340 



ELEMENTS OF ELECTRICAL ENGINEERING. 



The tendency is to favor the use of alternating current for 

 operating street lamps for the reason that a constant current can 

 be delivered to the arc-lamp circuit through a special transformer 

 from the same generator that supplies a constant-voltage distrib- 

 uting system, whereas the use of direct current requires a separ- 

 ate generator. Fig. 189 is a view of the General Electric Com- 

 pany's constant-current transformer for taking a varying current 

 from constant-voltage supply mains and delivering a constant cur- 



Fig. 188. 



rent at varying voltage to a receiving circuit. The action of this 

 transformer is discussed in the second volume of this text. 



A general view of the improved * Brush direct-current gene- 

 rator for supplying constant current to arc lamps is shown in Fig. 

 190. 



When many arc lamps are operated in series it is necessary 



* The multi-circuit Brush generator, American Electrician, Vol. XI., pp. 436- 

 437, September, 1899. 



