delivered would have been slightly increased
by the necessary amount so that the average of all power would
still amount to $10.90 per kilowatt as before. This change in
cost of power for line losses would have considerably changed
the final results. The cross-sections of conductors given in
Table 3, all of which are based on approximately 2500 circular
mils per ampere, would have been changed to the basis of 1750
circular mils per ampere, thereby reducing the total cost of con-
ductors about 30%. The economical voltages of Fig. 1 would
have been somewhat changed, while the curves of economical
energy drop of Fig. 2 would have been raised about 42%. By
referring to Fig. 2 we see that such increase in energy drop
would be permissible for all cases up to about 200 miles ; this at
least for the curves of larger outputs. For longer distances we
should meet serious objections, especially for the curves of
smaller outputs. These limitations are dependent upon the
character of apparatus supplied at the receiving end of the line.
In general the presence of different types of apparatus will limit
the maximum energy drop to the following amounts:
Synchronous converters, about 10%
Synchronous motors, about 15%
Induction motors, about 20%
This brings into play a new factor which is not taken into
account by the formulas. Any conclusions that might be de-
rived from the analytical treatment must be ultimately revised
MAXIMUM TRANSMISSION DISTANCE.
437
to meet the above requirements of maximum energy drop. In
the case of very long transmission lines, necessarily involving
large amounts of power, synchronous converters will usually
be found present under existing American conditions. This fact
not only would prevent us from reducing the cross-section of
conductors as given in the author's paper, but it would also
necessitate a further increase of cross-section for reducing the
maximum energy drop, and therefore cause a reduction in the
limiting distance of the present outlook for power transmission
as given in the concluding paragraphs of the paper, where the
limiting distance is given as approximately 550 miles.
In making further criticism, the speaker has in mind that
this paper is of a pioneer character, and therefore should only
be discussed upon broad lines. We must assume ideal condi-
tions and we must even allow something that may appear prob-
lematical at the present time. The author has correlated a
great amount of knowledge and information in the ten formulas
giving the elements of cost of the transmitting systems. The
speaker would like to question some of the items and assump-
tions, for instance; the use of a single pole line and single
route; the arrangement and number of transformers for the
different outputs; the 5% rate of interest for capital invested
in an enterprise of this character; and other items. But he be-
lieves it would not be fair nor profitable to open a discussion
upon these points. He believes, however, that exception could
be taken to some of the fundamental assumptions.
On page 411, first line, the author says; " It is certain that
with the course of time the value of power will increase." If
this statement is applied to a definite period of time covering
say 25 or even 50 years from now, we are entitled to question
its plausibility. The cost of power derived from coal will, for
centuries to come, apparently govern the cost of power through-
out the greater part of the North American continent. If other
sources of power be used, they must compete favorably with the
power from coal. The coal deposits of the United States and
Canada are so large that coal-trade experts have not yet made
an inventory of the probable supply. There are now immense
coal fields entirely untouched. At present the rate of con-
sumption of coal in the United States is exactly 1 000 000 tons
a day. Of this amount probably less than 5% is consumed
for generating electricity for all purposes. From the U. S.
Census Reports for the year ending June 30, 1902, we gather
the following approximate total current output and total station
Dynamo Capacity
Installed horse power
Total Yearly Out-
put Kilowatt-hours
Estimated
Load-Factor
Electric Light Station . .
Electric Railway Station
1 624 980
1 159 002
2 453 502 652
2 261 484 397
23%
30%
Total
( 2 783 982
1 2 075 000 kw.
4 714 987 049
26%
438 HIGH-TENSION TRANSMISSION.
capacity of all electric light and electric railway stations. (The
load-factors shown are obtained on the assumption that the
maximum load was equal to the dynamo capacity installed.)
If all electric current had been generated by steam, the total
coal consumption would have been less than 20 000 000 tons at
the most (on a consumption of five pounds per kilowatt hour
the total would have been less than 12 000 000 tons). This
amount is insignificant compared with the 1 000 000 daily
consumption for all purposes. Now if we consider the great
available supply of coal and the extent of its industrial and
domestic uses, and the fact thaf cheap coal will be one of the
fundamental factors enhancing the industrial supremacy of this
country, it is hardly probable that the cost of coal will be ab-
normally raised from the present level, except for the gradual
increase of cost of mining and the increase in wages that might
follow a general raising of prices for all labor and supplies and
an abnormal rate of increase of production of gold tending to
depreciate the money value. On the other hand, while we may
not expect to obtain coal at a lower price than at present, and
may probably have to pay more for it in future, it is also quite
probable that though the new rotary steam-engine, per se, will
not revolutionize the cost of power production, it will eventually
lead us to the development of the rotary-gas-engine, which will
make it feasible to realize enormous savings in the production of
power. Therefore, while we may have momentary fluctuations
of values of power, we are quite justified in expecting still fur-
ther reductions for many years, before the curve of values of
power shall have reversed its present lowering course and begun
to climb.
This preamble was necessary to bring on the proper plane
the discussion of the price of power assumed by the author.
He puts this value at $34.00 per kilowatt per year. Let us as-
sume that the equivalent of the total loads of all United States
electric light and railway stations operated during the year
ending June 1902 were grouped within a radius of 10 or 15 miles
of the ends of four 518 750-kw. transmitting lines 500 miles long.
On the basis of $34.00 per kilowatt per year the total power cost
would have been 2 075 000 X 34 = $70 550 000. This does not
include the cost of distributing the power to the several con-
sumers within the 10- or 15-mile radius.
Furthermore, the great bulk of the 25-cycle current would
have to be converted to some other form before being used for
the respective requirements, with attendant losses. Therefore
the above cost would have to be increased by 10 to 20% for
losses in transmission to and conversion of the 25-cycle current
at the customers' sub-stations, plus interest, depreciation, re-
pairs and taxes on lines, cables and subways, sub-station real
estate and buildings, and sub-station transforming and convert-
ing apparatus, plus the labor and operating charges for the opera-
tion of the sub-stations. The aggregate of these items would
MAXIMUM TRANSMISSION DISTANCE. 439
probably amount to about $22 500 000. For the sake of sim-
plicity let us assume that this amount would offset the capital
charges on real estate and buildings plus the labor production
charges for the present steam generating stations. Then we
should have left for direct comparison on one side the total cost
of water power of $70 550 000 and on the other side the cost
of fuel plus the interest and depreciation on the generating
equipment, excluding real estate and buildings. It is estimated
from the figures given in the Census Report that the electric
stations paid for all kinds of fuel to generate their total output
about 0.45 -cents per kilowatt-hour, or $21 200 000 total.
The first cost of steam generating equipment in large stations,
exclusive of real estate and buildings, making allowance for
future reduction of cost of apparatus, can be safely estimated
not to exceed $100.00 per kilowatt. The total cost of generating
equipment for 2 075 000 kw. would amount to $207 500 000,
and at the rate of 12.5% interest and depreciation, the
capital charges nev year would be $25 937 500. This added to
the cost of fuel would make the total $47 137 500, to be com-
pared with the $70 550 000 cost of water power. We therefore
see that the $34.00 per kilowatt per year is excessive, and that
on the basis of the operation of all the electric light and railway
stations of the United States for the year ending June 30, 1902,
the price should have been reduced to „^ ..^ _^^ x34= $22.72.
i\j ooU UOU
An approximately identical conclusion can be arrived at by figur-
ing the different elements of power cost from an ideal steam plant
and comparing them, with the corresponding costs of water-
power ; but it is not necessary to go into further discussion on this
point. Therefore the price of $22.72 per kilowatt per annum for
water-power transmitted 500 miles under the conditions given in
the author's paper, the speaker considers an outside limit, as
it would not give any financial inducement to the consumers to
sacrifice the safety and reliability of control of the local steam
plants in favor of long-distance transmission power with the
attendant dangers of breakdowns met in the operation of such
an extensive system of water-power generation and transmission
— all depending upon the safety of a single pole-line exposed
to all the dangers of weather, defective materials, or malicious
acts of men. It is only necessary to mention these drawbacks,
as persons familiar with the requirements of continuity of service
in large systems will at once draw the proper conclusions.
If water power will ever be transmitted to large markets like
New York, Chicago, etc., it will be necessary to keep at these
centres an equivalent reserve steam generating capacity; first,
for tying over shutdowns of the transmission power; and second-
ly, for taking care of a great proportion of the power required
during the periods of heavy loads, thereby utilizing the water
power for the 24 hours of each day with a load-factor of say
60% or over, and operating the steam plants at a very low load-
440 HIGH-TENSION TRANSMISSION.
factor so as to save fuel. On account of the uncertain duration
of shutdowns, storage-batteries could only be used to take care
of the loads during the period of starting up the steam-generating
plants.
P. G. Gossler: Mr. Torchio says that he considers the
author's statement of power sold at $34.00 per kilowatt to be
the outside limit; that he considers it necessary to sell power
at about $22.00 per kilowatt or $17.00 per horse power to com-
pete with the cost of steam. The speaker understands the
author's price, $34.00 is for the sale of the power at the time
of peak load. If Mr. Torchio's $22.00 per kilowatt is based
on the average load-factor of 23%, as he gives it, and the power
can be sold at about $97.00 per horse power, then the author
isjwell within the limit. If the $17.00 per horse power is for
the maximum the speaker fears that most of the water power
companies would be forced into the hands of receivers if that
price were maintained.
