May 



SCIENCE. 



337 



ELECTRIC-LIGHTING STATIONS IN EUROPE, AND 

 THEIR LESSONS. 



Professor George Forbes read on Feb. 28, before the Eng- 

 lish Institute of Electrical Engineers, a paper with the above title, 

 which gave the results of his inspection of the electric-lighting sta- 

 tions at Berlin, Rome, and Milan. He first described the Berlin 

 central stations. There are three of these, using a direct-current, 

 low-pressure system, and connecting with the same network of 

 mains. Of the three stations, that on Markgrafen Strasse is the 

 most important. It contains six engines of 160 horse-power each, 

 each driving an old-fashioned Edison dynamo ; with four other en- 

 gines of 400 horse-power each, driving a new type of dynamo di- 

 rect, at 80 revolutions per minute. These last dynamos are worthy 

 of notice : they are multipolar Gramme machines, with radial poles 

 inside the Gramme ring armature. There are ten poles ; the ar- 

 mature is 3 metres in diameter; the commutator is I J metres in 

 diameter. There are ten brushes, and the different circuits are 

 connected in parallel. The advantage of this type of dynamo, 

 provided it is an advantage, is in the slow speed at which it can be 

 run. The capacity of the station is about 2,600 horse-power, 

 which gives about 26,000 lamps of 16 candle-power. In the sys- 

 tem of distribution employed, the two-wire plan is adopted, 

 although in the later additions that are being made the three-wire 

 system is to be used. The network of mains is supplied at inter- 

 vals by " feeders," which are used to equalize the pressure at all 

 points and times, there being no less than forty-two pairs of feed- 

 ers. The cables consist of stranded wires covered with jute pre- 

 pared with a bituminous compound, enclosed in lead, then covered 

 with tape and a preservative compound, and finally armor-plated 

 with two crossed spirals of iron ribbon. The cost of the under- 

 ground cables for the whole system has so far amounted to about 

 _£90,ooo ; the greatest variation of pressure allowed in the mains is 

 li per cent ; the loss in the feeders at ma.ximum load is 15 volts. 

 The performance of the cables for three years was excellent ; but 

 Professor Forbes states that lately water has penetrated the lead, 

 has percolated to the copper, which is then destroyed. " What- 

 ever the cause may be, the fact seems to be established that such 

 a cable will not stand underground electric-light work for more 

 than about three years. These cables generally run under the 

 footways without any casing." 



The second of the three Berlin stations is in the Mauer Strauss. 

 Besides supplying incandescent, it supplies arc lamps. The low- 

 tension outfit consists of four Edison machines and six multipolar 

 machines, supplying altogether 11,000 lamps. 



The third station is small, and contains four Edison machines 

 driven by the same number of 75-horse-power Armington & Sims 

 engines. Fifty-two men are employed at the three stations in 

 eight-hour shifts. The company which does the central-station 

 work paid last year a dividend of 7J per cent. 



In the central station at IVIilan, both arc and incandescent lamps 

 are supplied. Of the former, there are 350 of the Thomson-Hous- 

 ton system ; of the latter, there are 16,000, fed by both the direct 

 system and the alternating system. For the continuous system, 

 Edison meters are used, and give great satisfaction. The distribu- 

 tion is on the two-wire system, as in Berlin, the current being sup- 

 plied from ten Edison dynamos. The high-tension alternating 

 system is the Zipernowski-Deri system, there being two machines, 

 each of 2,000 volts and 40 amperes. 



The capital of the company is $600,000, of which §120,000 has 

 been spent in conductors Wages is one-fifth of the total working 

 expenses; coal, one-half ; lamp renewals, 7 per cent. The com- 

 pany has paid dividends for several years. The last was 4 per 

 cent, and it is increasing. There is a large reserve fund. 



The central station in Rome was started by the gas company 

 there. The alternating system is used for both arc and incandes- 

 cent lighting. At present 9,000 incandescent and 200 arc lamps 

 are supplied. The number of alternations is 83 a second, or 41 

 complete periods a second. The greatest distance to which cur- 

 rent is at present supplied is about three miles. The voltage in the 

 primary circuit is 2,200; in the secondary, no volts. The con- 

 verter is an anchor ring built up of iron disks wound over with the 

 primary and secondary circuits. The dynamos are of two sizes. 



