mm mmx immm 086680 jiiii^^ iBP|j^.^j^^pjj^^i^^j^ pWMiiiiiiiiiii .,.*<*' ftUIt»lttit^K^j^[{tljj^!!Hit iliBIQili c. K Tkusi 63^ # ¥ (S[fxtmll InioBraita Sltbrary Mtfuta, S^em ^nrfe THE LIBRARY OF EMIL KUICHLING, C. E. ROCHESTER. NEW YORK THE GIFT OF SARAH L. KUICHLING 1919 Cornell University Library TK1191.S52 Power stations and power transmission. 3 1924 005 027 754 'M H\ Cornell University Library The original of tiiis book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/cletails/cu31924005027754 1 ■ » '"■'■■-'^ 1 ^H 1 1 >^^^^H 1 ^M P^f ■!■ '^B^IBiH^^^B aH SEm ^^^^H 9h ^^^^^H ^ '^ 1 ^pt- ^ 1 Q^^^l ^^^HSH^BSf'* "tB Hn \>''. 9 hh *^*"^ S ^NH ffAi ^_^* f *^ ( mI^^^^^I ^^H^o^Hj 1^;^'%^ ^n i y^H ^^^HHHb |H i Vi^^^^^^l THOMAS A. EDISON, Inventor of Telegrapnic Appliances, Pbonograpli, Incandescent Lamp, and Many Other Electrical Devices Power Stations and Power Transmission A Manual of APPROVED AMERICAN PRACTICE IN THE CONSTRUCTION, EQUIPMENT, AND MANAGEMENT OF ELECTRICAL GENERATING STATIONS, SUBSTATIONS, AND TRANSMISSION LINES, FOR POWER, LIGHTING, TRACTION, ELECTRO- CHEMICAL, AND DOMESTIC USES PART I— POWER STATIONS PART II— POWER TRANSMISSION By George C. Shaad, E.E Assistant Professor of Electrical Engineering, Massachusetts Institute of Technology ILLUSTRATED CHICAGO AMERICAN SCHOOL OF CORRESPONDENCE 1908 CoP-i-RIGHT 1907 BY Amep-Ican School of Cokrespondence Entered at Stationers' Hall, London All Rights Reserved Foreword N recent years, sueb marvelous advances have been made in the engineering and scientific fields, and so rapid has been the evolution of mechanical and constructive processes and methods, that a distinct need has been created for a series of ■pi'"<-''^'"'"^ worliiig (jn.idcs, of convenient size and low cost, embodying the accumulated results of experience and the most approved modern practice along a great variety of lines. To fill this acknowledged need, is the special purpose of the series of handbooks to which this volume belongs. e C In the preparation of this series, it has been the aim of the pub- lishers to lay special stress on the prm-fiail side of each suljject, as distinguished from mere theoretical or academic discussion. Each volume is written by a well-known expert of acknowledged authority in his special line, and is based on a most careful study of practical needs and up-to-date methods as developed under the conditions of actual practice in the field, the shop, the mill, the power house, the drafting room, the engine room, etc. C These volumes are especially adapted for purposes of self- instruction and home study. The utmost care has been used to brincj' the treatment of each subiect within the ranjj-e of tlie com- mon understanding, so that the work will appeal not only to the technically trained expert, but also to the beginner and the self- taught practical man who wishes to keep abreast of modern progress. The language is simple and clear; heavy technical terms and the formulae of the higher mathematics have been avoided, yet without sacrificing any of the requirements of practical instruction; the arrangement of matter is such as to carry the reader along by easy steps to complete mastery of each subject; frequent examples for practice are given, to enable the reader to test his knowledge and make it a permanent possession; and the illustrations are selected with the greatest care to supplement and make clear the references in the text. C The method adopted in the preparation of these volumes is that which the American School of Correspondence has developed and employed so successfully for many years. It is not an experiment, but has stood the severest of all tests — that of practical use — which has demonstrated it to be the best method yet devised for the education of the busy working man, C For purposes of ready reference and timely information when needed, it is believed that this series of handbooks will be found to meet every requirement. Table of Contents PART I— POWER STATIONS Location of Station and Selection of System . . . Page 3 Choosing Site — Provision for Future Extensions — Cost of Real Estate — Location of Substation — Factors Determining Choice of Generating and Transmission Systems — Advantages of Concentrating the Gener- ating Plant — Size of Plant. Steam and Hydraulic Plants Page Iff Boiler Requirements — Types of Boilers — Steam Piping — Interchange- ability of Units — Size, Location, etc., of Pipe.s — Loss of Pressure — Superheating — Feed-Water and Feeding Appliances — Scale and Otlier Impurities — Feed-Pumps and Injectors — Furnaces — Natural and Me- chanical Draft — Firing of Boilers — Steam Engines — Steam Turbines — Use of Water-Power — Water Turbines (Reaction and Impulse Types) — Pelton Wheel — Water-Pressure — Hydraulic Pipe Data — Head and Horse-Power — Governors — Gas Engines as Prime Movers. Electrical Equipment of Stations Page 36 Generators (Direct-Current, Alternating-Current, Single-Phase, Polj;- phase. Double- Current) — Exciters — Transformers — Storage Batteries — Switchboards and Connections — Standard Wire and Cable — Panels — ■ — Ammeters — Voltmeters — Rheostats — Circuit-Breakers — Bus-Bars — Oil Switches — Tripping Magnets — Lightning Arresters — Reverse-Cur- rent Relays — Speed-Limit Devices — Substations. Station Buildings, Records, and Office Management . . Page 63 Layout of Structure and Appointments — Station Records — Operating Expenses — Fixed Charges — Depreciation — Methods of Charging. PART II— POWER TRANSMISSION Conductors Page 1 Materials Used — Temperature CoefBcient — Weight — Mechonical .Strengtli — Effects of Resistance — Current-Carrying Capacity — Insulat- ing Co\'ering for Wires — Annunciator Wire — Underwriter's Wire — • Weatherproof Wire — Gutta-Percha and India Rubber. Distribution Systems and Transmission Lines. . . . Page 11 Series Systems — Parallel or Multiple-Arc Systems — Feeders and Mains — Parallel and Anti-Parallel Feeding — Series-Multiple and Multiple- Series Systems — Multiple-Wire Systems — Voltage Regulation of Par- allel Systems — Alternating-Current Systems (Series, Parallel) — Polyphase Systems (Two-Phase, Three-Phase) — Calculation of A. C. Lines — Wiring Formulffi — Transformers — Losses — EflScienry — Regula- tion — Overhead Lines— rPoles — Guying — Cross- Arms — Insulators — Pins — Temperature Effects — Underground Construction — Vitrified Con- duit — Fibre Conduit — Manholes — Cables — I^rotection of Circuit. Index Page 75 o El < ia O a H E-i u o u I u u Hi a ?! H U g en la o Z o u Q s o s o u o K POWER STATIONS. e With the rapid increase of the use of electricity for power, lighting, traction,, and electro -chemical processes, the power houses e(|iiipped for the generation of the electrical supply have increased in size from plants containing a few low-capacity dynamos, belted to their prime movers and lighting a limited district, to the mod- ern central station, furnishing power to immense systems and over extended areas. Examples of the latter type of station are found at Niagara Falls, such stations as the Metropolitan and Manhattan stations in New York City, the plants of the Boston Edison Illu- minating Company, etc. The subject of the design, operation, and maintenance of cen- tral stations forms an extended and attractive branch of electrical engineering. The design of a successful station requires scientific training, extensive experience, and teclmical ability. Knowledge of electrical subjects alone will not suffice, as civil and mechanical ngineering ability is called into play as well, while iiltimate success depends largely on financial conditions. Thus, with un- limited capital, a station of high economy of operation may be designed and constructed, but the business uiay be such that the fixed charges for money invested will more than equal the differ- ence between the receipts of the company and the cost of the gen- eration of power alone. In such cases it is better to build a cheaper station and one not possessing such extremely high economy, but on -which the fixed charges are so greatly reduced that it may be operated at a profit to tlie owners. The designing engineer should l)e thoroughly familiar with the natui'e and extent of the demand for power and with the prob- able increase in this demand. Few systems can be completed for their ultimate capacity at first and, at the same time, operated economically. Only such generating units, with suitable reserve cajjacity, as are necessary to supply the demand should be installed at first, bnt all apparatus should Ije arranged in such a manner tliat futTire extensions can be re;idily nuule. POWER STATIONS The subjects of power stations, as here treated, will consider the following general topics : Location of station and substation, with choice of system to be em- ployed. Bteam plants, boilers, piping, prime movers, etc. Hydraulic plants. The vise of other prime movers. Theelectrical plant, generators, and exciters, switching apijaratus, etc. lUiildiugs. Station records, methods of charging for power, etc. LOCATION OF THE QENERATINQ STATION. The choice of a site for the generating station is very closely connected with the selection of the system to lie used, which sys- teiii, in turn, depends largely on the nature of the demand, so that it is a little difficult to treat these topics separately. Several possi- ble sites are often available, and we may either consider the require- ments of an ideal location, selecting the availalile one which is nearest to this in its <-]iaracteristics. or we may select the best system for a given area and assume that the station may be located where it would l)e liest adapted to this system. "Wherever the site may be, it is possible to select an efficient system, though not always an ideal one. The following points should be considered in the location. of a station, no matter what the system irsed : 1. Accessibility. 2. Water supply. 3. Stability of foundation. 4. Surriiundinns. •5. Facility for extension. 6. Cost of real estate. The station should be readily accessible on account of the delivery of fuel and stores, and of the machinery, while it should be so located that ashes and cindeis n:ay be easily removed. If possible, the station should be located so as to be reached Ijy both rail and watei', though the former is generally more desirable. If the coal can be delivered to tlie bunkers directly from the cars, the very important item of the cost of handling fuel may lie greatly reduced. Again, the station should, be in such a location that it may be readily reached by the workmen. z 3 z 1 Z § H U3 < * fid " s w J; ce as POWER STATIONS Clieaj) and abundant -water snp])ly for botli boilers and con- densers is of utmost iniportaut'e in locating a steam station. The quality of the water supply for the boiler is of more importance than the quantity. It should be as free as possible from impuri- ties which are liable to corrode the boilers, and for this reason water from the town mains is often used, even when other water is available, as it is possible to economize in the use of ivater by the selection of proper condensers. The supply for condensing pur- ])oses should be abundant, otherwise it is necessary to install ex- tensive cooling apparatus which is costly and occupies much space. The machinery, as well as the buildings, miist have stable foundations, and it is well to investigate the availability of such foundations when selecting the site. In the operation of a power plant using coal or other fuels, certain nuisances arise, such as smoke, noise, or vibration, etc. For this reason it is preferable to locate where there is little lia- bility to complaint on account of tliese causes, as some of these nuisances are costly and ditticult or even imjjossible to prevent. A station should be located where there are ample facilities for extension and, while it may not always be advisable to pur- chase land sufficient for these extensions at first, if there is the slightest doubt in regard to being able to purchase it later, it should be bought at once, as the station should Ije as free as possi- ble from lisk of interruption of its plans. Often real estate is too high for purchasing a site in the best location, and then the next best point must be selected. A consideration of all the factors involved is necessary in determining whether or not this cost is too high. In densely populated districts it is necessary to econo- mize greatly with the space available, but it is generally desirable that the machinery uiay all be placed on the ground floor and that adequate provision may be made for the storage of fuel, etc. The location of substations is usually fixed by other con- ditions than those which determine the site of the main power house. Since, in the simple rotary converter substation, neither fuel or water are necessary and there is little noise or vibration, it may be located wherever the cost of real estate will permit, pro- vided suitable foundation may be constructed. The distance POWER STATIONS between substations depends entirely on the selection of the sys- tem and the nature of the service. Where low voltages are used it is essential that the station be located as near the center of the system as possible. This cen- ter is located as follows: Having determined the probable loads and their points of application for the proposed system, these loads are indicated on a drawing with the location of the same shown to scale. The center of gravity of this system, considering each load as a weight, is then found and its location is the ideal location, as regards amount of copper necessary for the distributing system. Consider Fio-. 1, which shows the location of five different loads, which in this case are indicated by number of amperes. Combining loads A and B, we have Ai? = By. x -j- y = a. Solv- ing these equations we find that ,.i,----^r6""^^ A and B may be considered as aI" / a load of A + B amperes at F. ,-3'7f , fonr machines should be the initial installment since one can be laid off for re[iairs if neces- sary, the total load being readily carried by tiiree machines. In planning extensions, the fact that at least one machine may require to be laid off at any time should not Ije lost sight of, while the units should be made as large as is conducive to the best operation. TABLE 1. Permissible Overload 3$ per cent. one ines :xdded It a time. Machines added two at a time. Machines added three at a time. No. Size. 500 666 888 1183 1577 2103 2804 No. Size. 4 500 2 1000 2 2000 2 4(X)0 4 40OO 8 4000 No. Size. 4 500 First extension 3 2000 5 5000 Third " 4 5000 Fourth " Fifth " Sixth " 10 POWER STATIONS Table 1 is worked out showing the initial installment for a 2,000-K.W. plant with future extensions. It is seen from this table that adding two machines at a time gives more uniformity in the size of units — a very desirable feature. The boilers should be of large units for stations of large capacity, while for small stations they must be selected so that at least one may be laid off for repairs. STEAM PLANT. BOILERS. The majority of power stations have their machinery driven by either steam or water power, though there are many using gas engines as prime movers. If a steam plant is being considered. one of the first subjects to be taken up is the generation of the steam. The subject of boilers is one of vital importance to the successful operation of steam-driven central stations. The object olthe boiler with its furnace is to abstract as much heat as possi- ble from the fuel and impart it to the water. The various kinds of boilers used for accomplishing this more or less sxiccessfully are described in books on boilers, and we will consider here the merits of a few of the types only as regards central-station operation. The requirements are: l^irst, that steam be available through- out the twenty-four hours; the amount required at different parts of the day varying considerably. Thus, in a lighting station, the demand from midnight to 6 a. m. is very light, but toward eve- ning, when the load on the station increases very rapidly, there is an abrupt increase in the rate at which steam must be given off. The maximum demand can be readily anticipated under normal weather conditions, but occasionally this maximum will be equaled or even exceeded at unexpected moments. For this reason a certain num- ber of boilers must be kept under steam constantly, more or less of them running with banked fir^s during light loads. If the boilers have a small amount of radiating surface, the loss durintr idle hours will be decreased. Second, the boilers must be economical over a large range of rates of firing and must be capable of being forced without dgti1>^ ment. Boilers should be provided which work economically for the hours just preceding and following the maximum load while they POWER STATIONS 11 may be forced, though rnnuing at lower efficiency, during the peak. Third, coining to the commercial side of the question, we have first cost, cost of maintenance, and space occupied. The first cost, as does the cost of maintenance, varies with the type and pressure of the boiler. The space occupied enters as a factor only when the situation of the station is such that space is limited, or when the amount of steam piping becomes excessive. In some city plants, space may be the determining feature in the selection of boilers. The Cornish and Lancashire boilers differ only in the num- ber of cylindrical tubes in which furnaces are placed. As many as three tubes are placed in the largest sizes (seldom used) of the Lancashire boilers. They are made up to 200 pounds steam pres- sure and possess the following features: 1. High efflciency at moderate rates of combustion. 2. Low rate of depreciation. 3. Large water space. 4. Easily cleaned. 6. Large floor space required. 6. Cannot be readily forced. The Galloway boiler differs from the Lancashire boiler in that there are cross tubes in the flues. In the Multitubular boiler the number of tubes is greatly increased and their size diminished. Their heating surface is large and they steam rapidly. They are used extensively for power- station work. The chief characteristics of the water=tube boilers, of which there are many types, are": 1. Moderate floor space. 2. Ability to steam rapidly. 3. Good water circulation. 4. Adapted to high pressure. 5. Easily transported and erected. 6. Easily repaired. 7. ^"ot easily cleaned. 8. Kate of deterioration greater than for Lancashire boiler. 9. Small water space, hence variation in pressure with var.ying demands for steam. 10. Expensive setting. Marine boilers require no setting. Among their advantages and disadvantages may be mentioned: 12 POWEE STATIONS 1. Exceedingly small space necessary. 2. Kadiatiug surface reduced. 'A. Good economy. 4. Heavy and difficult to repair. 5. Unsuitable for bad water. 6. Poor circulation of water. Another type of boiler, known as the Economic, is a combi- nation of the Lancashire and multitubular boilers, as is the marine boiler. It is set in brickwork and arranged so that the gases pass under the bottom and along the sides of the boiler as well aa through the tubes. It may be compared with other boilers from the following points: 1. Small floor space. 2. Less radiating surface than the Lancashire boiler, 3. Not easily cleaned. 4. Repairs rather expensive. 5. Requires considerable draft. As regards first cost, boilers installed for 150 pounds pressure and the same rate of evaporation, will run in the following order: Galloway and Marine, highest first cost, Economic, Lancashire, Bab- cock ife Wilcox. The increase of cost, with increase of steam pres- sure, is greatest for the Economic and least for the water-tube type. Deterioration is less with the Lancashire boiler than with the other types. The floor space occupied by these various types built for 150 pounds pressure and 7,500 pounds of water, evaporated per hour, is given in Table 2. TABLE 2. Kind of Boner. ^K^fT Lancashire 408 Galloway 371 Babcock and Wilcox 200 ^larine wet-back 1:20 Economic .' 210 The percentage of the heat of the fuel iitilized by the boiler is Oi. great importance, but it is ditiicult to get reliable data in re- gard to this. Table 3 is taken from Donkin's "Heat Efliciency of 8team Boilers", and will give some idea of the efficiencies of the different types. Economizers -were not used in any of these tests, but they should always be used with the Lancashire type of boilei'.- POWER STATIONS 13 TABLE 3. Kind of Boiler. Lancashire haud-flred Laucashire luachine-lired Coruish hand-lired Babcock and Wilcox haud-lired. Marine wet-back haud-lired Marine dry-back hand-lired Mean Effi- Nfo. of Ex- periments. ciency of two best Experi- Lowest Efllclency. ments. 42.1 107 79.5 40 78.0 51.9 ■Zo 81.7 53.0 49 77.. 5 50.0 6 09.6 (K.O •2i 75.7 64.7 Mean Effi- ciency of all Experi- ments. 02.3 o4.2 68.0 64. it 66.0 69.2 It is well to select a boiler from 20 to 50 pounds in excess of the pressxire to be used, as its life may thus be considerably ex- tended, while, when the boiler is new, the safety valve need not be set so near the normal pressure, and there is less steam wasted by the blowing ofE of this valve. Again, a few extra pounds of steam may be carried just previous to the time the peak of the load is expected. For pressures exceeding 200 or, possibly, 150 poiinds, a water-tube boiler should be selected. In large stations, it is preferable to malve the boiler units of large capacity, to do away as much as possible with the extra piping and fittings necessary for each unit. Water-tube boilers are best adapted for large sizes. These may be constructed for 150 pounds pressure, large enough to evaporate 20,000 pounds of water per hour, at an economical rate. To sum up — For stations of moderate size and witli medium pressures with plenty of space, use Lancashire or fire-tabe boilers; for high pressure or large units, select water-tube boilers; where space is limited, install marine boilers, although they are not as safe as water-tube boilers for high pressures. Steam Piping. The piping from the Ijoilers to the engines should be given very careful consideration. Steam should be available at all times and for all engines. Freedom from serious interruptions due to leaks or breaks in the piping is brought about by very careful design and the use of good material in construction. Duplicate piping is used in many instances. Provision must always be made for variations in length of the pipe with variation of temperature. For plants using steam at 150 pounds pressure, the variation in the length of steam pipe maybe as high as 2.5 14 POWEK STATIONS inches for 100 feet, and at least 2 inches for 100 feet should always be counted upon. Arrangement. Fig. 2 shows a simple diagram of the " ring" system of piping. The steam passes from the boiler by two paths to the engine and any section of the piping may be cut out by the closing of two valves. Simple ring systems have the following characteristics: 1. The range, as the main pipe is called, must be of uniform size and large enough to carry all of the steam when generated at its maximum rate. '2. A damaged section may disable one boiler or one engine. 