AC MACHINES-1 (66761) Theory

An induction motor is practically a constant speed motor, that means, for the entire loading range, change in speed of the motor is quite small. Speed of a DC shunt motor can be varied very easily with good efficiency, but in case of Induction motors, speed reduction is accompanied by a corresponding loss of efficiency and poor power factor. As induction motors are widely being used, their speed control may be required in many applications. Different speed control methods of induction motor are explained below.

Induction motor speed control from stator side

1. By changing the applied voltage:

2. By changing the applied frequency
3. Constant V/F control of induction motor
4. Changing the number of stator poles

Speed control from rotor side:

1. Rotor rheostat control
2. Cascade operation
3. By injecting EMF in rotor circuit