yune 



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NATURE 



153 



moment supplying partly by accumulators and partly by 

 dynamos — the former doing the whole work during the 

 hours of minimum supply, and the latter being employed 

 in charging the accumulators and supplementing the 

 direct supply from the accumulators during the hours of 

 maximum supply. The accumulators are all stationed at 

 the generating station, and merely serve as a reserve of 

 power. Since they are not employed to effect a transfor- 

 mation from a high to a low pressure, they do not intro- 

 duce any saving in the size of the distributing mains, as 

 in the case of the Chelsea system. Hence the Kensington 

 system, which the Notting Hill Company proposes also to 

 adopt, would require several generating stations for the 

 lighting of a large area. (<:) Direct supply at low pressure 

 without the use of accumulators, such as is at present 

 employed by the St. James's and Pall Mall Company. 

 This system is also only suited for distribution over small 

 areas, not exceeding half a mile in radius, since the 

 absence of any system of transformation necessitates the 

 employment of very large conductors. This last system has 

 also the disadvantage of alternate current distribution, as 

 the supply, being directly dependent on the steady working 

 of the machinery, is liable to be seriously affected by even 

 a temporary breakdown, which is, of course, not the case 

 v/ith the direct current systems {a) and {b). 



It is interesting to note that no system of direct current 

 transformation, other than that effected by the use of 

 accumulators, has been proposed by any of the companies 

 or referred to in Major Marindin's Report ; probably because 

 all direct current transformers, "motor-dynamos," &c., 

 that have yet been devised, employ moving parts, and are 

 therefore in their present form unsuitable for transforma- 

 tion in private houses. We cannot, however, but think 

 that such direct current transformers might be very 

 economically employed at distributing stations, the energy 

 being received at high pressure from the main generating 

 station, and distributed at low pressure to the houses in 

 the neighbourhood of the distributing stations. 



The House to House, the London Electric Supply, and 

 the Metropolitan use high-pressure alternate currents 

 with transformers, except in the case of the Whitehall 

 installation of the last company ; and it speaks well for 

 the alternate current system that, while the Metropolitan 

 Company commenced at Whitehall with direct currents 

 and accumulators, which they first thought so superior to the 

 use of alternate currents, they now state in their evidence 

 that in their extensions they propose employing alternate 

 currents and transformers. In the case of the London 

 Electric Company, a double system of transformation is to 

 be employed between the current leaving the dynamo 

 and the current in the houses of the consumers. The 

 supply will be obtained from a very large generating 

 station at Deptford, outside the crowded districts of the 

 Metropolis, and carried through trunk mains, at the unpre- 

 cedentedly high pressure of 10,000 volts, to transforming 

 stations inside, or near, the area of supply, whence the 

 current will be taken by distributing mains, at a pressure 

 of 2500 or 2000 volts, to the consumers' premises, and 

 transformed there to 100 or 50 volts. Or this second 

 transformation may be effected at secondary transforming 

 stations, the currents being conveyed from them to the 

 houses at the pressure of 100 or 50 volts. 



In the case of the House to House and Metropolitan 

 Companies only one transformation is proposed to be 

 employed, so that several generating stations must be 

 erected ; as even with a pressure of 2000 volts the con- 

 ductors would have to be inconveniently thick if the 

 electric energy were conveyed very far. The Metro- 

 politan Company have, therefore, selected sites in 

 Sardinia Street, Rathbone Place, South Mews (near 

 Manchester Square), Eccleston Place, and Waterloo 

 Bridge Wharf ; from each of which a current at looo volts 

 will be sent, to be transformed into loo or 50 volts inside 

 the consumers' premises. 



The Report contains a concise account, written by Major 

 Cardew, of the relative advantages of the direct and of 

 the alternate systems. He refers to the fact that the 

 employment of accumulators by the Chelsea Company at 

 their distributing stations enables small distributing mains 

 to be used ; makes the lighting of the district unaffected by 

 even a temporary total breakdown ofthe machinery, since 

 the accumulators that are at any time supplying current 

 to the houses are quite distinct from those that are being 

 charged ; enables a nearly constant pressure to be main- 

 tained at the houses, independently of the number of 

 lamps that are turned on ; and, lastly, the current being 

 a direct one is applicable for the supply of motive power 

 and for other uses besides the production of light and 

 heat, and can be more easily measured than an alternate 

 current. Major Cardew further adds, as an additional ad- 

 vantage possessed by supplying current from accumulators, 

 that " there is no doubt that a battery current is less 

 destructive to lamps than one supplied from dynamos, 

 whether alternating or continuous." We doubt, however, 

 whether there is sufficient experimental evidence on this 

 subject to justify this conclusion. 



As a set-off to these advantages the cost of accumu- 

 lators is great, as well as that of the skilled attention they 

 require, while their efficiency at maximum output is 

 probably rather low ; the automatic switches for switching 

 the accumulators into the charging circuit when dis- 

 charged and into the discharging circuit when charged, as 

 well as for regulating the discharge from each cell, are. 

 Major Cardew thinks, a weak point, and any failure in 

 their action would probably ruin the accumulators ; the 

 insulation of large batteries cannot be maintained at all 

 high; and the numerous joints that have to be main- 

 tained good in the presence of acid fumes are a source 

 of weakness. 



The special advantages of the high-pressure transformer 

 system Major Cardew considers to be : the smallness of 

 the mains ; the absence of difficulty in maintaining con- 

 stancy of pressure in the mains within 2 per cent, over a 

 large area ; the pressure in the houses may be different 

 in different cases according to the needs of the consumer ; 

 the system is simple to work ; the dynamos are simple, 

 and can be made in easily replaceable parts. 



The disadvantages are that the high pressure necessi- 

 tates great care and expense in insulation ; the conveying 

 of this high pressure to at any rate one point on the con- 

 sumer's premises involves some risk to life ; the main 

 cannot be handled nor connection made with it when 

 the pressure is on ; the transformers cause the regulation 

 in the houses to be not so good as in the mains ; the 

 system cannot at present be efficiently utilized for motive 

 power, or for electric deposition or other chemical uses, 

 such as charging accumulators ; " and it is very doubtful 

 whether a practically successful alternating motor is likely 

 to be brought out " ; the system depends entirely on 

 running machinery ; the general efficiency must be low 

 when the supply is near its minimum, which, so long as 

 it is utilized for lighting alone, obtains during about 

 eighteen hours out of the twenty-four ; a serious accident 

 at the generating station might stop the supply. " Al- 

 ternating machines cannot be so readily connected 

 together to run in parallel circuit as continuous current 

 machines"; the instruments and methods for making 

 measurements are far more restricted in number, and the 

 measurements are more difficult to make, when alternate 

 currents are in question. 



The sentences in the preceding paragraph that are placed 

 in inverted commas appear to us to be particularly rash. 

 So far from saying " it is very doubtful whether a practi- 

 cally successful alternating motor is likely to be brought 

 out," we should prefer to say that it is almost certain 

 that, as soon as there is a widespread demand for cheap 

 efficient alternate current motors, such motors will be 

 forthcoming ; and, after the experiments shown by Mr. 



