Part 3

The Eastbourne station is also on the transformer system. An alternating current dynamo, by Ellwell Parker, maintains a pressure in the primary circuit of 2000 volts, which is reduced by means of a Lowrie Hall transformer to a working pressure of 100 volts. There is a special arrangement for maintaining a constant electro-motive force in the mains, independent of the number of lights in use. The mains are carried underground, and have so far given no trouble as regards the insulation of the high-tension current which passes through them. The Eastbourne company commenced by lighting the parade only with arc lamps, but now supply the incandescent light to all parts of the town, and enjoy the unique position of having obtained power from the corporation to run the mains in the streets prior to the passing of the Act of 1882. Another small station has been successfully worked for the last six years at Brighton; the group system was originally adopted, the lamps, both arc and incandescent, being placed in series or multiple series; the high-tension current is led through overhead wires in a very similar manner to the installation at Temesvar, Hungary, which is described at page 58, as an example of multiple series lighting. The extensions at Brighton are to be carried out on the transformer plan, which will necessitate the running of separate circuits, the intention of the company, however, being to gradually convert its whole system of supply to the transformer system. The Brighton Company has regularly paid dividends to its shareholders since its formation.

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On the Continent the Goulard transformer is largely employed.

An important installation at Tours of 3500 lamps has been for some time successfully working. Another at Tivoli has some additional points of interest, in that the natural power of a waterfall is applied to generate electricity. Two turbines constructed by Escher Wyss, of Zurich, having an available head of 29·75 feet, give 80 horse-power each, which is employed to drive two Siemens alternating current dynamos, separately excited by two small continuous current machines. Two distinct circuits of chromo-bronze naked wire, 3·7 millimetres in diameter, are run overhead, in the same manner as telegraph wires, through the town for a total length of about nineteen miles. The street lamps are fixed alternately on each circuit, so that one-half can be extinguished at a late hour without interfering with the others, or having to turn out individual lamps. The number of lamps used in the streets is two hundred glow lamps of 50 candle-power; also one hundred and twenty glow lamps of 16 candle-power for the illumination of the narrower streets. Arc lamps are also employed, as well as a large reflector lamp, the rays from which are turned on the Temples of Vesta and Sibilla. A house-to-house system is also being established, and the company which has put up the work proposes to utilise the falls of Tivoli in order to transmit 2000 horse-power for lighting purposes in Rome.

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The firm of Ganz, of Budapest, who are the manufacturers of the Zippernowsky-Deri-Blathy system of transformers, have a similar installation completed in order to light a portion of Lucerne. The water power of Thorenburg 3·1 miles off, works the turbines, which drive two self-exciting alternating current dynamos of the Ganz type, similar to those shown at the Vienna Exhibition in 1884. The primary current of 38 ampères, at an electro-motive force of 1800 volts, is led by four uncovered wires, each six millimetres in diameter, to the first station, which is 2·4 kilometres distant; here 1500 watts are taken off, and at 2·3 kilometres further 7000 watts are utilised in two of the hotels at Lucerne. A large installation on the same system has been put down in Rome, and several Continental cities are adopting this method of supplying electric light by small overhead wires. An advantage claimed by the Zippernowsky system is the method of keeping the strength of the magnetic field of the dynamos in accordance with the external demand for current. The regulating apparatus employed consists of a small transformer, the primary coil of which is traversed by the whole, or by a proportionate part, of the main circuit, while the secondary coil is inserted into the exciting circuit. Thus, if the main current increases, the exciting current induced in the two armature coils of the dynamo is reinforced by the inductive action of the regulating transformer; and the field of the dynamo is strengthened when more current is required. The opposite takes place when, through the extinction of lamps on the external circuit, the demand for current becomes less. In an experiment made with the transformers, which supply some five hundred electric lamps for the Teatro dal Verone and adjoining houses at Milan from the central electrical station three-quarters of a mile away, the main current was often found to vary from one ampère to thirty-five ampères; it was stated that no variation in the service pressure could be detected, and the lamps burnt with equal brightness whatever the number in use. In the experiments at the Teatro dal Verone each transformer worked its own independent circuit of lamps; but, if the conditions of the different circuits were alike, they could be coupled up together in any manner desired, and thus a group of transformers could become a centre of distribution.

THE WESTINGHOUSE SYSTEM.

