THE ALTERNATING CURRENT GENERATOR 269 



Effect of Increasing the Voltage. If the voltage of 

 No. 2 is increased to OE2 f , there is a resultant voltage OR' 

 acting in the local circuit. As the armature circuits are 

 highly inductive, the e.m.f. will produce a current nearly 

 90 behind it in phase, shown in Fig. 165 by 01', lagging 

 behind OR', by the angle 0, where 



tan = 



inductance of both armatures 

 resistance of both armatures ' 



FIG. 165. Vector Diagram of Circulating Current. 



The current 01' is practically 90 behind the phase of 

 OE2, hence does not represent a load on machine No. 2; 

 also it is practically 90 ahead of OEi, and so does not 

 represent a load on machine No. 1. It is merely a reactive 

 current, circulating between the two armatures and repre- 

 senting no power in either of them. 



Effect of Decreasing the Voltage. If the voltage of 

 machine No. 2 is decreased to OE2 f , the resultant current 

 is again reactive but opposite in phase to what it was before 

 as shown at 01" in Fig. 165; it now leads OE% and lags 

 behind OE\. This circulating current is really a magnet- 

 izing current for one machine and a demagnetizing current 



