| D, alternating current dynamo; | M M, secondary conductors; |
| E, continuous current dynamo for exciting; | T T, transformers; |
| L L¹, main primary conductors; | S¹ S² S³ S⁴ S⁵ S⁶, lamps in parallel. |
The Goulard transformers were used at first, but have been superseded by others designed by Mr. Ferranti; they are of the No. 2 kind, or shell type, and have a core of hoop-iron, on which the two coils are wound; the hoop-iron is then bent over, and the ends joined so as to enclose the coils. The machinery is fixed in a basement excavated under the Grosvenor Gallery; the foundations are of massive concrete, in which stone supports for the engines and dynamos are embedded; the concrete does not touch the walls of the building, but a space of about 1 foot is left, which is filled in with clay; and by this simple plan all vibration of the machinery is isolated from the building. The power is obtained from two horizontal high-pressure engines, each of 600 indicated horse-power, in addition to the original two horizontal high-pressure non-condensing engines, each of 35 nominal horse-power, running at a speed of 55 revolutions per minute, which is maintained constant by means of a governor directly attached to the expansion slide-valve. The four engines drive on to a countershaft, which is cut up into lengths; each section is coupled to a dynamo and exciter by means of a conical friction-disk clutch; this permits of either length being started or stopped without interfering with the other. The speed of each engine is checked by means of a liquid speed-indicator, designed by the author. Two Ferranti alternating current dynamos, each capable of maintaining ten thousand lamps, are driven direct, one dynamo by each length of shafting: they are excited by two continuous current machines, the circuits from which are joined to a regulating apparatus, which by altering resistance keeps the electro-motive force of the large machines proportional to the number of lamps which are to be maintained. At present hand regulation is employed, but it is proposed to use automatic regulation, which will increase the life of the lamps, as they are severely tried by the variation of the current, which is more noticeable than in continuous current installations. The current from the machines is at a potential of 2400 volts, and that from the transformers is 100 volts. The primary wire which carries this high electro-motive force does not enter the houses, as the transformers are, as a rule, fixed in the cellars, and from them the house branch is led in the form of a cable of fine wires, having a total diameter of 7/16 inch; the lamps, which are placed in parallel across this cable, are attached to single No. 18 or No. 20 B. W. G. wires in the usual manner. When first established, the transformers presented an element of danger, in that they, in common with all induction coils, were also condensers, and therefore a dangerous shock might be given to any one touching some unguarded portion of the lighting system. This has been prevented by the simple plan of connecting one of the terminals of every secondary circuit to earth, a method which, however, is not to be recommended, as it throws an additional strain on the insulation of the primary circuit; in fact, by earthing the secondary the insulation is practically reduced to one-half. A safety device should be inserted, which would come into operation on any leakage from primary to secondary, and immediately cut out the transformer.
The primary-current conductor is led overhead, and still remains an objectionable feature of the system, although the original trouble with the neighbouring telephones and telegraphs has been overcome. The primary circuit is a small carefully insulated cable of high conductivity copper wire, nineteen strands of No. 15 B. W. G. It weighs about 1¾ ton per mile, and is suspended, where it crosses the streets, on a steel bearer whose tensile strength is 1⅕ ton. It is so arranged according to the droop of the cable that the strain of the bearer never exceeds 225 lbs., which means that the factor of safety is nearly 12 to 1. Double cut-outs or safety fuses, in many instances of the author’s design, are placed on each pole of the primary, at the point where it enters the house, so that, in the case of an excess current, the mica-foils would fuse, and all connection between that house and the supply main would cease.
Much credit is due to M. Goulard, who, in spite of great opposition to the use of his transformer system, initiated the Grosvenor Gallery installation three years ago. It has developed into not only the largest and most important central-station in Europe, but, as regards the transformer system, it supplies more lights than any in the United States. The original company has been taken over by the London Electric Supply Corporation, who are putting down plant capable of maintaining 30,000 lights, and are erecting another station at Deptford for 200,000 lights, which will be distributed by means of district transformers from mains, which it is proposed to run from Deptford through the Thames Tunnel and the Underground Railways. The electric current is supplied by meter at the price of 7¼d. per Board of Trade Unit, a price for light equal to gas at about 4s. 2d. per 1000 cubic feet.
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.
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.
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.