The alternating current system of the Westinghouse Company has come to the front in the United States with extraordinary rapidity, and, although it is not three years since the first plant was erected, at the present time over 190,000 incandescent lamps are operated from a number of central-stations. The fundamental principles of the Goulard system have been retained in the Westinghouse converter; but the manner in which these principles are applied has been greatly modified, while most of the details have undergone a radical change at the hands of the engineers and electricians whose researches have been utilised by the Westinghouse Company. The form of converter as now designed consists of a number of thin sheet-iron plates, shaped like the letter =E=, they are slipped alternately from opposite directions over the primary and secondary coils, which are disposed side by side; the inductive core is, therefore, composed of a mass of detached plates insulated from each other by paper, and forming a discontinuous magnetic circuit. In order to protect the converter from mechanical injury as well as dampness, and also to avoid the possibility of contact with wires carrying currents of high potential, it is enclosed in a cast-iron case or box, made in two parts and adapted to be secured to any convenient support. Fig. 12 is a transverse vertical section of such a converter box, with the converter in position. The terminals of the primary coil, P, of the converter are led into the compartment D¹, and the terminals of the secondary coil into D². The terminals are secured to bolts or couplings, _f f_, mounted upon insulating plates, _e_¹ and _e_². Fusible mica-foils, _g_, and switch plates, _h_ and _i_, with plugs _k_, are provided for protecting and disconnecting the circuits. The open front of the compartments D¹ and D² are closed by glass plates, T, which permit inspection of the connections without entering the box. The converter box occupies little space, and may be placed in any convenient situation in or about the premises to be lighted, much the same as a gas-meter. The practice where overhead conductors are employed, is to mount the converter box on a pole in the vicinity of the premises to be lighted, as shown by Fig. 13, and thus it is only necessary to lead the secondary or low potential wires into the building, the high potential wires remaining in an accessible position upon the pole. Fig. 14 is a view of North Street, Pittsfield, Massachusetts, engraved from a photograph, and shows a very neat form of tubular pole with its converter box on top. This arrangement is used throughout the city, and is a great improvement on the ordinary form of telegraph poles which so greatly disfigure American cities, and are really the most objectionable feature of the overhead wire system.

The potential ordinarily employed in the main circuits of the Westinghouse installations is about 1000 volts, and that in the lamp circuits 50 volts, the ratio of conversion, therefore, being as 20 to 1; the dynamos are manufactured, as a rule, in three sizes, No. 1 for 650, 16 candle-power lamps; Nos. 2 and 3 for respectively 1300 and 2500 lamps. The converters are also made in three ordinary sizes to supply 20, 30, and 40 lamps of 16 candle-power each. A 40-light converter contains about 85 pounds of iron and 25 pounds of copper, so that the total weight of metal is less than 3 pounds per lamp; the electrical efficiency of the converter is said to exceed 95 per cent. when the potential is reduced from 1000 volts in the primary to 50 in the secondary. “It is claimed that the trifling loss of energy in conversion from high to low potential at the point of consumption is made up for by gain at other points, especially in the increased efficiency of the lamps, so that an alternating current plant may be counted on to give 10-16 candle-power lamps per indicated horse-power, as against 7 with the direct system;” the comparative gain is doubtful, but by using 50 instead of 100 volts the life of the lamps is increased, the former having a much stronger filament and consequently a longer life.

ELECTRIC MOTORS.

Having slightly diverged from the original lines by describing a system which is at present not introduced into Europe, a few remarks on the subject of electric motors may not be inappropriate, as they are almost universally worked in the United States, from the installation which supplies electric light. There is a considerable profit to the electric company if electric power is taken in the district, the wires conveying the lighting current are thus economically employed during the day. In the diagram, Fig. 15, which represents a district at Boston, the curve on the right principally represents the demand for power which takes place between the hours of 8 A.M. and 3 P.M. A circular was addressed to all the leading electric companies in America a short time ago, asking if they supplied power as well as light, also for what purposes it was used.

Answers were received from 56 companies, who stated that the motors were employed for:—driving ventilator fans, collar-and-cuff machines, printing-presses, various apparatus in repair-shops, sewing-machines, coffee-mills, gun-shop tools, sausage-machines, elevators, lathes, pumps, saws, ice-cream freezers, organ-bellows, and washing-machines. The size of motors varied from one-eighth to 15 horse-power; 26 companies have supplied motors from arc light circuits, 14 from arc and incandescent, and 16 from incandescent circuits alone. The motors are principally owned by the subscribers, and are charged for at a rate varying from £3 to £15 per horse-power per month. The motor business is still in its infancy, but is cited to show how Electric Power can supplant the steam-engine, especially for those purposes in which the power required is small and complete control is desirable.

