AUXILIARY STATIONS 



693 



stations may be divided into four classes according to their utiliza- 

 tion, although, in reality, they may not differ essentially, as some 

 stations may serve two or three different purposes simultaneously. 



100 



200 



300 400 500 



Square Mile Foot of Storage 



600 



TOO 



800 



FIG. 404. Increase of Minimum Flow with Additional Storage. 



Class I. *Stand-6?/ &2afo'ons, which are intended to take care of the 

 load in case of a breakdown to the hydro-electric machinery 

 or the transmission lines. 

 Class II. Low-water ^Stations, which are intended to supplement 



the load during low-water periods. 

 Class III. PeoWoad &talivn&, which are intended to carry peak 



loads. 



Class IV. Base-Zoad /Sta&'ons, which are intended to operate con- 

 tinuously, the water power being supplemental to the 

 steam power. 



Prime Movers. There are four kinds of prime movers which 

 may be used for auxiliary stations; the steam turbine, the steam 

 engine, the gas engine and the oil engine. Of these, the steam- 

 turbine is used almost exclusively, but the question of deciding 

 on the most economical and practical equipment is, naturally, a 

 problem which involves a study of each case individually. 



