210 



ALTERNATING CURRENTS 



to obtain the neutral of an alternating-current three-wire system 

 in the same manner as a balancer set is used to obtain the neu- 

 tral in a direct-current three-wire system. The connections of a 

 compensator used in this manner are shown in Fig. 199. The 

 compensator is superior to the balancer set both in efficiency 

 and in maintenance. 



For moderate ratios of transformation, the compensator is 

 much more economical in the use of materials and has a much 

 higher efficiency than a transformer which transforms all the 

 power. With the higher ratios of transformation, more and 

 more of the power is transformed and less and less conducted. 

 So the auto-transformer is economical only for small ratios of 



100. ia 9i a 



FIG. 199. Compensator used to obtain FIG. 200. Lighting transformer used 

 a 3-wire lighting system. as a booster. 



transformation. Also the low side and the high side are con- 

 nected together conductively. Therefore, in commercial systems 

 the low side should be grounded at the proper point for reasons of 

 safety, if the high-side voltage is sufficiently high to be dangerous. 

 An ordinary lighting transformer can be used as an auto-trans- 

 former to change the voltage by a moderate amount. Figure 

 200 shows a 20-kv-a., 2,200 to 220-volt transformer. The rated 

 primary current 



20,000 



and the rated secondary current 

 = 20,000 

 220 



= 91 amp. 



The high and low sides can carry 9.1 and 91 amp., respec- 

 tively, without exceeding their ratings. The low side may be 

 connected to raise the voltage, as shown in Fig. 200. Ninety- 

 one amperes can flow to the load without overloading the low- 



