What are Crawling and Cogging of Induction Motor?

What  are Crawling and Cogging of Induction Motor?

Induction Motor Phenomena

Crawling and cogging are important characteristics to understand in the operation of squirrel cage induction motors.

Crawling Definition

This is when an induction motor runs at much lower speeds than its designed speed, primarily caused by harmonics like the 5th and 7th producing additional torque.

Cogging in Induction Motor

Occurs when the motor fails to start because the slots of the stator lock up with the rotor slots, often due to matching slot numbers or harmonic interference.

Preventing Cogging

• The number of slots in rotor should not be equal to the number of slots in the stator.

• Skewing of the rotor slots, that means the stack of the rotor is arranged in such a way that it angled with the axis of the rotation.

Understanding Harmonics

Recognizing how harmonic frequencies interact with the motor’s slot frequencies is crucial for diagnosing and solving motor issues like cogging and crawling.