14t> 



ALTERNATING CURRENTS 



emf. E' by 90. The armature reaction A is in phase with the 

 current, and the resultant field F is found by subtracting the 

 armature reaction A from the impressed field F\. E is the no- 

 load voltage due to field FI. 



In either Fig. 148 or Fig. 149 the no-load voltage E is found by 

 adding vectorially a voltage E'E to E', this voltage E'E always 

 being in quadrature with the current. 



If the voltage E'E adds in quadrature with the current, it 

 must be in phase with the IX component of voltage already 

 discussed. This is illustrated in Fig. 150. The current / is 

 shown lagging the terminal voltage V by an angle 0. The inter- 



-A 



FIG. 150. Complete vector diagram for the synchronous impedance method. 



flal voltage of the armature E' is found by adding IR and IX 

 vectorially to V. The resultant field F is 90 ahead of E'. By 

 adding voltage E'E to E' , and in quadrature with the current 

 /, the no-load voltage E is found. The voltage E'E does not 

 actually exist under load, for E is the no-load induced emf. and 

 E' the load induced emf. However, E'E represents the drop 

 in voltage due to the reduced flux caused by the armature reac- 

 tion A. E'E lags the armature mmf. vector A by 90 and 

 would be proportional to A if there were no saturation of the 

 iron. E'E may then be considered as an emf. induced by the 

 armature reaction, A. As a matter of fact, however, E'E is a 

 fictitious voltage which replaces the effect of change in flux due to 

 armature reaction. 



It is also evident that if IX be increased in value to IX 8 , where 

 IX 8 = IX + E'E, E may be computed without knowing E'. 