Philip Torchio: $22.72 was per kilowatt maximum and
not per kilowatt average. That was arrived at by taking the
dynamo capacity installed of . all the lighting companies and
railway companies of the United States to be equivalent to
their maximum load.
P. G. Gossler: It is hardly fair to let the impression go
out that the average price of power per horse power is $17.00.
The speaker does not think it is based upon facts, the facts
upon which commercial business is usually conducted.
Philip Torchio: The $17.00 per horse power referred to
in the speaker's remarks is not the retail selling price of power
delivered to the consumer. It only includes the interest and
depreciation of machinery, exclusive of real estate and build-
ings, plus the cost of coal, which items the speaker assumed
to represent the wholesale value of water power delivered at
the purchaser's switchboard under the specific conditions of
load factor, etc., given in those remarks. Nothing else is in-
cluded in that figure. On the other hand, the selling price
charged by a company retailing power will be dependent upon
the use and the load-factor; and furthermore, in that price
must be included a number of other items, as the production
labor cost, the interest and depreqiation, and taxes on real
estate and buildings, and also on ,the distributing lines and
subways; also the cost of distribution labor and repairs, and
if it is a lighting company, the cost of supplies and maintenance
of the customers' lamps; also it will include all the items of
general expense that make up the total cost of power deliv-
ered to the customer, including management, accounting,
canvassing, insurance, legal, medical, and damages, etc., and
finally the charge for profit to the company.
J. E. Wallace: Assuming that the mathematics underlying
the curves given in Fig. 1 are correct, the speaker considers that
a grave error in engineering judgment would be committed by
MAXIMUM TRANSMISSION DISTANCE. 441
following them. To substantiate this statement, the speaker
calls attention to a short press article written by him and pub-
lished in a recent issue of the Electrical World and Engineer*
One of the curves used to illustrate this article shows how the
cost per kilowatt of energy delivered decreases with increased
pressure. Beyond a pressure of 60 000 volts, in this particular
case, the drop in the curve is hardly worth considering. The
increased cost of insulators and transformers, due to increased
pressure, is neglected in the curve; if included, it would ulti-
mately overcome the slight drop beyond 60,000 volts and the
curve would take an upward turn, locating economic pressure.
Considering a factor for more reliable operation at lower
pressures, the slight advantages gained in costs' of delivered
energy, as economic pressure is approached, do not warrant the
very considerable increase in pressure.
With increase of output the cost of transformers is de-
creased to some extent, and the pole construction item de-
creases by a ratio that practically varies inversely as the output ;
possible failure of a line, however, should impose a limitation
which would not allow the process to go on to an almost in-
definite point. With a given increase in output the effect is to
make economic pressure higher, as found by the author. Engi-
neers agree that practical conditions govern theory, and it is
held by the speaker that in deciding on the transmitting pressure
to be employed, the advantages to be gained by increased pressure
should again be compared with the factor for more reliable
operation at a lower pressure, which factor naturally would
increase with increased load for which a given pole line is
responsible.
The conditions on which the curves in Figs. 4 and 5 of the
author's paper are based are somewhat special; the total invest-
ment does not include the principal item of cost in a transmission
scheme — the cost of the generating plant. Large profits could
easily be figured under such conditions. The market price of
delivered energy, and load-factor on both generating plant and
transmission line, af well as cost of energy delivered to the line,
are factors that have an influence on profitable efficiencies.
At the outset this paper claimed to be in the nature of a fore-
cast of what might be done in the future. The author has said
that a 12% profit is necessary to guarantee the bonds; it is
presumed that the full issue of the common stock will be rep-
resented in the construction costs. The author does not give
the proportion of stock to bonds, so we shall assume the usual
proportion, 50% of each. Five per cent, for interest, and seven
and a half per cent, for maintenance and depreciation are the
figures given; they will be allowed for the generating plant.
This means that one-half of the construction costs must earn
12.5% and the other half 19.5%, or an average of 16% on the
whole; $10.90 is given as the amount that the generating plant
will receive per kilowatt. Assumed that it does not cost more
'Electrical World and Engineer, Nov. 5, 1904.
442 HIGH-TENSION TRANSMISSION.
than 90c. per kilowatt for attendance; we fhen have $10.00 rep-
senting 16% of the construction costs per kilowatt of the plant.
162.60 is an exceedingly small figure with which to pay for
water rights, hydraulic developments, water-wheels, generating
apparatus and the various other accessories necessary to a gen-
erating plant.
Watt-losses are considered in terms of a delivered kilowatt.
It is apparent that if a line has 90% efficiency, there is a loss of
10% of the generated energy. Considering line resistance, it is
also apparent that the annual conductor charges vary inversely
as the per cent, loss; therefore the conductor charges are repre-
sented as a constant divided by the per cent, loss, thus j-.^ ,.. ..
where / equals line efficiency. At the other end of the
line the relation of conductor charges per generated kilowatt
to conductor charges per delivered kilowatt, is the same ex-
pression divided by the efficiency of the line ; this gives „^ , ^
In other words, the conductor charges in terms of a delivered
kilowatt vary inversely as the per cent, loss multiplied by the
efficiency of the line. If one considers conductor losses in the
per cent, of a delivered kilowatt, and neglects to consider that
the delivered kilowatt is a function of the efficiency of the line,
one is led into error. This error evidently led the author to
Kelvin's law. With all due reverence to Lord Kelvin, the
speaker contends that Kelvin's law does not deliver the cheapest
kilowatt. At any practical pressure the error in Kelvin's law
is, in the matter of a delivered kilowatt, rather inconsiderable;
but the error multiplies and soon becomes formidable when it is
carried into efficiencies for percentage returns. Anyone who cares
to look up the subject will discover the truth of this statement.
M. H. Gerry, Jr: A mathematical analysis of a subject of
this kind has always seemed to the speaker to be of doubtful
utility, not necessarily because of any defect in the process of
reasoning, but because there are so many variables entering
into the expressions. In order to apply such an analysis where
the conditions are so far in advance of current practice, it is
necessary to make arbitrary assumptions based on the judgment
of the individual engineer ; and the final deductions are so much
affected by the assumed values as to render them little more
than an individual opinion instead of being facts founded on
mathematical reasoning.
Taking the author's expressions and modifying his assump-
tions, it can be shown that the economical limit of distance of
power transmission in a given case may be either 100 miles or
1000 miles, and this being the case the mathematical develop-
ment is of little value from an engineering standpoint as a means
of predicting ultimate commercial results. This paper is, how-
ever, of considerable interest from its theoretical side. The
mathematical expressions are in good form, and will prove of
value in the future when more is known of the physical and
MAXIMUM TRANSMISSION DISTANCE. 443
commercial conditions surrounding the transmission of energy
at the excessively high pressures and great distances referred to.
At the present time the information before us regarding press-
ures above 100 000 volts is so limited as to make substitutions
in the various mathematical expressions of very doubtful value ;
it is certainly not wise to attempt to show in this way the
limitations of distance for future electrical transmissions. Such
statements are misleading and should not appear unchallenged
in the Proceedings of the Institute,
A. E. Kennelly: We are indebted to the author of this
paper for a careful analysis of the problem of the commercial
limits of electric power transmission under clearly -specified
conditions. There is no pretence that these conditions are
immediately available for general estimates. The pressures are
much in excess of those in commercial use to-day, and the
power assumed is also much greater than the power ordinarily
transmitted. Nevertheless, the solution of the economic prob-
lem for definitely assumed pressures and kilowatts is perfectly
proper matter for discussion, as an abstract proposition, quite
independently of the question as to when such pressures and
powers will be practically available in the future.
The history of electric power transmission in the past shows
that it is unsafe to prophecy the commercial limiting distance
of transmission. In the early days of the development of the
incandescent lamp it was demonstrated mathematically that it
would be commercially impracticable to transmit electric power
to such lamps more than a few hundred feet. The proposition
was valid at the time, but only for the conditions then existing.
The three-wire system and the 100-volt lamp upset both the
assumptions and the conclusions. The practical men carried
power to lamps distant several thousand feet from the generator.
Then the transformer became known and it was demonstrated
that it would^ be commercially impossible to transmit power
more than a few miles. But improvements in construction in-
validated the assumptions of this proposition also, and the prac-
tical men have now succeeded in carrying power commercially
to a distance of 230 miles in California at a pressure of about
60 kilovolts. The conclusion of the author's paper is that under
the conditions he has assumed, power may be carried about 500
miles and pay a profit, if the block of power is large, say 200
megawatts. This conclusion is interesting, because it would
place both New York and Chicago within the sphere of influence
of Niagara Falls. But a yet more important deduction in the
paper is that when power is transmitted in such bulk as is con-
sidered in the paper, it pays to use copper wires so large that
even at 170 kilovolts between them, there will be no dissipation
of power by brush discharge. In other words, aluminum wires
will not be rendered necessary for long distance transmission of
large blocks of power, since the copper wires would have suffi-
cient diameter to keep the electric gradient in the air down to
the safe working value and below the smashing point.
444 HIGH-TENSION TRANSMISSION.
Curiously enough, the distance the author arrives at (500
to 600 miles) is about the same as that to which telegraphers
generally carry their small amounts of power over wires for
transmitting messages. For distances exceeding 500 or 600
miles they usually insert a repeater.
