234 



ALTERNATING CURRENTS 



the extremity of the primary current vector. But since the simple 

 and elegant graphical representation of slip, torque, etc., is in this 



FIG. 146. Torque-speed Curves of Single-phase Induction Motor. 



case no longer possible as with the polyphase motor, the circle diagram 

 for a single-phase induction motor possesses but little practical 

 interest. 



139. Starting of Single-phase Induction Motors 



The single -phase induction motor not being self-starting, special 

 starting devices have to be provided for it. The arrangement most 

 commonly in use is one consisting of an auxiliary starting winding, 

 which occupies the same position relatively to the running winding 

 as the two windings of a two-phase induction motor do relatively to 

 each other. The motor will start if there is a sufficient phase differ- 

 ence between the currents in the two windings. The necessary 