3. Several large valves are required. 4. Provision may be readily made to allow for expansion of pipes. Cross connecting the ring system, as shown in P^io-. 3, changes these characteiistics as follows: 1. Bize of pipes and cousequent radiating surface is reduced. 2. More valves needed but tbey are of smaller size. 8. Tjess easy to arrange for expansion of the pipes. o us u o a. < as < a 3 O o POWEK STATIONS 15 If the system is to be duplicated, that is, two complete sets of ipain pipes and feeders installed (seeFig. 4), two schemes are in use: 1. Each system Is designed to operate the whole station at maxi- mum load with normal velocity and loss of pressure In the pipes, and only one system is in use at a time. This has the disadvantage that the idle ENG/NES BO/LCHS Fig. 3. section is liable not to be in good operating condition when needed. Large pipes must be used for each set of mains. 2. The two systems may be made large enough to supply steam at normal loss of pressure when both are used at the same time, while either is made large enough to keep the station running should the other section need repairs. This has the advantages of less expense, and both sections of pipe are normally in use; but it has the disadvantages of more radiating surface to the pipes and consequent condensation for the same capacity for furnishing steam. 16 POWER STATIONS Complete interchangeability of units cannot be arranged for if the separate engine units exceed 400 to 500 horse power. Since engine units can be made larger than boiler units, it becomes nec- essary to treat several boiler units as a single unit, or battery, these batteries being connected as the single boilers already shown. For still larger plants the steam piping, if ari'anged to supply any engines from any batteries of boilers, would be of enormous size. If the boilers do not occupy a greater length of floor space than the engines, Fig. 5 shows a good arrangement of units. Any "1 !~< 1 1 1 1 ■ 1 1 1 1 1 1 ._-, J- _ |l 1 1 1 1 i! ii 1 L ' 1| 1 1 . _ 1 1 II J |_ __ __. 1 <^^. ' U ij Fig. 4. entrine can be fed from either of two batteries of boilers and the liability of serious interruj)tions of service due to steam pij)es or boiler trouble is very remote. Material. Steel pipe, lap welded and fastened together by means of flanges, is to be recommended for all steam piping. The flanges niay be screwed on the ends of sections and calked so as to render this connection steam tioht, though in larne sizes it is better to have tlie flani>'es welded to thi V lies. This latter construction POWER STATIONS ir costs no more for large pipes and is much more reliable. All Talves and fittings are made in two grades or weights, one for low pressures, and the other for high pressures. The high-pressure fittings should always be used for electrical stations. Gate valves should always be selected and, in large sizes, they should be pro- vided with a by-pass. — Asbestos, either alone or with copper rings, vulcan- ized india rubber, asbestos and india rubber, etc., are used for packing between flanges to render them steam tight. Where there is much expansion, the ma- terial selected should be one that possesses considerable elasticity. Joints for high- pressure systems require much more care than those where steam is used at a low pressure, and the num- ber of "joints should be re- duced to a minimi^m by using long sections of pipe. A list of the various fit- tings required for steam piping, together with their descriptions, is given in books on boilers. One pre- caution to be taken is to see that such fittings do not become too numerous or com])licated, and it is well not to depend too much on autcmalic fittings. Steam separators should be large enough to serve as a reservoir of steam for the engine and thus equalize, to a certain extent, the velocity of fiow of ^-team in the pijies. — — -- -• ■ ■ ENG/NtLS J QOlLEFiS Fig. 5. 18 POWEE STATIONS In providing for the expansion of pipes due to change of temperature, " U " bends made of steel pipe and having a radius of curvature not less than six times, and preferably ten times the diameter of the pipe, are preferred. Copper pipes cannot be rec- ommended for high pressures, while slip expansion joints are most undesirable on account of their liability to bind. The size of steam pipes is determined by the velocity of flow. Probably an average velocity of 60 feet per second would be better than 100 feet per second, though in some cases where space is limited a velocity as high as 150 feet per second has been used. The loss in pressure in steam pipes may be obtained from the following formula: where jp, — p, = loss in pressure in pounds per sq. in. Q = quantity of steam in cu. ft. per minute. <1 = diameter of pipe in inches. L = length in feet. )/) — weight per cu. ft. of steam at pressure ^j. e — constant depending on size of pipe. Values of '■ are as follows: Diameter of pipe., i.," 1" 2" 3" 4" 5" 6" 7" 8" 9" 10" Value of c 36.8 4o.3 52.7 56.1 57.8 58.4 59.5 60.1 60.7 61.2 61.8 Diameter of pipe 12" 14" 16" 18" 20" 22" 24" Value of 62.1 62.3 62.6 62.7 62.9 63.2 63.2 In mounting the steam pipe, it should be fastened rigidly at one point, preferably near the center of a long section, and allowed a slight motion longitudinally at all other supports. Such sup- ports may be provided with rollers to allow for this motion, or ^he pipe may be suspended from wrought- iron rods which will give a flexible support. Practice differs in the location of the steam pip- ing, some engineers recommending that it be placed underneath the engine room floor and others that it be located high above the engine room floor. In any case it should be made easily access- ible, and the valves should be located so that nothing will inter- fere with their operation. Proper provision must be made for draining the pipes. POWER STATIONS 19 All piping as well as joints should be carefully covered with a good quality of lagging as the amount of steam condensed in a bare j)ipe, especially if of any great length, is considerable. In select- ing a lagging the following points should be noticed. Covering for steam pipes should be incombustible, should present a smooth sur- face, should not be easily damaged by vibration or steam, and should have as large a resistance to the passage of heat as possible. It must not be too thick, otherwise the increased, radiating surface will counterbalance the resistance to the passage of heat. The loss of power in steam pipes due to radiation is given as follows : II = .262/'L(7. H = loss of power in heat units. (J = diameter of pipe. L = length of pipe in feet. ')' = constant depending on steam pressure and pipe covering. Steam pressure lu pounds (absolute) 40 (l") 90 115 Values of r for uucoveied pipe 4:!7 65.5 GliO 684 Value of r for pipe covered with 2 inelies of hair felt 48 oS GO 73 Keferring to table in books on boilers, the relative values of different materials used for covering steam pipes may be found. Superheated Steam reduces condensation in the engines as well as in the piping, and increases the efficiency of the system. Its use was abandoned for several years, due to difficulties in lubricating and packing the engine cylinders, but by the use of mineral oils and metallic packing, these difficulties have been done away with to a large extent, while steam turbines are especially adapted to the use of superheated steam. The application of heat directly to steam, as is done in the superheater, increases the efficiency of the boilers. Table 4 shows the increase in boiler efficiency for a certain boiler test, the results being given in pounds of water changed to dry, satirrated steam. Tests on vari- ous engines show a gain in efficiency as high as 9% with a super, heat of 80" to 100° F, while special tests in some cases show even a greater gain. 20 POWER STATIONS TABLE 4. of superheat. Water evaporated per lb. of coal. Without superheat. With super- heat. 40 degrees F 42 " 7.82 6.42 6.00 6.78 7.15 9.99 7.06 5.5 7.00 .56.5 " 8.66 55.2 " 8.65 Superheaters are very simple, consisting of tubular boilers containing steam instead of water, and either located so as to util- ize the heat of the gases, the same as economizers, or separately fired. They should be arranged so that they may be readily cut out of service, if necessary, and provision must be made for either flooding them or turning the hot gases into a by-pass, as the tubes would be injured by the heat if they contained neither water nor steam. FEED WATER AND FEEDING APPLIANCES. All water, such as can be obtained for the feeding of boilers, contains some impurities, among the most important of which as regards boilers are soluble salts of calcium and magnesium. Bicar- bonates of the alkaline earths cause precipitations on the interior of boilers, forming "• scale ". Sulphate of lime is also deposited by concentration under pressure. Scale, when formed, not only decreases the efficiency of the boiler but also causes deterioration, for if sufficiently thick, the diminished conducting power of the boiler allows the tubes or plates to be overheated and to crack or burst. Again, the scale may keep the water from contact with sections of the heated plates for some time and then, giving way, large volumes of steam are generated very quickly and an explo- sion may result. Some processes to prevent the formation of scale are used, which affect the water after it enters the boilers, but they are not to be recommended, and any treatment the water receives should affect it j)revious to its being fed to the boilers. Carbonates and a small quantity of sulphate of lime may be removed by heating POWER STATIONS 21 BO/CC/=IS ECONOM/ZCRS fUMPS Kig. <;. in a separate vessel. Large quantities of sulphate of lime must be precipitated chemically. Sediment, small particles of matter in suspension, must lie removed by allowing the water to settle. Vegetable matters are sometimes present, which cause a film to be deposited. Certain gases, in solution — such as oxygen, nitrogen, etc. — cause pitting of the boiler. This effect is neu- tralized by the addition of chemicals. Oil, from the engine cylinder, is particu- larly destructive to boilers and when present in the condensed steam must be carefully removed*. Both feed pumps and injectors are used for feed- ing the water to the boilers. Feed pumps uiay be either steam or motor-driven. Steam-driven pumps are very inefficient, but they are simple and the s])eed is easily controlled. Motor-driven pumps are more efficient and neater, but more expensive and more difficult to regulate efficiently over a wide range of speed. Direct-acting pumps niay have feed- water heaters attached to them, thus increasing the efficiency of the apparatus as a whole. The supply of electrical energy must be constant if motor-driven pumps are to be used. Feed pipes must be arranged so as to reduce the risk of fail- ure to a minimum, and for this reason they are almost always du- plicated. More than one water supply is also recommended if there is the slightest danger of interruption on this account. One com- mon arrangement of feed-water apparatus is to install a few large pumps supplying either of two jnains from which the boiler con- 22 POWER STATIONS TABLE 5. Giving Rate of Flow of Water, in Feet per Minute, through Pipes of Various Sizes, for Varying Quantities of Flow. Gallons per Min. ".; in. 1 in. IX in IVj In, sin. 2H in. 3 in. 13X 4 in. 5 218 1223,^ 7Si,C 54X 30X 19X 7% 10 43() 245 157 109 61 38 27 15X 15 653 367X 235X 163X 91X 58X 40X 23 20 872 490 814 218 122 78 54 30% 26 1090 612X 392X 272X 152X 97X 67X 38K 30 735 451 327 183 117 81 46 35 857X 549X 3813< 213X 136X 94X 53% 40 980 628 436 244 156 " 108 61% 45 1102V 706X 490X 274X 175X 121X 69 50 785 545 - 305 195 135 76% 75 1177X 817X 457X 292X 'mx 115 100 1090 610 380 270 • 153X 125 762X 487>.; 337X 191% 160 915 58-") 405 230 175 1067X • 1821..' 472X 268% 200 1220 7S(I 540 306% nections are taken. This is a complicated and costly system of piping. Fig. 6 shows a scheme used for feeding two boilers in which each pump is capable of supplying both boilers. Pipes should be ample in cross-section, and, in long lengths, allowance must be made for expansion. Cast iron or cast steel is the mate- rial used for their construction, while the joints are made by means of flanges fitted with rubber gaskets. Table 5 gives the rate of flow of water in feet per minute through pipes of various sizes. A flow of 10 gallons per minute for each 100 H. P. of boiler equipment should be allowed without causing an excessive velocity of flow in the pipes. BOILER FOUNDATIONS, FURNACES AND DRAFT. The economical use of coal depends, to a large extent, on the setting of the boiler and proper dimensions of the furnaces. Internally-fired boilers require support only, while the setting of externally-fired boilers requires provision for the furnaces. Com- mon brick, together with fire brick for the lining of portions exposed to the hot gases, are used almost invariably for boiler, settings. It is customary to set the boiler units up in batteries of two, using a 20-inch wall at the sides and a 12-inch wall be- tween the two boilers. The instructions for settings furnished by PC^WER STATIONS 23 the manufacturers should be carefully followed out as they are l)ased on conditions which give the hest results in thu operation of tlieir lioilers. Natural Draft is the most commonly used and is the most satisfactory under ordinary circumstances. In determining the size of the chimney necessary to furnish this draft, the following formula is given by Kent: .06 F , , .OC.F., A = area of chimney in sq. ft. // = height of chimney in ft. F = pounds of coal per hour. The height of chimney should be assumed and the area calcu- lated, remembering that it is better to have tlie chimney too large than too small.' The chimney may l)e of either brick or iron, the latter having a less first cost b\it requiring repairs at frequent intervals. Gen- eral rules for the design of a chimney may be given as follows: The external diameter of the base should not be less than -ji,, of the height. Foundations must be of the best. Interioi-s should be of uniform section and lined with fire brick. There must lie an air space between the lining and chimney proper. The exterioi- should have a taper of from J. to | i'nch to the foot. Flues should be arranged symmetrically. Ficr. 7 shows the construction of a l)rick chimney of gooil design, this chimney being used with Ixiilei's fnrnishing nigines which develop 14,000 TT. P. Mechanical Draft is a term which may lie used to embrace both forced and induced draft. The different systems of mechan- ical draft are described in books oji boilers. The first cost of mechanical -draft systems^ is less than that of a chimney, l)ut the operation and repair are much more expensive and there is always the risk of break-down. Artificial draft has the advan- tage that it can be varied witliin large limits and it can be increased to any desired extent, thus allowing the use of low grades of coal. Firing of Boilers and Handling of Fuel. Coal is used for fuel to a greater extent than any other material, though oil, gas. 24 POWER STATIONS availability, cost, etc., and no general rules wood, etc., are used in some localities. Local conditions, such as should determine the material to be used an be given. Data regarding the relative heating values of different fuels show the following general figures: One pound of petroleum, about i of a gallon, is equivalent, when used with boilers, to 1.8 pounds of coal and there is less deterioration of the fur- nace with oil. 7i to 12 cubic feet of natural gas are re- quired as the equivalent of one pound of coal, depending on the quality of the gas. 2i pounds of dry wood is as- sumed as the equivalent of one pound of coal. When coal is used, it requires stoking and this may be accomplished either by hand or by means of me- chauical stokers, many forms of which are available. Me- chanical stoking has the ad- vantage over hand stoking that the fuel may be fed to the furnace more uniformly and the fires and boilers are not subjected to sudden blasts of cold air as is the case when the fire doors are opened ; a poorer grade of coal may be burned, if nec- essary, and the trouble due to smoke is much reduced. It may be said that mechanical stokers are used almost universally iu the more important elec- Space ; Ground Line POWER STATIONS 25 trical plants. Economic use of fuel i-eqnires great care in firing, especially if it is done l)y hand. Where gas is used, the firing may be made nearly automatic, and the same is true of oil firincr thonah the latter requires more complicated burners, as it is necessary that the oil be vaporized. In large stations, operated continuously, it is desirable that, as far as possible, all coal and ashes be liandled by machinery, though the difference in cost of operation should be cai-efuUy con- sidered before installing extensive coal-handling machinery. jMa- chinery for automatically handling the coal will cost from $T.r)0 to $10 per horse-power rating of boilers for installation, while the ash- handling machinery will cost from 31-50 to S3. 00 per horse power. The coal-handling devices usually consist of ehain-oj>e rated conveyors which hoist the coal from railway cars, barges, etc., to overhead bins from which it may be fed to the stokers. The ashes may be handled in a similar manner, by means of scraper conveyors, or small cars may be used. Either steam or electricity may be used for driving this auxiliary apparatus. It is always desirable that there be generous provision for the storage of fuel sufficient to maintain operations of the plant ovei' a temporary failure of supply. STEAM ENGINES AND TURBINES. The choice of steam prime movers is one which is governed by a number of conditions winch can be treated but briefly here. The first of these conditions relates to the speed of tlie engine to be used. There is considerable difference of op)inion in regard to this as both high and low-speed plants are in operation, which are giving good satisfaction. Slow-speed engines have a higher first cost and a higher economy. Probably in sizes up to 250 K.W. the generator should be driven l)y high-speed engines, above which the selection of either type will give satisfaction until sizes of say above 500 indicated horse power, when the slow-speed type is to be recommended. Drop valves cannot be used with satisfaction for speeds above about 100 revolutions per minute, hence high- speed engines must use direct-driven valve gears, usually governed by shaft governors. Corliss valves are used on nearly all slow- ipeed engines. 26 POWER STATIONS The steam pressure used should be at least 12."j pounds per square incli at the throttle and a pressure as high as 150 to 160 pounds is to he preferred. ( 'lose regulation and uniform angular velocity are required for driving generators, especially alternators wliich are to operate in parallel. This means sensitive and active governors, carefully designed fly-wheels and proper arrangement of cranks when more than one is used. For large plants or plants of moderate size, compound con- densing engines are almost universally installed. The advantage of these engines in increased economy are in part counterbalanced by higher first cost and inci-eased complications, together with the pumps and added water supply necessary for the condensers. The approximate saving in amount of steam is shown in table 0, which applies to a 500 horse-power unit. TABLE 6. _ . Pounds oi Steam Simple non-condensing 30 Simple coiideusing -2 ( 'ompound non-condensing l'4 Compound eondensinu ] il Triple expansion engines are seldom used for di'iving electrical machinery as their advantages under variable loads are doubtful. Compound engines may be tandeiu or cross compound and either horizontal or vertical. The use of cross-compound engines tends to ])i'oduce uniforn^ angular velocity, but the cylindei' should be so ])i'oporti(>ned that the amount of work doiu^byeach is nearly i^iual. A cylinder ratio of about oh to 1 will approximate average condi- tions. Either vertical or horizontal engines may be installed, each having its own peculiar advantages. Vertical engines re(|uire less floor space, while horizontal engines have a better arrangement of ])arts. Either type should be constructed with heavy parts and erected on solid foundations. Recently steam turbines have come into use, and the number of stations at present under process of design or constrnction which will use steam turbines is very large. Several types of turbines are described in the books on engines. In addition to these, a POWER STATIONS 27 short review of the Curtis turbine will not be out of place since this is one of the types which is coming into extended use. The Curtis turbine is divided into sections, each section of which may contain one, two, or more, revolving sets of buckets and stationary v;ines supplied with steam from a set of expansion nozzles. By this arrangement of parts the work is divided into ■stages, the nozzle velocity is rediiced in each stage, and the energy of the steam is effectively given up to the rotating parts. This type admits of lower speeds than the other forms of turbines. Fig. i>. shows the arrangement of nozzles, buckets, and stationary blades or guidiiiir vanes for two staws. Governinii; is accom- plislii'd by shutting off the steam from some of the nozzles. A conijilete Curtis turbine of the vertical type, direct connected to a 5,000 K.W. three-phase alternating-current generator, is shown in Fig. '•). The advantages claimed for this turbine are; 1. High steaiu ecouoniy at all loads 2. High steaiu economy with rapidly fluctuating- loads. ;!. Small floor space per K.W. capacity, red nfiiii; to a minimum the (.-(ist of real estate and buildings. 4. Unilorin angular velocity. 5. Kimplicity in operation and low e.xpeuse lor attendance, (i. Kreedom from vibration. 7. Steaiu economy not appreciably imijaired by wear or lack of adjustment in long service. 8. ^Vdaptability to high steam pressure and high superheat without practical difficulty and with consequent improvement in economy. 