OPERATION OF THE DYNAMO AS A GENERATOR. 75 



alternating current distribution ; for long distance power trans- 

 mission, for electric railways, and in general for the supply of 

 current to motors and to lamps. 



The only case in which it is distinctly advantageous to use the 

 constant current system is for street lighting in cities where a fixed 

 number of widely distributed lamps, arc or incandescent, are to 

 be operated. 



The shunt generator driven at constant speed, and especially 

 the compound generator, maintains automatically an approxi- 

 mately constant voltage even though the current output varies. 



100 



80 



60 



40 



Volts 



Amperes 



\ 



150 



250 



300 350 



Fig. 64. 



This is shown by the so-called characteristic curves in Figs. 64 and 

 65. The ordinates of the curve in Fig. 64 represent the voltages 

 of a shunt generator, and the abscissas represent the correspond- 

 ing current outputs. The voltage of a shunt generator decreases 

 slightly as the current output increases, as is evident from Fig. 

 64. The ordinates of the curve in Fig. 65 represent the voltages 

 of a compound generator (flat-compound), and the abscissas repre- 

 sent the corresponding current outputs. The voltage of a flat- 