The smaller are of a size to supply 1,000 lamps. There are 20 poles, 

 and the machine makes 250 revolutions a minute. The larger size 

 have 40 magnet-poles, and make 125 revolutions. " When the 

 machine is illuminated by an arc light, to which it supplies current, 

 a curious optical effect is produced. The arc being periodically 

 made and broken, the revolving magnet-poles are seen fixed in 

 position, and the amount of lag with different loads can be seen 

 distinctly. The efficiency of these machines is said to be 90 per 

 cent, including the exciting current. There are 50 converters now 

 at work, each of 10 horse-power. The efficiency of these conver- 

 ters is 95 per cent at full load ; of the 5-horse-power converters, 92 

 per cent; of the 2i- horse-power, 88 per cent. After describing 

 these stations. Professor Forbes proceeded to draw from his ob- 

 servations some lessons which will be of use to English engineers 

 in the remarkable extension of electric lighting which is going on in 

 that country, especially in London. He called attention to the fact 

 that the continental low-pressure systems used a two-wire instead 

 of a three-wiie distribution ; this he condemned as causing a great 

 and needless expenditure for copper. Again the importance of 

 feeding-wires was emphasized. Professor Forbes contrasted the 

 variation in the potential of the lamps that would occur at a point 

 960 yards distant from the central station, using conductors which 

 carried 1,000 amperes per square inch. For a two-wire system, 

 the variation would be 48 volts in 100; a three-wire system, 12 

 volts ; a three-wire system with feed-wires, the total amount of 

 copper being the same as in the last case, i volt. The first two 

 would evidently not be practical systems ; the last would be satis- 

 factory. In this connection, Professor Forbes pointed out that 

 feeding-wires were also necessary in the high-potential alternating 

 system, in order that the lamps should maintain a uniform bril- 

 liancy, and referred to the unsatisfactory showing of the Grosvenor 

 Gallery Station, where the alternating system is used, and where 

 no feeders are employed. Professor Forbes seems inclined to take 

 a somewhat pessimistic view of the future of underground cables. 

 Those in Berlin, he states, only last three years, and, " on looking 

 through the testimonials of makers, he does not find that cables, 

 when placed under ground, have ever worked electric-light circuits 

 satisfactorily beyond the three years fixed by the Berlin people 

 as being destructive." On this side of the water the Edison Com- 

 pany has done much better than this with their insulated copper 

 rods carried in iron pipes. As the result of his observations on 

 this point, however, Professor Forbes says, " At the present 

 moment it seems to me that the only types of underground cables 

 proved suitable for permanent work are either bare copper sup- 

 ported on insulators, or else vulcanized India-rubber, or perhaps 

 okonite. Especial care must be taken to avoid an insulator which 

 is injured by the gases which permeate the soil of a town, or which 

 has the property, like pitch, of becoming viscous, and so letting the 

 copper become decentralized. 



It seems the experience of most electrical companies, that it pays 

 better to use a meter on the consumer's premises, and charge for 

 the actual amount of current consumed, than to supply light by 

 contract. Of the different types of meters, the Edison and Avon 

 meters can be used for continuous currents ; the Schallenberger 

 meter, for alternating currents. Professor Forbes thinks that the 

 efficiency of converters for the alternating systerri is overrated. 

 While the maximum efficiency might be from 90 to 95 per cent, 

 yet the efficiency is much less on small loads, and he would be sur- 

 prised if the average efficiency for all except two types would be 

 over 70 per cent. 



A great difference between the practice in this country and 

 abroad is in the speed of the dynamos. Here very high speeds are 

 used ; abroad low speeds are aimed at. The advantage of the 

 former is in the greater output and efficiency from the same-sized 

 machine ; the disadvantage is in the greater liability to accident ; 

 but, as these are extremely rare, the possibility of failure can hardly 

 be regarded as balancing the advantages. 



To an American reading the paper, there is the satisfaction that 

 our own central stations are far in advance of those described ; 

 while nearly, if not quite, all of the recommendations are in the 

 direction of the established practice in this country. 