9. Condensed water is kept entirely free from oil and i/aii be returned to the boilers. Many of these advantages apply equally well to the other types of turbines now on the market. All turbines are especially adapted to operation with superheated steam. Engines should preferably be direct-connected aB already stated, but this is not always feasible, and gearing, belt, or rope drives must be resorted to. Countershafts, belt or rope driven, arranged with pulleys ^nd belts for the different generators, and with suitable clutches, are largely used in small stations. They consume considerable power and the bearings require attention. Careful attention must be given to the lubrication of all run- uing parts, and extensive oil systems are necessary in large plants. 28 POWER STATIONS In sucli systems a continuous circulation of oil over the bearings and through the engine cylinders is maintained by means of oil pumps. After passing through the bearings, the machine oil goes to a properly arranged oil-filter where it is cleaned and then pumped to the bearings again. A similar process is used in cyl- Stzisorrt CT/^ie-si wm\ \miiicf G/ac^GS XiiiiauiiUiHiiiiiiA A^o >^/r7^3/'acfG s TOD!))DDi))i)DDD)ni)l)>i)l)i)l))»i)l I I I 1 1 1 UIACIKAM OF NOZZLES AND BUCKETS IN C'UETIS STEAM TURBINE. Fig. 8. inder lubrication, the oil being collected from the exhaust steam and only enough new oil is added to make up for the slight amount lost. The latter system is not installed as frequently as the con- tinuous system for bearings. In the Curtis turbine, vertical type, the oil is forced in between the t^vo plates, forming the step bear- ing, at such a pressure that a thin film of oil is constantly main- taiiu'd between these plates. It may be arranged so that if, for any reason, this pressure fails, the steam will be cut off from the o u 0. X Ph kJ Ed Q H < Ol. o u H Z u z u z o en < o o X o z o PLC 3 o u POWER STATIONS 29 . turbino automatically. The bearings which support the shafts used with the generators at the Niagara Falls Power Companies' plants are generously flooded with oil and the turbines are arranged so as to remove a great deal of the- weight of the rotating part from this bearing. HYDRAULIC PLANTS. IJecause oE the relative ease with which electrical energy may be transmitted long distances, it has become quite common to locate Fig. 9. large power stations where there is abundant water power, and to transmit the energy thus generated to localities where it is needed. This type of plant has been developed to the greatest e.xtent in the western part of the United States, where in some cases the trans- mission lines are very extensive. The power houses now completed, or in the course of erection at Niagara Falls, are examples of the enormous size such stations may assume. 80 POWER STATIONS Water Before deciding to utilize water power for driving the ma- cliinery in central stations, the following points should be noted: ] . The amount of water power available. '2. The possible demaud for power. ':>. Cost of developing this power as compared with cost of plants using other sources of power. 4. Cost of operation compareil with other plants and extent of trausmission lines. Hydraulic plants are often much more e.xpensive than steam plants, but the first cost is more than made up by the saving in operating ex- penses. LCethods for the devel- opment of water powers vary with the nature and amount of the water supply, and they may be studied best by considering plants which are in successful operation, each one of which has been a special problem in itself. A full description of such plants would be too extensive to be incorporated here, but they can be found in the various technical journals. Water Turbines used for driving generators are of two general classes, reaction turbines and impulse turbines. The former may be subdivided into Parallel-flow, (.)utward-flow, and Inward-flow tur- bines. Parallel-flow turbines are suited for low falls, not exceeding 30 feet. Their efiicieney is from 70 to 72''/. Outward-flow and inward-flow turbines give an efficiency from 70 to 8H''/r. Impulse turbines are suitable for very high falls and should be used fronr heads exceeding say 100 feet, though it is diflicult to say at what head the reaction turbine would give place to the impulse wheel, as reaction turbines are ■gi\'ing good satisfaction on heads in the neighborhood of 200 feet, while impulse wheels are operated Low Water Fig. 10. z o H < O 4 12 18 350 16 ^>4 4 12 16 525 ■ 16 3 5 20 18 325 25 ■^X ■^ 20 16 500 25 4J^ 5 20 14 675 25 6 (i 28 18 296 36 4% (1 28 16 487 36 55I 6 28 14 743 36 "1% 7 ;',8 18 254 50 5% 7 ;!8 16 419 50 6% 7 ::8 14 640 50 8% H 50 16 367 63 7X 8 50 14 660 63 9X 8 50 12 854 63 13 <) K) 16 327 80 8X .) i;'. 132 10 696 170 24% 14 1.53 16 211 200 13 " 14 153 14 324 200 16 14 1.53 12 404 200 2P„ 14 153 11 54:! 200 231-;; 14 1.53 10 648 200 26 " 1.5 176 16 197 225 1-5J4 lo 176 14 302 225 17 1.5 176 12 460 225 *>;j 15 176 11 .507 225 24 1/.; 15 176 10 606 225 28 " k; 201 16 185 255 14% ]<; 201 14 283 255 1'% ]() 201 12 432 255 24% IB 201 11 474 255 -0'>2 POWli]? STATIONS ;« Riveted Hydraulic Pipe. (Continued.) (.'u. fl. Water Diam. ot Pipe in inches. Area of Pipe in sq. inches . Thickness of Iron by wive gauge. Head in "Feet. Ihe Vi-[>f will safely si ami. Pifie H'lll eon- \-ey per min, atvfl. 3 ft. "Weight per linral fl.inlhs 1 per sec. 16 201 10 567 255 2!)!;; 18 2.54 16 165 :!20 161^ 18 254 14 252 :!20 20 k' 18 2.",4 12 :-!85 820 2714 18 254 11 424 820 80 18 254 10 505 :!20 84 liO :!14 16 148 400 18 -!0 814 14 227 400 221/ 20 .■!14 12 846 400 80 ■j.n 314 11 8.S0 400 ;;.>! ' a) 814 10 456 400 861/ 'J.)l 880 16 185 480 20 " lili 880 14 206 4.SO 24^4 "2 880 12 :!16 4S0 82% >■>•> 880 11 .■;47 480 85% llli 380 10 415 480 40 1^4 452 14 188 570 27% ■M 452 12 290 570 85% ■2i 452 11 318 570 8!) ■24: 452 10 87!) 5"0 48'.^ •24 452 8 466 570 ')■"! lit) 58(J 14 175 670 2i)% ■2>i 580 12 267 670 88',, ■Mi 580 11 204 670 42" •2li 580 10 852 670 .87 •2ii 580 8 482 670 57%' ■2H 015 14 102 775 81% ■2H 615 12 24 / 775 41% L'8 615 11 27n 775 45 1:8 615 10 827 ! 775 50% 2H 615 8 400 i 775 e Alterniitnr EXfilnr L'!assirit-:itioii. I Classitication. 8 _ (K) - !l(IO I li -1..T - 1900 8- ilO-iMJO' 1! -1..") - lillKI 8 - 1:^0 - (100 1 :i- 1-5 -1900 lii- isd - (;()(! •J.--J..o-Mm 16 -800- 450 i 2-4.5-1800 If direct-connected, the speeds of the generators will be determined by the ])rime mover selected. If belt-driven, small machines may be run at a high sjteed, as high-speed machines are cheaper than slow- or moderate-s])eed generators. In large sizes, this saving is not so great. When shunt-wound dynamos ai'e used, the inherent regula- tion should not exceed 2 to ;i% f*^'" large machines. For alterna- tors, this is much greater and de])ends (in the ])()wer factor of the load. A fair value for the regulation of alternators on non- • inductive load is 10 per cent. Exciters may be either direct-connected or belted to the shaft of the nuix'hiiie which they excite, or they may be separately 40 POWER STATIONS driven. They are usually compound-wound and furnish current at 125 or 250 volts. Separately driven exciters are preferred for most plants as they furnish a more flexible system, and any drop in the speed of the generator does not affect the exciter voltage. Ample reserve capacity of exciters should be installed, and in some cases storage batteries, used in conjunction with exciters, are recommended in order to insure reliability of service. Motor-generator sets, boosters, frequency changers, and other rotating devices come under the head of special apparatus and are governed by the same general rules as generators. Transformers for step- ping the voltage from that generated by the machine up to the desired line voltage, or vim versa, at the substation, may be of three general types, according to the method of cooling. Large transformers require artificial means of cooling, if they are not to be too bulky and expensive. They may be air-cooled, oil- cooled, or water-cooled. Air-cooled tranxfonncrs are usually mounted over an air- tight pit fitted with one or more motor-driven blowers which feed into the pit. The transformer coils are subdivided so that no part of the winding is at a great distance from air and the iron is pro- vided with ducts. Separate dampers control the amount of air which passes between the coils or through the iron. Such trans- formers give good satisfaction for voltages up to 20,000 or higher, and can be built for any capacity, (lare must be taken to see that there is no liability of the air supply failing, as the capacity of the transformers is greatly reduced when not supplied with air. Fig. 13 shows a three-phase air-blast transformer. Fig. 18. POWER STATIONS 41 Oil-cooled tf(.nisfy('d for the liigliest voltages now in use. Fig. 14 shows a transformer of this type. 42 POWER STATIONS W'lfei'-codled ti'iniifo/'i/ie/'s. When large transformers for high voltages are required, the water-cooled type is visually selected. This type is similar to an oil-cooled transformer, but with water rig. 15. Wuler-CoolBd Translormer. tubes arranged in coils in the top. < okl water passes through tiiese tubes iind aids in removing heat from tlie oil. Some types Imvf tlie low-tension windings mude "up of tubes througli whirli the wuter circulates. AVater-cooled transformers must not have POWER STATIONS 43 the supply of cooling water shut off for any length of time when under normal load or they will overheat. Fig. 15 shows a water- cooled transformer. For connections of transformers, see "Power Transmission". Fig. 15. 400 K.W. Water CoDli-d Oil TransJormer. One or more spare transformers should always be on hand and they should be arranged so that they can be put into service on very short notice. Three-phase transformers allow a considerable saving in iloor space, as can be seen by refei'riiig to Fig. l!!; tliey are clieajjer than three separate transformers which make up the same ca|)acity, but they are not as flexilile as a single-jihase tranKforuici- and one 44 POWER STATIONS complete unit must be held for a reserve or "spare" transformer. Storage Batteries. The use of storage batteries for central stations and substations is clearly outlined in " Storage Batteries ". The chief points of advantage may be enumerated as follows: mi^ii£lM^i^iihi^miM^\ Single-Pliase Air-Blast Translormers. Total Capacity 3,000 K.W. _^ . ^ I ^d t i i to ^ ^1 b / ^te, Y^gy ,^b, ^ Three-Phase Air-Blast Transformers. Total Capacity 3,000 K.W. Fig. 16. 1. Reductiou in fuel eousumptlou due to the geueratiiig inaclilnei-;y being run at its greatest economy. 2. Better voltage regulation. S. Increased reserve capacity and less liability to interruption of service. The main disadvantage is the high cost. Switchboards. The swilcliboard is tlie most vital part of the whok' system of supply, and should receive consideration as such. Its ol)jc<'ts are: to collect the energy as supplied by tlie gen- erators and direct it to the desired feeders, either overhead or POWER STATIONS 45 under ground; furnish a support for the various measuring instru- ments connected in service, as well as the safety devices for the protection of the generating apparatus; and control the pressure of the supply. Some of the essential features of all switch- boards are: 1. The apparatus and supports jiuist be flre-proof. 2. The conducting parts must uot overheat. 3. Parts must be easily accessible. 4. Live parts except for low potentials must not be placed ou the front of the operating panels. 5. The arrangement of circuits must be symmetrical and as simple as it is convenient to make them. 6. Apparatus must be arranged so that it is impossible to make a wrong connection that would lead to serious results. 7. It should be arranged so that extensions may be readily made. There are two general types — in the iirst, all of tlie switching and indicating apparatus is mounted directly on panels, and in the second, the current-carrying parts are at some distance from the panels, the switches being controlled by long connecting rods; op- erated electrically or by means of compressed air. The first may again be divided into direct-current and alternating-current switch- boards. It is from the first class of apparatus that the switchboard gets its name and the term is still applied, even when the board proper forms the smallest part of the equipment. Switchboards have been standardized to the extent that standard generator, ex- citer, feeder, and motor panels may be purchased for certain classes of work, but the vast majority of them are made up as semi-stand- ard or special. The leads which carry the current from the machines to the switches should be put in with very careful consideration. Their size should be such that they will not heat excessively when carry- ing the rated overload of the machine, and they should preferably be placed in fire-proof ducts, although low-potential leads do not always require this construction. Curves showing sizes for lead- covered cables for different currents are given in " Power Trans- mission "- Table 12 gives standard sizes of wires and cables to- gether with the thickness of insulation necessary for different voltages. Cables should be kept separate as far as possible so that if a fault does occur on one cable, neighboring conductors 46 POWER STATIONS will not be injured. For lamp and instrument wiring, such as leads to. potential and current transformers, the following sizes of wire are recommended : No. 16 or Xo. 14, wiring to lamp sockets. No. 12 wire, «■/' rubber insulation, all other Sinall wiring under COO volts potential. No. 12, sV' rubber insulation for primaries of potential transformers from 600 to 3,500 volts. No. 8, aV' rubber insulation for primaries of potential trauslbnuers up to 6,600 volts. No. 8, a', rubber insulation for primaries of potential transformers up to 10,000 volts. No. 4, li rubber insulation for primaries of potential transformers up to 15,000 volts. No. 4, li rubber insulation for primaries of potential transformers up to 20,000 volts. No. 4, u rubber insulation for primaries of potential transformers up to 25,000 volts. Where high-tension cables leave their metallic shields they are liable to puncture, so that the sheath should be flared out at this point and the insulation increased by the addition of com- pound. Fig. 17 shows such cable bells, as they are called, as recommended by the General Electric Company. Central -station switchboards are usually constructed of panels about 90 inches high, from 1(3 inches to B() inches wide, and 1-| inches to 2 inches thick. 8uch panels are made of Blue Vermont, Pink Tennessee, or AVhite Italian marble, or of black enameled slate. Slate is not recommended for voltages exceeding 1,100. The panels are in two parts, the sub-base being from 21 to 28 inches high. They are polished on the front and the edges are beveled. Angle and tee bars, together with foot irons and tie rods, form the supports for such panels, and on these panels are mounted the in- struments, main switches, or controlling apparatus for the main switches, as the case may be, together with relays and hand wheels for rheostats and regulators. Small panels are sometimes mounted on pipe supports. The usual arrangement of the panels is to have a separate panel for each generator, exciter, and feeder, together with what is known as a station or total-output panel. In order to facilitate extensions and simplify connections, the feeder panels are located POWER STATIONS 47 at one end of tlie board and tlio generator panels are placed at the other end, and the total-outpnt panel between the two. Tlie main bus bars extend throughout the length of the generator and feeder panels, and the desired connections are readily made. The instru- ments required are very numerous and a brief description only of a few of the more important can be given here. Area. Circular Mils. Diam. Inches. TABLE 12. Standard Wire and Cable. VSrire (Solid). ^a 2,r>H-2 .051 No. ;i 4,l()(i .064 ;j (i,.oSO .081 ,-; ](;,5i<» .128 ] i'(),iir)i .](!2 41,74;! .1-04 ()ii,:^/.H .2.-,7 88, ( 111.') .28!t 1 l()r),r,'.i;i . 1-125 1HH,()7'.) .;ibo lf>7,8().') .410 211, (i(K) .460 :', l)r 10 ;o 8 Amps. Thickness of Bnbbcr Insulation. Gauge. Con. X o ^ ° ^ „ Current Capacity. ,-5 i^ o ^ ?, % B. & S ill Insulati in. 4 - 16 6 U4 14 10 11 T :i2 12 25 III A i-i •A-' 8 40 6 f) ) 1 1 ir h 'I-i Ii-i 1 4 'Ai 1 7 4 00 1 11 2 110 (l-t 1 i:-iO ll'.l" :i2 ■;t'V wi \', 170 .1 r 00 205 ii-i 000 250 .1 f ":( 'i I! '• li 1 :i2 \'i 0000 Circular Mils. 250,000 800,000 850,000 400,000 500,000 600,000 800,000 1,000,000 1,500,000 2.000,000 Diameter. Inches Bare. ,.568 ,637 ,680 ,735 ,820 ,900 ,037 ,157 ,412 1.65 Cable. (Stranded.) Terminal Drilling 1" l-l" ir' Con. Ciirr. r'apa.city. ..Vinps. 290 340 380 420 500 575 710 880 1100 1350 Thickness of Rubber Insulation. (For 60no V. only.) T.T b't •18 POWER STATIONS Wiped joint alberene soctpstone „v^ or wood Three-Conductor Cable Without Joints. Wiped joint -^--^^ insulation alberene soapstone ^'^' or wood Jf- C-- I ^;^ ^ no 6 7 connpoundl i«-r->' - -B Three-Conductor Cable With Joints. _Jextra insulation ' X=3.15CL-h2.l5Y+4.3d Wiped joint a lberene soapstone insulation K-'^C - - >, °'' ^"""^ f /^^^ 3|Z3T:±IJ^ J=3 D DdEir 33 no-67 compound -- B >H--E->J Two-Conductor Cable With Joints. extra insulat'ion4__^^^^^^^ X=30 +2Y + 4d Wiped joint alberene soapstone i r.iLiT no 67 compound B ♦' Single-Conductor Cable With Joints. ' iGxtrcL insulation x=2a-t-Y-i-2d Vdi/rs. A K ( ' 5 ]> E K 6600 1 12 1 ^ 2X 1 13200 IX. 1.5 8 1 ' . 4 4 O 26400 O 19 14 1,' 7 1 ^ -incli Lead, or I'e-incti Brass Bells. Fig. 17. POWER STATIONS 49 Ammeter Equalizer Shunt For direct current generator panels there are usually re- quired: 1 iSIaiu switch, 1 Field switch. 1 Amioeter. 1 Voltmeter. 1 Field rheostat with controlling ineclianism. 1 Circuit breaker Bus bars and various connections. These may be arranged in any suitable order, the circuit breaker being preferably located at the top so that any arcing which may occur will not injure other instruments. Fig. IS gives a wiring diagram of such a panel. The main switch may be single or double throw, depending on whether one or two sets of bus bars are used. It may be tri]>le pole as shown in Fig. IS, in which the middle bar serves as the equalizing switch, or the equal- izing switch may be mounted on a pedestal near the machine, in which case the generator switch would be double-pole. The held switch for large ma- chines should be double-pole fitted with carbon breaks and arranged with a discharge resistance con- sisting of a resistance which is thrown across the terminals of the field just before the main cir- cuit is opened. One voltmeter located on a swinging bracket at the end of the panel, and arranged so that it can be thrown across any machine or across the bus bars by means of a dial switch, is sometimes used, but it is preferable to have a separate meter for each generator. Small rheostats are mounted on the back of the panel, but large ones are chain operated and preferably located below the floor, the controlling hand wheel being mounted on the panel. The circuit breaker may be of the carbon break or the mag- netic blow-out type. Fig. 10 shows circuit breakers of both Voltmeter Q ^itch Oischarqe Resistance Rheostat Generator Fisi;, IH. 50 POWEE STATIONS types. Lighting panels for low potentials are often fitted with fuses instead of circuit breakers, in which case they may be open fuses on the back of the panel or enclosed fuses on either the front, or back of the panel. Direct=Current feeder panels contain: 1 .Vmmeter. 1 C'ireuit Breaker. 1 or jiiure main .switches, single-pole, and siiiule- or doiilile-tlirow. 1 recording wattmeter, not always used .Vpparatus tor eoiitrolliug regulators when such are used. One voltmeter usually serves for several feeder panels, such a UH-ter beintr mounted al)Ove the panels or on a swinging bracket at the eiul. Switches should preferably lie of . the qniek-break type. Fig. ~() shows some standard railway feeder iianels. Exciter Panels are nothing more than generator panels on a small scalp. POWER HOUSE OF NlTW YOnK' SUBWAY. Showing Five of the Nine 12,000 Horse-Power AUls-Chalmers Engines, POWER STATIONS 51 Total Output Panels contain instruments recording the total power delivered by the plant to the switchboard. Alternating- current panels for potentials up to 1,100 volts follow the same general construction. Synchronizing devices are necessary on the generator panels, and additional ammeters are used for polyphase boards. Sometimes the exciter and generatca* panels are combined Fig. 19. in one. Fig. 21 shows such a combination. The same construction is sometimes used for voltages up to 2,500, though it is not usually recommended. The paralleling of alternators is treated in "Man- agement of Dynamo Electric Machinery". For the higher voltages, the measuring instruments are no longer connected directly in the circuit, and the main switch is not mounted directly on the panel. Current and potential trans- 52 POWEK STATIONS formers are iised for connecting to the indicating voltmeters and ammeters, and the recording wattmeters and potential transformers are used for the synchronizing device. These transformers are mounted at some distance from the panel, while the switches may RAILWAY FEEDER PANELS FOHM B FDRM B AN3LE IRONS FORM E m llilii ill I 5BSE H X Engineering Dept No.i3559.^™.