Charles F. Scott: The author's paper is the outcome of
several years of study of the problem of long-distance transmis-
sion in which he has dealt with it in various ways. Several
years ago he did some excellent work in determining ex-
perimentally in Colorado, on a circuit of the Telluride Power
Transmission Company, the loss through the air between wires
at low pressure. The curve representing this loss shows that
it is extremely small under the conditions which the author
employed until approximately 60 000 volts was reached, when
the curve took an upward turn and a slight increase in pressure
caused a very great increase in loss. It was evident that a
pressure much above 60 000 would cause a loss so great as to
be prohibitive. The wires which the author used were small
in diameter. The critical point at which loss begins occurs at
a higher pressure when the wires are of greater diameter. This
matter was admirably set forth in Professor Ryan's paper before
the Institute about a year ago.
The author now considers the general problem of power trans-
mission from the commercial rather than from the scientific side,
and one may readily imagine that the problem was one which
grew larger and larger as he worked upon it, for the paper shows
the result of painstaking labor. Nearly all of the papers which
are written upon transmission deal with certain specific elements
and do not take up the subject in a broad way. At the In-
ternational Electrical Congress, for example, there were many
papers in the Transmission Section, but these papers dealt with
specific or with local matters such as details of construction,
types of insulators, characteristics of conductors, methods of
operation and the like. There was no broad general paper,
except one which was read by title. That paper was prepared
by an official representative to the Congress from the Institute
and it is the paper which has been presented to us this evening.
Some objection has been raised to the use of specific figures
by the author. The particular value of the paper is found in
its treatment of a general engineering problem and in the
bringing together and showing the relation between the various
elements which enter into commercial power transmission.
The paper, however, would lose much in interest and in value
if it presented simply the formula showing the relation between
various variables and constants without assigning definite com-
mercial values. These values are of course liable to change,
but the whole matter assumes a much more definite, and satis-
factory condition, if in addition to the abstract relationships
there are given also the concrete values which result when cer-
tain reasonable values are given to the different quantities
MAXIMUM TRANSMISSION DISTANCE. 445
involved. It is, for example, a satisfaction to know that
under conditions which are fairly commercial the distance
from Niagara Falls to New York City is not beyond the limits
of commercial possibility.
This paper deals with something outside of the range of elec-
trical operation with which we are familiar. If we were
to refer to the wire tables of 15 years ago we would find
that the units then used were 16 c-p. lights and that the dis-
tance ran up into a few hundred or a few thousand feet. Elec-
trical work at |;he present time is on a much larger scale, and
the present paper goes far beyond our present needs. The curves
give little attention to units less than 50 000 kw. , which is
about the output of the largest stations which are now in op-
eration. Many of the conditions set forth in the present paper
do not apply to less than 200 000 h.p., which is probably about
the amount of electrical power used in New York City. The
field of power transmission which is considered in the present
paper is therefore one which does lie in the present, but which
we may encounter a decade hence. It gives us a vision of
the electrical future.
An interesting point may be noted relatively to the per-
centage of loss in transmission. Most of us would probably
estimate the desirable loss in transmission over considerable
distances at 10 or 15%. The curves in the present paper
show that for 100 miles the economic drop does not exceed
more than about 5% and that for less than 100 miles the loss
would be considerably smaller. Up to even 200 miles the
losses on the curves representing all the conditions considered
do not exceed nine per cent.
High pressures have usually involved the idea of a small
wire, and in some of the earlier transmission systems the limit
of the size of wire was fixed not by its conductivity but by its
mechanical strength — electrically the conductor could be made
smaller than was made necessary by the requirements of me-
chanical strength. The present paper shows that we have
gotten into a new order of things in power transmission on a
large scale, as the size of wire for economic transmission for
large power at high pressure is so great as to bring about the
surprising result that the atmospheric losses which have been
assumed to be the determining element in high pressure trans-
mission no longer determine the maximum pressure; the size
of wire required at a given pressure to insure economic trans-
mission is so great that the atmospheric losses are avoided.
C. L. DE Muralt: In the author's paper the fact stands out
prominently that it is in all probability the economical side of
the problem and not the technical side, which determines the
distance to which energy may be transmitted electrically. Let
us therefore look more closely at the economical variable of his
equations.
The author has taken the price of $34.00 per kilowatt per year
446 HIGH-TENSION TRANSMISSION.
as a selling price for the transmitted energy. In Switzerland,
which may be called the power transmission country par excel-
lence, electric energy is sold in most cases at about $20 per horse
power per year, or approximately $30 per kilowatt per year.
But you know that coal is very high in Switzerland — it is here
about $2 per ton, and there $6 or $8 — if therefore in Switzer-
land competition of coal has to be met by selling the kilowatt
per year at $30, it would seem difficult to obtain $34 in this
part of the world where fuel is so much cheaper. The author's
curves, notably Fig. 5, show very nicely how the maximum
distance, over which energy can be economically transmitted,
may be increased by increasing either the amount of energy
transmitted or the pressure of transmission, or both. But if in
his curves the selling price is reduced to what it will have to be
to compete with coal, then the distance of transmission will in
a great many cases be materially decreased, no matter how
large the amount of transmitted energy or how high the pressure
of transmission. If, for example, conditions are taken as they
are now around New York it would seem doubtful if this dis-
tance would be more than half of that shown in Figs. 4 and 5.
This is the point the speaker wishes to bring out.
Ralph D. Mershon: The difference of opinion which has
developed here to-night is no greater than was to be expected.
Probably there never were two engineers who estimated in
exactly the same way on everything, or whose estimates on
a proposition, if examined in detail, would agree exactly; one
man would be higher on one item and lower on another, al-
though the total estimates made by them might agree very
closely. Moreover, in making estimates, it is not an uncom-
mon experience to have the figures on sortie details higher
and on others lower than the figures actually' obtained in the
construction for which the estimate was made; the result
being an equalization of the positive and negative errors, and
the total estimate comparing very closely with the cost of
the completed work. Such a condition of affairs does not
argue any lack of skill in estimating, especially on work along
new and untried lines, and the engineer is legitimately entitled
to such equalizing chances as those mentioned.
This paper, in so far as the numerical values are concerned
at least, represents simply a piece of estimating. In consid-
ering the numerical values of the paper, therefore, too much
stress should not be laid upon details. The principal con-
sideration should be given to the work as a whole.
On the different items of the paper there will be differences
of opinion among engineers, both as to assumptions and numer-
ical values; but the average opinion, if one could get at it,
would probably come very close to the figures given in the
paper.
Suppose, however, that there were errors in the paper suffi-
ciently great to cause an error in the limiting distances de-
MAXIMUM TRANSMISSION DISTANCE. 447
duced, as great as 20%. Even with that error the value
of the paper, as giving a general view of the subject, would
not be diminished to any considerable extent.
As Mr. Scott has said, such a paper as this is more inter-
esting with some definite figures than if it gave simply an an ■
alysis, and hence the numerical values were introduced. No
exceptions worthy of notice have been taken to the method
of analysis employed.
The two extremes that Mr. Gerry mentioned, namely, 200
miles and 2000 miles, between which the limiting distance of
transmission might fall, are pretty far apart. Probably the
idea that Mr. Gerry means to convey is that the conditions
under which a transmission might be undertaken might
vary so widely in different locations, especially as to the cost
and selUng price of power, as to render very uncertain the
limiting distance when treated as a general question. But,
as the paper shows, the limiting distance of transmission will,
among other things, depend very greatly upon the total output
of the plant, the distance being greater for greater outputs.
Now the assumption of a large market and a large source of
power to supply it narrows the location of the transmission
very considerably, and this in turn fixes the values of cost
between narrower limits than those which Mr. Gerry probably
has in mind.
In this paper there is done, in a general way, just what Mr.
Gerry does when he estimates on a particular plant. He
takes a specific case and makes an estimate. The speaker has
tried to make the estimate in a general way; that is, instead of
considering various plants separately and undertaking to work
out something for each one, by means of formulas the problem
is put in such shape that by working out a comparatively
few values, results can be obtained for plants whose outputs
cover a considerable range, thus enabling one to get a much
clearer idea of the trend of results as the various quantities
are varied.
Mr. Stott brought out a number of interesting points, one
of them the question of the sale of power on a flat rate;
another, the consideration of the load-factor. But in this
problem there is no need to consider the load-factor, or any
charge except the flat rate, for the reason that no matter what
the load-factor or what the price we may sell the power for,
there is always a certain peak and certain income; divide the
income by the peak, and you have a certain flat rate. That
is the figure which must be considered in a problem of this
kind, for the reason that in the water power plant — which
we are necessarily considering — there is practically no variable
factor. In the steam plant there is a variable factor, the cost
of fuel. In a water-power plant it costs practically the same
per kilowatt whether you deliver one-quarter of the output
or the whole. It makes little difference what proportion of the
448 HIGH-TENSION TRANSMISSION.
full capacity is carried; some, perhaps, but not enough worth
considering in a paper of this sort. Mr. Stott also spoke
of the question of carrying the peak load. The problem does
not necessarily assume that the peak load will be carried. Take
the case of bringing power to New York City. There are
pretty large steam plants here. It would be cheaper, in gen-
eral practice, to carry the peaks on these steam plants and
get a more uniform load on the water-power plant, which
would enable the purchaser to pay a higher price per kilowatt
per year than otherwise.
