Electrical Railways : the City and South London Railway.” by EDWARDHOPKISSOX, M.A., D.Sc., M

r’roccedin,ns.] HOPEINSON ON ELECTRICAL RlILWhYS. 200

14 February, 1593. HARRISON HAYTER, President, in the Chair.

(Paper No. NGG.) ‘‘ Electrical Railways : the City and South London Railway.” By EDWARDHOPKISSOX, M.A., D.Sc., M. Inst. C.E. FIVEyears have elapsed since the Author had the honour of describing before the Institution the electrical system of tractios adopted on the Bessbrook and Newry Tramway,’ at that time the only line in the United Kingdom upon which the operation of trains as distinguished from individual tramcars had been carried out electrically. The line has beenworked since October, 1885, with perfect regularity,and at accst satisfactory to the pro- prietors. A Table showing the traffic upon it in successive years, and the cost of haulage, is given in the Appendix. In the course of the discussion upon the Paper alludedto, it was shown that the United States were conspicuously in advance of this country in the application of electrical traction to street tramways. At the present time, in almosfi every town in America, horse-traction has been either wholly or in part superseded by electrical traction ; and it was stated,during the last Session of Parliament, in evidence before aJoint Select Committeeof both Houses, appointed to consider theElectric Railway schemes proposed withinthe Netropolis, that in the year 1892, the number of electric tramways in the UnitedStates was 436, with 3,532 miles of track, an& 5,851 motor cars, travelling in theaggregate 50,000,000 miles, andcarrying 250,000,000 passengersannually. Although the advance on the Continent has not been so marked as in the United States, still many important city tramwaysystems are now worked electrically. On the other hand, during the past fiveyears, the 8British and Irish electricaltramways, aggregating 22 miles of track, have been reduced by three, on account of the abandon- ment of electrical working on those lines, whilst only 6 new lines havebeen added to the list, making 33& miles of track in all. Such a disparity as this is indeed difficult of explanation. In the use of accumulatorsfor tractive purposes, the experience of all Minutes of Proceedings Inst. C.E., vol. xci. p. 193. [THE INST. C.E. POL. CXII.] P

Downloaded by [ Syracuse University] on [13/09/16]. Copyright © ICE Publishing, all rights reserved. 210 HOPEINSON ON ELECTEICAL RAILWAYS. [Minutes of countries has been equally discouraging, and on few of the lines upon whichthe system had been triedhas it come intoper- manent use. Theadvantages of sucha system areuniversally recognized, but repeated and protracted experiments have proved that, with the types of accumulators at present generally available, the cost of maintenanceisprohibitive; and that the several presentwell-known forms of accumulators, whichare doing excellent service in connection with electric lighting, must be greatly improved before they canbe generally adopted for tractive purposes. Many improvements have recently been intro- duced, tending to diminish thedepreciation to which the plates of accumulators are subject when employed under the difficult conditions obtaining in tramway work, and there can be no doubt that success will be ultimately achieved. Again, -in conduit systems, IittIe more has been done abroad than in England. The line constructed at Blackpool, in 1886, still remains the onlyone of thattype in England; on theContinent there are but afew examples of the system-the Buda Pesthtramways, which are on an extensive scale and are worked with great success, being the most notable of them ; whilst in the United States,9fr miles of tramway, out of the total of over 4,000 miles worked electrically, are on the conduit system. Probably the considerable first cost of construction is the chief cause of the slow progress made in thisdirection. In theUnited States, electrical traction has become general entirely with overhead systems of conductors, whilst in England exist only the two working examples of the short line at Leeds, comprising 2 miles of double and 15 mile of single line on the Thomson-Houston system, opened for traffic in October, 1891, and the recently-opened line of theSouth Staffordshire Tramways Company, 73 miles inlength. It is generallystated that the reason for overhead systems failing to find a footing in English towns, is the objection on the part of municipal authoritiesto the more or less unsightly erections involved thereby in the streets. Thisexplanation has not been refuted, and no better one has been offered; and it is to some extent substantiated by the fact that, only comparatively recently,Boston, with one of the largest tramway systems in the world, adopted an overheadconductor, whilst Philadelphia and New York are still without this form of electricaltraction on their extensivelines. Theline at Leeds will be useful in testing the realityof this apparently unsatisfac- tory explanation. If, however, in street tramways, Englishpractice has fallen short of American practice, in another directionit has advanced much further than anything that has been attempted

Downloaded by [ Syracuse University] on [13/09/16]. Copyright © ICE Publishing, all rights reserved. Proceedings.] HOPKINSOX ON ELECTRICAL RAILWAYS. 211 inother countries. Atthe conclusion of the discussion on his Paper on “the Bessbrook andNewry Tramway,” the Author expressed an opinion that enough had been shown to prove that the system of electrical traction with a continuous conductor was applicableto the great schemes of overhead andunderground railways in our large towns. An opportunity for a practical test soon afterwards presented itself. In the session of 1884, the City of London and Southwark Sub- way Company obtained Parliamentary powers for the construction of a subway from King TYillianl Street in theCity, to the Elephant and Castle in Southwark. Mr. J. H. Greathead was the engineer of the undertaking, and Sir John Fowler and Sir Benjamin Baker were the consul.ting engineers. In pursuance of theoriginal intention, contracts had been arranged for working the lines on the cable system, but the success that hsd attended the Bessbrook and Newry line, and the progress made in electrical traction in the United States and on the Continent, induced Messrs. Mather and Platt, of Rfanchester, to make definite proposals to thedirectors of the Company, for working the line electrically, and to submit designs and estimates. After a most careful investigation of the whole subject, during which various schemes of electrical working were considered, their plan of electrical working was adopted, and a contract wasmade with them in January,1889, for its execution. This contract provided for the supply of 14 locomotives to draw trains consisting of three carriages accommodating 100 passengers, andweighing 44 tons each, and thegenerating-plant was to be sufficient for working aservice of 20 trainsper hour. The contractors further undertook to work the line for a term of two years, or to guarantee the cost of haulage for a similar period, at the option of the Company. In October, 1889, a locomotive, the design of which is described below, was run experimentally on a short section of the line; and a few months later a second locomotive of a different type was experimented with-the original design being finally adopted. The works were formally opened by H.R.H. the Prince of Wales, accompanied by H.R.H. the late Duke of Clarence, on the 4th of November, 1890; and on the 18th of December, the line was opened for public traffic. It is no part of the Author’s intention to refer to the details of design of the City and South London line, except to such extent as may be necessary to explain the electrical working ; much less to deal with the system of constructing the tunnels, which has made the formation of such a railway possible ; but he proposes to describe as briefly as possible the electrical plant adopted, for the r2