CLASS II.

THE EDISON PARALLEL SYSTEM, WITH CONTINUOUS CURRENT.

It will be found, on examining Appendix II., that in European stations by far the larger number of lamps are maintained from installations employing the Edison system; the Ferranti plan of using transformers comes next, closely followed by Goulard and Zippernowsky; the distribution with secondary batteries follows, and the high-tension multiple series comes last.

The Edison system has frequently been discussed, in connection with small installations, but in magnitude the stations in Berlin and in Milan exceed anything that has been started here with continuous current.

Before describing the central electric light station at the former city, it may be well to recall to mind that the Edison plan is the combination of a number of machines which pump electricity into a network of feeders, mains, and conductors, the lamps being placed in parallel circuit, as shown at L _l_, Fig. 16, and maintained at a constant potential of 110 volts.

M M′ are the flow and return mains, the dynamos bridging them across at one end. If the mains were very long, those near to the dynamos would be exhausting the supply, and the lamps at the remote end would not get the full pressure. A system of feeders has been devised so that each lamp, no matter where it may be, shall have approximately the full 110 volts working through it. Fig. 17 shows a long circuit consisting of two branch mains bridged by a large number of lamps, _l l_, and D D are the dynamos at the central-station. Series of feeders, _f f′_, have to be taken from the dynamo mains and fed direct into the branch mains at various points, _d d′_, _b b′_, _c c′_, in order to distribute the electrical pressure equally.

THE THREE-WIRE SYSTEM.

The ordinary parallel system is undoubtedly suitable for small installations; but when the area to be lighted is extensive, it is impossible to proportion the mains, with a view to economy in the cost of copper, without sacrificing energy wasted in heating the conductors.

In Figs. 16, 17, the lamps are shown in simple parallel; but if two dynamos are connected together, and a main wire is run from each of their two extreme terminals and a third wire from the branch connecting the two machines, we have what is known as the three-wire system, which was invented by Edison in America, and Hopkinson in England, almost simultaneously. Although by using the third wire there is a saving in copper over the parallel plan, the maximum gain is not more than 25 per cent., under the best conditions; when the district to be illuminated is not more than 400 to 600 yards from the central-station, the three-wire system answers well, but as soon as this distance is exceeded the cost of the mains begins to mount up at a most alarming rate. Although there are many Edison installations in the United States on this system and a few on the Continent, it has only been used here in a few instances for factory lighting.

THE EDISON SYSTEM AT MILAN.

