SYNCHRONOUS MACHINERY 



269 



With inductive load a much larger increase of field current is 

 required to counteract the effect of the lagging current. 



With capacity load the field current must be decreased in order 

 to maintain a constant terminal e.m.f. 



The same results are shown in the diagrams, Figs. 240, 241 and 

 242. 



150 



140 

 130 

 120 

 110 

 100 



^90 



| 80 

 O 

 jj 70 



100 200 300 400 500 600 700 800 900 1000 

 Amperes Load Current I 



FIG. 247. Compounding curves of an alternator. 

 These compounding curves can also be calculated from equation 



E = V(E cos + 7r) 2 + (E sin 



255, E remains constant, a certain value of cos <j> is chosen, I is 

 varied and the value of E is calculated. The corresponding value 

 of // is obtained from the saturation curve, Fig. 248, and is plotted 

 on the armature-current base. 