Downloaded by [ Syracuse University] on [13/09/16]. Copyright © ICE Publishing, all rights reserved. 212 HOPUSON ON ELECTRICAL RAILWAYS. [Jfinutes of design of whichhe was responsible, andthe results obtained in working it. The line consists of two independent tunnels,formed of cast-iron rings.The sleepers are transverse, restingdirectly upon these rings,and the rails are spiked thereto, and leave a minimum headway of 9 feet from the rail-level to the highest point of the tunnel. Fig. I, Plate 5, showsa section of the tunnel and the space available. Where the linepasses under the Thames between Great Dover Street and Eing William Street, there is on the up- line o down-gradient of 1 in 30 for a distance of 264 feet, and an up-gradient of 1 in 30 for 462 feet, and on the down line a down-gradient, with the trafic, of 1 in 14, followed by an up- gradient of 1 in 30. Atother points of theline the gradients arenot severe, theprincipal being an up-gradient of l in l00 approaching St.ockwel1 Station.The total length of theline is 3 miles 270 yards. There are four intermediate stations.

GENERATOR-STATION,FIG.2, PLATE5. Thegenerator-station is situatedat Stockwell, at a distance of about 500 feet from that terminus. There were originally 6 boilers of Lancashiretype, each 28 feetlong and 7 feetin diameter, fitted with Vicar’s automatic stokers. The boiler-floor is 12 feet ci inches below the ground-level, and the boiler-house is roofed over exceptimmediately above the stoke-hole, so as to provide room for a fuel store. By this arrangement the fuel can be shovelled direct into the hoppers of the stokers. Two similar boilers have subsequently been added. The steam-pressure at the boilers is 140 lbs. per square inch. In addition to prdviding steam for the electric generating-engines, theboilers are requiredfor pro- ducing steam for the powerful hydraulic plant, and the auxiliary engines for the repairing-shop, the compressed-air pumps, and the hauling-engine for drawing the loco~notives and carriages up tllc inclined way connecting the Stockwell terminus with the depdt. The boilers are set on Livet’s principle, and are arranged in two groupsof four,withindependentfluesand chimneys. Noeconomizers are provided. The steam-pipes from the two groups are arranged so that either or both can be connected to the main pipes crossing beneath the yard to the engine-house, otherwise there is no dupli- cation of the steam-pipe system. The exhaust steam from all the engines passes by a single pipe through the water-heaters to the chimney. As there is no water available for condensing purposes, all the engines arenon-condensing ; steam-power, therefore, is not

Downloaded by [ Syracuse University] on [13/09/16]. Copyright © ICE Publishing, all rights reserved. Proceedings.] HOPKINSON ON ELECTRICAL RAILWAYS. 213 produced underthe most economical conditions. Therewere originallythree engines,each driving one generatingdynamo; the Company has since added a fourth similar engine and dynamo in view of the extension of the line to Clapham, and to meet the requirements of the Board of Tradeas to reservepower. The enginesare of thevertical compound open type; the cylinders are side by side, 17 inches and 27 inches in diameter respectively, and 27 inches stroke. The fly-wheels are 14 feet in diameter, and carriedbetween the cranks,which are of disk for'm. Both cylindersare steam-jacketed inthe barrels,with high-pressure steam, andare fitted with slide-valves, with cut-off valves on bothcylinders, controlled bythe governors. The engineswere builtby Messrs. John Fowler & Co., of Leeds. Theyrun at 100 revolutionsper minute, and are each capable of indicating 400 HP., and drive the dynamos with link-leather belts,which are provided with jockey pulleys to allow of the distance between the engineand dynamocentres being reduced withoutunduly diminishing the areaof contact on the driven pulleys. It is frequently asserted that the use of a jockey-pulley involves considerableloss of power in friction.Consider the dynamical problem of a chain moving longitudinally with tension T and velocity V. Let it be subjected to a transverse disturbing force, acting at afixed point and causinga deformation, which will generate two waves moving relatively to the- diameter in opposite directions along its length with velocity 2/ :, where m is the - mass of unit length of the chain. If V = one wave will 2/ r,m move backwards withthe velocity of the chain,and therefore remainfixed in- space, and the other will travel onwardswith 'T relocity 2 2/ m. A link-belt may be considered as such a chain, and a jockey-pulley- as the disturbingforce. If the belt move with velocity 4' and the jockey-pulley be placed on its slackside, one wave will be stationary in space, tendingto maintain the deformation of the belt round the jockey-pulley, and the other wave will move with twice the velocity of the belt towards the driven pulley, and will there be absorbed owing to the increased tension; thus the power absorbed is that required to maintain the single harmonic disturbance- only. Thecondition V = 2/ is easily attainedin practice. Let p

Downloaded by [ Syracuse University] on [13/09/16]. Copyright © ICE Publishing, all rights reserved. 214 HOPKMSON ON ELECTRICAL RAILWAYS. Pfinutes of bethe coefficient of friction between thebelt anCi thedriven pulley, 0 the angular measure of that part of the circumference of thedriven pulley embraced bythe belt, and T, and T, the tensions in the tight and slacksides of the belt respectively; T then 2 = e'', where p is the coefficient of friction between the T, pulley ind the belt. If the walre is stationary-

link-belt weighing 8 lbs. per foot is suitable for a working tension of 1.600 lbs.