As to the cost of the generating plant, as represented in he
price assumed in the figure for cost of power, it is low; but
not impossibly low. There are some water powers throughout
the country where the cost of the plant, and therefore of
the power, is very low, because of advantageous physical con-
ditions. But aside from that, supposing the development to be
similar to that at Niagara Falls ; in the case of blocks of power
as large as those considered and as more power plants are in-
stalled, and more skill and experience is brought to bear
upon them, the cost of power from, such developments will
be very considerably diminished from what it is now. Mr.
Stott brought up the question of higher frequency in order to
get better power-factors, but there are a good many arguments
against that. If the load were very well distributed, along
the transmission line, higher frequency is a matter which
might be worthy of consideration; but generally the load is
bunched at the end of the line, and in such cases the lower
frequency would undoubtedly be preferable.
Mr. Torchio's contribution is a very interesting .one, but
there is so much in it that one can not follow it closely enough,
hearing it for the first time, to reply to it. After reading it
more carefully, the speaker may perhaps reply with a written
communication. The cost Mr. Torchio has taken for power
is remarkably low, certainly lower than any that the speaker
has investigated. The criticism which Mr. Torchio made in
regard to assimaing one cost for the power produced is, from
some standpoints, a legitimate one, although if he will
turn to page 432, in the middle of the page he will see a para-
graph which deals with this question and calls attention to a
compensating factor. The reason for taking one cost of
power was simplicity. The aim was to determine the maxi-
mum distance to which power could be transmitted, and with
that in view perhaps the curves of small output should have been
omitted. But they are of interest in connection with the com-
pensating advantage, mentioned on page 781, which will have
some efEect. The power cost assumed, therefore, is that which
would best apply to very large outputs, to those large out-
puts determining the maximum distance of transmission. As
Mr. Torchio can see, it would complicate the equations still
more to introduce a variable factor in the cost of power.
MAXIMUM TRANSMISSION DISTANCE. 449
Strictly, the proper method of applying the equations is to
start with a certain cost of power, and a certain sale price
of power, and determine how far it could be transmitted. In
that case there might be a different cost of power and dif-
ferent selling price for each size of plant.
Replying to Mr. de Muralt, in regard to power prices in
Switzerland: he should bear in mind that as a general thing
apparatus, labor, and money are cheaper in Switzerland than
in this country.
In regard to the question of bonds mentioned, 5% interest
was assumed on the actual investinent, and 12% of the in-
vestment taken as profit. That does not mean necessarily
that the bonds should be rated at 5%, or issued on the
basis of returning 5%. It means that the return has
been divided into two amounts, one 5% and the other
12%. The total return is 17%, and you can divide it be-
tween dividends and bonds as you please.
As regards Mr. Wallace, his quarrel seems to be with Lord
Kelvin, in which case no reply is necessary. Mr. Torchio will
find, if he carefully examines the equations, that the Kelvin
law has been given full weight and has been modified only
by those elements of cost of transmission affected by change
of pressure.
Ralph D. Mershon (by letter, after adjournment): Mr.
Torchio has criticised the assumption of the same cost of power
for plants of all capacities; to this the writer has already re-
plied. But in addition, Mr. Torchio discusses the question of
squeezing a little more power out of a generating plant to make
up for the line loss, and the possibility of obtaining this incre-
ment of power at a lower cost than the bull: of the power pro-
duced by the station. The writer cannot agree with his argu-
ment, even if it be made on the assumption that the same com-
pany owns both the transmitting plant and the generating plant.
In the case of a generating plant of a given capacity, the cost
of power produced by that plant would be computed; and for
any increased output, no matter how great, there would be com-
puted the corresponding cost in accordance with the law gov-
erning the variation of such cost with output. Why the law
of variation should be any different for large or small incre-
ments is not quite clear to the writer. The fallacy of Mr. Tor-
chio's argument can be shown by carrying it a little further.
After having obtained 10% more by the method he advocates,
why not obtain another 10% by the same squeezing process,
and so on to any amount of power required?
Touching the drop limitations mentioned by Mr. Torchio as
imposed by the various kinds of apparatus, the writer believes
that the limitations in this direction, due to synchronous ap-
paratus, will be removed in the near future. The assumption
that large numbers of synchronous conveners must of necessity
be used is not in any case in accord with the writer's ideas on
450 HIGH-TENSION TRANSMISSION.
the subject. He believes the time will come when there will
be little use for synchronous converters, alternating currents
being used for almost all industrial purposes.
There is a point in regard to the transmission line which
Mr. Torchio has overlooked; namely, that the paper assumes
three transmission lines. Perhaps it is not so clearly stated as
should be that these three are distinct and separate and on
separate structures, but such is the assumption.
The writer has not at hand the data for entering into a dis-
cussion on the probability of an increase of fuel costs. The
statement that the value of power will increase was based partly,
but not wholly, upon this consideration. The writer believes
it is generally deduced by statisticians that it will not be very
long before the price of fuel will increase to a point where it
will be seriously felt; this of course being due, not only to the
diminution of the source of supply, but also to increase of
population and its increased demands for fuel and the materials
whose production involves its consumption. But there is an-
other reason why the value of electric power will increase, and
that is that as the delivery of such power becomes more and
more reliable, the price will be regulated, not, as now, by the
consideration of supplying power to a customer who has a dupli-
cate steam plant, the fixed charges on which must be carried,
but on the basis of supplying a customer who has no steam
plant except such as is necessary for carrying his peak. Carry-
ing the peak by steam will make it possible for the purchaser
to pay a higher price for water-power than he otherwise would,
and yet result in a lower total cost of power to him than though
he carried the whole load by steam. This question of a com-
bination plant would, if considered by Mr. Torchio, compel
him very materially to modify the figures of his general and
very interesting discussion as to the selling price of power.
The writer questions very strongly the statement made by
Mr. Torchio, that it is necessary to carry " equivalent reserve
steam generating capacity " in the case of transmitting power
to Chicago or New York. A certain amount of reserve may
have to be carried to provide for extreme emergencies, but the
writer thinks that in time the amount of such reserve will be
more and more reduced. This has been the experience with
transmission on a smaller scale, and the writer sees no reason
why, as the art advances, it should not be the case even in a
greater degree with larger enterprises.
Referring to Mr. Wallace's statement, as based upon some
figures he has made for a specific case, if he had selected a plant
of an output or distance of transmission differing from that
assumed by him and had applied the same criterion as he has
applied to the question of economical pressure, he would have
arrived at a different pressure for each output and distance;
in other words, he would have obtained results resembling
those in the writer's paper.
MAXIMUM TRANSMISSION DISTANCE. 451
Regarding the question of the figure assumed for the cost
of power ($10.90 per kilowatt at the step-up transformers),
the assumption made is a possible one, commercially. The
best proof of this statement is that power has been and is being
produced for less than the price named. Some of the members
present at the meeting at which the writer's paper was dis-
cussed could, if they had felt at liberty to do so, told of power
being produced at a considerably less figure. It is well known
that, in a city not very far from New York, power is sold at
$15 per horse power, this price to fall to $14 when the total
load shall exceed 10 000 h.p. This power is transmitted from
a -water-power 85 miles away, and is sold at a profit. One can,
if he chooses, figure back and determine roughly what the power
must cost at the terminals of the step-up transformers.
If any one desires to purchase power at the point of gen-
eration for $10.90 per kilowatt per annum, he can perhaps
be accommodated up to 200 000 h.p.
In view of the discussion which has taken place in regard
to the selling price of delivered power, the writer purposes to
plot another set oi curves which will apply to a lower selling
price than that assumed in the paper, and shall include them
in the paper with the curves applying to the selling price of
$34 per kilowatt already assumed.
In the numerical calculations of the paper, which are
long and somewhat involved, there crept in an error in the
cost of synchronous motors, although extreme pains were taken
to have all figures carefully checked by two or more persons.
In the final printing of this paper in the Transactions of the
Institute, this error will be corrected. The correction will
modify the distance curves, Figs. 4 and 5 already given, by
increasing the profitable distance of transmission under the con-
ditions assumed ; it will not change the other curves.
452 HIGH TENSION TRANSMISSION.
Discussion on " The Maximum Distance to Which Power
Can Be Economically Transmitted," at Pittsburg, Pa.,
January 9, 1905.
S. M. Kintner: The author has given us a paper that is
exceedingly broad in its scope, so broad that few, if any, are in a
position to check it. The author has probably got more good
out of the paper than any one else, in the very thorough inves-
tigation that was necessary for its preparation. In saying
this it is not intended to detract from its value, for it is the
belief of the speaker that this paper will prove of great value
to more of us when we learn more about the constants involved
and when higher pressures and larger powers are used com-
mercially. The author has committed himself to but few en-
gineering points, but some of these involve quantities of such
magnitude that one is astonished in considering them, yet that
is no reason for condemning the paper.
Such high pressures, which are now looked upon as abnormal
commercially, and such large sized plants, also far beyond
anything known in present practice, may bring about changes
in design that will readily take care of present anticipated
troubles. There is always great uncertainty in drawing con-
clusions from curves extended far beyond the observed values,
for the curve is just as liable to go down as up. The author's
range of constants will provide considerable latitude.
Though there may be many points of detail upon which one
may not agree with the author, yet it is the opinion of the speaker
that a thorough study of the paper will repay one and give a
broad view of all the most important elements considered, a
view so broad that corrections can readily be made from time
to time, as experience dictates.
