THE CONTINUOUS CURRENT GENERATOR 133 



the armature reaction and the armature resistance drop 

 and in addition, the shunt field current falls as the load is 

 increased, because of the lowered terminal voltage. The shunt 

 field current is evidently proportional to the terminal 

 voltage and so decreases with load increase. 



If the resistance of the external circuit of a shunt gen- 

 erator is continually decreased, the external character- 



Pield Current 

 Loud Current 



FIG. 85. External Characteristic of a Compound Generator. 



istic doubles back because of the decreased field current. 

 From B to F (Fig. 84) the machine is stable and this is the 

 working part of the external characteristic. The part 

 of the curve from F to E is generally difficult to obtain 

 as the machine does not definitely maintain any special 

 load on that part of the curve. 



Even when the terminal voltage is zero (E t Fig. 84) 

 there will be some current circulating through the armature. 