= about 3,500 feet per minute, which is an ordinary speed for belting. GENERATIKGDrx-axos.

These are of the '' Edison-Hopkinson " type, with bar armatures 19: inches in diameter. The field-magnet coils are wound with both shunt andseries coils, but the lattercan be half short-circuited or entirely so, at will, by means of switches fixed on the dynamo. Each dynamo is capable of giving an outputof 460 amperes at 500 volts, runningat a speed of 500 revolutions perminute. The following are the electrical constants of the machines :- Ohms. Resistance of armature ...... 0.01';

,9 shunt coils ...... 96.0 Y, coilsserics ...... 0.015 The electrical efficiency at fullload is 96 per cent. The weight of the armature is 37 cwt. The weight of the entire machine ia 17 tons. Careful independent experiments were made upon the efficiency of conversion showing that the frictional losses amounted to 2 * 7 per cent. of thefull load. Hence the commercial full-load efficiency is 93.4 per cent.

SWITCII-BOARDS. The switch-board is arranged so that any of the four generators can be coupled to anyof the four feederseither independentlyor in parallel, and that any fresh combination can be instantly effected

Downloaded by [ Syracuse University] on [13/09/16]. Copyright © ICE Publishing, all rights reserved. Proceedings.] HOPEINSOB ON ELECTRICAL EAILWSTS. 215 without interruption of the working. The electromotive force of each dynamo is measured by a Kelvin electrostatic multicellular voltmeter,and the current passing through eachfeeder is measured by an ampere-meter. The leakage of any part of the entire system of conductors when subjected to the full potential can be measured by a special low rangeampere-meter. The feeders are provided with fusible cut-outs and quick-acting safety switches,which automatically throw a resistance into circuit if the current exceeds a certain amount ; the object being to prevent injury if an accidental short circuit should take place on any part of the system. CONDUCTORS. From the switch-board there are four feeders, two of which are connected to the workingconductors at Great Dover Street station, D distance of 12,800 feet from the generating station. The other two are coupled in parallel as faras Stockwell, and one is continued to the Oval, where it is connected to the working conductors at a distance of 4,330 feetfrom the generator-station.The cables, which were manufactured by the Fowler-Waring Company, and consist of a stranded core of 61-14 B.W.G., insulated and sheathed with lead,have an insulation resistance of not less than 500 megohms per mile. They are carried along the tunnels supported on the brackets carrying the hydraulic pipes (Fig. l, Plate 5). The working conductor is similar to thatadopted by the Author for the Bessbrook and Newry Tramway, and consists of channel steel laid between the rails and carried on glass insulators fixed to alternate sleepers. The channelweighs 10 lbs.per linealyard, and was rolled from mild ductile steel of special composition. The suitable proportions of carbon,silicon, and manganesefor steel conductorshave already been discussed bythe Aut11or.l By eliminating the silicon and slightly diminishing thecarbon, a steel was obtained having a specific resistance as low as 0*0000105ohm at 24O Centigrade, although the amountof manganese allowed was somewhatincreased. This corresponds to aresistance of 0.0503 ohm per 1,000 feet. It,will be observed that the level of the conductor is 1 inch below that of the rail-level. This necessitates arrangements for the lifting of the collectors over the crossing-rail at points. The conductor is broken on either side the crossing-rail and replaced by inclined planes of wood, up which the collectors slide till raised to a level of 1 inch above the crossing-rail, which passes through a gap left in the wooden runners. The collect.ors

~~ l Ninutes of Proceedings Inst. C.E., vol. xci. p. 208.

Downloaded by [ Syracuse University] on [13/09/16]. Copyright © ICE Publishing, all rights reserved. 216 HOPRIXSON ON ELECTRICAL RAILWAYS. Winutes of cross the gap at an angle, and are wide enough to bridge it. AS each locomotive is provided with three collectors, the continuity of the circuit is never broken, as the leading collector makes contact with the steel conductor in advance of the break before the trailing collector leaves the conductor behindthe break. The conductor is also divided into sections, and arranged so that any section can be coupled through automatic cut-outs to the adjacent sections or independently to the’ feeders. Thus any section can be isolated for the purpose of testing or repairs, and is automatically disconnected in case of any accident causing a shortcircuit to earth. The return circuit is through the rails, which are practi- callyuninsulated. In such a systemhigh insulation from the earth is neither aimed at nor required, provided the power lost inleakage is inconsiderable. Theactual leakage on theentire system, consisting of dynamos,feeders and working conductors, tested at 500 volts pressure, is generally about 4 ampere, corresponding with a loss of 0.3 horse-power, and rarely exceeds one ampere under the most unfavourable atmospheric conditions. The use of the uninsulated rails as a return, although contact is made at an average depth of 60 feet below the ground surface, causes differences inearth potential, whichare appreciable at considerabledistances. Continuous observa,tions of difference in the earth’s potential between two points approximately north-east and south-west of Greenwich, anddistant 3 miles fromeach other,and alsobetween twopoints approximately north-west and south-east of Greenwich distant 2& miles apart, are recorded at the Royal Observatory. The former of these lines is parallel tothe general course of theCity and South London line at a distance of 44 miles, and the latter almost at right angles, the nearest point being 2$ miles distant. It has been observed that alongboth lines differences of earthpotential varying from a sinall fraction of a volt up to 4- volt occur simultaneously with theworking of therailway, and that the magnitude of the potential differences are approximately the same in both circuits. Theseobservations show thatthe earth is of small value as a channel of return for large currents. As the disturbance is very erratic, and apparently has no definite direction, it is impossible to deduce any conclusions as to the resistance of the earth to the passage of large currents.’ Observations have also been made on the magnetic disturbances -__ See a communication to Nature, by Mr. W. Ellis, with thepermission of thc Astronomer Royal. Nature, vol. xxiv. p. 129; also AnnualReport of the Astronomer Royal, 1892, p. 15.

