SYNCHRONOUS GENERATORS 



285 



Fio. 154. Armature Reaction. 

 Current in Phase. 



no explanation beyond the statement that the voltage drop is in 

 phase with the current flowing. 



The armature reaction, which represents the resultant e.m.f. 

 of the armature currents, de- 

 pends on the current and the 

 number of effective turns in 

 series per pole per phase. It 

 may have a magnetizing or 

 demagnetizing effect, or it may 

 shift the field flux from one 

 side of the pole to the other, 

 or its effect may be a com- 

 bination of the two. The 

 energy component of the cur- 

 rent will only cause a shifting 

 or distorting effect, while the 

 wattless component will cause 

 a demagnetizing or magnetiz- 

 ing effect, depending on 

 whether the current is lag- 

 ging or leading. These effects 

 are illustrated in Figs. 154 to 

 156. 



Fig. 154 represents two 

 conductors of an armature 

 coil. These are midway under 

 a north and south pole, re- 

 spectively, and the e.m.f. in- 

 duced in the coil is obviously 

 a maximum for this position. 

 The current in the coil will 

 also have the maximum value 

 as it is in phase with the e.m.f. 

 and the flux produced by the 



same will have a cross-magnetizing effect not directly opposing 

 the field ampere-turns, but simply causing a distortion of the field 

 flux. The current in the armature, however, always lags behind 

 the induced e.m.f. by reason of the inductance, and even with 

 unity power factor in the external circuit, the armature reaction is 

 demagnetizing to a certain extent. 



FIG. 155. Armature Reaction. 

 Current Lagging. 



FIG. 156. Armature Reaction. 

 Current Leading. 



Armature Conductor 

 Iii-phase Component 



of Armature Current 

 Wattless Component 



of Armature Current 