„... General Electric Co. Approved. J^i^kClci^^ TA. Chief En^i^ee^ I May I900 Fig. 20. be located near the panel and operated by a system of levers, or they may be located at considerable distance and operated by elec- tricity or by compressed air. Oil Switches are recommended for all high potential work for the following reasons: By their use it is possible to open cir- cuits of higher poteatial and carrying greater currents than with POWER STATIONS 53 any other type of switch. They may be made quite compact. They may readily be made automatic and thas serve as circuit breakers for the protection of machines and circuits when overloaded. SWITCHBOARD PANEL FOR ONE THREE-PHASE ALTERNATING CURRENT GENERATOR TO 2500 VOLTS CLASSIFICATION || Typo Volts Amperes Form Switch Field Ammeter Synchroniung Device ATQ 25CO 130 A 1 ST, with «.th ATG 230O 130 A2 ST. w.th without AT6 2300 130 A 3 ST wrthout with ATG 2500 130 A4 ST without w.thout ATG 2500 130 A5 0,T. with without Axe 2500 130 AO D.T. without Fig. 21. Tliere are several types on the market. One constructed for three- ])hase \vork, to be closed by hand and to be electrically tri})ped or opened by hand, is shown in Fig. 22. This shows the switch without the can containing the oil. Fig. 23 shows a similar switch hand-operated, with the can in place. Both of these switches are arranged to be mounted on the panel. Fig. 24 shows how the same switches are mounted when placed at some distance from the panel. For high voltages, they are placed in brick cells and often three separate single-pole switches are used, each placed in a separate cell so that injury to the contacts in one leg will in 54 POWER STATIONS no way affect the other parts of the switch. A form of oil switch used for the very highest potentials and currents met with in prac- tice, is shown in Fig. 25. This particular switch is operated by means of an electric motor, though it may be as readily arranged to operate by means of a solenoid or by compressed air. General practice is to place all high-tension bus bars and circuits in separate compartments formed by brick or cement, and duplicate bus bars are quite common. FiK. 22 Oil switches are made automatic by means of tripping mag- nets, which are connected in the secondary circuits of current transformers, or they may be operated by means of relays fed from the secondaries of cui-rent transformers in the main leads. Such relays are made very compact and can be mounted on the POWEE STATIONS 55 front or back of the switchboard panels. The wiring of such trip- ping devices is shown in Fig. 26. With remote control of switches, the switchboard becomes in many instances more properly a switch house, a separate building being devoted to the bus bars, switches, and connections. In other cases a framework of angle bars or gas pipe is made for the support of the switches, bus bars, current and potential transformers, etc. Fig. 23. Additional types of panels which may be mentioned are trans- former panels, usually containing switching apparatus only; rotary converter panels for both the alternating current and direct-current sides; induction -motor panels and arc-board panels. The latter AAA AAA Form K Oil Switches Located Aljove and Form K Oil Switches Located Below and Back Back of Operating Panel. ot Operating Panel. AAA AAA _L Y Form K Oil Swilchps Tjocated Abovu FuriiL K Oil Switches Located Back of Operating Operating Panel. Panel. Fig. 24, H !S a S M 6 z £ 3 I H W « a, p a 0. o ►J 5 •o! W u -a H " % -a " I M t « POWER STA'IiONS 57 are arranged to operate with plug switches. A single panel used in the operation of series transformers on arc-lighting circuits is shown in Fic£. 27. Safety Devices. In addition to the ordinary overload trip- ping devices which have already been considered, there are various safety devices necessary in connection with the operation of cen- tral stations. One of the most important of these is the Jlglitiinuj (trrmter. For direct-current work, the lightning arrester takes the foi'm of a single gap connected in series with a high resistance and fitted with some device for destroying the arc formed Ijy discharge IIS Red Indicatinq Lamp /(Oil Switch Closed) ^''-^^i^ losinq Contact >Openinq Contact iQreen Ind icatinq Lamp flOil Switch Open) fuse Gear Case 125 Volt Buses ^Se^ies Motor pOperatinq Oil Switch ~,Q 1 utch Maq n et 3Coll Automatic Contact Flnqers Cam Actuated Oil Switch in Closed Position Fig. 25. to the ground. One of these is connected between either side of the circuit and the ground, as shown diagrammatically in Fig. 28. A " kicking " coil is connected in circuit between the arresters and the machine to be protected, to aid in forcing the lightning dis- charge across the gap. In railway feeder panels such kicking coils are mounted on the backs of the panels. For alternating-current work, several gaps are arranged in series, these gaps being formed l^etweeu cylinders of " non-arcmg" metal. High resistances and reactance coils are used with these, 58 POWEK STATIONS Source Load Current : Transformers: Oil Switch 1 2 3 y~ - -o o- . -o o- J Overload Co ^'is Source I Current [Transformer: .utomatic Oil Switch Load Double Pole Rday Circuit Normally Closed source Load Oil Switch OpenCircuitinq Switch r-o!j° f- t TripCoil ""I—I-- Ground Relay lb Continuous Current Supply Fig. 26. as in direct-current arresters. Fig. 29 shows connections for a 10,000-volt lightning arrester. Lighting arresters should always be provided , with knife blade switches so that they can be discon- nected from the circuit for inspection and repairs. A typical installation of light- ning arresters is shown in Fig. 30. lieverse-current relays are installed when machines or lines are operated in parallel. If two or m.ore alternators are running' and connected to the same set of bus bars, and one of these should fail to generate voltage by the opening of the field circuit, or some other cause, the other machine would feed into this generator and might cause considerable damage before the current o flowing would be sufficient to operate the circuit breaker by means of the overload trip coils. To avoid this, re- verse-current relays are used. They are so arranged as to operate at say ^^ the normal current of the machine or line, but to operate only when the power is being delivered in the wrong direction. Speed limit devices are used on both engines and rotary con- verters to prevent racing in the one case and running away in the POWER STATIONS 59 second. Such devices act on the steam- supply of engines and on the direct-current circuit breakers of rotary converters, respectively, (lomplete wiring diagram for a railway switchboard is shown in Fig. 31. Substations. Substations ai-e for the purjjose of transform- ing the high potentials down to such potentials as can be used on -gr-^ motors or lamps, and in many cases to convert alternating current into direct current. Step-down transformers do not differ iu any respect from step-up transformers. Either motor-generator sets or rotary converters may be used to change from alternating to direct current. The fonner consist of synchronous or induction motors, direct connected to direct-current generators, mounted on 60 POWER STATIONS the same bedplate. The generator may be shunt or compound wound, as desired. Rotary converters are direct-current genera- tors, though specially designed; they are fitted with collector rings attached to the winding at definite points. The alternating cur- rent is fed into these rings and the machine runs as a synchronous Connections for series arc liaVitinq circurts up to coco volts oenerator reactance coil -^i 3 E Connections forliqhtinq or power circuits/ uptoaso volts (metallic circuits) qenercitor reactance coil motor spark ^ap' blov^-out coil Connections for railway circuits up to 650 volts reactance coil (one side q rounded) qenercL- ^ tor I Reaction coil 13 composed ofss' of conductor wound cnacoil of two or more turns as con venient- Fig. 28. motor, while direct current is delivered at the commutator end. There is a fixed relation between the voltage applied to the alter- nating-current side and the direct-current voltage, which depends on the shape of the wave form, losses in the armature, pole pitch of the machine, method of connection, etc. The generally accepted values are as follows: MANHATTAN 74th ST. POWER STATION, NEW YORK. Showing Carey's Carbonate of Magnesia Pipe Coverings. Steam Connections. POWER STATIONS 61 TABLE 13. Full Load Ratios. Current. Potential. Continuous 100 Two-phase ( 550 volts ............................'.'.'.'.... 72.5 and Six-phase < 250 " 7;; (diametrical) ( 125 " 73.5 Three-phase ( 550 " ..........]....... 62 and Six-phase ^250 " 62 ( Y or delta) (125 " .'.'.'.'.'.'.'.'.'.'.'. 6:; iiuu'hiiu's 14. otl ler Alternator The 'increase of capacity of six-pliaso machines of the same size is given in Table This increase is due to the fact that, with a p;reater number of phases, less of the winding is tra\-t'rsed by the current which passes through the converter. The saving by increasing the number of phases beyond six is but slight and the system be- comes too complex, liotaiy converters may be over-com- pounded by the addition of series fields, provided tlie re- actance in the alternating cii'- cuits be of a proper value. It is customary to insert re- actance coils in the leads from the low-tension side of the step-down transformers to the collector rings to bring the reactance to a value which will insure the desired compounding. Again, the voltage may be controlled by means of induction regu- TABLE 14. Capacity Ratios. Continuous-current generator 100 Single-phase converter 85 Two-phase converter 164 Three-phase converter 134 Six-phase converter ,,-,... 196 &1 POWER STATIONS POWER STATIONS 63 lators placed in tlie alteriiatiuir-cui'i-iuit leads. Motor-o;eneratoiM are more ccisthaiid occupy iiKire s|)aee than rotary converters, bnt the regulation of the voltaire is inneli better and tliey are to be preferred for ligliting piirposes. Buildings. The power station usually bas a building devoted entirely to this work, while the sulistations, if small, are often made a part of other buildings. While the detail oF design and construction of the buildings for power plants belongs primarily to the architect, it is the duty of the electrical engineer to arrange the macliinery to the best advantage, and he should always be con- sulted in regard to the general plans at least, as this may save much time and expense in the way of necessary uiddifications. The general arrangement of the machinery will be taken up later, but a few points in connection with the construction of the build- ings and foundations will be considered here. Space must be ])rovided for the boiler, — this may be a sepa- rate building — engine and dynamo room, general and y)ri\ate offices, store rooms and repair shops, ^'ery careful consideration should be given to each of these departments. The boiler room should be parallel with the engine room, so as to reduce tlie neces- sary amount of steam piping to a minimum, and if br)th rooms are in the same building a brick wall should sej)arate the two, no openings which would allow dirt to conie from the b;)iie)' room ti) the engine room beino; allowed. The height of bnth boiler and engine rooms should be such as to allow ample headway for lifting machinery and space for placing and repairing boilvrs, while ]iro- vision should be made for extending these rooms in at least one direction. Both engine and boiler rooms should be fitted M'itli proper traveling cranes to facilitate the handling of the units. In some cases the engines and dynamos occupy separate rooms, but this is not general practice. Ample light is necessary, especially in the engine rooms. The size of the oflices, store rooms, etc., will depend entirely on local conditions. The foundations for both the walls and the machinery must be of the very best. It is well to excavate 'the entire space xmder the engine joom to a depth of eight to ten feet so as to form a basement, while in most cases the excavations must be made to a greater depth for the walls. Foundation trenches are sometimes a:_i l-z">, 9^§ POWEE STATIONS 65 filled with concrete to a depth sufficient to form a good under- footing. The area of the foundation footing should be great enough to keep the pressure within a safe limit for the quality of the soil. The walls themselves may be of wood, brick, stone, or concrete. Wood is used for very small stations only, while brick may bo used alone or in conjunction with steel framing, tbe latter con- struction being used to a considerable extent. If brick alone is 66 POWER STATIONS used, the walls should never be less than twelve inches thick, and eighteen to twenty inches is Lettei' for large buildings. They must be amply reinforced with pilasters. Stone is used only for the most expensive stations. The interior of the walls is formed of glazed brick, wlien the expense of such construction is war- ranted. In fireproof construction, which is always desirable for power stations, the roofs are; supported by steel trusses and take a great variety of forms. Fig. 32 shows what has been recommended as standard construction for lighting stations, showing both brick and wood construction. The tioors of the engine room should be Fig. 33. made of some mater-Jal whicii will not form grit or dust. Hard tile, unglazed, set in cement or wood floors, is desirable. StoraL'^e l)attery I'ooms should l)e separate from all others and should have their interior lined with some material which will uot Ije affected by the acid fumes. The best of ventilation is desirable for all parts of the station, but is of particular importance in the dynamo room if the machines are l)eing hea\ily loaded. Substation construction does not differ from that of central stations when a separate build- ing is erected. They should he fireproof if possible. The foundations for machinery should be entirely separate from those of the building. Not only must tlie foundations be stalile, but in ■some locations it is jiarticularl v desirable that no POWEK STATIONS 67 vibrations be transmitted to adjoining rooms and buildings. A loose or sandy soil does not transmit such vibrations readily, but tirm earth or rock transmits them almost perfectly. Sand, wool, tiair, felt, mineral wool, and asphaltum concrete are some of the materials used to prevent this. The excavation for the foundation is made from two to three feet deeper and two to three feet wider on all sides than the foundation, and the sand, or whatever material is used, occupies this extra space. K-3" for bricK foundation al2"footinao^ concrete snoijld be laid. Oept-h orfcunoL- atio^ nn-J5t be Qpvernezi bythe char- acter of tHe soil Qatter 1 to 6. Fouociation timbers and f loortn^ should be independent of station floor. Fig. :jl. Brick, stone, or concrete is used for building up the greater part of machinery foundations, the machine's being held in place by means of bolts fastened in masonry. A template, giving the location of all bolts to be used in holding the machine in place, should be furnished, and the bolts may be rim inside of iron pipes with an internal diameter a little greater than the diameter of the bolt. This allows some play to the bolt and is convenient for the final alignment of the machine. 'Fig. 33 gives an idea of this con- struction. The brickwork should consist of hard-lnirned brick of the best quality, and should be laid in cement mortar. It is well to lit brick or concrete foundations with a stone cap, forming a level surface on which to set the machinery, though this is not necessary. .Generators are sometimes mounted on wood bases to 68 POWER STATIONS furnish insulation for the frame. Fig. 34 shows the foundation for a 150 K.W. generator, while Fig. 85 shows the foundation for a rotary converter. I*- BZ% *, For brick foundation a IS'Vooting of concrete sHould be laid -DeptVi of founddtlon must be governed by the character of the soi I- Batter i to 6 ■ Fig. 35. Station Arrangement. A few points have already been noted in regard to station arrangement, but the importance of the subject demands a little further consideration. Station arrange- ment depends chiefly upon two facts — the location and the ma- chinery to be installed. Un- doubtedly the best arrangement is with all of the machinery on one floor with, perhaps, the oper- ating switchboard mounted on a gallery so that the attendants may have a clear view of all the machines. Fig. 3(3 shows the simplest arrangement of a plant using belted machines. Fig. 37 shows an arrangement of units where a jack shaft is used. Direct-current machines should be placed so that the brushes and commutators are easily accessible and the switchboard should- be placed so as to not be liable to accidents, such as the breaking of a lielt or a, iiy-wheel. ~ 1 1 hJ^i-, 1 1 1 1 1 1 DVWAAIOS BOAI=t,a SWITCH 1 1 BO/LCR HOUSE ENGINE. ROOM Fig. 36. POWEK STATIONS 69 "When tlve cost of real estate prohibits the placing of all of the machinery on one floor, the arrangements shown in Fig. 38 pay be used when the machines are belted. It is always desirable to have the engines on the main floor, as they caiise considerable vibration when not mounted on the best of foundations. The boilers, while heavy, do not cause such vibration and they may be placed on the second or third floor. Belts should not be run vertically, as they must be stretched too tightly to prevent slipping. Fig. 39 shows a large station usino- direct-connected CLUTCH!^ Q L BOILEH HOUSE. ENGINE HOOfA Fig. 37. m •W- units, while Fig. 40 shows the arrangement of the turbine plant of the Boston Edison Electric Illuminating Company. This sta- tion will contain twelve such 5,000 K.W. units when completed. Note the arrangement of boilers when several units are required for a single prime mover. The use of a separate room or building for the cables, switches, and operating boards is becoming quite common for high-tension generating plants. The remark- able saving in floor space brought about by the turbine is readily seen from Fig. 41. The total floor space occupied by the new Boston station is 2.64 square feet per K.W. This includes boilers — of which there are eight, each 512 IT.F. for each unit — turbines, generators, switches, and all auxiliary apparatus. When transformers are -used for raising the voltage, they may be placed in a separate building, as is the case at Niagara Falls, or the transformers may be located in some part of the dynamo room, preferably in a line parallel to the generators. BO/I.EH HOUSE ENOIf^E FKOOrA Fig. 39. 70 POWER STATIONS ov 1' « NAMO 1 / /Mf ^f-fAF~T- ^^ rLOOR 7 \ ^^^, £-NG/NE- \_ 1 ^^"^C^ ) \ v y 1 GROUND Fig. 42 shows the arrangement of units in an hydraulic plant. Fig. 43 is a good example of the practice in substation arrange- ment. Here the switchboard is mounted at one end of the room, while the rotary coiiverters and transformers are arranged along either side of the building. o Large cable vaults are installed at the stations operating on underground systems, the separate ducts being spread out, and sheet-iron partitions erect- ed to prevent damage be- ing done to cables which wei'e not originally de- fective, by a short circuit in any one feeder. Station Records. In order to accurately deter- mine the cost of gener- ating po\\'er and to check up on uneconomical or improper methods of oper- ation and lead to their im- provement, accurately kept station records are of the utmost importance. 8uch records should con- sist of switchboard rec- ords, engine-room records, boiler -r(,)om records, and distributing-system rec- ords. Such records accu- UN£. s.iArr £:NGIN£- Fig. 38. rately kept and properly plotted in the form of curves, serve admir- ably lor tjie coujparison of station operations from day to day and for the same ])eriods for different years. It pays to keep these records even when additional clerical force must l}e employed. Switchboard records consist, in alternating stations, of daily readings of feeder, recording wattuieters, and total recording watt- POWER STATIONS 71 meter, together with voltmeter aiid ammeter readings at intervals of about 15 minutes in some cases to check upon the average- power factor and determine the general form of the load curve. For direct-current lighting systems volt and ampere readings serve to give the true output of the sta- tions, and curves are readily plotted from these readings. The voltage should be recorded for the bus bars as well as for the centers of distri- "bution. Indicator diagran)s should be takcji from the cngiues at fre- quent intervals for the purpose of determining the operation of the valves. Eno-ine-room records include labor, use of waste oil and supi)lies, as well as all repairs made on engines, dynamos and auxiliaries. s o o K be s 74 POWER STATIONS Boiler-room records include labor and repairs, amount of coal used, which amount may he kept in detail if desirable, amount of water used, together with steam-gauge record and periodical analysis of flue gases as a check on the methods of firing. Kecords for the distributing system include labor and ma- terial used for the lines and substations. For multiple- wire POWEK STATIOISrS 75 on 'Ost systems, frequent leailiiiirs of the ciifrent in the different feeders will serve as a cliedc on the l>alanc'e of the load. The cost of ejenerating power varies greatly with the rate at which it is ])i'odneed as well as •upon local conditions. Statio operating expenses include cost of fuel, water, waste, oil, etc., coj of repairs, labor, and superintendence. Fixed charges include insui'anee, taxes, iiitei-est on investment, depreciation, and general office ex])enses. Total exjienses divided by total kilowatt hours gives tlie cost of generation of a kilowatt hour. The cost of dis- tributing a kilowatt hour may be determined in a similar manner. The rate of depreciation of appaiatns differs greatly with different machines, but the following figures may 1)e taken as average values, these figures representing percentage of first cost to be charged up each year : Fireproof buildings froui 2 to ." per cent. Frame buildinss from .5 U. 8 ]ier eeiit. Dynamos from 2 to 4 per cent. Priiiie mo\ ers from 2'jA to 5 per rent. Boilers from 4 to T) per cent Overhead linjs, best coristruete l(i .05082 2,583 .004009 .004479 .004904 17 .04526 2,048 .005055 .005648 .006259 18 .04030 1,624 .00ii:!74 .007122 .007892 Resistance. The resistance of electrical conductors is ex- pressed Ijy the formula: L where E A / E = total resistance of the conductors considered. L = length of the conductors in the units chosen. A = area of the conductors in the units chosen. / = a constant depending on the material used and on the vmits selected . POWEK TRANSMISSION For (.•ylindrical conductors, L is usually expressed in feet and A in circulai- rails. By a circular mil is meant the area of a circle .001 inches in diameter. A square rail is the area of a square whose sides measure .001 inches and is equivalent to 1.27 circular rails. Cylindrical conductors are designated by gauge number or by their diameter. The Brown & Sharpe (B. & S.) or American wire gauge is used almost universally and the diameters corre- sponding to the different gauge numbers are given in Table I. "Wires above No. 0000. are designated by their diameter or by their area in circular mils. TABLE II. Resistances of Pure Aluminum Wire. Resistance at 75' F. A. W. G. or B. & S. R Ohms 1,000 ft. Ohms per mile. 0000 .08177 .43] 72 000 .10310 .54440 00 .13001 .68;i45 .16.385 .86.515 1 .20672 1.09150 ■J, .26077 1.37637 3 .32872 1 . 7357 4 .41448 2.1885 6 .52268 2.7597 6 .65910 3.4802 7 .83110 4.3885 8 1.06802 5.. 5355 9 1.82135 6.9767 10 1.66667 8.8000 11 2.1012 11.0947 ]^ 2.6497 18.9900 1.) 3.8412 17,642 14 4.3180 22.800 15 5.1917 27.462 16 6.6985 35.368 17 8.4472 44.602 18 10.0518 56.242 A cdiivenient way of determining the size of a conductor from its gauge number is to remember that a number 10 wire has a diameter of nearly one-tenth of an inch and the cross-section is doubled for every three sizes larger (Nos. 7, 4, etc.) and one-half as great for every three sizes smaller (Nos. 13, 16, etc.). 