1893.] on Electrical 'Railways. 51 



The first of these, here in England at any rate, is dependent upon 

 the economical production of steam power, although there are 

 essential points of difference between the conditions under which 

 steam-power is required for electric traction purposes and for 

 electric lighting. But in Scotland and Ireland, and in many 

 countries abroad, there is abundant water power, now only very 

 partially utilised. The Portrush line is worked in part by water and 

 in part by steam-power, but for the Bessbrook and Newry Tramway 

 (of which there is a working model on the table) water-power is 

 exclusively used. 



A few experiments will show that the demand for power on the 

 generating plant is greatest at the moment of starting the car or 

 train, when, in addition to the power required to overcome the 

 frictional resistances, power is also required to accelerate the velocity. 

 Thus, if instead of a single car there are a number of trains moving 

 on the one system, and it so happens that several are starting 

 together, the demand made upon the generating plant may at one 

 moment be three or four times as great as that made a few seconds 

 after. This is shown in the diagrams which exhibit the variation of 

 current supplied by the generators on the City and South London 

 Railway, with eight trains running together, the readings being taken 

 every ten seconds. The maxima rise as high as double the mean ; 

 thus the generating plant must be capable of instantly responding to 

 a demand double or even treble the average demand upon it. 



In electric lighting it is true there is not less variation between 

 the maximum demand and the mean taken during the ordinary hours 

 of lighting, but it is only in the event of sudden fog that the 

 probable demand cannot be accurately gauged beforehand, and 

 provided for by throwing more generators into action. Thus in a 

 lighting station each generator may be kept working approximately 

 at its full load, and therefore under conditions of maximum economy, 

 whereas in a traction station the whole plant must be kept ready to 

 instantaneously respond to the maximum demands which may be 

 made upon it, and must therefore necessarily work with a low load 

 factor, and consequently with diminished economy. So important is 

 the influence on cost of production of the possible demand in relation 

 to average demand, that the Corporation of Manchester, under their 

 order for electric supply, have decided, upon the advice of their 

 engineer, to annually charge a customer 31. per quarter for each unit 

 per hour of maximum supply which he may require, in addition to 2d. 

 for each unit actually consumed, i. e. for being ready to supply him 

 with a certain amount of electrical power if required to do so, 

 they charge an additional sum equivalent to the charge for its actual 

 consumption for 1440 hours. 



In one respect water-power has an economic advantage over steam- 

 power, because although steam engine and turbine alike work with 

 greatly reduced efficiency at reduced loads, when the turbine gates 

 are partially closed and the water restrained in the reservoir it is not 



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