The speed of a squirrel cage induction motor is changed by
The speed of a squirrel cage induction motor is changed by Pole changing method.
In this method, the motor is wound with two or more pole numbers, and these poles can be interconnected in various ways to achieve different speeds.
The stator winding of a squirrel cage induction motor has a fixed number of poles, and the speed of the motor is determined by the synchronous speed equation:
Synchronous speed = (120 x frequency) / number of poles
To change the speed of the motor, the number of poles must be changed. This can be achieved by adding or removing stator windings or by using a multi-speed switch that connects different combinations of the windings.
For example, a 4-pole motor can be converted to a 2-pole motor by disconnecting half of the stator windings and connecting the remaining windings in series.
This will double the frequency of the stator current, which will double the synchronous speed of the motor.
Similarly, a 4-pole motor can be converted to an 8-pole motor by connecting two sets of windings in parallel.
This will halve the frequency of the stator current, which will halve the synchronous speed of the motor.