1,000 POWEK TRANSMISSION feet of number 10 copper wire has a resistance of 1 ohm and weighs 'iilA pounds. When/" is expressed in terms of the mil foot, a wire one foot in length having a cross-section of one mil, its value for copper of a.])urity known as Matthiessen's Standard, or copper of 100% conductivity, is 9.58G at 0° C* For aluminum its value is given as 15.2 for aluminum iJ9.5% pure. Table II gives the resistance of aluminum wire. This shows the conductivity of akiminum to be aljout 63% of that of copper. The conductivity of iron wire is about J- that of copper. Matthiessen's standard is based on the resistance of copper supposed, by Matthiessen, to be pure. Since his experiments, im- provements in the refining of copper have made it possible to produce copper of a conductivity exceeding 100%. Copper of a conductivity lower than 98% is seldom used for power transmission purposes. Temperature Coefficient. The specific resistance (resistance per mil foot) is given for copper as 9.586 at 0" Centigrade. Its resistance increases with the temperature according to the approx- imate formula: Ph = K^ (1 + at) where K^ = Kesistance at temperature f-', Centigrade. K„= " " C. a = .0042, commercial value. The value of a for aluminum does not differ greatly from this. It is given by Kempe as .0039. Weiglit. The specific gravity of copper is 8.89. The value for aluminum is 2.7, showing aluminum to weigh .GOT times as much as copper for the same conductivity or resistance. It is this property which makes its use desirable in special cases. Iron, as used for conductors, has a specific gravity of 7.S. Meclianical Strength. Soft-drawn copper lias a tensile strength of 2."j,000 to 35,000 lbs. pei' sq. in. Ilard-dra\vn copper has a tensile strength of 50,000 to 70,000 lbs. per sq. in., depending on the size; the lower value corresponding to Xos. 0000 and 000. "The cominercial values given for the mil foot vary from 10.7 to 11 ohms. POWER TEANSMISSION Aluminum Las a tensile strength of about 33,000 lbs. per sq. in. for hard-drawn wire J inch in diameter. Effects of Resistance. The effect of resistance in conductors is three-fold. 1. There Is a dioi) in voltage, determined Irom Obnj's law, I = g or E = IK. 2. There is a loss of energy proportional to the resistance and the E2 sfiuare of the current flowing. Loss in watts = PK = -^5- 3. There is a heating of the conductors, due to the energy lost, and the amount of heating allowable depends on the material surrounding the conductors. The drop in voltage or the heating limit is usually more im- portant in the design of a transmission system than the loss of energy. Capacity of Conductors for Carrying Current. The tem- perature of a conductor will rise until heat is lost at a rate etpial to the rate it is generated so that a conductor is only capable of carrying a certain current with a given allowable temperature rise. The -limit of this rise in temperature is determined by lire risk, or injury to insulation. A general rule is that the current densit)' should not exceed 1,000 amperes per square inch of cross-section for copper conductors. This value is too low for small wire and too high for heavy conductors, and it is governed by the way in which the conductors are installed. This value serves for bus-ljars where the thickness of the copper used is limited to |-inch. Curves shown in Fig. 1 are applicable to switchboard wiring, and Table VII of "Electric Wiring" gives safe carrying capacity of conductors for inside wiring. Perrine tcives the followintr table showing the class of conductors to be used under various conditions: TABLE III. Conductors for Various Conditions. PART 1. Reference Reference No. Kemarks. No. .i\emarks. ]. >i'ot allowed. 8. In insulating lubes. w. (,'lear spaces. !(. In wood moldiuKw. ■6. Through trees. 10. Without further precaution 4. On glass insulators. 11. If necessary. 5. On porcelain knobs. 1:2. Below 350 volts. 6. In porcelain cleats. 13. Above 350 volts. 7. In wood cleats. POWER TRANSMISSION -i CO < o a 3 _o 3 "O C o U tn in cs ,—1 LO 01 1 1 c-i I— 1 i-H rH 1-H o I-H 1— I .—1 l-( I-H I-H T— 1 r-< 1— 1 I— 1 I— 1 I— 1 1—i r— I— ( r— 1 I—" I-H -t- r-l IC -P < ! 1 1 IT -r 1 1 I 1 I-H I-H rH - rH I— 1 T— 1 i-H T— 1 i-H I— 1 I— ( ^2^3 SIo ^S >.5 rt c3 ^ ^ ^ rt*:^ " ^ Insulation, in the form of a coyering, is required for elec- trical conductors in all cases with the exception of switchboard bus- bars and connections and wires used on pole lines, and even these are often insulated. It may serve merely to keep the wires from making contact, as is the case with cotton or silk-covered wire. Again, the wire may be covered with a material having a high POWER TRANSMISSION specific resistance but being -weak mechanically, and this combined with a material serving to give the necessary strength to the insu- lation. For this purpose yarns are iised as the mechanical sup- port, and waxes and asphaltum serve for the insulation proper. f:. CuffhcNT dAfi^YING C/^P^CITY ^Of*, S, Vl'/TCH-eo^kD W, RINQ mm •fiCNTC, Ci/»V€S qF,^*A>JiCIMIJM CQI^TINUQIJS ffl ffi fflffl 1 1 1 1 1 1 1 1 1 1 1 1 1 1 tttH rOR ffUBBEFt AND LEAD • Ji ll 1 1 . ttn-r coVkhkh ' (,Wb l £3 Bascd on 25 1 C._ Rise ArrrR I Houf^RuN 20 4 60-—BO y- -/:: -^\ t n mm i % M io-miQ-l4ii4q4-| I6cl44 led -Haoo Usso 1-|a4Q Hgeo Fig- 1. Annunciator wire is covered with heavy cotton yarn saturated with jiaraffine. The so-called Underwriter's wire is insulated with cot- ton braid saturated with white paint. Asphaltum or mineral wax is used for insulating Weatherproof wire. It may be applied in several ways, the best insulation being made by covering the con- ductor witii a single braiding laid over asphaltum and then passing 10 POWER TRANSMISSION the covered wire through the liquid insulation, at the same time applying two cotton braids, and finishing by an external application of asphaltura and polishing. The most complete insulation is made up of a material which gives the most perfect insulation and which is strong enough, mechanically, to withstand pressure and abrasion without additional support. Fig. 1. Qutta Percha and India Rubber, Gutta percha is used for submarine cables, but rubber is the insulating material most used for electrical conductors. Gutta ])ercliM, cannot be used when ex- posed to air, as it deteriorates rapidly under such conditions. POWEK TRANSMISSION H llubber, when used, is vulcanized, and great care is necessary in the process. This vulcanized rubber is usually covered with braid having a polished asphaltum surface. The insulation of high-tension cables will be considered in the topic, " Underground Construction." DISTRIBUTION SYSTEMS. I r- L L ^-A /■ '^ (O^ - R^ — ><— y ■^ y ^ 1 Distribution systems may be divided into nerics systems, jn iiUcI systems, or combinations, such as fierhix-pa nilld m jki rallcJ - sci'icx s\stems. X^arious translating devices may be connected in circuit, changing from one system to the other, and the parallel system may be divided into H/iKjle and m idt'iph;-(:h'cu'it systems commonly known as ^//jc-wire and three-^ ov five-irirc systems. Series Systems are applied to series arc lighting, series incan- descent lighting, and to constant-current motors driving machin- ery, or generators feeding secondary circuits. They serve for both alternating and direct currents. Fig. 2 shows the arrangement of units in this system. The current, generated by the dynamo D, passes from the positive brush A (in direct- current systems) through the units L in series to the negative brush B. p- ^ For lighting purposes, this current has a constant value and special machines are used for its gener- ation. The voltage at the generator dej)ends on the voltage required by the units and the number of units connected in service. As an example, the voltage allowed for a direct-current open-arc lamp and its connections may be taken as 50 volts. If -iO lamps are burning, the potential generated will be 50 X 40 = 2,000 volts. The numl)er of units is sometimes great enoiigh to raise this poten- tial to 0,000 volts; but by a special arrangement of the Brush arc machine, known as the multiple-circuit arc machine, the potential \* so distributed that its njaximum value on the line is but 2,(100 volts, ])i-ovided the lamps are equally distributed, while the total clectronjotive force, generated is (5,000 volts, when the, machine is fully loaded. The machine is supplied with three commutators and the lamps connected as siiown in Fig. 3, which also shows the distri- bution of potential. 12 POWEK TKANSMISSION All calculations for series systems are simple. The drop in voltage is obtained from Ohm's law, I E = . A wire smaller than ii ISIo. 8 should never be iised for line construction, as it would not be strong enough mechanically, even though the drop in voltage with its use should be well within the limit. The current taken by arc lamps seldom exceeds 10 amperes. For series incandesceiit lighting, the current may be lower than (b) f >: n —^ — — y^ — ' X ' + IO00,r - aT\ b Fig. .3. this, having a value from 2 to 4 amperes. Special devices are used to prevent the breaking of a single filament from putting out all of the lights in the system and automatic short-circuiting devices are used with series arc lamps for accomplishing the same purpose. As an example of the calculation of series circuits, required the drop in voltage and loss of energy in a line fovir miles long and composed of No. 8 wire, when the current flowing in the line is !•.() amperes. From Table 1 we have a resistance of .0007007 ohm per foot for No. 8 wire at 50° C. This gives a resistance of 3.7 ohms per mile, or a resistance of 14.8 ohms for the cir- cuit. The drop in voltage' frojii OlniTs law equals current times resistamv^ oi- equals 9.0 X 14.8 = 142 volts. The l Fig. 7. 9 ^^ <><><> ^ i? <> POWEE TRANSMISSION 15 Additional formulae ' are given in "Electric Wiring," whicii will aid in determining the size of wire to he used for a given installation. As examples of calculation we Lave tlie following: System consists of 20 lamps, each taking .5 amperes. L = 80 feet. R = .01 ohm per foot at feeding point. Find the maximum difference of potential on the lamps in each of the first three cases. I =r 20 X .5 = 10 amperes. Case I. D = "^"^ ^ ^q ^ ^^ X (160 - 80) = 8 volts. Case IT. D = 2 X .01 X 10 X 80 = 16 volts. 80 X "80 .01 X 10 X 2 / 80\ Case III. D = ^^ x (80 - ^j=: 2 volts. In Case IV" the difference in potential applied to the lamps and the potential of the feeders would be .01 X 10 X 80 = 8 volts. Again, with the maximum allowable drop given, the resist- ance of the wires at the feeding point may be determined. For tapering conductors, the current density is kept approximately con- stant by vising wire of a smaller diameter as the current decreases. Thus supposing, as in the case considered, that the resistance at the feeding point was .01 ohm per foot. At a distance of 40 feet from the feeding point the current would be only -| of 10 or 5 amperes and the size of the wire would be one-half as great, giving it a resistance at this point of .02 ohm per foot. Feeding Point, In order to determine the point at which a system of mains should preferably, be fed, that is, the point where the feeders are attached to the mains, it is necessary to find the electrical center of gravity of the system. The method employed is similar to that used in determining the best location of a power plant as regards amount of copper required, and consists of sepa- rately obtaining the center of gravity of straight sections and then determining the total resultant and point of application of tliis resultant of the straight sections to locate the best point for feed ing. Actual conditions are often such that the system cannot be 16 POWER TRANSMISSION fed at a point so determined, but it is well to run the feeders as close to this point as is practical, as less copper is then required for a given drop in potential. Consider, as an example, a system such as is showii in Fig. 9. The number of lamps and location of the same are shown in this figure. The loads, A B C D, may be considered as concentrated at A', a point 33.8 feet from I and equal to A + B + CI + D. This point is obtained as follows: Kx = By. 10 .y = 20 ... x + y = 400. A + B = 30. ■' = ^^-^-^ ^^"'• C.r' = By'. 15a?' = 20//'. x' + if = 500. x = 285.7 feet. C + D = 85. (A + B) a." = (C + D) f. «." + ./' =. 632.4. ., _ 30y = 852/". ~ A + B + C + D = 65 A' is 6.2 feet from V or 33.8 feet from I. E and F may be combined to form a group of 30 lamps and the resultant of E, F, G, and H is 70 lamps located at B', a point 310 feet from J, this point being located in the same manner as A'. Similarly we find the resultant of the loads at A' and B' to be 135 lamps located at C, a point 331.1 feet from I, and the proper feeding point for the system. A' = 65 lights, 33.8 feet from I. B' = 70 lights, 310 feet from J. Distance IJ = 360 feet. Distance from A' to B' = 360 + 310 + 33.S .= 703.8 feet. 65,/' = 70y. X + y = 703.8 feet. X = 364.9 feet. 364.9 - 38.8 = 331.1 feet. The above is a simple definite case. Should the load be variable, the proper feeding point will change with the load, and, in extensive systems, the location of this point can be obtained approximately only. The same method of calculation is employed in locating the points from which sub-feeders are run out from the terminals of the main feeders as is the case in large systems. POWER TRANSMISSION 1? the voltage being maintained constant at the pdint wliere the snh- IVeders are connected If) the feeders. Good practice sliows the drop in potential to he witliin tlie following limits: From feeding points (points where sub-feeders or mains are attached) to lamps 5 per cent. Loss in sub-feeders "> " Loss in mains 1.5 " Loss in service wires 0..t " The actual variation in voltage should not exceeil 8%. A 30 B I A C 35 c k- X — >i^ -y- 1 1 -•)! 1 !<-_- - x'-- 1 1 - -y'- - -M Fig. 9. In Series=Multiple and Multiple-Series Systems, groups of units, connected in multiple, are arranged in series in the circuit, or groups of units are connected in aeries and those, in turn, con- nected in multiple, respectively. The application of such systems is limited. They are used to some extent in street-lighting when incandescent lamps are used. 18 POWER TRANSMISSION MULTIPLE=WIRE SYSTEMS. The Three=Wire System. We have seen that in any system of conductors the power lost is e(|ual to I"E.. For a given amount of power transmitted (lEj the current varies inversely with the voltage and consequently the amount of power lost, which is directly proportional to the square of the current, is inversely pro- portional to the square of the voltage. Hence, for the same loss of power and the same percentage drop in voltage, doubling the voltage of the system would allow the resistance of the conductors to be made four times as great, and wire of one-fourth the cross- section or one-fourth the amount of copper would be required. The voltage for which incandescent lamps, jnig_ 10. having a reasonable efficiency, can be economically manu- factured is limited to 220, while the majority of them are made for 110. In order to increase the voltage on the system, a special connection of such lamps is necessary. The three-wire and five- wire systems are adopted for the purpose of increasing this voltage. Fig. 10 shows a diagram of a three-wire system. Consider the conductor B removed, and we have a series-multiple system with two lamps in series. This arrangement does not give independent control of individual lamps, and the third wii-e is introduced to take care of any unbalancing of the number of lamps or ^ _^^ _^3 _^2 units connected on either side Q in iQ 'O'O of the system, and to allow ^^ icSiini iiiiiiO more freedom in the location -^~r2- — of the lights. The current Fir. 11. flowing in the conductor B, known as the neutral conductor, depends on the difference of the currents required by the units on the two sides of the system. Fig. 11 shows a system in which the loads on the two sides are unequal, an unbalanced system, \vith the value of the current in the neutral wire at different points. Each unit is here assumed to take one ampere. POWER TRANSMISSION 19 As stated alxjvo, were no neutral wire ]-e(jnire(l, the anionnt of copper necessary for a system with the laiujis eouueetcd, two in series, for the same percentage drop in voltage would bo one-fourth the amount necessary for the parallel connection. This may be shown as follows: The current in the wire in the first case is one- half as great, so that the voltage drop would be divided by two for the same size wire. s^ ^ C^ D The voltage on the sys- tem is twice as great, so that, with the same jx'rcfn tctiji' regulation, the actual voltage drop would be doubled. Consequently wire of one -fourth the cross- section and weight may be used. If the neutral wire is made one-half the size of the outside conductor, as is usually the case in feeders, the amount of copper re- quired is -^-^ of that necessary for the two- \v i r e system. For mains it is customary to make all three con- ductors the same size, inci'easing the amount of copper to |- of that re([uired foi- a two-wire system. For a five- wire system with all conductors the same size, the weight of coiJijei- necessai-y is .150 times that foi' ;i, two-\vire system. Multiple-wire systems have no advantage other than saving of coj)])er, except when used for multiple-voltage systems, while among their disadvantages ma^- be mentioned: ( '(implication of generating apparatus. Cciinplication of iustrunients and wiring, Liability to variation iu voltage, due to uubalauciug of load. 20 POWER TRANSMISSION Fig. 12 shows some of the methods employed in generating current for a tliree-wire syHU-iii. A. Two dynamos connected in series, tlie usual inetliod B. A double dynamo. C. Bridge arrangement, using a resistance R with the neutral con- nection arranged so as to change the value of resistance in either side of the system. Has the disadvantage of continuous loss of energy in R. D. Storage battery connected across the line with neutral connected at middle point. B. Special dynamo supplied with three brushes. F. Special machine having collector rings, across which is con- nected an impedance coil, the neutral wire being connected to the middle point of this coil. G. Compensators or motor-generator set used in connection with generator. The motor-generator set is known as a balancer set. Compensators are usually wound for about 10% of the capac- ity of the machine with which they are used. In the motor-gen- erator set, one side becomes a motor or generator depending on whether the load on that side is less or greater than the load on the opposite side. Voltage Regulation of Parallel Systems. It is customary to keep the voltage on the mains constant, or as nearly so as possible, at the point where the feeders are attached. Where but one set of feeders is run out from the station, this miay be readily accom- plished by the use of over-compounded dynamos, adjusted to give an increase of voltage equal to the drop in the feeders at different loads. Again, the field of a shunt- wound generator may be con- trolled by hand, the pressure at the feeding points being indicated by a voltmeter connected to pilot wires running from the feeding point back to the station. When the system is more extensive, separate regulation of different feeders is necessary. A variable resistance may be placed in series with separate feeders, but this is undesirable on account of a constant loss of energy. Feeders may be connected in along a system of mains and one or more of these switched in or out of service as the load changes. Bus-bars giving different voltages may be aranged so that the feeders can be changed to a higher voltage bar as the load increases. Boosters — series dynamos — may be connected in series with separate feeders and these may be ar- ranged to regulate the voltage automatically. The use of boosters is POWER TRANSMISSION 21 not to be recom mended except for a few very long feeders, and then the total capacity of boosters should equal but a small percentage of the station output if the efficiency of the system as a whole is to remain high. Fig. 13 is a diagram of a system using different methods of voltage regulation. Alternating-Current Systems of Distribution may be classi- fied in a manner similar to direct-current systems, that is, as series and parallel systems; but in addition to these we have a classifica- tion depending on the number of ])hases used, such as suKjle-phase^ (fuartcr- or tini)-2)]mi36 .01452 .182 12 18 24 48 .01830 .01690 .01602 .01426 .ll>2 12 18 24 48 .01788 .01654 .015(J0 .0140 .144 12 18 24 48 .01746 .01618 .01538 .01374 .128 12 18 24 48 .01708 .0158(i .01508 .oi;;5() .114 12 18 24 48 .01660 .01552 .01478 .oi;;2(i .102 12 18 24 48 .01636 .01.522 .014.'i2 ,01304 38.S8/;iO-' ., (J =z per niilB. ion "^ ,1 lusulated cable wUh lead sheath. (J = :j.s.s;5 / lu- V.).\-l / 10- Siii^'le coudtiekir vvilli euilli return. A Iter mile of circuit. Parallel conductors I'oriiiiiiii; a metallic circuit. 26 POWER TEANSMISSION C = Capacity iu micro-farads, capacity in farads.) (Divide by 1,000,000 to give 1 for h = specific inductive capacity of insulating material air = 2.25 to 3.7 for rubber. D = inside diameter of lead sheath. d — diameter of conductor. A = distance of conductors above ground. A = distance between wires. Common logarithms apply to these formulie and C for a metallic circuit is the capacity between wires. TABLE V. Inductance Per Mile of Three=Phase Circuit. Size Diameter Distance Self-induct- ance L Jieurys, Size Diameter Distance Sel(-induct- B. &S iu incli. (Uninchey. B.&S. in inch. (Uuinches. auce Iv lieurys. 