CHARACTERISTIC CURVES. 



405 



The curve OA, Fig. 38, is the external characteristic of a given 

 shunt generator, the line BC is the characteristic of a receiving 

 circuit consisting of a storage battery of which the counter electro- 

 motive force is e volts, and P is the point which represents the con- 

 ditions of operation of the generator when charging the battery. 

 Before the battery circuit is connected to the generator, the gen- 

 erator is allowed to build up and reach the point P 1 of its char- 

 acteristic. When the battery is connected the current output 

 quickly increases, the terminal voltage falls off slightly, and the 

 running conditions represented by the point P are quickly estab- 

 lished. No difficulty is encountered in charging a storage battery 

 by means of a shunt generator. 



Two shunt generators in parallel. The curves OA and OB t 

 Fig. 39, are the external characteristics of two different shunt 

 generators. The curve OB is plotted to the left of the origin 

 with its current output measured to the left for convenience. 



Fig. 39. 



These two generators are connected in parallel to a receiving 

 circuit. Under these conditions the terminal voltage must be the 

 same for both generators. Therefore, if the two machines to- 

 gether deliver a specified current, this current is divided between 

 the machines in such a way as to make their terminal voltages 



