THE INDUCTION MOTOR. 



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curve A y Fig. 239, shows the relation between torque and speed 

 of a two-phase induction motor with both phases connected to 

 the supply mains, and curve B shows the relation between 

 torque and speed of the same motor with but one phase connected 

 to the supply mains. This figure shows that when driven by 

 single-phase current (at normal voltage), the motor runs at a 

 slightly lower speed to develop a given torque, it shows that the 



maximum or break-down torque occurs at a higher speed and is 

 less in value than the break-down torque of the same motor when 

 driven by two -phase currents, and it shows that the single-phase 

 induction motor develops zero torque at stand-still. In fact, the 

 single-phase motor must be started either as a polyphase induc- 

 tion motor or by other means as described in the next article. 



134. Starting of the single-phase induction motor, (a) Hand 

 starting. Small single-phase motors are sometimes intended to 

 be started by closing the supply switch and giving a pull on the 

 belt which connects the motor to the machine which it is intended 

 to drive. 

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