392 



ELEMENTS OF ELECTRICAL ENGINEERING. 



When the receiving circuit consists, say, of a storage battery 

 which is to be charged by the generator, then the terminal elec- 

 tromotive force E x of the generator is equal to the sum of 

 R I and the counter electromotive force e of the battery ; where 



Volts 



Amperes 



Volts 



Amperes / 



Fig. 24. 



Fig. 25. 



R r is the resistance of the battery and connecting wires. In 

 this case the receiving circuit characteristic is the straight line 

 AB, shown in Fig. 25. 



A receiving circuit containing motors has no definite charac- 

 teristic in the sense in which the term is here defined, inasmuch 

 as with a given applied voltage the current may have a great 

 variety of values depending upon the motor load. 



Now, evidently, the terminal electromotive force of a generator 

 is identical with the electromotive force applied to the receiving 

 circuit, including the line wires, and the current output of a gen- 

 erator is identical with the current flowing through the receiving 

 circuit. Therefore a generator supplying a given receiving circuit 

 operates at that point of its characteristic where the receiving 

 circuit characteristic intersects it. 



The point P in Fig. 26 shows the operating conditions of a 

 given series generator running at given speed and supplying cur- 

 rent to a receiving circuit of given resistance. With increase of 

 the resistance of the receiving circuit, the line OP becomes 

 steeper, that is, the angle 6, Fig. 26, increases, inasmuch as the 



