ELECTRICAL ENERGY. 209 



of different apparatus to obtain the maximum economy for each type. 

 For lighting stations triple-expansion engines may be used, while for 

 traction work, where the variation in the load is sudden and may occur 

 after the steam is cut off from the high-pressure cylinder, it is not well 

 in general to go beyond compound engines, and there is even a question 

 as to whether simple engines are not more economical when condensing 

 water can not be obtained. In any case, however, it is of the utmost 

 importance, as regards economy of operation, that the load should be 

 made as constant as possible. 



Two distinct types of distribution are used for incandescent lighting 

 in this country — the single-phase alternating current and the direct 

 current 3-wire system. At the present time the former does not permit 

 the supplying of power. As alternating distribution is at high poten- 

 tial, it does permit the location of the station where the conditions of 

 maximum economy can be fulfilled. The 3-wire incandescent system, 

 using low voltages, may be used for supplying motors, but the amount 

 of copper necessitated by the low pressure has caused such stations to 

 be located near the center of distribution, irrespective of the best con- 

 ditions for the economical operation of the plant. 



With the alternating system it seems impossible to provide even a 

 moderately steady output, but with the continuous-current system the 

 motor load during the day gives an average output greater in propor- 

 tion to the maximum. Some years ago the question of the relative 

 values of the alternating and direct-current systems was discussed, and 

 for a while most of the stations installed were of the alternating type. 

 At present the tendency seems rather in the direction of continuous- 

 current stations, especially in towns where there is a large demand for 

 current within a comparatively small area. There is a great advan- 

 tage of direct currents, in that they allow the employment of storage 

 batteries, which equalizes the load on the station. In almost all of the 

 large lighting plants, both here and abroad, this plan has been adopted 

 to a greater or less extent, and the results have been so favorable, 

 that the battery equipments in many of our stations are being increased. 

 The efficiency of batteries in lighting stations is comparatively high, 

 while the depreciation has been greatly reduced, and is not now over 

 5 or 6 per cent per annum. In most systems, however, the full benefit 

 of the storage batteries is not realized, as the batteries are placed in 

 the station, and while the advantage of an approximately constant 

 load is obtained, yet the further advantage offered in distribution is not 

 secured. I will take this question up later. 



In New York, Brooklyn, Boston, and Chicago a large proportion of 

 the direct- current lighting stations are situated where it is expensive 

 to handle the coal and ashes, and where the economy, due to condensa- 

 tion, is not obtained. It is also the custom to use several stations 

 instead of a single large station, and this increases the cost of produc- 

 tion both in operating expenses and fixed charges. The question arises 

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