P. M. Lincoln: It seems to the speaker that the author's
deductions are open to considerable criticism. He has devel-
oped a number of laws for costs of the various elements which
go to make up a transmission line, and these laws are expected
to hold true for an amount of power up to at least 500 000 kw.
and pressures up to at least 200 000 volts. These limits are
far beyond anything which is in existence to-day. The speaker
does not believe that the author, or anyone else, can say what
will be the law of variation of costs for these elements at the
pressures and outputs with which he deals. For instance, the
author assumes the variation of cost of insulators to be as a cube
of the pressure ; this assumption may hold with the pressures in
use at present, but how does the author know that it will hold
when pressures are increased to 150 000 or 200 000 volts? The
law of variation of sizes of cost of transformers is also given:
how can he tell that it is going to hold for the large powers
and high pressures?
The author has figured upon using synchronous apparatus
at various points of the line for the purpose of maintaining
unity power-factor; the desirability of using such devices as
MAXIMUM TRANSMISSION DISTANCE. 453
this is as yet a mooted question, nevertheless they are incor-
porated in the general scheme when considering the subject
of cost of long-distance transmission.
The right of way is taken as simply proportional to the dis-
tance of transmission. Evidently a factor depending upon the
amount of power should also be included, as well as something
to determine the density of the territory which is to be served.
This later is a very considerable element.
It has been remarked that the author has paid no attention
to the matter of load factor. His assumption of buying power
at a fixed figure eliminates the question of cost of generating
plant, and in dealing with the transmission problem only the
load factor of course may theoretically be neglected. The com-
plete problem should, however, take into consideration the cost
of generation of power as well as its transmission and distribu-
tion, for in the cost of generation the load factor is one of the
most important factors. Strictly speaking, the author is
dealing simply with a transmission problem and therefore the
matter of load factor may be omitted.
Mr. Skinner: On the author's assumptions of number of
units and ultimate output of station, the size of transformer
unit required would be 30 000 kw. at 200 000 volts. A single
transformer of this capacity would have power approxi-
mately equal to that of the first Niagara station. The
largest size of transformer with which the speaker has had
anything to do is of 3000 kw. capacity. In the manufacture of
large transformers one of the most important things to be con-
sidered is the mechanical construction of the high-pressure
coils. In ordering insulating material for the 3000-kw. trans-
former, the manufacturers were asked to install larger machin-
ery, as they had no machines of suitable size to manufacture
the insulating material required for this size of transformer ; size of
coils and insulation are not insurmountable obstacles in the way
of making larger units, however, as it is possible to piece the
various parts that enter into this construction. The speaker
admits that at the present time he is unable to imagine the
construction of a 30 000-kw. transformer for 200 000 volts. A
different general design of transformer must be perfected before
the larger sizes can be built successfully.
Another interesting phase of the a;ithor's paper is that re-
ferring to line insulation. In the opinion of the speaker, the
line construction is one of the simplest parts of the problem;
this part of the problem can finally be solved by the introduc-
tion of steel towers and as few insulators as possible.
H. W. Fisher: Unquestionably this paper is an excellent
one and shows much thought and careful mathematical de-
duction. Without attempting to consider the mathematical
side of it, the speaker is of the opinion that the price charged
per kilowatt per annum, namely, $34.00, may be higher than
that which large users of power would be willing to pay.
454 HIGH-TENSION TRANSMISSION.
In connection with the author's paper, comes very naturally
the question: what will be the limiting maximum pressures
which can be operated on underground electric cables? The
speaker has designed and made short lengths of cable which
have withstood 150 000 volts; this also has been accomplished
abroad. The lasting qualities, however, of very high-pressure
cables can only be determined by operating them under prac-
tical conditions for long periods of time. On account of the
much greater stress on the insulation near the surface of the
conductor, the greatest care has to be used in the design of
cables for high pressures. The speaker has made a calculation
that will illustrate this point. Suppose there are two cables
consisting of No. 6 and 0000 B. & S. gauge solid conductor,
homogeneously insulated with 0.1875 in. of good insulating
material. If these cables are subjected to 10 000 volts, the
stress on the insulation near the conductor will be:
1608 volts per 1/64 for the No. 6.
1138 " " " " No. 0000.
The stresses on the insulation near the lead will be:
485 volts per 1/64 for the No. 6.
627 " " " " No. 0000.
Here we see that the insulation of the No. 6 is subjected to a
much greater stress than that of the 0000, and practice demon-
strates that it is more difficult to make small conductor than
large conductor cables for high pressures. It will also be noted
that the insulation of the No. 6 near the conductor is subjected
to more than three times the stress on the insulation near the
lead. Theory also shows us that if 7.73/64 in. of insulation be
applied to the 0000 cable, the insulation near the conductor
will be subjected to the same stress as that of the No. 6 above;
namely, 1608 volts per 1/64. It would appear, therefore, that
a No. 0000 cable insulated with 8/64 in. would be stronger than
a No. 6 with 12/64 in. Referring to the first mentioned cable,
14 120 volts on the 0000 cable would produce the same dielectric
stress near the conductor as 10 000 volts on the No. 6 cable.
For stranded conductors, the stresses near the conductor may
be from 20 to 30% greater than those for solid conductors of
the same area.
To compensate for this unfortunate condition, two things may
be done: first, place near the conductor insulating materials of
great dielectric strength; secondly, use insulating material the
specific inductive capacity of which will be greatest at the con-
ductor and which will decrease toward the lead cover at the
right rate to make the dielectric stress the same all over the
insulation. The speaker mentions these few points because they
are of the utmost importance in the correct design of high-
pressure cables. It is scarcely probable that underground
cables will ever be needed to withstand as great pressures as
conductors placed on the best insulators. Transmission over
long distances will generally be done by the latter plan, but if
MAXIMUM TRANSMISSION DISTANCE. 455
the pressures are very high, cables operating from the secondary
of step-down transformers will no doubt be used in city limits.
Connecting long lengths of aerial conductors to long lengths of
cables is not desirable because of danger to the cables from light-
ning and resonance.
N.J. Neall: a value should have been inserted in the equa-
tions having for its base the probable loss due to interruption of
service; uninterrupted service will undoubtedly be more and,
more demanded, and the proportional cost of interruption of
service by lightning-arresters will become greater.
If one were to think of a 500-mile line running, say, from
Buffalo to New York, such advanced line construction might
be conceived of as to enable one to estimate the cost of main-
tenance confined to general wear and tear only, but lightning
disturbances would certainly be more numerous per line, al-
though possibly not much greater per length of line. Even
with simpler lightning-arresters there seems no reason to aban-
don our theories concerning their functions. For this reason
we should consider the recommendations made by Mr. A. J.
Wurts — ^that a line should fairly bristle with discharge-points.
This for a high -pressure, high-power line would perhaps mean
the employment of section-houses where lightning-arresters
could be installed and where section-foremen could live and
have apparatus for keeping the line intact. The telephone
for such a plant must receive careful installation; it might
perhaps prove inadequate and would have to be supplanted by
wireless telegraphy. These factors seem worthy of considera-
tion in such a discussion and their bearing on the cost of trans-
mission might assume a value which would materially change
the figures given by the author.
456 ' HIGH-TENSION TRANSMISSION.
Discussion on " The Maximum Distance to which Power
Can Be Economically Transmitted," at Philadelphia,
Pa., January 9, 1905.
Wm. McClellan: The chief value of the author's paper
is its exposition of the methods used. So far as results are
concerned, there will be widely differing opinions. The speaker
believes that the author has been very liberal except in what
might be called the factor of safety. Apparently, three cir-
cuits have been provided, each with one-third load capacity.
If one of these nine wires should fail only two-thirds of the
rated load could be carried. We have, however, plenty of
reserve in the converters, etc. In a line projected some time
ago there was one extra wire provided for emergencies. The
provision in this respect does not seem quite consistent. On
the other hand, one must remember that these conductors are
of solid copper, one inch and a half in diameter, and not likely
to get in trouble except in the land of cyclones.
One should naturally ask, does the paper settle anything
definitively? It does tell us definitely that when we have
our wire large enough to suit our economic conditions, it will
be plenty large enough to suit our electrical conditions. When
we heard of Professor Ryan's paper last February, we thought
that we might have to increase our wires above economic
diameters in order to prevent coronal loss, but we are sure now
that we shall not have to do so.
At present there are so few cases where we shall have to
transmit such large blocks of power over such distances that
the speaker does not believe that the problem is of great in-
terest to many men. A more interesting problem, and one
that is becoming more and more prominent, is the combination
and development of the many small water-powers in various
localities. In many cases these are separately worth little,
but taken together, and properly developed, they become divi-
dend earners. Some time ago a commission was examining all
the water-powers of New England for this very purpose. It
seems almost certain that a great deal of our future transmission
work will move in this direction; it will become a part of our
future railroad development.
A. B. Stitzer: The speaker knows of one company installing
some high-pressure apparatus where there are two cables to
each station. Either cable is large enough to carry the sta-
tion's full load, so that if one cable breaks down the load can
still be carried with less than eight per cent, drop ; the two wires
working together will give one half this drop.