0000 .46 12 .00234 4 .204 12 .00280 18 .00256 18 .00800 24 .00270 24 .00315 48 .00312 48 .00358 000 .41 12 .00241 .182 12 .00286 IS .00262 18 .00807 24 .00277 24 .00323 48 .00318 48 .00356 00 .365 J2 .00248 6 .162 12 .00291 18 .00269 18 .00313 24 .00285 24 .00829 48 .00830 48 .00869 .a2.5 12 .00254 7 .144 12 .00298 18 .00276 18 .00310 24 .00293 24 .00336 48 .00381 48 .00377 1 .289 12 .00260 8 .128 12 .00303 18 .00281 18 .00325 ' 24 .00808 24 .00341 48 .00838 48 .00384 >> v.2o8 12 .00267 9 .114 12 .00310 18 .00288 18 .00332 24 .00304 24 .00348 48 .00314 48 .00389 8 .229 12 .00274 10 .102 12 .00318 IS .00294 18 .00340 24 .00310 24 .00355 48 .00351 48 .00.396 POWER TRANSMISSION 27 If the capacity be taken between one wire and the neutral point of a system, or the point of zero potential, the capacity is given as: C (in nucro-faradsj = ;j-r— per mile of i-'inui/ii. 2 loar ^ ° d Table I\^ gives the capacity, to the neutral point, of different size wire used for three-phase transmission lines. The effect of this capacity is to cause a charging current, 90' in advance of the impressed pressure, to flow in the circuit, and the regulation of the system is affected by this charging current as will be seen later. Capacity may be reduced by increasing the distance between conductors or in lead-sheathed cables, by using an insulating material having a low specific inductive capacity, such as paper. Inductance. The self-inductance of lines is very readily cal- culated. Following is a formula applicable to copper or alumi- num conductors: L = .OUO^TjS r2.;i()8 log (—) + •■-•3"! per mile of rh-cuJt when L := inductance of a loop of a three phase circuit in lienrys. The inductance of a complete circuit, single ])liase, is equal to the above value iiiultiplied by 2 -:- ). ;3. Self-inductance is reduced by decreasing the distance between wires and it disappears entirely in concentric conductors. Sub- dividing the conductors decreases the drop in voltage due to self- inductance but it complicates the wiring. Circuits formed of conductors twisted together have very little inductance. When alternating-current wires are run in iron pipes, both wires of the circuit must be run in the same pipe, inasmuch as the self-induc- tance depends on the number of magnetic lines of force passing between the conductors or threadinor the circuit, and this number will be increased when iron is present between the conductors. The effect of self-inductance in a circuit is to cause the current to lag behind the impressed voltage and it also increases the impe- dance of the circuit. The effect of self-induclauce niay be neutralized by capacity or vtce-oc/vii. The relative value of the two must be as follows: 28 POWER TRANSMISSION • A C = -^ — 7-^- when C and L are in farads and henrys respectively, and/' is the frequency of the system. Mutual=Inductance. By mutiial-indnctance is meant the in- ductive effect one circuit has on another sep- - arate circuit, generally a parallel circuit in power transmission. An alternating current flowing in one circuit sets up an electromotive force in a parallel circu.it which is opposite in direction to the E.M.F. impressed on the first 3 circuit, and is proportional to the number of the lines of force set up by the first circuit which thread the second circuit. The effects of mutual inductance may be reduced by increas- ing the distance between the circuits, the distance between wires of a circuit remaining the same. This is impractical beyond a •d Fig. 16. A -M3.00 ■riaoo-. ♦1300-. Uppe •■ ci-o aSCLr ■n > : : : : : ■* "' s. \ > > ; : > ;c ;: ^ \ E B C : 3 / \ E 3 C ; E ^U v-zer c 3 c -TOSS cLrm S : ; : / ^ N > : pn • ■ Fig. 17. certain extent, if the circuits are to be run on the same pole line, so tliat a special arrangement of the conductors is necessary. Figs. 1(5 and 17 show such sjoecial arrangements. In Fig. IG AB forms the wires of one circuit and CD the wires of the other roWER TRANSMISSION 29 circu-it. Lines of force set up by the circuit AB do not thread thfi circuit VD, provided A B (! and D are arranged at tlie corners of a square so that there is no effect on the circuit CD. In Fig. 17 assume an E.M.F. to be set up in the portion of the circuit CD in the direction of the arrows. The E.M.F. in the section DE will then be in the direction of the arrows shown and the effects on the circuit AB will be neutralized, provided the transposition, as the crossing of the conductors is called, is made at the middle of the line. Such transpositions are made at frequent intervals on transmission lines to do away with the effects of mutual indirctance which, at times, might be considerable. When several circuits are run on the same pole line, these transpositions must be made in such a manner that each circuit is transposed in its relation to the other circuits. Thus in Fig. 17 is also shown the transposi- tion of the circuits of a line composed of ten two-wire circuits. CALCULATION OF ALTERNATINQ=CURRENT LINES. In dealing with alternating currents, Ohm's law can be applied only when all of the effects of inductance and capacity have been eliminated, and, since this can seldom be accomplished, a new for- mula must be used which takes such capacity and inductance effects into account. Not only the inductance or capacity of the line itself must be considered, but the nature of the receiver must be taken into account as Mell, when the regulation of the system as a whole is being considered. The following (piantities must lie known in the complete solution of problems relating to alternating- current systems. 1. Frequency of the current used. 2. yelf-ind action and capacity of the receivers. 3. Self-lniluction and capacity of t)ie lines. 4. Voltage of, and current flowing in, the lines. 6. Besistance of the various parts. Following is a set of formula and an appropriate table for cal- culating transmission lines proper when using direct or alternating current and for frequencies varying from 25 to 12.5, and for single and polyphase currents. This table is issued by the General Elec- tric Company. 30 POWER TRANS.MISSION GENERAL WrRINQ FORMULA. 1^ X W X c Area of condTiftor, ('ircular ]\[ils CuiTeiit ill main fonductors — r X F W_X T ~E A\" = Total Avatts dclioerci]. Y) = Distance of traiisinission (one way) in feet. l> = Loss in line in per cent of power ijrl ivi-rrJ, that is, of "\V. E =; \''oltage between main condnctors at receii:iii.(j or cmi- sniiii/r's end of circuit. For continuous current C = 2.1()(), T = 1, B = 1, and A = 6.04. T- u 1 • r y> X E X B \ olts Joss in lines =^ 1(10 TV, 3>' X ^y X <" X A JLbs. copper = — . ^^ . /* X E' X 1,000,000 The following formula will also be found convenient for cal- culating the copper required for long-distance three-phase trans- mission circuits: r, ^ iPx K.W. X 300,000,000 Jjbs. Copper = - „ ' M is the distance of transmission in miles, K.W. the power delivered in kilowatts, and the power factor is assumed to he approximately 05%. APPLICATION OF FORMUL/E. " The value' of C!' for any particular power factor is obtained by dividing 2,160, the value for continuous current, by the square of that power factor for single-phase, by twice the square of that power factor for three-wire three-phase, or fonr-wire two-phase. The value of B depeiids on the size of wire, frequency, and power factor. It is equal to 1 for continuous current, and for alternating current with 100 per cent power factor and sizes of wire given in the following table of wiring constants. "The figures given are for wires IS inches apart, and are suffi- ciently accurate for all practical purposes provided the displacement in pVase between current and E.M.F. at the receiving end is not POWEE TKANSMISSION 31 TABLE VI. Single-phase Two-phase (four-wire) . . . Thre-phase (three-wire) . . ^ allies off. of A. Per Cn {In 2,400 1,200 1.200 U I'liw.v FiU-tnr. 100 Wl 0,04 iL'.OH 9 0(1 2,1 BO 1,080 1,080 2,(1B0 i :',,0(I0 ; 1,:'!H0 i 1,500 l,:;:iii ! 1,500 :i,:;so 1,690 1,090 Values (if T. System. Single-phase Two-phase (four-wire) . . Three-phase (three-wire) Per Cent Power Factor, 1.00 1.05 .50 .53 .58 .01 90 ai 80 1.11 1.17 1.25 . 55 .59 .62 .64 .68 .72 O0(XJ 000 00 9 10 VAr.UES OF B. eO C'yrlfs. Per Cent Pmspr Factor. 9.-> 1.G2 1.49 1.34 1.31 1.24 1.18 1.08 1.05 1.03 1.02 1.00 1.00 90 H.5 1.84 1.66 1.99 1.77 l.r,2 1.40 l.GO 1 40 1.30 1.23 1..34 1.25 1.17 1.12 1.18 1.11 1.08 1.04 1.00 1,02 1.02 1.00 1.00 1.00 1.00 l.(X) 1.00 1.00 80 2.09 1.95 1.66 1.49 1.17 1.10 1.04 1.00 00 00 1.00 1.00 125 Cycle- Per Cent Power Factor. 2.35 2.08 l.SG 1.71 l.oO 1,1.5 1 3.5 1.27 21 16 1.12 1.09 1.06 1.04 90 2.86 2.48 2.18 1.96 1.75 1.60 1.46 1.35 1.27 1.20 1.14 1.10 1.06 1.03 85 3.24 2.77 2.40 2.13 1.88 1.711 1.53 1.40 1.30 ' 1.21 1.14 1.09 1.04 1.00 3.49 2.94 1.97 1.77 1.57 1 43 1.31 1.21 1.13 1.07 1.02 l.(X) 32 POWER TEANSMISSION I> CO t-O I—* I-H ss i§ 88 88 o ■X rH i—t T— 1 1—1 I— ' I— 1 I-H I-H I-H 1-H >-H rH I-H rH iC I— X }H >0 ID CC CI CC CI I-H I-H '-T i2 o o Q S' 88 O D i-H I— ( I-H i-H I-H --H I-H I-H 1—t 7—i o Ph ^ C* T— 1 v^, 1- CI 9£S - = ?8 Q x! fl m 1— 1 1— 1 T-1 .—* I-. I-H »-H rH I-H rH I-H I-H I-H ,—t (M O iC C5 -p I-l 1^ lO CC C^l S8 88 g lO -^ CI ^ r-1 I-H O O o o c ■X 1—1 I— I r-H I-H ^rH ^^ I-H I-H I-H rH 1-H rH O OS CC O OO o o 88 o -^ ^ s 1-hO OO oo o o ^' o ■ 1-H rH I-H I-H t< CC -+I CO O lOCl o o O ^' o o 88 X' in OD i-l i-f O' o o o o o O 1—1 -—1 I— 1 i—t I-H I-H I-H 1-H I-H I-H I-H 1-H 1—f I-H C5 CI CI o oo oo oo O C'l CI I-H <-H o o o o o o o o oo 1=1 Ol I-H I— 1 1— I I-H r-H I-H I-H r-i I-H I-H 1-i 1-t I-H 1-i CO QO -t^O t"- iQ CC c-i o o o o o o s W^' I— 1 i-H I— 1 l—i OO I-H I-H oo 1-H I-H oo 1-H I-H oo I-H 1-H o c 1-t ^ g:' CO -f 1^ •smqo -0 oSE o:^ CI Ol Oi CO O CI rfi O CC. O lO CC -p CO I- Oi C-l LO O lO 1-H CC I-H 1-H amoGjooo'i Jsd o c: o o i-H 1-H ClC^l CC -t* LO '--O CC O 8.IT AV JO aoxiu^stsaa 1-H LO CO -*< Tf lO QJXJ^ ■sqi--'jjo(K)'i-iad: L8Ji!a JojuSraAi CO O O (M Tt^ CO CO C'l »o O OS CO LO CI I-H I-H 8g I-H s§ OS 1-H CC CO O O oo O ■"' O O oo o o o o o o oo OO oo snw auino.no oo "<:P CD I-H C<* o-^ nS CC O t-H 1—1 "" lO ^ CO CI CI rH ^ r-t ■a3ni;o -g ^ 'a go OO r-H CI CO tM IQ CO 1-^00 C:0 8.T tAV io ■ON o very much greater than that at the generator; in other words, pro- vided that the reactance of the line is not excessive or the line loss unusually high. For example, the constants should not he applied at 125 cycles if the largest conductors are used and the loss 20% or more of the power delivered. At lower freqaencies, Jiowever, the constants are reasonably correct even under such extreme conditions. They represent about the true values at 10% line loss, are close enough at all losses less than 10%, and often, at least for frequencies up to 10 cycles, close enough for even much larger losses. Where the conductors of a circuit are nearer each other than 18 inches, the volts loss will be less than given by POWER TRANSMISSION 33 the fonnulai, and if close together, as with multiple-conductor cable, the loss will be only that due to resistance. " The value of T depends on the system and power factor. It is equal to 1 for continuous current and for single-phase current of 100 per cent power factor. The value of A and the weights of the wires in the table are based on .00000302 pound as the weight of a foot of copper M-ire of one circular mil area. " lu using the above formuhe and constants, it should be particularly observed thatp stands for the jier cen t loss iu the lineof the delivered power, not foi the per cent loss iu the line of the power at the generator; and that Eis the potential at the delivery end of the line and not at the generator. " "When the power factor cannot be more accurately determined it may be assumed to be as follows for any alternating system oper- ating under average conditions: Incandescent lighting and syn- chronous motors, 95%; lighting and induction motors together, 85% ; induction motors alone, 80%. '• In continuous-current three-wire systems, the neutral wire for feedei's should be made of one-third the section obtained by the for- mula' for either of the outside wires. In both continuous and alter- nating-current systems, the neutral conductor for secondary mains and house wiring should be taken as large as the other conductors. " The three wires of a three-phase circuit and the four wires of a two-phase circuit should all be made the same size, and each conductor should be of the cross-section given by the first formula". Numerical examples of the application of this table, as well as of other forraulfe, are given later. A better idea of the way in which the different quantities in- volved affect the regulation of an alternating-current line may be obtained from graphical representation or from formulfe which are not so empirical. Before taking up other methods of calculation, however, let us consider the meaning of power factor. By power factor we mean the cosine of the angle by which the current lags behind or leads the electromotive force producing that current. It is the factor by which the apparent watts (volts times amperes) must be multiplied to give true power. The formula for power in a single-phase circuit is then, Power = IE cos 6 when 6 is the lag or lead angle; and for three-phase circuits. 34 POWER TRANSMISSION single coiuhietor. For two-phase circuits, balanced load, this becomes, Power = 2 IE cos d; and. Power ^ 2 1 8 IE cos 9, for six-phase circuits. For single and three-phase circuits E is the voltage between lines. For two-phase circuits it is the voltage across either phase, and for six-phase circuits it is the voltage across one phase of what corresponds to a three-phase connection. Considering the formula for single phase, we find that the current flowing in the line may be taken as made up of two com - ponents, one in phase with the voltage and one 90° out of phase, lagging, or leading, depending on conditions. In Fig. 18 let OE equal the impressed pres- sure and OC the current ^ flowing. 6 = angle of lag. The current OC may be resolved into two compo- ^. ,„ " nents, one in phase with riff. Jo. ^ r OE = OB, and one 90 de- grees behind OE = EC. OB = OC3 cos 6 and is known as the active component of the current. EC = OC sin 6 and is known as the wattless component of the current. The capacity and inductance are distributed throughout the line, that is, the line may be considered as made up of tiny con- ^c:— 'Tsw^ — I — 'WW" — I — omri — | — rwir^ — | — nsntr^ — ns^ — | — r^r^ — , ^— Tfire^ 1 T!OT") 1 rsW' 1 TRRT 1 OITO^J Tmr> I T!W> I Fig. 19. densers and reactance coils, connected at short intervals as shown in Fig. 19. Considering the inductance and capacity as distributed in this manner, the regulation of a syjstem may be calculated, but the process is very difficult, and simpler methods, which give very close results, have been adopted for practical work. Probably the POWER TRANSMISSION 35 methods presented by Perrine and Baum are as simple as any ex- cept those based on purely empirical formulse. Tables giving the capacity and inductance of lines, together with the formula for the calc^^lation of these quantities, have already been given. It has also been stated that the effect of the capacity of a line is to cause a charging current to flow in the line, this current being 90° in advance of the impressed voltage. The value of this chai'ging current is: (.barging current per wire = ^ ^, single-phase. ^ X J-" C = capacity in micro-farads of one wire to neutral point. _/ = frequency of the. circuit. E ^ voltage between wires. 2 Charging current, three-phase, = — ~'-__- or l.l."),^) x charging I ■' current, single-phase. Since the voltage across the lines is not the same all along the line, the value of the charging current will not be the same, but the error introduced by assuming it to be constant is not great. For our calculation, then, we assume that the charging current in an open -circuited line is constant throughout its length, and also that the capacity of the line may be taken as concentrated at the center of the line. — I ^acwip 1 B 1 Pig. 20. Consider a single-phase line such as is shown diagrammatically in Fig. 20. Let E^ = the voltage at the generator end of the line. E = the- voltage at the receiver. L = self induction of the line. Tg = charging current per wire. I = current flowing in the line due to tlie load on tlie line. 36 POWER TRANSMISSION 6 = angle by which the load current differs from the impressed voltage. E = resistance of the line. e = drop in voltage in the line. o) = 2 ,7/. + _/ is a symbol indicating that the current is 90" in advance of the pressure. - j indicates that the current is 90^ behind the pressure. The expression, VW + (2 tt/L)^ = VW+'JlJ may be represented by E. + iLco, the factor -\- j indicating that the square root of the sum of the squares of these two quantities must be taken to obtain the numerical result. The quantity _y^ may be con- sidered as - 1. Taking the capacity of the line and considering it as a con- denser located at the middle of the line, we may assume the charg- ing current as flowing over only one-half of the line, or one-half the charging current may be considered as flowing over all of the line. The impedance of the line is equal to VH^ + &>" 1/ = H + ./Lcd. The power factor of the load = cos 6. The active component of the current is I cos 6. The wattless component of the ciirrent is - j\ sin 6 {-j indicat- ing that the current lags 90° behind the pressure). The charging current may be represented by + j -rf • Then the drop due to the active component of the load is I cos e (R -\- jLco). The drop due to the wattless component of the load is -jl sin 0{R +jLai). The drop due to the charging current is + _/' -.," (E. + j'L&j) The total drop is equal to the sum of these three vahies = e, 80 that, \=~E + e = lcos e(R+ jLoj) -jl sin 6 {R + JLo)) + j^(R+jLco) Expanding this and substituting - 1 for^' we have. POWER TEANSMISSION 37 E„ = E + I cos 61 K + ,/I cos 6 'Loy-jl sin (9 R + I sin 6 Leo Referring to Fig. 21 we have these various values plotted gruphically. >,/ = E, >fh = -j L,R , I„Lcu 00 = ^ 2~' 2 de = + /I cos ^ Lro, f(/=-^ TLq) sin ^, rv/ = + I cos R, ^;/= -,ylR sin 0, o'J = e', «J is plotted 90° in advance of c«c- on account of tlie symbol + J- lie is plotted in the opposite direction from oit on account of the negative sign. (^ IS plotted downward on account of the symbol - j. /'X 1 ^ . ? .--''' b a o *^ Fig. 21. If we let oa' , Fig. 21, represent the current vector, then B = angle of lag, and eg which equals IR is plotted parallel to <>a' and c'e — ILcB is plotted perpendicular to on' . It is seen from this that the charging current tends to pro- duce a rise in E.M.F. instead of a drop in pressure. The above takes into account only the constants of the line. In order to determine the regulation of a complete system, the 38 POWEK TRANSMISSION resistance, capacity, and inductance of the translating devices must be considered as well. In Fig. 22 is shown a diagram of a com- plete system with both step-up and step-down transformers con- nected in service. The charging current may be considered as flowing through half of the system only, namely, the generator, the step-up transformers, and one-half of the line. L R Fig. 22 Let Ej = the equivalent resistance of the step-down trans- formers. Kj ^ the equivalent resistance of the step-up trans- formers. Lj = inductance of the step-down transformers. Lj = inductance of the step-up transformers. K = equivalent resistance of the generators. Lg = equivalent inductance of the generators. K, = resistance of the line. L = inductance of the line. L, = L, + L, + L^ + L. K, = K, + K, + E, + R. All quantities should be converted into their equivalent values for the full line pressure. Thus the generator and re- ceiver voltages should be multiplied by the ratio of transforma- tion of the step-up and step-down transformers, respectively, to change them to the full line pressure. The resistance and induc- tance of the transformers must include the resistance and inductance of both windings, and the value must correspond to the line voltage. Thus the resistance of the step-up transformers will be j\ iv' -\- r^, when r^ = resistance of primary coil, r^ = resistance of secondary coil, n = the ratio of transformation. In the same way, the equivalent resistance of the step-down transformers will be r^-{- in? r,^. The generator resistance and inductance must be multiplied by n? to bring them to equivalent values for the full line pressure. POWER TRANSMISSION 39 Our formula then becomes: — Eq = E + Icos 6 (Et -j-JLt^m) -ylsin 6 (E^ +jLt.q}) + ^c [(I + Ps + E,) +JCO (I + L, + L,)] Plotted graphically we have, Fig. 21: oa = E al = I cos 6 E^ , . /E , T3 ^ t/e = i 1 cos ^ Lrp tu ■^ ° \2 ' ' ' ^/ cf — -jl E^, sin 6* /L , T , T \ f X ^' D = 25 X 5,280 = 132,000 W = 1,000 X IjOOO = 1,000,000 POWER TRANSMISSION 41 i" = 1,500 for tliree-phase three wire system and 85% power factor. J, = 10 E ^ 20,000 E^ = 400,000,000 ,,. , ., l:]:300() X 1000000 X 1500 Circular lails :=^ 10 X 400000000 18^X150^ = 40,500. 4 Number o wire has a cross-section of 52,400 cir. mils. W X T b Current in each conductor = — ,^— = 34. K T = .(is for three-phase system, 85% power factor. ^^ , 1 • ,• 7^ X E X B c \ oits lost m line = r— — B = 1.18 for number 3 wires, IK) cycles and 85% power factor. 10 X 20,()()() X 1.1.^ ^ oltS lost = :rT~^ = 23(10 d Pounds copper = ^;-^-ng. -^i^uOOTOOO ' ^^ "'''^ ciliated directly from the weight of wire given in the tables after the size of wire has been determined by other formulas. Thus 75 miles of numlier 3 wire is re(piired. This weighs 150 pounds per 1,000 feet. 150 X 5.280 X 75 = (■)2,'.l(;4 pounds. 5. A single-phase line 20 miles in length is constructed of number 000 wire strung 24 inches apart. It is desired to trans- mit 500 K.W. over this line at a fre(jueiicy of 25 cycles and a power factor of 80%, the voltage at the receiver end being 25,000. Considering the line di'op only, what must be the voltage at the tjenerHtor end of the line? E^ = K + I (Mis II + J 1 ri,H \.a} — j i sin R + I sin L O) -f- / --^ B. - ' L a). E ^ 25,000 500,000 .,. I — := 2.J ( rowei- = IE cos 0) 25,000 X .80 ^ 42 POWER TRANSMISSION Cos e =: .80 Sin = .60 (from trigonometric tables) R = resistance of 40 miles of number 000 wire = 14.56 ohms at 50° C. L = .00277, X -^ X 20 = .064 (calculated from Table V). 1/3 o) = 27r/'= 2 TT X 25 = 157 _ ExCx27rX/ 25,000 X .3752 X 157 _ ^<= ~ 2 X lO'' "" 2 X 1,000,000 " "P- C ^ .3752 (Table IV or calculated). Siibstituting these values in the above formula we have, Eo = 25,000 + 291.2 +y 200.8 -,; 218.4 + 150.6 +,;5.36 - 3.7 Eo = 25,000 + 291.2 + 150.6 - '3.7 + j>'(200.8 - 218 4 + 5.36) Eo = 25,000 + 291.2 + 150.6 - 3.7 - j (218.4 - 200.8 - 5.36) Eo = 1/(25,000 + 291.2 + 150.6 - 3.7)^ + (218.4 - 200.8 - 5 36)^ Since the symbol ;' indicates that the quantities must be com- bined geometrically. Eo = 1/(25,438.1)2 + (12.24)2 ^ 25,438.1 volts. 6. A three-phase line 20 miles in length is constructed of number 000 wire strung 24 inches apart. We wish to transmit 1,000 K.W. over this line at a frequency of 25 cycles and a power factor of 85%, the voltage at the receiving end being 2,000. Three Y-connected 500 K.AV". transformers having a ratio of 10 : 1 step the voltage up and down at either end of the line. The resistance of the high-tension winding of each transformer is 4 ohms. The resistance of the low-tension windings is .04 ohms. The induc- tance of each transformer is 4 henrys. Neglecting the generator constants, what must be the voltage applied to the low-tension windings of the step-up transformers? Eo = E + I cos 6* (Rt + j Lt(b) -j I sin 6 (R^ + j 1^0)) + j I^ [(I +iO+>(t + !■.)] Since this is for a three-phase circuit we will work with the voltage to the neutral point and will change all values to corre- spond to the line voltage. Hence, POWER TRANSMISSION -13 E E I 8 > 3 I = 34 amperes. Since 1 3 IE Cos 61 = 1,000,000 E = 10 X 2,000 = 20,000 Cos d = .85 I = 34. lir|. :-- Resistance of one line + equivalent ivsistH.nee of one transformer at each end of the line. IIt = T.28 ohms + 1 + 100 X .04 + 4 + 100 X -04. = 28. 2S ohms. Lt = .0554 H- 1-3'+ .4 + .4 = .832 henrys. <» = 157 sin =-- .52 •) I^. = .5811 X — -= = .077 amp. = charging current single- • ) Tihase X - ^=. ^ I 3 ^-=3.64 E, = s ^,y = .010 L, = .4 Substituting these values in our formula we have, %^/' = ^+072..