Downloaded by [ Syracuse University] on [13/09/16]. Copyright © ICE Publishing, all rights reserved. Proceedings.] IIOPKINSON ON ELECTRICAL RAILWAYS. 217 caused inthe immediate vicinity of therailway, due to the electricalworking. Professors Ayrton and Rucker erecteda magnetometer in a house situated above the tunnels, and recorded readings at distances of 92 and 212 feet respectively from the line. Their observations are not expressed in absolute measure, but showed the disturbances to be considerable in comparison with the normal intensity of the earth's magnetic field, and that they were approximatelyinversely as the square of the distance from the line.' It is difficult to account for these magnetic disturbances, as the currentflowing in the steelconductor would magnetize the iron of the tunnel circularly, and the tunnel itselfwould mask disturbances dueto the passage of the motors. It would appear more probable that they arise from the return currents flowing through the earthoutside the tunnels, which theobservations at Greenwich show to be considerable. In this connection it may be noted that the tunnels do not in themselves form a complete metallic circuit, being broken by the brickwork at thestations, but at these points they are electricallyconnected by copper cables ; the rails arealso connected one to another bycopper strips in addition to the ordinary fish plates. Although the Author must admit that such disturbances, however insignificant, are inconvenient in the immediate neighbour- hood of physical laboratories, they possess in themselves scientific interest; and in the case of the City and South London line they are not of sufficient magnitude to be of practical importance in connection withthe working of thetelegraph and telephone systems in the vicinity. In evidence before the Joint Committee, Mr. Preece stated, as the result of many experiments, that he had been unableto trace any disturbance of the Metropolitan tele- phones, or to the working of the telegraph lines, arising from the passage of the trains. In theReport of the Joint Committee previously alluded to, the attention of the Board of Trade is drawn to a memorandum, pre- ,paredby Lord Kelvin, one of the members of the Committee, dealingwith certain conditions withregard to the working potential and the position of the conductor to be observed in the case of the several Metropolitan Electric Railway schemes under their consideration. This memorandum recommends that if the working conductor is maintained at a pressure exceeding 500 volts, it shouldbe carried overhead. Suchwas the original intention inthe caseof theCity and South Londonline; but it was found to be impracticable on account of the exceedingly limited See a Paper read before the British Association, 1891.

spaceavailable for such a conductorabove the carriages. This will be seen by reference to Fig. 1, Plate 5, but even the space there shown is still further reduced on the curves. With the con- siderably larger tunnels now projected(in no case less than 11 feet 6 inches inIdiameter), this difficulty will not occur. On the other hand, it should be observed that since the opening of the South London line there has not beena single instance of injury to the public from shock ; and no complaint whatever has been made by the publicof danger in thisrespect. Such also has been the experience on the Bessbrook line, where the potential is but littleless, and the conductor is practically entirelyunprotected. The Author ventures to think that mechanical facilities of treatment at points and crossings which an overhead conductor affords, is a stronger argument for its adoption than the publicsafety. The methoas already described, of dealing with the conductor on the South London lineat the pointsand crossings,have proved entirely satisfactory inpractice; but exception may be justlytaken to them on the ground that they arenot universally applicable.

LOCOMOTIVES,FIGS. 3 AND 4, PLATE5. The essential feature in the design of the locomotives is that thearmatures of the motors arebuilt directly upon the axles, while the magnets are supported partly on the axle and partly on the frame. Thus gear of any description is entirely obviated, and the mechanism is reduced to its simplest elements. Although this principle of direct driving was suggested many years ago by the late Sir William Siemens, it has not previously been applied in practice. The field-magnetsembrace thearmature, leaving but an exceedingly narrow " gap," and are supported in part by bracketsparallel to the axle with bearings upon it, and partly by links connecting the yoke to a cross-beam of the locomotive frame, thuspermitting limited freedom of angular motion of the field round the axle,compensating for therise and fall of the axle-boxes inthe horn-blocks (Fig. 3). Theweight of one axle with its wheels,axle-boxes and springs, and with the armature attached, is 24 cwts., and the part of the weight of the magnets resting on the axle is 10 cwts., whence the total dead weight on each axle is 34 cwts. In ordinary locomotive practice, where the speeds are much greater, and the permanent way more elastic, the deadweight, including wheels,cranked axle, axle- boxes, springs, eccentrics, and the large ends of the connecting- rods, is much greater, and there appears to be no reason why the

Downloaded by [ Syracuse University] on [13/09/16]. Copyright © ICE Publishing, all rights reserved. Proceedings.] HOPKINSON ON ELECTRICAL RAILWAYS. 219 limit allowed in the case of ordinary steam-motors is not per- missiblefor electric-motors; in fact, the perfect freedom of the axlelaterally, and the fact that the two driving-axles are not coupled, but have entire freedom of motion relatively, together with the consideration that the forces acting on the axle, apart from itsweight, constitute a pure couple wibhout anythrust, make it probable that a much higher limit of dead weight may be safely allowed in a system of electric-motors, so applied, than in the case of ordinary steam locomotives. It has, however, been contended that the vibration must have an injurious effect upon thearmature. In reply, it is sufficient to pointout that the experience of two years’ working has not revealed a single case of deterioration of an armature, which can be attributed t,o this cause ; and the bearings supporting the field-magnets have shown no signs of undue wear. Geared traction-motors have the following advantages, real or apparent, over direct-acting motors :- (l) The introduction of gear allows the use of a motor running at amuch higher speed than the axle,consequently the motor itself is of less weight, occupies less space, and is less costly. (2) The weight of the motor can be taken almost entirely on the springs insteadof acting directly on the axle. (3) The motor runningat a higher speed isin itself, when considered irrespective of the gear, of higher efficiency. (4) The dimensions of the motor are not directly limited by the gauge of the line and the diameterof the driving-wheels. The first argumenthas much force in tramway-work. Here reduction in weight and in bulk are of the utmost importance. As the whole weight of thecar is available for adhesion, any reduction inweight is cleargain. Againthe motor must necessarily be placed entirely beneath the floor, and must often be combined with a bogie construction; hencereduction in the dimensions of the motor is frequently of primary importance. It is no doubtthese two considerations, combined withreduction in first cost, which have led to some form of gear being almost universally adopted on the American tram-lines;but it isin- terestingin this connection to note thatthe leading American construction-companies have abandoned motors with double- reductiongear forsingle-reduction gear;thus proving, asthe result of extended experience, that the wear and tear and loss of efficiency ingear more than counterbalances theadvantages of reduced weightand bulk, when carried beyond certain limits. On the other hand, in the case of independent locomotives, the

