ARMATURE REACTION IN ALTERNATORS 97 



shown in Fig. 79 (a) ; the field being supposed to rotate counter- 

 clockwise as indicated by the arrow, and the radially outward direction 

 of the flux being regarded as positive. It is evident at once that the 

 effect in this case is a purely Distorting or cross-magnetizing one (such 



ARMATURE fLUX WAVE 



FIG. 7'J. To illustrate Armature Reaction iu Alternators: (a) Current in Phase with 

 e.m.f. ; (6) Current lagging by 90 ; (o) Current leading by 90. 



as occurs in a continuous-current dynamo whose brushes have no 

 lead), the field being weakened on the advancing side of each pole- 

 piece, and strengthened on the other side. When the current lags by 

 90, the rotating flux wave takes up the position shown in Fig. 79 (6), 

 and it is at once evident that there is a powerful demagnetizing effect ; 