+;3774-;411..;-|-.3OU 1./3 1.(3 + J 1.H8 - 44.2 -- 11,.j5() + 672.8 -I 2,-300 - 44.2 + j (3,774 ^ 411.6 + 7.88) = I 14,487.6^ + 3370.3^ == 14,874 £o = 2,578 volts. TRANSFORMERS. A transformer consists of two coils made up of insulated wire, the coils being insulated from each other and from a core, made up of laminated iron, on which they are placed. One of these coils, known as the primary coil, is connectcil ;ktoss the circuit, in constant-potential transformers, and the other coil, known as the U POWEK TEANSMISSION secondary coil, is connected to the lamps or motors, or whatever makes up the receivers. As a matter of fact, these coils are each usually made up of sevei-al sections. The voltage induced in the secondary windings is equal to the voltage impressed on the j)ri- mary winding multiplied by the ratio of the number of turns in the secondary to the number in the primary coil, less a certain drop due to impedance of the coils and to magnetic leakage. This drop is negligible on no load. If trausforiners are used to raise the voltage, they are termed )-uj) transformers. If used to lower the voltage, they are called ^tc'j>-Jot':n. transformers. Losses of power occurring in transformers are of two kinds namely: Iron or core losses which are made up of hysteresis and eddy- current losses in the iron making up the core, and Copper losses which are due to the PE losses m the windings with the addition, in some cases, of eddy currents set up in the conductors themselves. The efficiency of a transformer depends on the value of these losses and may be expressed as the ratio of the watts output to the watts input. w, W,-^ (W, + ^\\ + w,) Wp- Wp Wj, = watts secondary. "W^p ■= watts primary. Wj. = copper losses. Wjj = hysteresis losses. We = eddy current losses. The iron losses remain constant for any given voltage regard- less of the load, while the copper losses are proportional to the square of the current. The efficiencies of transformers are hio-h, varying from 94 to 'J5% at l load to 98% at full load for sizes above 25 X.W. By AlUDay Efficiency is meant the efficiency of a trans- former, taking into consideration its operation for twenty-four hours, and it is calculated for the ratio of watt-hours output to watt-hours input for this length of time when in actual service. For calculation, the transformer is often assunu-'d to be fully loaded POWER TEANSMISSION 45 for five hours and run with no load for the remaining nineteen. The all-day efficiency is then determined as follows: Output, K.W. hours = watts output at full load X 5- Input, K.W. hours = watts output at full load X 5 + I'H loss at full load X 5 + core loss at normal voltage X 24. . 11 , rn . output, watt-hours All-day eihciency = •. — C — I input, watt-hours. The assumption that a lighting transformer is fully loaded five hours out of the day is not always a correct one. On many circuits from two to three hours of full load would be more nearly the proper value to use in calculating the all-day efficiency. By Regulation of a transformer is meant the percentage drop in the secondary voltage from no load to full load when normal pressure is im- pressed on the primary. This drop is due to the IE, drop in the windings and to magnetic leakage. In well designed transformers the loss due to magnetic leakage is about 10%, or less, of that due to the resistance drop. For non-inductive load (power factor = unity) the regulation is from 1 to 3% in good transformers. With in- duction load this is increased co 4 or AWVVAW .vv^^ww^' A/V^VWWv )%, or even more. Fig. 23. Both the efficiency and the reg- ulation should be considered in selecting a transformer for given service. Thus, if a transformer is to be used for lighting, its reg- ulation should be of the best, since drop in voltage due to the trans- former is in addition to that due to the conductors. In the same way the regulation of any system as a whole depends to a certain extent on the regulation of the transformer installed. If the efficiency of a transformer is low, it means a direct loss of considerable energy as well as greater heating of the transformer and consequent deterioration. If a transformer is to be used for lighting purposes, or is lightly loaded, a large portion of the time, 46 POWER TRANSMISSION a tjjie should be selected which has a relatively low core loss so as to increase the all-day etiiciency. If fully loaded all day, the losses should be divided about equally between the copper and the iron losses. Transformer Connections. Transformers for three-phase work may be connected in two M-ays. "Where three transformers, are used, they may be connected in Y or star, that is, with one terminal of each primary brought to a common point and the other terminal connected to a line wire (see Fig. 23), or they may be con- nected in A. or mesh when the three primaries are connected in series and the line wires are connected to the three corners of the triangle so formed (see Fig. 24). The second- aries may be connected in Y the same as the primaries or the second- aries may be connected in Y when the primaries are in A, or vice versa. The voltage relation may be best de- termined from vector diagrams as shown in Fig. 25, which gives the voltage relation of step-down trans- when the voltage across the primary vAAA/vW\A^ ^vVvv^A,^^^AA'l ^^^A.A/\AA/v^ Fig. 24. 1, formers with a ratio of 10 lines is 1,000. Changes may be made from two to three phases, or from three to two phases, with or without a change of voltage, by means of transformers having the required ratio of transformation by use of what is known as the Scott connections. Fig. 26 shows such a connection together with a corresponding vector diagram showing the relations when the change is from two to three-phase with a 10 : 1 transformation of voltage. The i/iain transformer is fitted with a tap at the middle point of the secondary wiring to which one terminal of the teaser transformer is connected. The teaser has a ratio of transformation differing from that of the main trans- former, as shown in the figure. S'/'.r Phases are obtained from three phases for use with rotary converters by means of transformers having two secondary POWER TEANSMISSION -17 windings or by bringing both ends of each winding to opposite points on the rotary-converter winding, utilizing the converter winding for giving the six phases. The latter, shown in Fig. 27, is known as a diametrical connection. When transformers with 1000 1000 -^ !- 1000 -> - 1000 1000- -1000 A'VVA' V^AAA.^Vu' .M [\A'^WWV\^ NV/VW>AA^ fA'W\A'VV//'T"*AA^^^\AA'V~ "\W^VvV^AA1 -100 -100 100 ■57&|*57SH *- 576 1000 1000 578 -1000 -» loookooo < Ooi-1 |AV> VVVW\VTVvVvW^ ■^W^lOO 100 — 1000 — . '1000-+1000- ->j<10i •AA^TV^^AA^WAI ^^^AAAAAAfl hAA'WW^AI [^^^/V^^^AA1 1000 Fig. 25. 1000 two secondaries are nsed, the secondaries may be connected in six- phase Y or six-phase A as shown in Figs. 28 and 29. When the y -connection is used, the common connection of each set of sec- ondaries is made at the opposite ends of the coils. This leaves the free ends directly opposite or 180° different in phase. The way in 48 POWER TRANSMISSION which these ends are brought out to give six phases is best illus- trated by means of the two triangles arranged as shown in Fig. 30. which have their points numbered corresponding to the connec- TEASER o o o T D D 4-2- o o o o o CO MAIN 1000 Fig. 26. 100 tion in Fig. 28. In Fig. 29 one A is reversed with respect to the other, and six phases are brought about in this manner. Single transformers, constructed for three-phase and six-phase work, are now being manufactured in this country, and they ai-e ^A^A^AAAA/V~^"^A/AV^A^A~^"V\AAA/WVW 4- 3 6 5 2 1. o scwagj 1 c \^ # ? 61 ^jO^^lj— 5 V^^A/NAM I V\A/\V\M 1 V\/\AAAM/ hAAA/W\ KAA^AW^ Fig. 27. 43 65 2 Fig. 28. being used to an increasing extent. They are a little cheaper to build for the same total output, and save floor space, but are not so flexible as three single-phase transformers. Where other conditions allow, a A to A-connection is prefer- able, for with this connection, if one transformer is injured, it POWER TRAXSAirSSTOX ■19 may be taken out of circuit and the remaining two will maintain the service, and may he loaded up to § of the former capacity of the system. In the Y-connection, however, the voltage impressed oil the transformer winding is only -- = .5S times the volt- age of the line, thus making it jwssihle to construct a transformer with a fewer number of turns. The windings must be insulated from the case, however, for a potential eipial to the line potential, unless the neutral point be grounded when the potential strain to which the transformer is liable to be snbjecteil, under ordinary conditions, is reduced to — -= of its value when the neutral is not grounded. For small transformers wound for high ])otential the cost is in favor of the 'i'-connection. K^\AA'^VV\r"T"VSA/WvV^"r"W\^VV\A1 ^/V\A^AA4 PVVVWWV 6 3 4-52 Fig. yf). Choice of Frequency. The frequencies in extended use at present in this counti-y are 2.j, 40, and (iO cycles, 2."j or (iO cycles being met with moi'e frecjuently than 40 cycles. Formerly, a fre- (juency of 125 or 13-3 cycles j)er second was quite often employed for lighting jjui-poses, but these are no longer considered standard. The advantages of the higher fre(pieney are: 1. Less fii-sl cost and smaller size cil'uenerators and transformers for a uiven output. 2. Better adajited to the oiieration of arc or incandescent lamps. Lamps, when run below 40 cycles, esi)ecially low candle-power incandes- cent lamps at 110 volts or higher, are liable to be trying to the eyes ou accoimt of the flicker. 50 POWEE TKANSMISSION Its disadvantaifes aj'e: 1. Inductance and capacity eflects are greater, hence a poorer regu- Jation of the voltage. The charging current is directly proportional to the frequency and this amounts to considerable in a long line. 2. There is greater djfliculty in parallel operation of the high-fre- quency machines due to the fact that the armature reactions of the older types of high-frequency machines are high. :'>. IMaclii-nes for high frequencies are not so readily constructed for operation at slow speeds. This, however, will cease to be an objection with the increasing use of the si:eam turbine. 4. Not well adapted to the operation of rotary converters and single- phase series motors on account of added complications in construction and increased eojii mutator troubles. A frequency of (id cycles is nsnally adopted if tlie powei- is to Le used for lighting only, and 2.^ cycles are l:)etter for railway work alone. By the use of frequency changers the frequency of any sys- tem may he readily changed to suit the requirements of the service. OVERHEAD LINES. Ilavino; considered the calculation of the electrical constants of a transmission line and distrihuting system, we turn next to the mechanical features of tlie installation of the conductors and find two general methods of running the wires or cahles. In the first method the conductors are run overhead and sup- ported by insulators attached to pins in cross-arms which, in turn, are fastened to the supporting poles. In the other methods the cables are jilaced underground and are supported and protected by some form of conduit. Overhead construction is used when the lines are run through o])en country or in small towns. It forms a cheap method of pro- viding satisfactory service and is reliable when carefully installed. It has the advantage that the wires may be placed some distance a])art and, being air-insulated, the capacity of the line is much less than that of. underground conductors. The old practice in overhead line construction has always been to consider the design and erection of the line as work that anyone could do, it being taken as the simplest part of the electrical system. As a result, the line was a source of a great deal of trouble which was laid to almost any other catise than poor construction. The overhead line, when used, must be considered as a part of the POWER THAXS.MTSSIOX r,l powei- plant and it should receive as i-ai'efnl attention as any part oF tin- eenti'al station or substation. It often lias to meet iiiui-h more sexerc eonditions than the jiower plant itself and it is respon- sible to a very larjre extent for the reliabilit\' of service. The new ^\•n\ of treatino- the (piestion of o\erliead lines is to consider them as structures which must l)e desjoiied to iiLeet cer- tain strains just as a briduv or similar structure is desiirned. This is especially true -when steel or iron poles are used as is the case in nearlv all transmission lines abroad. Thedesign of an overhead linemav lie divided into ti\e parts: 1. Location of line. 2. Supports for the line, pole, anil cross-arms. :;. Insulators and pins. i. Stresses sustained \>y the pole line, o. Conductors, material, si/.e. Some of these ai'e purely nieclianical featui'es while others are both mechanical and electrical. Let us take them uj) in the order named. Location of Line. The location of the line takes into account the territory over which the line must be run with respect to contour, direction, and freedom from obsti'uctions as well as iios- sible right of wav. AV^idth of streets, kind and heig-ht of biiildins/s, liability to interfeirnce with or from other systems must be con- sidered, when such are present. The rioht of way for electric lines may be secured, in some cases, along a i-ailway or public I'oad when its location is comparatively simple, ])rovided it is not necessai'v to interfere with adjoining ])ropertv. When adjoining jiropei'ty must be interfered with, or when the line is to I'un over sections containing no roads, it is usually jiossible to form contracts with the proj)ert\- owner such as shall free the line from future inter- ference liy the pi'o|iei-ty owner. In general, the cost of such ccni- tracts will be comparatively low. i\gain, the right of way may be purchased outright as is preferable when right of way is being secured for higli-sjieed electric railways. When the demands for right of May ai'e in excess of a reasonable amount, the process of condemnation of pro[)erty may be rt^soi'ted to or the direction of the line may be changed so as to avoid such locations. A iiivlijni- uary survey of the line should be made at the time the route is POWER TRANSMISSION being located, such a survey consisting of the approximate location of the poles, notes of the changes in direction and level of the trround as well as of its character. This snrvey aids in the selec- tion of material to l)e delivered to tlie different parts of the line. Chanoes in level are compensated for as much as possible by selecting long poles for the low places and short poles for the higher elevations, thus reducing the unbalanced strains in the line. The heavier poles should be used where there is a I I change in direction, where the line is especially ex- ^T31*~ posed to the wind or where branch lines are taken off. It is sometimes necessary that power lines be run on the same poles as telephone wires, in which case the power conductors should, preferably, be located above the telephone wires. Supports, Poles. In this country, the support for ferial lines consists almost universally of wooden poles to which the cross-arms, bearing the insulator pins, are attached. These poles mav be either natural grown or sawn. Abroad, the use of metal poles pre- vails.. In order to determine the proper cross-section of a pole it may be regarded as a beam fixed at one end and loaded at the other, this load consisting of the weight of the wire, with attendant snow or sleet, which tends to produce compression in the pole, and the tension of the wires together with the effect of wind pressure, which tends to produce flexure. Only the Fig- 31. latter stresses need be considered in selecting a pole for ordinary transmission lines. The poles are in the shape of a truncated cone or pyramid, the equation of which is: v/ = '/, + .' OIlzAX See Fig. 81. // ■= diameter of any section. .'• = distance from the top of the pole. I = length of pole. r/| and fJ.^ = diameter of the pole at the top and bottom re- spectively. POWEK TRANSMISSION 53 The proper taper for a pole should be such that <1 ., = jj of V,. If (/, > jS c/, the pole is heavier than need be as it would tend to break below the ground. If less than |- i;/,, the ])ole will tend to break above the ground and the material is not distributed to the best advantatje. In calculating the size of jwie necessary to stand a certain stress, we have, from the principles of Mechanics, ]\I =: moment of resistance. I = moment of inertia. S --^ stress in the section at V, at which ]ioint tlie jiole is least able to withstand the strain Avhich comes on it. ^r = P/ where P is the tension in the wires and / ^^ lenjith of pole in inches. ■n <1\ For a round pole, I = ,v, - ' ( 1+ and we have, P/ = , — ^TTj" Solvini'' for S, S :^ ,, ^ 77'/", For a sawn pole with s(juai'c (■i-(Jss-sections the \alue of I is: I = ''^ and // = -^- or S - — 7=— The value for S should not exceed a certain jtroportion of the ultimate strength of the material. If T represents the ultimate T sli'engtli in pounds ])er s(piare inch, then P =: - where // is known as tlie factor of safet\' and is ordinaiiU' imi taken less than 10 for wooden structures. A liii^h factor of safety is necessai-y on account 54 POWEK TRA^^SMISSION of the material not lieiiio- uniform, and the iincertaintj' of the vahie of T. P'ollowiiiij; are commonly accepted values of T: Yellow pine 5,000 - 12,000 pouuds Chestnut 7,000-18,000 •' Cedar Il,o00 " Redwood 11,000 " T The value of — should not be over about SOO for natural poles //. '- and (300 for sawn poles. f7., is measured at the ground line of the ]»ole. not at the base. Consider a pole of circular cross-section having a length of 35 feet and a diameter at the ground line of 12 inches. Using T — = (iOO. what is the inaximuni allowal;le stress that should be II ajiplied at the end of the pole '( TTt/ ., p = (;oo / - ;i.-) X 12 = 4-20 inches. ri72s = ^'^^'^ ""■ Tt is customary to select a general type of pole for the whole line determined from calculations based on the above formuhe, after the tension in the wire has been found, and not to apply such calculations to evei'y section of the line. The line is then reinforced, M'here necessary, by means of guy wires or struts. l-i'ollowing are some of the general requirements for poles: Spacing should not exceed 40 to 4-5 yards. Poles should be set at least five feet in the grouud with an addi- tional six inches lor e\eiy five feet increase in length over thirty-five feet. Siiecial care in- setting is necessary when, the ground is soft. End and corner poles sliould be braced and at least every tenth pole along the line should be guyed with ^ ^ or '^-inch stranded galvanized iron wire. li,egular inspection of poles, at least yearly, should be main- tained and dcfectivf p.oles )'ej)laced. Tlic condition of poles is best detcnniiicd 1)V examination at the base. PO^YER TRANSMISSION 55 Poles slioukl preferably l>e of good, sound chestnut, cedar, or redwood. Other kinds of wood are sometimes used, the material depending largely on the section of the country in which the line is to be erected and the timber availaljle. Natural poles should be shaved, roofed, gained, and given one coat of paint Ijefore erecting. Special methods of preserving poles ha\e been introduced, chief among which may be considered the process of creosoting. C'reosoting consists of treating the poh-s with live steam at a tem- perature of 225 to 250", so as to thoroughly heat the timber, after which a vacuum is formed and then the containing cylinder is pumped full of the preserving material, a j)ressure of about 100 pounds per square inch being used to force the desired amount of material into the wood. The butts of poles are often treated with pitch or tar, but this should only be applied after the pole is thoroughly dry. Guying of pole lines is one of the most important features of construction, (iuys consist of three or more strands of M'ire, twisted together, fastened at or near the to]) of the poTe, and car- I'ied to the ground in a direction o])posite to that of the resulting strain on the pole line. The lower end is attached to some form of guy stub or guv anciior. This ma\- lie a tree, a neiglil)oring pole, a short length of pole set in the ground, or a, jiatent guy anchor. Guy stuljs ai-e set in the ground at an inclination such that the guy makes an angle of DO' with the stub or with the axis of the stub in the direction of guy, the stub in the lattci' case beilig held in place h\ timlji'r or ])late fastened at right angles to the bottom of the stub. Such a timber is known as a '• dead man ". The angle the guy wire makes witli the pole should be at least 20". "When there is not room to cai'i'y the guy far enough away from the base of the pole to bring this angle to 20 or more, a strut may be used. This consists of a pole slightly shorter and lighter than the one to be reinforced. It is framed into the line pole near the top and set in the ground at a short distance from the base of the pole on the opposite sitle ot the jiole from that on which a guy would be fastened. Stranded galvanized steel guy wire is used for guys. There are two general inethods of attaching the guys to the top of the T)ole. In the one, a single guy is )'un, attached at or near the 56 POWEK TRANSMISSION iiiiddle cross-ami, while in the other, known as " Y" guying, two wires are run to the top of the pole, one nt Uiv np])er the other at the lower arm, and these united into a single line a short distance from the pole. Head guying, guying in the direction of the line, is used when the line is chaneine level and for end poles. The guys are attached Pig. 32. near the top of one pole and run to the bottom of the ])ole just above. Fig. 32 shows several methods of reinforcing pole lines. ^Special methods are adapted as necessary. Cross-Arms. The best cross-arms are made of southern yellow pine. Oak is also used to a large extent. They should be of selected well-se;isoued stock. The usual method of treatment is to paint them with white lead and oil. The size of cross-arms and spacing of jjins have not been thoroughly standardized. For cir- POWER TRANSMISSION euits up to 5,000 volts, 3^ X ij or S'-^^ X ij-" cross-arms with spacing between pins of Ki inches, the pole pins being spaced 22 inches, are recommended. For higher voltages, special cross-arms and s])aciiigs are necessary. The cross-arms should be spaced at least 24 inches between ceiitei's, the top arm being ])laced 12 inches l)elo\v the top of the jiole. They are nsnally attached to the pole by means of two bolts and are braced by galvanized iron braces not less than l]j X xii '"^'^ ^"*^^ abont 2s inches long. ("ross-arms are placed on al- ternate sides of the poles so as to prevent several of them from being pulled off should one liecome broken or detached. On cornel's or curves double arms are used In Euro])ean pi'actice, the cross-arm is done away with to a large extent, the wire beincr uiounted on insula- tors attached to iron brackets mounted one alio\-e the other. Fig. 33 gives an idea of this con- struction. Insulators. Electrical leak- age between \\ires must be pre- vented in some way and \arious forms of insulators are depended upon for this purpose. The ma- terial used in the construction of these insulators should possess the following properties: high specific resistance; surface not readily de- stroyed and one on which moisture does not readiU' collect; mechanical strength to I'csist 1)()th strain and yibratino; shocks. Its desig-n must I)e such that the \\ire can be I'eadily fastened to it and the tension of the wire will be trans- mitted to the pin without producing a strong strain in the insu- Fig. 33. 