consideration of weight in general entirely loses its force ; as the naturalweight of the locomotive, whatever form of motor be adopted, isnot more than sufficient for adhesion, and the form of the motor is not restricted by consideration of clear floor space. The second argument has already been dealt with incomparing the dead weight on the axles on theSouth London linewith ordinary locomotive practice; but here, again, it is of interest to observe that, although with thesystem of gea.r adopted,in America it is quite feasible to remove the dead weight almost entirely from the axle, it is not found necessary to do so. The Short Company of Cleveland, Ohio, have recently worked out devices for spring- connections betweenthe axle and the armature, while still retaining theprinciple of directdriving. Their system hasalready been adopted on a number of lineswith satisfactory results. The interposition of springs may be advantageous for rough roads, but it yet remains to be proved by exhaustive trial that the simpler form, with the armature keyed directly on the axle, is unsuitable even for ordinary street-tramways. A complete discussion of the third argument involves a deter- mination of efficiency of the different systems of gear available, sincealthough the high speed motor is initself more efficient than the slowspeed, there is loss of power in the gear, which may more than compensatefor thesaving in the motor. Consider a 20-HP. direct-acting motor with driving-wheels 30 inches in diameter. At 20 miles per hour the number of revolutions will be 224 per minute; theefficiency of a motor at this speed will not in general exceed 88 per cent., and the weight will be about 50 cwts. If such a motor acted through gear reducing the speed in the ratio of 3 : 1, the number of revolutions corresponding to a speed of 20 miles per hour is 672 per minute; at this speed the motor should be of not less than 96 per cent. efficiency, and will weigh with its gear about30 cwt. ; hence, if the efficiency of the gear is less than 96 per cent., there is no gainin the total efficiency. TheAuthor has no dataavailable as to the actual efficiency of the gear as realized in American practice, but it is not probable thatthe frictional losses inactual workcan be brought within 10 per cent. ; at least such is the result of his own experience bothwith spur-gear and chain-gear. Both Mr. Reckenzaun and Mr. Holroyd Smith have strongly advocated the adoption of worm-gear, and the former has made experiments on the efficiency obtainableby it, but his best results show an efficiency of less than 90 per cent. As regards the fourth argument in favourof other than direct-

Downloaded by [ Syracuse University] on [13/09/16]. Copyright © ICE Publishing, all rights reserved. Proceedings.] HOPRINSON ON ELECTRICAL RAILWAPS. 221 acting motors, it is sufficient to remark that the limits imposed on the dimensions of the latter have proved no bar to the construction of the 100-HP. locomotives on the South London line. Whether such willbe the case when locomotives of 300 to 400 HP. are required,it is beyond the limitsof the present Paperto discuss ; but the difficulty, if such it prove to be, can be met by increasing the number of driving-axles, or by the adoption of a different form of field-magnets-allowing thearmature tobe increased in diameter to the full diameter of t,he wheels, less what may be necessary for clearance. In order toobtain experience of therelative advantages of geared and direct-acting locomotives under the same conditions, one geared locomotive wasbuilt for theSouth Londonline. Though of the same power as the others, and yieldinggood results in experimental running, its relative value may be best gauged by the fact that it was soon relegated to the work of a stand-by engine, while the regularwork of the linewas undertaken entirely by the direct-acting type. To sum up, it appears that the balance of argument is infavour of direct-acting motors for both locomotives and street-tramway work;but that, with regard to the latter, experience isyet insufficient to warrant the formation of a final opinion. The two motors on each locomotive on the South London line are each capable of developing 50 HP. at a speed of 25 miles per hour, corresponding to 1310 revolutions of the axle per minute. The magnets are of the t‘ Edison-Hopkinson ” form, and series- wound;and the armatures are of the Gramme ringtype. The resistance of the magnet coils of each motor is 0.087 ohm, and of thearmature 0.3 ohm. Thetwo motors are connected elec- tricallyin series. Thecurrent from the conductor is conveyed from sliding collectors through a fusible cut-out and main switch to a rheostat-switch for inserting resistance at starting; thence it passes through a reversingswitch to the motors, andfinally through the axle-boxes and wheels to the rails of the permanent way. Themotor-magnets are proportioned relativelyto the armature precisely as in a dynamo, and are wound so as to be nearlysaturated with the mean workingcurrent. Above this point, the curve of tractive force and current is approximately a straightline, giving a tractive force of 1,180 lbs. with 100 amperes, and amaximum of 3,000 lbs. with 226 amperes. The trainsare fitted with the Westinghousecontinuous automatic brake, applied,however, in a novel mannersuggested by Mr. Greathead. In place of a pumpworking continuously on the

