Cogging in Three-Phase Induction Motor

What is Cogging?

Cogging is when a motor has trouble starting because the rotor gets stuck due to magnetic forces between the rotor and stator teeth.

Why It Happens:

1. Tooth Alignment: The teeth of the rotor and stator line up in a way that creates a strong magnetic lock.
2. Harmonics: Unwanted frequencies in the electrical supply can create additional magnetic forces.
3. Design Flaws: Poor design choices like having the same number of slots on the rotor and stator.

How to Fix It:

1. Skewed Slots: Tilt the rotor slots so they don’t align perfectly with the stator slots.
2. Different Slot Numbers: Use a different number of slots on the rotor and stator to prevent alignment.
3. Good Design: Choose the right combination of poles and slots during the design phase.

Effects of Cogging:

• Motor won’t start easily.
• Can cause vibrations and noise.
• Reduces motor efficiency.