58 POWER TRANSMISSION HEIGHT 3} TESTED AT 50,000V HEIGHT 3" TESTED AT 30,000V. HEIGHT 4^ TESTED AT 70,000 V. HEIGHT 7^ TESTED AT 80,000 V. HEIGHT 4| TESTED AT 50,000V. HEIGHT 4^ TESTED AT 50,000V. HEIGHT 3^ TESTED AT 40,000V. HEIGHT 4^ TESTED AT 40.000V. Fig. ,34. POWER TRAMSMISSIOX 59 Cut Eccentric in BoH Cutter Composite Pin for Hiqh Teniron Insulator lator. Leakage surface must be ample for the voltage of tlie line and so foiistructed that a laroe portion of it will l)e protected from moisture during rainstorms. The principal materials used are glass and porcelain. Poi'celain has the advantaue over irjass that it is less l>rittle and generally strongei' and that it is less hygroscopic, that is, uiois- ture does not so readily collect on and adhere to its surface. y means of a paste formed of lith- arge and glycei'ine. The ad\'antau;es of this form of construction are gieater uniformity of stiiicture, and each part may be tested separateh'. f'ig. 'H shows several forms of insulators now in use M'ith tlie \oltage at which they ai'e tested. The test aj)j)lied to an insulator for high-tension lines should be at least double the xoltanc of tlie line, and some engineers recommend three times the normal voltaire. Pins. Pins made of locust wood lioiled in linseed oil are pre- ferred for voltages up to 5,000. Above this special ])ins are used. Wood pins are often objected to on account of the Imrniug or cliarring which takes place in certain localities, and iron pins are beinii- used to a larire extent. Vl". '■'>'> shows the diiiieiisiiins of such 66 POWEK TRANSMISSION a pin nsed on a GO.OOO-volt line. The insulator is fastened to the ]»in by means of a thread in a lead lug which is cast on top of the pin. The insulators in the construction shown in Fig. 3B are cemented to the iron biackets. The Stresses sustained by the line may he classified as follows : 1. Weight of wire, which includes insulation, and snow and sleet which may be supported by the wire. :2. Wind pressure upon the parts of the line. The strain produced by the weight of the wire on the jwle itself need not be considered except in exce])tional cases, because if the pole is sufticiently strong to withstand the bending strains, it is more than strong enough to withstand the compression due to the weieiit of the wires. 3. Tension in the wire itself. Langley shows the pressure of the wind normal to liat sur- faces to l)e equal to: p -= .003(1 r^ .. ;;,,. j> = pressure in j)0unds per s([. ft. /' - - velocity in miles per hour. For cylindrical surfaces the amount of pressure is § that ex- erted on a. flat surface of a width e(|ual to the diameter of the cylinder. Without great error we ma^- assume that the maximum wind pressui'e, and that for which calculation is necessary, is that at right-angles to the line, and a value of thirty pounds per sipiare foot is sufficient allowance for exposed places, while twenty pounds ])er square foot is considered sufficient where the line is par- tially sheltered. E.rdiiipl,'. What is the pressure, due to the wind, on the wires of a pole line containing three number 0000 wires, the poles being spaced 45 yards and the velocity of the wind such that the pressure may 1)e taken as 30 pounds ])er square foot. The diameter of a numl)er 0000 wire is .460 inch. The area against \vluch the wind exerts its force may be considered as: •J 3 -1.-) :■; / VI X Am — / - — ^ — .j-K)!) S(piare feet. POWER TKAXSJIISSIOX 61 5. Kit) X 30 = 155 pounds pressure due to wind on wires. The most important strain-producino- factor in a line is that due to the tension in the wire itself. A wire suspended so as to hang freely between two supports assunies the form of curve known as a catenary, but for ordinary work the ciii've may be taken as a parabola the ecpiation of which is simjile ;ind from which the fol- lowing e(]uations are derived : _ Ur^Y "" SI) When 1) = deflection oi' sair at lowest jioint in feet. L = actual length of wire lietween supj)orts in feet. 11 = distance between su])ports in feet. W = weight of wire in jionnds jier foot. F^. = Iiorizontal tension in the wire at the middle point. Pu = - where T = tensile strength of the wii'e and // = /I factor of safety. // = 2 to (i under the conditions existing when the wire is erected. The temj)erature changes in the wire affect the value of this factor, it being gi'eatest when the teni])erature is a maximum, and a minimum when the temperatui'e is lowest, and calculation should be for the maximum strain that may come on the wires. If Lj = length of a wire at a given temperature, t i\ and L,,|, = length of a wire at a given temperature, 20' ('. Then, Lt : . J.,, [1 + k (i - 20)|. k = .000012 tor iron. .OOOOIOH to .110(10114 lor aluininum. .0000172 tor eoiiper. The following table gives the deflection of spans of ^ire in inches for different temi)ei'atures and different distances l)etween poles, a maxiumm stress of 30,000 pounds ])er s((uare inch being allowed at - 10 F, which gives a factor of safety of 2 for hard- drawn co])per wire. f)2 POWEi; TKAXSMTSSION TABLE VII. Temperature Effects in Spans. -10 30' TEMPK 10 l.VrTTHK N DKCJiBK.S I'AHKKNHB:IT.' 00' Spans in oO' (iO 70" 80 ' 100^ Pec*. Deflectiini In Ini'lie.s. ~50 .5 6 8 9 9 10 1 11 11 12 60 .7 S 10 11 11 12 13 13 14 TO 1. 10 11 12 13 11 15 15 17 • 80 1.2 11 13 11 15 16 17 18 19 90 1.6 13 11 16 17 18 19 20 21 KK) 1.9 11 16 17 19 20 21 23 24 110 2.3 16 18 19 21 22 21 25 26 120 2.8 17 19 21 22 21 i 26 27 28 110 3.7 20 23 25 27 28 30 32 33 160 4.9 23 26 28 30 32 31 36 38 180 6 2 26 29 32 34 37 39 11 13 200 7.7 31 o--» 36 38 11 43 15 48 Tlie above foniiuln' a])])lY directly to lines in which the poles are the same distance apart and on the same level, and any number of s])ans may be adjusted at one time by ap]>lYing the calculated stress at the end of the wire and the line will be in equilibrium; that is, there will be no strain on the poles in the direction of the wires. Special care must be taken to juvserve this equilibrium when tlie lenirth of span chano-es or when the level of the pole tops varies, and this is accomplished l)y keepino- P^. and // constant for every span. AVliat is the tension in pounds ])er s(juare inch at the center of a span of number 0000 wire when the ])oles are 120 feet apart and the sao; is l(^) inches ( TPW ' '■ '^ M) II = 120 10 .1) ::=^., = lifeet. AV = .04- pon ds P. - (120V^ .04: .S04 pounds S X 1;^ The cross-section of number 0000 wire is, — Ti" X (•2'))" ~= .ll)(')2 square inches. 804 H- .1002 = .")200 pounds per square inch. POWER TKANSAITSSION fi3 The regulation of the system and the amonntof power kist in transmission togetlier delerniine the cross -sect ion of tiie condnctors to l)e used. The amount of powei' lost, for most eeonomical opera- tion ean lie determined from the cost of generating; jiower and the tixed eharges on the line investment. Eitbei- copper or aluminum wire or cables may be used. The latter is lighter in weight but more care must be taken in erecting and it is moi'e ditHcult to make joints. UNDERGROUND CONSTRUCTION. In large cities or other localities wheiv. if overhead construc- tion be used, tlie numl)er of conductors becomes so crreat as to be objectionable, not alone on account of ap|)earanee but also on acc(Uint of complication and danuvr, the lines ai'e run underfi-round. The exjiense of installing undergi'ound systems is vei'y great com- pai'ed with that of overhead construction, but the cost of mainten- ance is much less and the liability to interruption of ser\ice, due to line troubles, greatly i'edu('(Ml. The essential elements of an undei'ground system are the condiictoi', the insulator, and the pro- tection. The conductor is invariably of copper, the insid;itor may be ruljber, p)a])er, some insulating comjiound, or individual insu- lators, depending on the system, while the pnjtection takes one of several forms. The s^-stem. as a whole, may be di\'ided into Solid or built-in s\-steins. Treneli systems. I)rawiug-in systems. As an example of the first, «-e have the Kd'ixnn Tiihi' xi/xfi'm. which is especially adapted to house-to-house distribution and is used to a large extent for direct-current thi'ee-wire distribution in congested districts. It is made up of copper rods as conductors (three of e(ptal size for mains and the neutral but -rl thi' size of the main conductors in feeders), which are insulated from each other by an asphaltum compound. This comjjound also serves as an insulation from the protecting case, which consists of wrought- iron T)ipe. Pilot wires are also often installed in the feeder tubes. This tabe is built u|) in sections about tM'eiity feet long. In insu- lating the conductors, they are first loosely wrapped with jute rope so as to keep them from making contact with each other. 6i POWER TEANSMISSION V\g. 30. POWER TRANSMISSION 05 and with the pipes, and tlie heated asphaltum forced into Uie tubii from the bottom, when the tnbe is in a vertical position. Thi- ends of the conductors and the tultcs must 1k' joineil and pi-ojierly insulated in a completed system. Special connectors are furnished for the conductors, and cast-iron coupling l)oxes are fitted to the ends of the tube as shown in Fig. .'ili. After tlie conduct(jrs are properly connected, the cap is put on this coujilino; box and the inside space then filled with insulating compound through a hole in the cap. This hole is later fitted with a plug to render the box air-tight. The system is a cheap one, though the joints are expen- sive. It is not adapted to high potentials. The tiiciihens-IIiilxlic system of iron-taped cables consists of insulated cables encased in lead to keep out uioisture, this lead sheathing being in turn w'rapped with jute which forms a liedding for the iron tape. The iron tape is further protected by a wrap- ping thoroughly saturated with asphaltum compound. These cables may be made up in lengths of from 5(lO to fiOO feet. In unexposed places, such as across private lands, the steel taping may be omitted and the lead sheathing simply protected by a braid or wrapping saturated with asphaltum. The Tri'iicli system consists of bai-e or insulated conductors supported on special forms of insulators as in overhead construc- tion, the whole being installed in small closed trenches. As this system is not used to any extent in America, but one system, the Crompton system, will be described. In the Crompton system, bare copper strips are used, each 1 to li inches wide and -]; to \ inch thick. These strips rest in notches on the top of porcelain or glass insulators, supported by oak timbers embedded in the sides of the cement-lined trench. This trench is covered with a layer of flagstone. These insulators are spaced about 50 feet and about every 800 feet a straining device is installed for taking up the sag in the conductors. Hand- holes are located over each insulator. There are several of the -'-o feCEMENT 1 PT SAND 2PTS. STONE SiPTSi X o q: Q_ a. < m^\ 's^M^j^MMtsmy^^m^mM' '-IC\i Pij?: 37. pipes. The latter is known as "pump log"' conduit. The wood vised for this purpose must be very carefully seasoned and then ti'eated with some antiseptic compound, such as creosote, in order for the duct to give satisfactory service. Tf impro])erlY treated, acetic acid is formed during the decay of the wood, and this attacks the lead covering of the cable, destroying it and allowing moisture to deteriorate the insulation. Wood offers very little resistance to the drawing in of the cables, and it is a cheap form of conduit, though it cannot l)e depended on for long life. One of the best and at the same time most expensive systems is the one using tri'D/jglif-iroii j>!]ier next to the conductors and using the vulcanized rublier outside of this. One or two layers of pure rub- ber tajie are put on spirally, the spiral being reversed for each layer. Kubber com- pound in two or more laye]'S is a])plied over this in the form of two strips which pass between rollers which fold these stri])s around the core and press the edges together. Prepared rublier ta|ie is ajt- ])lied over -this, after which the insulator is vulcanized and the cable tested. If sat- isfactory the external protection is applied. Cable for polyphase w(.irk is made up of three conductors in one sheath. Fie. 41 shows a cross-section of cable manufactured for three-phase transmission at (i,(iOO volts. The ccHiductors of this cable have a cross-section e(|uivalent to a number 0000 wire, to which an insulation of rublier ^e^-inch thick is applied. These three conductors are twisted together with a lay of idjout 20 inches. Jute is used as u tiller, and, a second layer of rublier insu- lation ./,,-inch thick is then ajiplied. The lead sheath employed is 1-inch thick, and is alloyed with 8'/, of tin. Joints in caliles must be carefully made. Well-trained men only should be em]iloye(l. Tlw insulation ap])lied to the joint should be c^ui\■^de]lt lends on the distance the power is to be transmitted as well as its amount, and on the use to l)e made of lln^ power. If a Jigliliii^' load is coiicejiti'ated in a small district, a 2'JO-volt three-wire s\stem will gi\'e very good service. If the POWER TKANSMISSION 73 region is a little more extended, possibly a 4-l:()-volt three-wire system using 220-volt lamps would serve the purpose without an excessive loss of power or a prohibitive outlay for copper. For location when the service is scattered, a distribution at from 2,200 to 4,000 volts alternating current is used, transformers being located as required for stepping down the voltage for the units which may be fed from a two- or three-wire secondary system. 2,800 volts (alternating) is a standard voltage for lighting purposes and for polyphase systems; 2,300 volts is often taken as the voltage between the outside wires and the neutral wire of a four-wire three-phase distribution. For railway work, 550 to COO volts direct current is used up to distances of about 5 or miles, beyond which it becomes more economical to install an alternating-current main station and sup- ply the line at intervals from substations to which the power is transmitted at voltages of from 0,600 to 30,000 or even higher, depending on the distance it is to be transmitted. At present, the highest voltage used in long-distance transmission is 60,000, though higher values are contemplated. Such voltages are used only on very long lines, and each one becomes a special problem. It is always well to select a voltage for apparatus which may be considered as standard by manufacturing companies, as standard apparatus may always be purchased more chea])ly and furnished in shorter time than special machinery. Protection of Circuits. Lightning arresters are installed at intervals along overhead lines for the protection of connected apparatus. For ordinary lighting circuits, such arresters are in- stalled for the protection of transformers, and are located preferably on the first pole away from the one on which the transformer is installed. Care should be taken to see that there are no sharp bends or turns in the ground wire and that there is a good ground connection. Vnf the high-tension lines, lightning arresters at either end of the circuit are I'elied on to afford the greater part of the protection. In some localities, a wire strung on the same pole line at a short distance from the power wires and gi'ounded at very frequent intervals has been found to reduce troublesdue to lightning. The ifi'oundintf of the neutral of thi'ee-wire Keeondarv systems forms a means of protection of such circuits against high jiutentials 74 POWEK TKANSMISSION which might arise from accidental contact with the primaries, and is recommended in some cases. The grounding of the neiitral of high-tension systems reduces the potential between the lines and the ground, but a single ground will cause a short-circuit on the line with any grounded system. Grounding, through a resistance which will limit the flow of current in such a short-circuit, has been recommended and is employed in some instances. Spark arresters are installed at the ends of high-tension underground systems to prevent high voltages which might injure the insulation in case of sudden changes in load, grounds, and short-circuits. INDEX Part I — Power Staiions; Part II — Powioit Tuans.misski.v I'iirl Page All-day efficiency II, 44 Alternating-current line calculation , II, 2\) examples of.. II, ,3(j Alternating-current systems of distribution II, 21 Annunciator wire .....' II, 9 Boiler efficiencies, table I, 13 Boiler foundations I, 22 Boilers I, 10 Cornish I, n economic I, 12 Lancashire I, n marine I, n multitubular I, n water-tube I, n Boilers, firing of I, 23 Cable, standard, table I, 47 Cable construction, taljlc II, 72 Cables II, 70 Capacity of conductors for carrying current II, 7 Capacity ratios, table ." I, 61 Central station I, 3 Charging for power, methods of I, 7o Circuits, protection of II, 73 Conductors II, 3 capacity of for carrying current. II, 7 for various conditions, table , II, 7 Copper losses ^ II, 44 Copper wire table II, 4 Cornish boilers I, 11 Cross-arms II, 56 Curtis turbine I, 27 Direct-current feeder panels I, 50 Distribution systems II, 11 multiple-series II, 17 parallel II, 13 ijcries II, 11 series-multiple II, 17 II INDEX Part Page Draft mechanical. I, 23 natural I, 23 Earthenware conduits II, 67 Economic boiler I, 12 Efficiency of transformer II, 44 Electric distribution of power II, 3 Electrical plant I, 36 Engines, gas I, 34 Exciter panels I, 50 Exciters I, 39 Feed water I, 20 Feeding appliances I, 20 Feeding poiat II, 15 Firing of boilers I, 23 Formula, general wiring II, 30 Frequency, choice of II, 49 Fuel, handling of I, 23 Full load ratios, table I, 61 Galloway boiler I, 11 Gas engines. ' I, 34 Generating station, location of I, 4 Generator efficiencies, table I, 38 Generators I, 36 Governors I, 34 Gutta percha II, 10 Handling of fuel I, 23 Hydraulic plants I, 29 Increase in boiler efficiency, table I, 20 India rubber II, 10 Inductance II, 27 per mile of circuit, table II, 26 Insulation II, g Insulators II, 57 Iron or core losses.... II, 44 Lancashire boilers I, H Location of generating station. I, 4 Loss of power in steam pipes I, 19 Loss in pressure in steam pipes, formula for I, 18 Manholes II, 68 Marine boilers I, 11 Matthiessen's standard II, 6 Mechanical draft I, 23 Mechanical strength of different materials... II, 6 Multiple-series system of distribution II, 17 Multiple wire system II, 18 parallel II, 21 polyphase II, 22 INDEX 111 Part Puge Multiple wire system series II, 21 three-wire II, 18 Multitubular boiler I, 11 Mutual inductance' II, 2S Xafural draft I, 23 Oil-cooled transforni;'rs . I, 41 Oil switches I, 52 Overhead line^ II, 50 cross-arms II, 50 insulators II, 57 location of II, 51 pins . II, 59 stresses sustained Ijy II, 00 supports for II, 52 Panels direct -current I, 50 exciter I, 50 total output I, 51 Parallel systems of distribution II, 13, 21 voltage regulation of II, 20 Powerfactor II, 33 Power station buildings.. I, 63 Pressure of water, taljle. I, 31 Plant, size of I, 8 Pump log conduit II, 66 Regulation of a transformer II, 45 Resistance, effects of II, 7 Resistance of electrical conductors II, 4 Riveted hydraulic pipe, table I, 32 Safety devices I, 57 Selection of system I, 6 Series system of distribution II, 11 Series-multiple system of distribution II, 17 Size of plant I, ,s Station arrangement I, 68 Station records I, 70 Steam engines I, 25 Steam piping I, 13 arrangement I, 14 material for I, 16 Steam plant I, 10 Steam turbines - I, 25 Storage batteries - I, 44 Stresses sustained by pole line II, 60 Substations I, 59 Superheated steam I, 19 Switchboards I, 44 IV INDEX Part Page System, xelection of I, 6 Tables boiler efficiencies I, 13 boiler efficiency, increase in I, 20 boilers, floor space for I, 12 cable, standard I, 47 cable construction II, 72 capacity in Micro-Farads per mi. of circuit for three phase system II, 25 capacity ratios I, 61 conductors for various conditions II, 7 conductors for various positions II, 8 copper wire II, 4 exciters for single-phase A. C, generators I, 39 full load ratios I, 61 generator efficiencies I, 38 horse-power per cu. ft. of water per min. for different heads.. . . I, 34 inductance per mile of circuit II, 26 permissible overload 33 per cent I, 9 rate of flow of water, in ft. per min,, per pipes of various sizes. . I, 22 resistances of pure aluminum wire II, 5 riveted hydraulic pipe I, 32 temperature effects in spans II, 62 transinission line calculation II, 31 water, pressure of I, 31 wire, standard I, 4 7 Temperature coefficient.. II, 6 Three-wire system of distribution II, 18 Total output panels I, 51 Transformer connections ' II, 46 Transformer regulation II, 45 Transformers I, 40; II, 43 efficiency of II, 44 oil-cooled I, 41 water-cooled I, 42 Transmission lines - II, 24 capacity II, 24 Turbines I, 25 Curtis.. I, 27 .steam I, 25 water I, 30 Underground construction II, 63 Crompton system II, 65 Edison tube system II, 63 Siemens-Halske system II, 65 French system II, 65 Underwriter's wire •- II, 9 Variation m voltage II, 17 INDEX V Part I'aKB Voltage, selection of II, 72 Voltage regulation of parallel systems II, -" Water-cooled transformers I, I- Water-tube boilers I, H Water turbines I, 30 Weatherproof wire. . • .' II, 9 Weight of materials II, Wire, standard, table I, 47 Wiring formula II, 30 ANNOUNCEMENT OF COMING . IBOOICS I CARPENTRY. By G. Townsend. 150 pp., 224 illus. A -working: manual for Carpenters and Wood- workers in general. Not a theoretical treatise, but a practical working guide. Price, $1.00 GAS ENGINES AND PRODUCERS, By Marks and Wyer. 150 pp., 90 illus. Latest information in this rapidly developingf field. For E^ngfineers, Machinists, Automobilists. Price $1.00 MASONRY CONSTRUCTION. By Phillips and Byrne. 140 pp., 44 illus. Latest and best American methods. 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