What is what does it mean to split the pole?

Splitting the pole, in the context of electric motors and generators, refers to a technique used to create additional poles in the magnetic field without physically adding more salient (protruding) poles to the stator. This method is primarily employed to:

• Reduce the synchronous speed: The synchronous speed of an AC motor is inversely proportional to the number of poles. By effectively increasing the number of poles via pole splitting, the motor can operate at a lower speed.

• Improve starting torque: Pole splitting can sometimes enhance the starting torque characteristics of the motor.

Here's how it generally works:

1. Shading Coils or Shading Rings: The main way to split the pole is by using shading coils or shading rings. These are typically made of copper and are placed around a portion of the pole face.

2. Induced Current: The alternating magnetic field produced by the main winding induces a current in the shading coil/ring.

3. Phase Delay: The current in the shading coil creates its own magnetic field, which is out of phase with the main field. This creates a "split" in the magnetic pole. Effectively, the pole is now divided into two sections with a slight phase difference in their magnetic fields. The unshaded portion of the pole will have a stronger and earlier field than the shaded area.

4. Directional Torque: The difference in phase and strength between the magnetic fields of the shaded and unshaded portions produce a small starting torque. This method is most common in small AC induction motors like those used in fans, clocks, and other low-power applications.

Important Considerations:

• Efficiency: Motors that employ pole splitting often have lower efficiency compared to other motor designs. This is due to the losses associated with the current circulating in the shading coils/rings.

• Applications: Pole splitting is most suitable for low-power applications where simplicity and low cost are more important than high efficiency.

• Types of Motors: This technique is most often applied to shaded-pole induction motors.

In summary, splitting the pole is an economical but relatively inefficient method to effectively increase the number of poles in an AC motor, thereby reducing its speed and providing a small starting torque.