Most of the speaker's experience has been with underground
transmission work; 13 200 volts is high enough for underground
transmission. The insulation is 0.0219-in. paper around each con-
ductor and 0.0219-in. paper over all. In the power house we use
0.375-in. rubber. We were using 0.3125-in. rubber but that
is hardly sufficient. The paper is treated with compotmd; it
MAXIMUM TRANSMISSION DISTANCE. 457
is three-conductor cable with 0.09375 inches of lead on the out-
side.
Carl Hering: The author bases his figures on the present
cost of steam power in cities, but it seems to the speaker that
there are prospects of reducing the cost of power from coal quite
appreciably. Take the case of steam turbines, for instance.
A few years ago very little was known about them ; with con-
tinued improvements the steam turbine has progressed won-
derfully. If further improvements are made in the future,
electrical transmission of energy may net be as able to com-
pete then as it is now. It seems to the speaker that there
are so few cases where power would be transmitted to such
enormous distances as 500 miles that each case must be figured
out by itself, and that any such general laws are of little use.
H. A. Foster: The speaker believes he is correct in saying
that the best steam turbine has not reduced the cost of steam
power below the cost at full load of the best of reciprocating
engines. Below full load the steam turbine has somewhat
reduced the cost of steam power, but at any time a slight in-
crease in the cost of coal will effect all the economies produced
by such methods.
Most of us who have had to deal with electric light stations
or railway power plants have the matter of the load factor
before us all the time. With large water powers the speaker
thinks the load-factor of little moment, because there are
other loads that come on during the day, many of them that
make the load factor nearly 90. A few years ago, at Niagara
Falls, the load line could be drawn with a ruler. At that time
the lij^liting load was hardly noticeable.
INDEX OF SUBJECTS.
Accumulation of charge on lines, io8,
109.
Aluminum fuses, 203.
vs. copper, 324, 342.
Answers to questions, 366.
Apparatus, disabled, disconnection of.
Balancing motors, 306.
Barbed wire, 102, 339.
Blower equipment, for transformers, 223.
Bushings, for transformers, 258.
Cable, apparatus and methods for care
of, 187.
faults, 198.
indicators and protecting devices,
186.
Cables, 388.
fireproofing of, 284, 286, r^go.
high-voltage, 180.
allowable temperature in, 183,
202.
independent vs. parallel opera-
tion, 184
installation of, 182.
maintenance of, 184.
manufacture of, 181.
operation of, 182, 184.
rubber vs. paper, 180, 203.
protection of, 282.
testing, 184, 195, 199, 200.
Charging current, 137, r4i.
effect on regulation, 138.
Choke coils for protective purposes in
testing dielectrics, 120, 125, 127.
Circuit-breaker, reverse current, 188,
194, 204, 347.
over-load time limit, 193, 194, 274.
Climate, eftect on insulation, 92.
Coal consumption in United States,
437- , . r
Compound wound exciter for synchro-
nous motor, 307.
Condenser, rotary, 303.
Conductor, most economical diameter,
415-
Conductors, 372.
elasticity of, 312, 321.
mechanical strength of, 311.
sags in, 313.
Conductors, span and sag curves, 314.
strains in, 313, 333.
Conduit, 288.
Continuous service over lines in parallel,
343-
Control of potential in tests, 138.
Copper vs. aluminum, 324, 342.
Cost of generators, 308.
of installation of group switches,
236, 243-
of pole line, 342.
of power, 434, 436, 438, 440, 44 1 , 446.
of steel poles, 328.
of synchronous motors, 299, 308.
of towers, 310, 323.
of transformers as affected by con-
nection, 149.
Creepage of oil from transformers, 266.
Cross-arms, 378.
methods c fastening, 376.
specifications, 316.
Crossing of power lines, 371.
railways, highways, etc., 371.
Dampers on synchronous motors, 297,
305-
Dielectric strength, 117.
of apparatus, 117.
testing of, 117, 121.
Dirt, effect on insulation, 128.
Disconnection, automatic, of genera-
tors, 189, 201.
of feeders, 190, 201.
of receiving apparatus, 192.
Distance (maximum) of transmission,
410, 419, 433.
Drop, 136.
Eefect of heat on insulation, 118.
Elasticity of conductors, 312, 321.
Electrolysis of cable sheaths, 285, 290.
Electromagnetic induction, 12.
Electrostatic induction, 12, 96.
End strains, 86, 95.
Energy discharged to atmosphere, 331.
Entrance of power lines vertically
through roof, 90.
Entrance of high-tension wires, use of
false dormers, 87.
use of glass plates, 85, 88, 92.
use of sewer-pipe, 80, 86, 89.
460
INDEX OF SUBJECTS.
Fatigue tests on insulation, 131.
Faults, cable, igS.
caused by strong currents, 200, 285.
Feeder, limiting current in, 197.
Feeders, caused by strong currents, 184.
Fire extinguisher, steam, 223.
Fireproofing, cables, 284, 286.
Fire-risk of transformers, 207, 210, 216.
Flash point of oil, 219, 254.
Frequency, choice of, 136.
Fuses, use of, 203, 243.
Gauze ventilators, 226.
Generators used as balancing motors,
306.
Glass vs. porcelain, 39, 93, 94, 340.
Grounded plate, line protection, 362.
wire, 96, 102, 134, 339, 352, 362,
363-
Ground nets, 400, 4or.
shields (transformers), 348, 350.
wires, methods of installation, 100,
134-
Group switches, 233, 237, 271, 280.
cost of, 236, 243.
Guard wire, 73.
Heat and voltage in dielectric, 119.
High vs. low frequencies, 139.
potential, method of applying in
tests, 129.
High-tension conductors, entrance into
buildings, 79.
transmission, answers to ques-
tions, 366.
High-voltage cables, 180.
Inductance volts, 137, 141, 145.
Insulation, effect of heat on, 118.
of high-pressure terminals, 259.
saved by grounding neutral, i49._
Insulator pin (Etheridge), 72.
pins, I, 26, 58, 61.
mechanical, specifications for, i .
protection of, 28, 74, 78.
standard, i, 26.
strength of, 62.
testing of, 30, 62.
Insulators, 6, 58, 63, 377.
specifications, 316.
testing of, 6, 37, 65.
pressure of, 40.
Kelvin's law, 435.
Lightning arrester, 356, 358, 361, 363.
a novel, 115.
and grounded wires in Ger-
many, 115.
steel tower as, 310, 320, 321,
332, 334) 359) 361.
protection, 96, 102, 134, 339, 387.
Line in general, 366.
pressure regulation, 291.
protection, 352, 387.
Lines operated in parallel, 343.
Load factor, 434.
Long spans, 73, 309, 320.
Losses on grounded wires, 102, 104, 106.
Minimum frequency for lighting, 142.
Moisture in insulation, 128.
Neutral grounded, 149, 154, 168, 172,
178, 196, 261.
Neutrals, grounded vs. ungrounded, 161),
170.
unstable, 150.
Oil, combustion point, 213, 219.
flash point, 219, 254.
quality to be used in transformers,
219.
specifications for, 254.
switches, 238, 248, 250, 275.
installation, 276, 277.
specifications, 254.
vapor, pressure of explosion, 213.
Operation of transmission lines, 389.
Overhead vs. underground lines, 404.
Overload circuit breaker, 193, 196.
Over-potential for tests of dielectrics,
127.
Pms, 380.
specifications, 316.
Pole lines, cost of, 342.
top pin, 58.
Poles, 378.
life of, 405.
wooden, life in Utah, 341.
Porcelain vs. glass, 39, 93, 94.
Potential rise in transformer banks, 151.
strains, effects on dielectrics, 118.
Power and telephone wires, relative
position of, 11, 45.
factor constant, 307.
regulation, 307.
wires, transposition of, 11, 45.
Precautions to be observed in testing
dielectrics, 121.
Pressure rise, air-switch opened, 406.
due to opening line, 406.
oil switch opened, 406.
Profit, net, for different distances of
transmission, 417.
Rain shed, 93, 94.
Rating of synchronous motors for reg-
ulating purposes, 304.
Reactive coils, protection of transmis-
sion lines, 354.
Regulating characteristics of synchro-
nous motors, 293.
INDEX OF SUBJECTS.
461
Regulation as effected by charging cur-
rent, 138.
automatic, of pressure and power
factor with synchronous motors,
3°7-
of power factor, zyi.
Resistance volts, 137, 141, 145.
Resonance, 138, 140, 163, 173.
Reverse current circuit-breaker, 188,
194, 204, 347.
Rotary condenser, 303. '
converters as regulators, 298.
Sao and span, 313.
and span curves, 314.
Shielding action of ground wires, 98.
' of ground wires, calculation,
99, Ill-
Size of transformers as affected by con-
nection, 149.
Skilled labor, 220.
Sleet, 313, 325.
Span and sag curves, 314.
Sparking distance, 7, 65.
in fog, 7.
in steam, 7.
Specifications for installation of trans-
formers, 215. ,
for long span lines, 316.
Static discharges, protection of high-
pressure lines, 352, 360.
voltmeter for high voltage, 129.
Steam as fire extinguisher, 223.
Steel poles, cost of, 328.
Strains in conductors, 313, 333.
Stray currents, 200, 285, 287.
Strength of various conductors, 311.
Stress on insulation, 454.
Switches, classified, 250.
group, 233, 237, 271, 280.
oil, 238, 248, 250, 275.
installation, 276, 277.
specifications, 254.
Switching stations on long lines, 205.