Downloaded by [ Syracuse University] on [13/09/16]. Copyright © ICE Publishing, all rights reserved. 222 HOPKINSON ON ELECTRICAL RAILWAYS. [l\linutes of locomotive, the latter isprovided with two reservoirs placed under the curved side-plates of the cab, each of about 8.25 cubic feet capacity. At the end of eachdouble journey these arecharged with air, at 80 Ibs. pressure, from a small reservoir erected at Stockwell, the pressure inwhich is maintained by two small pumps in the engine-house. The reservoirs on the locomotives are of sufficient capacity toprovide for about 30 stops from full speed. This system has proved both convenient in practice, and economical, thetotal amount of steamrequired for the brakes being about 1.5 per cent. of the entire consumption. In addition to the Westinghouse brake, a powerful hand-screw brake is fitted on each locomotive. The locomotives and carriages arelighted with glow-lamps, supplied direct from the conductor, an arrangement which has the merits of simplicityand cheapness, but is open to the objection that the light is necessarily subject to some fluctuation owing to the variations of the electromotive force of the”conductor. Thexfollowing are the leadingdimensions of the locomotives ; of which Fig. 3, Plate 5, shows a longitudinal section, and Fig. 4 a perspective view:- Feet. In. Length over central buffers .....14 0 ,, )) cab ...... 10 0 Wheel base ...... G 0 Diameter of wheels ...... 2 3 Gauge ...... 4 S$ Extreme widthExtreme of cab ...... G 3 .Height, rail-levelto floor-plate .... 2 5f ,, floor-plateto roof ...... G 0 Weight of entire locomotive, 10 tons 7 cwt. ,, ,, motors only, with wheels and axles, G tons. Of the 14 locomotives first supplied, 13 are of the direct-acting type and one is a geared locomotive. Since theopening of the linetwo additional locomotives have been furnishedby Nessrs. SiemensBrothers. In thesethe general features of the design described have been followed, but the armatures are of drum in place of the Gramme type. Mr. Alexander Siemens described the working of these locomotives before theBritish Association, in 1892, and gave a series of curves showing the relation between the speed, current and electromotive force at short intervds as observed on several runs under variedconditions. The whole of the electrical plant was constructed by Messrs. Mather and Platt,for whom Dr. John Hopkinson acted as consulting engineer, and Mr. G. Annesley Grindle as resident engineer; Mr. C. E. Spagnoletti acting as consulting electrician to the Company.

EFFICIEXCY. The discussion of the efficiency of an electric railway-system may be considered under three heads :- 1. The production of electric power. 2. The distribution of electric power. 3. The re-conversion of electrical into mechanical power. (1) It is unnecessary to enter into the details of the efficiency of the steam production, as the installation in thisrespect presents no distinctive features. The daily consumption of water for all power purposes is about 330,000 lbs., which is evaporated by the combustion of 21 tons of north country slack, including in this the fuel required for starting and banking thefires, i.e., 7 lbs. of steam at 140 lbs. pressure per pound of fuel, a result which may be considered as normal for aninstallation working under varying loads, and not provided with an economiser. The division of the steam-consumptionbetween the electric generating engines, the hydraulic engines, and other small enginesemployed on the works cannot be accurately determined,as all are suppliedfrom the same range of steam pipes ; but suffieient data have been obtained to show that from 60 to 67 per cent. of the total steam produced is absorbed by the electric generator engines ; representing a daily consumption of about 14 tons of north country coal. No direct measurements have been madeof the fuel-consumption per indicated HP.-hour of the engines, but a rough approximation can be made by calculating the average indicated HP. taken through the day from theaverage electrical output of thegenerating dynamos. This calculation shows that about 230 HP. is the average load on each engine, i.e., a little more than one-half of their maximum load. On this basis the water-consumption per indicated HP.-hour is 27 * 5 lbs. Probably no testshave beenpreviously made on enginesworking under the abnormal conditions of loada constantly varying at very short intervals from one-fourth, or a less fraction, of the full load, up to themaximum, and averaging a little more than one-half the maximum. It is not,therefore, possible to institute a comparison between this result and others; but it has been shown that with a Willans central-valve engine, which realises as high an efficiency as 18 * 25 lbs. of water per indicated HP.-hour, non-condensing, atfull load, the efficiency is reduced to 22 lbs. at half load and 36 lbs. at one-fifth load.1 The efficiency of the engines and dynamos combined was ascer-

1 Minutes of Proceedings Inst. C.E., vol. ovi. p. 67.

Downloaded by [ Syracuse University] on [13/09/16]. Copyright © ICE Publishing, all rights reserved. 224 HOPEINSON ON ELECTRICAL RAILWAYS. [&hnItcs Of tained by indicating the engines and measuring the electricalOut- put at the terminals of the dynamos, when working on a steady load. These experiments show an average efficiency of available electrical HP. against indicated HP. of-at full load, 78 per cent. ; at three-quarters load, 70 per cent. ; at half-load, G5 per cent. Somewhat higher efficiencies than these are constantly obtained with high-speed enginesdriving dynamos directwithout the intervention of belting. Mr. Crompton has stated the efficiency of the combination of an Edison-Hopkinsondynamo drivenby a Willans engine to be 86 -2 per cent. at full load, and 77 * 8 per cent. at half load; and that of a Crompton dynamo with the same engine 85 * 8 per cent. at fullload, and 78 1 per cent. at half load ; the dynamos beingin both cases of approximatelythe same efficiency as the generator-dynamos. The loss is therefore in the greater engine friction and in the belt. It is, however, doubtful, or at any rate, remains tobe proved, whether a high-speed engine driving direct will give as relatively satisfactory results, without undue wear and tearand liability toaccident, when working under the abnormal conditions of load obtaining in tractionwork. The daily consumption of electrical energy is about3,700 Board of Trade units, which areproduced from the combustion of 14 tons of coal, or 8.4 lbs. of north country coal per Board of Trade unit, corresponding to about 7 5 lbs. of Welsh coal per unit. The diagrams, Figs. l and 2, pages 226 and 227, show the quantity of current passing through the feeders at consecutive intervals, when seven and eight trains respectively are running. A momen- tary inspection of these shows at once the magnitude and rapidity of the mriations in load, which make the realization of a high load-factor impossible. Ifan efficient accumulator, capable of workingas a regulatorunder these conditions, could be intro- duced, it would be possible to reduce the capacity of the generating-plantby at least 40 per cent., and atthe same time con- siderably increase its efficiency. (2) The efficiency of distribution is not of generalinterest, as it dependssolely upon the resistance of the conductors. It is sufficient tostate that the average full load loss inthe long feeders runningto Great Dover Street is 5.7 per cent., andin the short feeders 3-5 per cent. Thusthe total loss in the feeders is 9 * 2 percent. Thedistant feeders areusually coupled to a generator-dynamo working full-compound, while the home-feeders are connectedto a generatorworking half- compound, thus compensating for the loss of electromotive force illinutes of Proceedings Inst. C.E.,~vol.cvi. p. 31.

