Question

Why single phase induction motor has zero starting torque

Answer 1

Hey there..❤

So the net torque developed is zero and hence single phase induction motor is not self starting. BUT in single phase induction motor there is single phase supply to the stator of motor.A SINGLE PHASE SUPPLY CAN NOT PRODUCE A ROTATING MAGNETIC FIELD BUT IT PRODUCE A PULSATING MAGNETIC FIELD WHICH DOES NOT ROTATE.

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Answer 2

Hope you would like it:-

• During the positive half cycle the rotor will rotate in one direction and in negative half cycle it rotates opposite to that. So the net torque developed is zero and hence single phase induction motor is not self starting.

• To convert it into self starting we need to add one more winding (starting winding) and that should be resistive than main winding. So When a single phase supply is given to motor two fluxes will setup one is due to main winding which lags the flux due to starting winding. Since two flux can't exist in an air gap, both will combine and create an unidirectional flux which makes the motor to rotate in one direction. Once the motor reaches 70 percent of its rated speed the starting winding can be removed and the motor will continue to rotate.