Synchronous converters as regulators,
298.
machines as regulators, 297.
motors, 291.
cost, 299.
for compensation of inductive
drop in line, 143, 145.
for regulating purposes, rat-
ing of, 304.
on long lines, 296.
Telephone and power wires, relative
position of, 11, 45.
arrester, 73.
line, 380.
use of transformers on, 74.
wires, transposition of, 11, 45.
Telephones, bridge, 13, 15, 16, 51.
Telephones, installation of, in proxim-
ity to power lines, 15.
Temperature rise (cables), 202.
Terminals, for transformers, 258.
Test of apparatus, where to be made,
/Si-
Time element in over-voltage test, 129.
Towers, calculations for, 326.
cost of, 310, 323.
height of, 316.
specifications, 317.
Transformer, for high-voltage measure-
ment, 130.
Transformer case, construction, 225, 226.
strength, 214.
Transformer connections. Delta to Star
system, 160.
lowering system, 160.
raising system, 162.
Star or Delta, when to use, 148, 153,
175-
Star to Delta lowering, 162.
raising, 161.
system, 160.
tables of connections giving maxi-
mum voltage strains obtainable,
164, 168.
three-phase Delta system, 156, 171.
Star system, 157.
T system, 156.
V system, 156.
two-phase, four- wire system, 155.
three-wire system, 155.
Transformer practice, in Europe, 221.
Transformers, 384.
air-blast, 212.
blower equipment, 223.
displacement of oil with water in
case of fire, 218, 222.
draining oil in case of fire, 211.
fire risk, 207, 210, 216, 269, 279.
flooding of, in case of fire, 211, 21S,
227.
gauze ventilators, 226.
ground shields, 348, 350.
grounding neutral, 149, 351.
installation, 231, 270.
oil vs. air-blast, 207, 210, 220, 221,
224, 228, 230.
protection, 364.
quality of oil, 219.
specifications for installation of, 215.
terminals and bushings, 250, 264,
276.
thin metal case, 212.
use of, in testing insulators, 8, 41,
74-
use of, on telephone lines, 74.
Transmission, maximum distance, 410.
line troubles, 71.
lines long spans, 309.
causes of interruption, 309.
462
INDEX OF AUTHORS.
Transposition of power wires, ii, 45,
369-
of telephone wires, 11, 45.
Voltage in telephone circuits near high-
tension transmission lines, 60,
78.
most economical, 414.
regulation, 136, 291.
Voltmeter, static, for high-voltage, 129.
Volts per mile, 331.
Wave form, correction of, 307.
effect on insulation, 43.
in potential tests, 132.
Wind velocity, 324.
Wooden pins, i, 26, 61, 340.
burning of, 18, 52, 59, 74, 77.
INDEX OF AUTHORS.
[D indicates discussion and C communication.]
Alveeson, H. B.
Protection of Cables (D), 288.
Long Spans (D), 336.
Oil Switches (D), 407.
Static Discharges (D), 409.
Armstrong, J. R.
Insulator Pins (C), 59.
Arnold, B. J.
Long Spans (D), 328, 337.
Ground Nets (D), 400.
Overhead vs. Underground (D),
404.
Ball, W. D.
iLong Spans (D), 329.
Baum, F. G.
Choice of Frequency (D), 141.
Bayne, Howard.
Fire-iisk of Transformers (D), 223.
Bchrend, B. A.
Choice of Frequency (D), 140.
Bell, Louis.
Entrance of High-Tension Wires
(C), 95-
Testing Apparatus for Dielectric
Strength (C), 133.
Star or Delta Connection for Trans-
formers (C), 178.
Blackwell, F. O.
The Testing of Insulators, 6.
Y or Delta Connection of Trans-
formers, 142.
Regulation of Power Factor and
Pressure with Synchronous Mo-
tors (D), 303.
Long Spans for Transmission Lines,
3°9-
Discussion, 321, 323, 327, 338.
Line Protection (D), 358.
Blanck, W. A.
Grounded Wire (D), 115.
Fire Risk of Transformers (D), 270.
Blanck, W. A. (continued).
Time-Limit Switches (D), 274.
Oil Switches (D), 275.
Bhzard, J. W. F.
Protection of Cables (D), 290.
Bond, A. B.
Fire Risk of Transformers (D), 280
Brooke, Q. E.
Oil Switches (D), 276.
Buck, H. W.
Burning of Pins (D), 53.
Burch, E. P.
Underground Systems (D), 194.
Carlton, W. G.
Underground Systems (D), 195.
Group Switches (D), 271, 274.
Terminals and Bushings of Trans-
formers (D), 276.
Protection of Cables from Arcs due
to the Failure of Adjacent Cables,
282.
Discussion, 287.
Overhead vs. Underground (D),
404.
Cable Protection (D), 408.
Chesney, C. C.
Burning of Wooden Pins on High-
Tension Transmission Lines, 18.
Testing Insulators (D), 41.
Burning of Pins (D), 57.
Oil Switches (D), 250.
Clark, Eugene.
Long Spans (D), 329, 329, 333.
Ground Nets (D), 402.
Converse, V. G.
Entrance High-Tension Wires (D),
93-
Star or Delta Connections for
Transformers (D), 171.
Corson, W. R. C.
Standard Insulator Pin (D), 29.
INDEX OF AUTHORS.
463
Cory, C. L.
Standard Insulator Pin (D), 30.
Curtis, C. C.
Grounded Wire (D), 112.
Dow, Alexander.
Group Switches (D), 237.
Oil Switches (D), 255.
Dunn, G. S.
Testing Apparatus for Dielectric
Strength (D), 138, 131.
Eastman, G. N.
Time-Limit Switches (D), 274.
Oil Switches (D), 276, 278.
Oil vs. Air Switches (D), 406.
Static Discharges (D), 409.
Elgin, C. L.
Underground Switches (D), 196.
Ensign, O. H.
Entrance of High-Tension Wires
(D), 86.
Etheridge, H.
Transmission Line (D), 70.
Farley, J. W.
Fire Risk of Transformers (D), 279.
Fisher, H. W.
Electric Cables for High-Voltage
Service, 180.
Underground Systems (D), 201,
202.
Maximimi Transmission Distance
(D), 453-
Floy, Henry.
Potential of Telephone Circuits (C),
60.
Entrance of High-Tension Conduc-
tors (D), 85.
Foster, H. A.
Maximum Transmission Distance
(D), 457-
Frankenfield, B.
Telephone in Time of Emergency,
(D), 78.
Gear, H. B.
Synchronous Motors for Line Regu-
lation (D), 305.
Gerry, M. H., Jr.
Standard Insulator Pin (D), 26.
Testing of Insulators (D), 38.
Transposition of Wires (D), 45.
Burning of Pins (D), 52.
Line Insulation for High-Voltage
(C), S8-
Entrance of High-Tension Wires
(D). 38.
Testing Apparatus for Dielectric
Strength (D), 126.
Star or Delta Connection of Trans-
formers (D), 170, 176.
Gerry, M. H., Jr. (continued).
Conditions for Continuous Service
Over Lines Operated in Parallel,
343-
Maximum Transmission Distance
(D), 442.
Gossler, P. G.
Grounded Wire (D), 134.
Cost of Power (D), 440.
Hammer, W. J.
Grounded Wire (D), 115.
Harisberger, J.
Entrance of High-Tension Wires
(D), 87.
Hatch, A. S.
Long Spans, 321, 342.
Hawkins, L. A.
Testing the Dielectric Strength of
Apparatus (D), 125.
Hayward, R. F.
Entrance of High-Tension Wires
(D), 92.
Grounded Wire (D), 109.
Star or Delta Connection of Trans-
formers (D), i6g.
Long Spans (D), 340.
Line Protection (D), 358.
Hazard, W. J.
Fire Risk of Transformers (D), 231.
Hering, Carl.
Maximum Transmission Distance
(D), 457-
Hewlett, E. M.
Oil Switches for High Pressures,
248.
Hoopes, William.
Long Spans (D), 324.
Hunt, A. M.
Protection of Cables (D), 290.
Huntington, D. L.
Standard Insulator Pin (D), 34.
Jackson, D. C.
Grounded Wire (D), 113.
Jackson, W. B.
Group Switches (D), 239.
Synchronous Motor for Line Regu-
lation (D), 306.
Long Spans (D), 334.
Grounding Ring (D), 402.
Junkersfeld, Peter.
Star or Delta Connection for Trans-
formers (D), 175.
Fire Risk of Transformers (D), 270.
Time-Limit Switches (D), 275.
Installation of Oil Switches (D),
276, 277, 278.
Long Spans (D), 336.
Ground Nets (D), 400.
Cost of Underground System (D),
404.
464
INDEX OF AUTHORS.
Kelly, J. F.
Grounded Wire (D), 107, no.
Kelsch, R. S.
Grounded Wire (D), 107.
Disconnection of Disabled Appa-
ratus (D), 203.
Fire Risk of Transformers (D), 228.
Kennelly, A. E.
Grounded Wire (D), 105.
Maximum Transmission Distance
(D), 443-
Kintner, S. M.
Maximum Transmission Distance
(D), 452-
Lake, E. M.
Protection of Cables (D), 288
Lardner, H. A.
Fire Risk of Transformers
(D),
227.
Lamme, B. G.
Synchronous Motors for Regulation
of Power Factor and Line Press-
ure, 291.
Langsdorf, A. S.