The Santa Radegonda station at Milan is at the present moment the second largest Edison station in Europe. The building, which was formerly a theatre, is well adapted for the work required; the dynamos and engines are fixed in a deep basement, while the boilers are a few feet above the street level, the upper floors being used as stores and testing-rooms. The dynamos, eight in number, are of the old Edison type, with horizontal magnets; seven of these machines are connected to the feeders which supply the mains, and these cover the district to be lighted on the Edison network system. The motive power is furnished by six Armington-Sims, and two Porter-Allen engines, each connected direct to the armature of a dynamo, the speed being maintained at the uniform rate of 350 revolutions per minute, except in the case of the spare engine and dynamo, which is kept turning slowly, ready to be switched on should occasion demand. The starting or cutting-out of circuit of these large machines requires some care. In the first place, to start, it is necessary to insert resistance into the shunt circuit of the dynamo, which is done by a switch; but to throw 150 horse-power into the main circuit would be dangerous to the lamps, so that the current is first sent into a bank of one thousand lamps used as a resistance, and these are cut out step by step; similar care is taken when a machine is stopped. To control the electro-motive force, which varies greatly from time to time, hand regulation is used during the day, with the help of the Edison tell-tale, consisting of two lamps, a red and white one, which light up when the current is high or low; but when the night service comes on, as it may happen that two thousand lamps may be turned out at once, an attendant has to carefully watch the electric regulator, and be ready to insert resistance into the field-magnet circuits by moving a wheel connected by a shaft and bevel-gear to a system of commutators. The principal difficulty to be overcome, in an installation where the current is distributed over a large area, is the regulation of the electro-motive force at the various points, as at Milan; there are no return galvanometer wires, which are now used in both the two and the three-wire Edison systems in the United States. The plan devised by the company’s electrician at Milan is very ingenious, and enables the pressure at the ends of the various feeders to be kept practically the same, although they are of different lengths and sectional area. In the first place, resistance was added to each feeder to equalise the resistance in each conductor; and, in order to provide for the varying amount of current the feeder has to supply, a peculiar form of commutator, having a guillotine-shaped contact-piece, was inserted in the circuit. By moving this, suitable resistance is inserted or cut out, and the attendant, having a series of numbers, has only to set this instrument to the number shown by the ampère meter. By far the largest amount of current is drawn off for the lighting of the Scala Theatre, the stage-lighting alone taking more than one thousand lights: if these were all turned on suddenly, the other lights in the district would be dimmed; to obviate this, auxiliary feeders have been run, which are used only when any great increase is expected; commutators similar to those referred to above also regulate these feeders without any special attention. The pressure at any point in the system is by this means easily controlled, and affords an illustration of what is perhaps not the most economical, but is found to be the most practicable, way of maintaining a constant potential in a district where the amount of output of current is suddenly doubled. Fig. 18 is a plan of the network system of conductors laid through a large portion of the city; the conductors are in outward appearance similar to gas-pipes, the current passing through semicircular bars of copper, embedded both for the flow and return in the same iron tube, which is laid underground in a shallow trench. The house-supply is drawn from the mains, and these are connected to the feeders by means of ordinary junction-boxes, which each contain a fusible cut-out. The bridge-boxes allow of expansion of the line, and have connections for testing purposes. The insulation is extremely good, mainly on account of the favourable nature of the ground, which is chiefly gravel; no trouble has been experienced with leakage, nor has the service ever been interrupted. The cut-outs are of an improved Edison form, but have the disadvantage attending all lead plugs where the current is great, in that, to guard against accidental melting due to the heating effect of the current, the sectional area of the lead has to be much larger than would be otherwise necessary. In fact, these cut-outs will protect the cable against a bad short circuit, but nothing else.

In addition to the glow lamps, eighty arc lamps are worked in derivation, two in series; most of these lamps require 45 volts, to which 10 per cent. of idle resistance is added, constituting a total loss of current which is extremely low for a combined arc and incandescent system of lighting. The service commenced in 1882 with a little over one hundred lamps, and at present there are over ten thousand glow lamps, and two hundred arc lamps are in use. At first the new enterprise had to struggle against very great difficulties; not only the technical difficulties of distribution by means of a network of feeders and mains had to be overcome, but also those arising from the prejudices of consumers and the competition of the gas company, who tried to deter consumers from introducing electric light into their houses. One of these means consisted in offering to the private consumers, resident in the district which was threatened by competition with electricity, an agreement by which the gas company bound itself to supply gas at 5_s._ 8½_d._ per 1000 cubic feet, instead of 7_s._ 7_d._ as charged hitherto; and even now those inside the “charmed circle” of the electric light conductors get their gas cheaper than the public outside. One of the reasons which accelerated the adoption of electric light was the introduction of the Edison meter, in consequence of which consumers could be charged exactly for the amount of light they had received, and were relieved from paying a lump sum according to the number of lamps fixed, which was customary in the early days of the company. The prices at which the company now provides light, at all hours of the day and night, are as under:—

Installation Charge per Type of Lamp. charge per lamp. lamp·hour. _s._ _d._ 10-candle 18 0·26 16- ” 28 0·40 32- ” 56 0·80

that is, a little over ½_d._ per ampère-hour; the 10-candle lamps requiring 0·5, the 16-candle lamps 0·75, and the 32-candle lamps 1·5 ampère.

The company lends meters for 50, 100, and 150 lamps, at an annual rent of 4_s._ 10_d._, 7_s._ 3_d._, and 9_s._ 7_d._ respectively, and replaces, without charge to the consumer, any lamp the filament of which has broken, but it does not replace lamps where the glass is broken. For arc lamps requiring 9 to 10 ampères, an annual rent of £2 must be paid for the lamp itself, and a charge of a little over ½_d._ per hour for every ampère-hour. The carbons are charged for at 1_d._ per pair, lasting for about seven hours. Now that the installation has been in use for several years, and that the company has arrived at a very accurate estimate of the time during which an average consumer requires the light—about one thousand six hundred lamp-hours per annum—it proposes to simplify the method of charging large consumers, by omitting the initial charge of each lamp, and, instead, to charge 0·6_d._ for each 16-candle lamp-hour.