THE CONTINUOUS CURRENT GENERATOR 141 



which, or only one of which, may be operated to supply 

 the station output. 



Use of Several Generators Instead of One. The reasons 

 that several small sized generators are used to supply the 

 station output, instead of one large one, are two in number; 

 reliability and efficiency. Suppose the load on a station 

 is represented in the form of a curve, load in kw. being 

 plotted against time. An average curve would be as 

 shown in Fig. 90; the supposed load being made up of rail- 

 way traffic, lighting, and power for factories. The peak 



12 2 4 6 8 10 12 2 4 6 8 10 12 

 Night A.M. Noon P.M. 



FIG. 90. A Possible Load Curve for a Small Power Station. 



load occurs at 8 o'clock in the evening, and is about 5000 

 k\v. As the peak lasts only a short time, one generator 

 of 4000 kw. rating would fit the needs of the station in so 

 far as quantity of power was concerned. Such a generator 

 would be run overload for a short time but as a machine 

 must be able to carry 25% overload for two hours no harm 

 would result. But there would be two bad features about 

 such a station: 1st, if an accident happens to the machine 

 the station is without power of any sort until the machine 

 is repaired, and 2d, during most of the day the machine 

 would be operating with a load of less than 50% of its 