Testing Apparatus for Dielectric
Strength (D), 131.
Lieb, J. W., Jr.
Maximum Distance of Transmis-
sion (D), 433.
Lincoln, P. M.
Transposition and Relative Loca-
tion of Power and Telephone
Wires, 11.
Testing Insulators (D), 39.
Transposition of Wires (D), 51.
Burning of Pins (D), 53.
Grounded Wire (D), 106.
Testing Apparatus for Dielectric
Strength (D), 128.
Choice of Frequency for Very Long
Lines, 136.
Discussion, 145.
Star and Delta Connection for
Transformers (D), 174.
Fire Risk of Transformers (D),
220.
Maximum Transmission Distance
(D), 452-
Lyford, O. S., Jr.
Fire Risk of Transformers (D),
222.
Lyman, James.
Fire Risk of Transformers (D),
269.
Oil Switches (D), 275.
Cable Failures (D), 403.
Mailloux, C. O.
Transposition of Wires (D), 50.
Grounded Wire (D), 102, 116.
Choice of Frequency (D), 142.
Mailloux, C. O. (continued).
Underground Systems (D), 197,
199.
Fire Risk of Transformers (D),
224.
McClellan, William.
Maximum Transmission Distance
(D), 456-
Mershon, R. D.
Mechanical Specifications of a Pro-
posed Standard Insulator Pin, 1.
Discussion, 37.
Testing of Insulators (D), 38, 39,
41.
Transposition of Wires (D), 46.
Burning of Pins (D), 54.
Bringing Wires Into Buildings (D),
91.
The Grounded Wire as a Protection
Against Lightning, 96.
Discussion, 114, 116.
Testing of Electrical Apparatus for
Dielectric Strength, 130.
Choice of Frequency (D), 143, 145,
147-
Y or Delta Connection of Trans-
formers (D), 175.
Operation and Maintenance of
Underground Systems (D), 198,
202.
Fire Risk of Transformers (D),
217.
Use of Group Switches (D), 237.
Oil Switches (D), 255.
Terminals and Bushings for High-
Tension Transformers (D), 264.
Protection of Cables (D), 286.
Long Spans (D), 320, 329, 333,
334-.
Conditions for Continuous Service
over Lines Operated in Parallel
(D), 347-
Use of Ground Shields in Trans-
formers (D), 350.
Line Protection (D), 356.
Ground Nets (D), 400.
General Discussion, 405, 406, 407,
408.
Maximum Distance to which
Power can be Economically
Transmitted, 410.
Discussion, 446,. 449.
Moody, W. S.
Fire Risk of Transformers (D),
232.
Terminals and Bushings for High-
Pressure Transformers, 258.
Mudge, A. L.
Entrance of High-Tension Wires
(D), 86.
Star and Delta Connection of
Transformers (D), 176.
INDEX OF AUTHORS.
465
De Muralt, C. L.
Burning of Pins (D), 55.
Fire Risk of Transformers (D),
221.
Oil Switches (D), 256.
Maximum Transmission Distance
(D). 445-
Neail, N. J.
Fire Risk of Transformers (D),
279.
Long Spans (D), 323, 330, 339.
Line Protection (D), 357.
Rubber Insulation (D), 403.
Depreciation of Poles (D), 405.
Maximum Transmission Distance
(D), 455-
Nunn, P. N.
Star or Delta Connections for
Transformers (D), 171.
Fire Risk of Transformers (D),
220.
Oil Switches (D), 256.
Parshall, H. F.
Fire Risk of Transformers (D),
228.
Group Switches (D), 247.
Oil Switches (D), 257.
Pearson, John.
Line Protection (D), 363.
Peck, J. S.
Testing Insulators (D), 75.
Testing Apparatus for Dielectric
Strength (D), 127.
Y or Delta Connection of Trans-
formers (D), 153.
Fire Risk of Transformers (D),
212.
The Use of Ground Shields in
Transformers, 348.
Line Protection (D), 356.
Perrine, F. A. C.
Standard Insulator Pin (D), 62.
Transposition of Wires (D), 63.
Grounded Wire (D), 102, 105.
Choice of Frequency (D), 145.
Disconnection of Disabled Appa-
ratus (D), 204.
Fire Risk of Transformers (D),
210.
Oil Switches (D), 254.
Synchronous Motors for Line Regu-
lation (D), 307.
Long Spans (D), 331, 337.
Ground Nets (D), 401.
Pierce, F. C.
Entrance of High-Tension Wires
(D), 86.
Pratt, A. C.
Fire Risk of Transformers (D),
226.
Pratt, A. C. (continued).
Terminals and Bushings (D), 267.
Radley, G. R.
Static Discharges (D), 409.
Rice, E. W.
Relative Fire Risk of Oil and Air-
Blast Transformers, 207.
Roberts, E. P.
Fire Risk of Transformers (D),
231.
Roper, D. W.
Fire Risk of Transformers (D),
270.
Rowe, B. P.
Group Switches (D), 280.
Rushmore, D. B.
Grounded Wire (D), 107.
Choice of Frequency (D), 144.
SCHtLDHATJER, Edw.
Installation of Oil Switches (D),
277.
Schuchardt, R. F.
Oil Switches (D), 277.
Schuler, L.
Ground Nets (D), 400.
Schwartz, Carl.
Disconnection of Disabled Appa-
ratus (D), 194.
Scott, C. F.
Telephone Near High-Voltage Line
(D), 76.
Star or Delta Connection of Trans-
formers (D), 169.
Long Spans (D), 336.
Safety Devices (D), 409.
Maximum Transmission Distance
(D), 444.
Sessions, E. O.
Installation of Oil Switches (D),
276, 277.
Skinner, C. E.
Transposition of Wires (D), 50.
Burning of Pins (D), 56.
Line Insulation (D), 65.
Methods of Bringing High-Tension
Conductors Into Buildings, 79.
Discussion, 86.
Testing Apparatus for Dielectric
Strength (D), 129.
Fire Risk of Transformers (D),
218.
Terminals and Bushings (D), 265.
Ground Shields (D), 350.
Maximum Transmission Distance
(D), 453-
Smith, W. N.
Standard Insulator Pin (D), 36.
Testing Insulators (D), 39.
Burning of Pins (D), 57.
Top Pin (C), 58.
36
INDEX OF AUTHORS.
lyder, N. M.
Terminals and Bushings (D),
267.
Line Protection (D), 362.
iUwell, L. B.
The Use of Group Switches in
Large Power Plants, 233.
Discussion, 238.
itzer, A. B.
Maximum Transmission Distance
(D), 456-
orer, S. B.
Long Spans (D), 339.
Ground Nets (D), 401, 402.
:orrs, H. A.
Choice of Frequency (D), 146.
.ott, H. G.
Testing Apparatus for Dielectric
Strength (D), 127, 128.
Choice of Frequency (D), 142,
143-
The Use of Automatic Means for
Disconnecting Disabled Appa-
ratus, 139.
Underground Systems (D), 200.
Group Switches (D), 238.
Fire Risk of Transformers (D),
219.
Maximum Transmission Distance
(D), 434-
AYLOR, I. A.
Fire Risk of Transformers (D),
225.
Group Switches (D), 242.
Terminals and Bushings (D), 265.
'aylor, J. B.
Group Switches (D), 244.
'homas, P. H.
Standard Insulator Pin (D), 37
Testing Insulators (D), 41.
Transposition of Wires (D), 48.
Transmission Line (D), 72.
Entrance of High-Tension Wires
(D), 94-
Grounded Wire (D), 104.
Testing of Electrical Apparatus for
Dielectric Strength, 117.
Star or Delta Connection for Trans-
formers (D), 172.
Continuous Service Over Parallel
Lines (D), 347.
Ground Shields (D), 350.
Line Protection (D), 360.
'obey, H. W.
Fire Risk of Transformers (D),
230.
Torchio. Philip.
Burning of Pins (D), 56.
Operation and Maintenance of
High-Tension Underground Sys-
tems, 184.
Maximum Transmission Distance
(D), 435-
Cost of Power (D), 440.
Townley, Calvert.
Fire Risk of Transformers (D),
216.
Wallace, J. E.
Maximum Transmission Distance
(D), 440.
Waterman, F. N.
Testing Insulators (D), 40.
Waters, W. L.
Testing Insulators (D), 43.
Grounded Wire (D), no.
Testing Apparatus for Dielectric
Strength (D), 128.
Underground Systems (D), 203.
Synchronous Motors for Line Regu-
lation (D), 304.
Ground Shields (D), 351.
WeUs, W. F.
Disconnection of Disabled Appa-
ratus, (D), 193.
Underground Systems (D), 199,
200.
Protection of Cables (D), 286.
Wilcox, N. T.
Fire Risk of Transformers (D),
226.
Wirt, H. C.
Long Spans (D), 339.
Ground Shields (D), 350.
The Protection of High-Pressure
Transmission Lines from Static
Discharges, 352.
Discussion, 358.
Woodbridge, J. E.
Star and Delta Connections for
Transformers (D), 176.
Static Discharges (D), 409.
Woodmansee, F.
Oil vs. Air Switches (D), 407.
Cable Protection (D), 408.
Woodward, F. S.
Burning of Pins (C), 59.
Grounded Wire (D), 107.
Wright, G.
Group Switch (D), 243.
Wurts, A. J.
Grounded Wire (D), 103.