in the feeders. The loss in the working conductorscan onlybe estimated from the average current in each section and the known resistance. It probably does not exceed 1 percent., making the total loss in distribution a little more than 10 percent. of the total electrical power generated. This represents a daily expenditure of fuel of about 13 ton of north country coal, which is almost the exact equivalent of the interest on 57,000, the actual cost of the conductors. Thusthe continuingcost of distributionis a minimum. (3) The efficiency of the motors with known electromotive force and current is easily determined, but it is of greater interest to ascertain the average efficiency of the locomotives as a whole, while working under the constantly varyingconditions of speed, load, and electromotive force. By a statistical method this may be ascer- tained with fair accuracy.Observations were made at intervals of ten seconds on locomotives with varying loads running in the regular service to ascertain the current and speed at each interval. Theseresults were plotted in twoseries of curves, with time as abscissa and current and speed as ordinates. Since the counter- electromotive force1 of the motors depends only upon the current and speed, and can be determined directly from the characteristic curves of the motors, when these elements are known; a second series of curvescan be drawnwith the counter-electromotive force as ordinates and time as abscissa. These can be integrated to givethe average counter-electromotive force. Simultaneous observations were made onthe electromotive force at thegenerator dynamos, and were in like manner integrated to give the average electromotiveforce. Theratio of the averagecounter-electromotive force tothe averageelectromotive force atthe generators is the electrical efficiency of theentire system. The results of a number of such observations, made’at different times with train-loads varying from 35 to 40 tons, are in close accord- ance, and show the electrical efficiency of theentire system to be about 62 per cent. It hasalready been shown thatthe loss inthe conductors is a little over 10 percent., hence the average electrical efficiency of the locomotives is 70 per cent. In the 30 per cent. lost, the power absorbed in the starting resistance

The terms ‘‘ counter-electromotive force” or “ back-electromotive force” are not satisfactory, but are used in dcfault of any authoritative nomenclature. Let E be the electromotive force at the terminal of R series wound generator or motor, R the resistance of magnets and armature, and C the current; thcn E + E C is commonly known as the “trueelectromotive force ” for a generator, and - R C as the “ counter-” or ‘cback-elect,romotive force” for a motor. [THE INST. C.E. VOL. CXII.] Q

Downloaded by [ Syracuse University] on [13/09/16]. Copyright © ICE Publishing, all rights reserved. 22 6 HOPEINSON ON ELECTRICAL RAILWAYS. [Minutes of is included,and probablyaccounts for about one-half. Various devices have been proposed in order to reduce this loss. Dr. John Hopkinson, in 1881, patented a nlcthod of throwing the twomotors into series atstarting, and into parallel circuit as the speed increases;and others have suggested varying the effective con- volutions on the magnets; but such devices, although reducing tlae loss, do not entirely obviate the need of starting-resistances. Moreover, they involve complications in the switching-gear, and the simplicity of the simpleresistance appearedto the Author to more than counterbalance any small increase in efficiency. Fias. 1.

100 200 300 400 SO0 600 700 800 900 I 30 SE( )NW (a) Curve from ithC7Lilw working Full Compound.

100 200 300 400 so0 600 700 800 so0 moo SECONDS (b) Curve from Naehine working Half Compound. SEVENTRAIXS AND Two SHUNTIX-ctLOCOMOTITES. These results, obtained in actual practice, fully substantiate the estimates of efficiency given in evidence before the Committee on The Central London Railway Bill by Sir Benjamin Baker andDr. John Hopkinson. Theformer stated, before the Select Com- mittee of theHouse of Lords, in 1890, thatthe efficiency as between indicated power and effective power on the railswould be from 50 to 60 per cent., assumingthat the load wasfairly averaged, so that the generating-plant worked at approximately full load, and the motors at their proper efficiency. This result would have been attained on the City and South London line if the service of 20 trainsper hour, as originally contemplated,

Downloaded by [ Syracuse University] on [13/09/16]. Copyright © ICE Publishing, all rights reserved. Proceedings. J HOPEINSON ON ELECTRICAL RAILWAYS. 227 had been carried out, and the loaded trains had not exceeded their specified weight. Owing to the actual weight of the trains being over 40 tons, arising from the fact that the carriages weigh over 7 tons each, instead of tons, as specified at the time the electrical plant was designed, the service has been reduced to fourteen or sixteen. trains per hour, and the motors are much overloaded, thus working at an efficiency materially less than they would do, if worked with the loads for which they were constructed. From the Ffae.8.

EIGHTTRAINS AND Two SHUBTINGLOCOMOTIVES. foregoing analysis, it appears that the efficiency of the generating- plant would have been 78 per cent., and the locomotives would have been of at least 80 per cent. average efficiency, including all losses in resistances and otherwise. Takingthe loss inthe conductors as usually observed, thetotal efficiency as between indicatedpower and effectivepower would thus havebeen 78 80 90 - X - X - = 56.2 per cent. 100 100 100

