2 5 8 



ELEMENTS OF ELECTRICAL ENGINEERING. 



152.5 volts, when they are nearly charged, see Fig. 143. This 

 high voltage for charging is usually obtained by connecting the 

 batteries to the station mains through a small shunt-wound gen- 



Main 



Shant field 

 winding 



Main 



Fig. 148. 



erator, which is called a booster, as shown in Fig. 148, in which 

 G is the main generator of the station and B is the booster. 



110. Automatic boosters. When the station load changes 

 slowly, as is usually the case in an electric lighting station, there 

 is ample time for an attendant to connect up a shunt booster and 

 charge a storage battery when the station load is small, and to 

 disconnect the booster and make the necessary arrangements for 

 discharging the battery when the peak of the load comes on. 

 When, however, the station load fluctuates rapidly and irregularly 

 as is usually the case in an electric railway power station, hand 

 control of the storage battery is impossible. In such cases auto- 

 matic boosters must be used. 



The floating battery. The simplest arrangement for causing 

 a storage battery to operate automatically and tend to equalize 

 a station load, is that which is frequently employed in connection 

 with long feeders over which a considerable drop of voltage takes 

 place when a large current is delivered. This arrangement is 

 shown in Fig. 149, in which G is the main generator and Ba is 



