Phase squirrel cage induction motor:
A phase squirrel cage induction motor is a type of electric motor that is widely used in various industrial applications. It is known for its simplicity, robustness, and reliability. However, it has a fixed speed which may not be suitable for all applications. To overcome this limitation, various speed control methods are employed.

Pole changing method:
The pole changing method is one of the speed control methods used for a phase squirrel cage induction motor. It involves changing the number of poles in the motor's stator winding. By altering the number of poles, the synchronous speed of the motor can be changed, which in turn affects the motor's operating speed.

Working principle:
The pole changing method works by using a multi-speed switch or a pole-changing switch to change the motor's winding configuration. The stator winding of the motor is divided into multiple sections, each with a different number of poles. By connecting the appropriate sections together, the number of poles can be changed.

Procedure:
The pole-changing method typically involves the following steps:

1. Determine the desired speed range: Before implementing the pole-changing method, it is important to determine the desired speed range for the motor. This will help in selecting the appropriate number of poles and winding configuration.

2. Determine the number of poles: Based on the desired speed range, the number of poles required for each speed can be calculated. This will determine the number of sections in the stator winding.

3. Connect the appropriate sections: Using a multi-speed switch or a pole-changing switch, the sections of the stator winding are connected in a specific configuration to achieve the desired number of poles.

4. Control the motor speed: Once the stator winding is configured, the motor can be operated at different speeds by changing the selected sections. This can be done manually or automatically, depending on the application requirements.

Advantages:
- Wide speed range: The pole changing method allows for a wide range of motor speeds, making it suitable for applications that require variable speed operation.
- Simple implementation: The pole changing method is relatively simple to implement compared to other speed control methods.
- Cost-effective: Since it utilizes the existing motor and only requires changes in the stator winding configuration, the pole changing method is a cost-effective solution for speed control.

Limitations:
- Limited number of speeds: The pole changing method provides a limited number of discrete speeds based on the number of poles available in the motor's stator winding.
- Mechanical complexity: Implementing the pole changing method may require additional mechanical components, such as a multi-speed switch or a pole-changing switch, which adds complexity to the motor system.

In conclusion, the pole changing method is a speed control method used for a phase squirrel cage induction motor. It involves changing the number of poles in the motor's stator winding to achieve different motor speeds. It offers a wide speed range and is relatively simple and cost-effective to implement. However, it has limitations in terms of the number of speeds available and the mechanical complexity involved.