Downloaded by [ Syracuse University] on [13/09/16]. Copyright © ICE Publishing, all rights reserved. 228 HOPEISSON ON ELECTRICAL RAILWAYS. [Ninutcs of Again, Dr. John Hopkinson, before the Select Committeo of the House of Commons on the same Bill,estimated, under similar conditions, the loss between the power actually absorbed by the generating dynamos and the effective power of the locomotives as 33 per cent. With generators as efficient as those of the Edison- Hopkinson type employed for the SouthLondon line, theefficiency betweenelectrical power delivered from the dynamos andthe power absorbed by them is 93 per cent. ; hence the efficiencyof the 93 90 80 entire system as defined wouldbe X -- X - = G7 per loo 100 100 cent., which is in exactaccordance with the evidence quoted. Although the analysis of the efficiency of the several compo- nentparts of the system may be of interest to theengineer engaged in thedesign of railway plant, thefinal question remains : what is the expenditure of fuel per mile run ? On theSouth Londonline, theaverage speed of working, including intermediate stoppages, is 11 *5miles per hour, and of actual running between stations 13.5 miles per hour. The maximum speed attained between stations mries from 20 to 25 miles per hour. Theweight of anormally loaded trainis 40 tons. The daily mileage fur the half-year ending June 30, 1892, was 1,120; hence the consumption of fuel per train-mile is 28 lbs. of northcountry coal, equivalent to about 25 lbs. of Welsh coal. Thisresult compares veryfavourably with the best results of American tramway practice, having regard to relative loads and speeds. COSTOF WORKING. The following Table, extracted from the half-yearly returns of the Company, shows the total cost of locomotive power, and t.he train-mileage from which the cost pertrain-mile is deduced. It will be seen that for the half-year endingDecember 31st, 1892, it is 7.1d. per mile. Whilstthere is a continued increase inthe mileage, the workingexpenses show a continuous decrease, a result due to the management of Messrs. Basil Nott and T. C. Jenkin, who arerespectively engineer and general manager to thecompany. The contractors’ parantee of working cost was 3-5d. per train- mile, for a service of 14,800 train-miles per meek, and 6.3d. for a service of 8,247 milesper week, as actuallyrun. This figure included theentire cost of runningthe generating-plant, i.e., supervision,fuel, stores, wages, andrepairs; also the cost of maintenance of the conductors and locomotives, but was exclnsire of the drivers’ wages. These latter at present average about 2d.

Downloaded by [ Syracuse University] on [13/09/16]. Copyright © ICE Publishing, all rights reserved. Procecdiugs.] IIOPEINSON os ELECTRICAL ~AILWBTS. 229 pertrain-mile, hence theactual cost of working, exclusive of

drivers' wages, is 5 6 Id. per train-mile, against6 * 3d. per train-mile

Half-Pear endit~g - I 1 June 30, 1891. Dec. 31,1891. ! June 30,1892. 1 Dec. 31, 1892.

! Wagesconnected with ! working the generat- 3,403 16 10 (3,2581 9 12,720 S 1 3,588 12 G engines . . . .I l Fuel ...... 2,054 4 10 ~1,98518 6 1,970 19 4 2,li2 0 9 Waterand gas . . ' ' 9 0 9 . 251 5 6 263 253 11 0 252 9 Oil and stores . . . 18 1 415 :I i l1 ~ 2 1 I 371 G 434 4 ~ 455 I l Repairs and Iie~~eccctl~., Wages . . . . . ' 150 0 0 26 3 9 205 0 0 210 0 0 Materials . . . . 223 2 1 25i 15 10 ' 289 3 1 ~ 193 13 0 ~ Total . . . . ,6,587 3 4 ~6,19912 11 16,035 2 11 ~6,348 4 8 Totalelpenses of runningon,y .})6,14S 9 3 15,859 7 10 !5,360

Train-mileage . . . ~ 154,435188,666 1 1SS,914 ~ 214,417

7.8d. ~ $.;

guaranteed.Thus the actual cost is less, by 20 per cent., than the contractors' guarantee,although the trains are 30 percent. heavier than the weightupon which their guaranteewas founded. Since the opening of the line two years ago, the locomotives have run more than 820,000 miles, and have provided for a traffic of over 12,000,000 passengers;and the yearly mileage of each locomotive in regular runningexceeds 30,000 miles. The growing popularity of this new means of locomotion is abundantly proved .by the steadily-continuedincrease in the numberof passengers and traffic receipts. The Paper is accompanied by six tracings, from which Plate 5 and the Figs. in the text have been prepared. [ ArrExDIx.

APPENDIX.

BESSBROOKAND NETRY ELECTI~ICTI~AMWAY.

- ' Tonnage. 1 Mileage. Passengers.

~~ ~~~ ~ ~ ~~~ ~ ~~____~~ ~ 1886 ...... 12,238 1 19,872 97,636 1887 ...... 13,464 l 19,212 81,275 ...... 14,92820,37685,450 1888 1889 ...... 17,055 1 85,97820,424 1890 ...... 20,47816,173 1 92,447 ...... 15,852 1 21,46894,1651891 Total ...... 1 89,710 i 121,830536,951 l

Cod of haulage for year 1891. € S. d. Wages(drivers, guards, anddynamo engineer) ....123 12 G Maintenance andrepairs of electricalmachinery, materials 60 64

99 >P 9, mazes18 . 23 9 Oil,grease, and waste ...... 9 26 Waterrent ...... 128 11 0 -__ Total ...... C345 14 9 Train-mileage, 21,468. Hence cost pcr train-mile, 3.94d.

ELECTRICALTRAMWAYS IN THB UXITEDEINGDON.

jPortrushand Giant) 1883 Sideconductor Water-power. ( Causeway ...J . . ! 1883 BrightonBeach . . Rails ..... Gas-engine. . Bessbrook and Nemryi 1885 { Tramway ...J Central conductor . Nater-power. 1886 Ryde Pier .... Sideconductor . . Gas-engine. 1886 Blackpool .... Conduit ....' Bteam. I

1889 Carstairs .... Sideconductors . ~ Water-power. 1890 Birmingbam ... Accumulator . . 1891 ' SouthendPier . . Centralconductor . Steam. 1891 I Guernsey .... Overheadconductor l1 ,,

~ 1891 7) ~ ,, 1893 I " i "

. GENERALVIEW OF LOCOMOTIVE

SECTION OF TUNNEL BETWEEN CITY & "ELEPHANT & CASTLE". Fys: 2.

GENERATINGSTATION

l i I i

LA_._._._