• 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.