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What is Cogging in Induction Motor

The motor is the main strength of the industry. So we need to know about the problems and solutions of the motor. We have heard of loss, effect, etc. But the term of cogging may be new for some of us. Today we will define cogging in induction motor.

Define Cogging in Induction Motor

Cogging means matching. But what is matching here? The number of slots of stator and rotor. But how?

Sometimes induction motor doesn’t want to start because of insufficient torque. But why it’s not getting enough torque? It happens for low voltage. But one of the main reasons for the induction motor not getting started is cogging. Stator slots get attached with rotor slots magnetically.

We know that the stators and rotors have so many slots. If the number is the same, stator slots and rotor slots stay in a position by facing each other. As a result, there is a minimum flow of magnetic flux/reluctance. That’s why there is no starting torque and the motor stays still. This condition of induction motor is called cogging. 

There is another reason for cogging. If there is Harmonix in voltage flow, Harmonix frequency matches slot frequency and causes torque modulation. As a result, cogging happens. This characteristic is also known as magnetic teeth locking.

Cogging in Induction Motor

Cogging and Tug of War

Let’s think of tug of war. In this game, two team pulls a rope to their side.  If the rope stays in the middle and the result of the game is a tie, it means two teams put the same force and that’s the reason the rope is still. 

In the same way, if the slot number of stator and rotor is the same, both make equal magnetic field and there will be no force. As a result, the motor finds no torque for rotation and the motor stays still.

Cogging and Tug of War

How to Prevent Cogging

If there is a problem, there is a solution. We can prevent this problem by taking some steps.

  1. The number of slots of rotor and stator shouldn’t be the same.
  2. Row of the rotor’s slot has to be at an angle with its rotation field.

That was all for today. Hope you can now define cogging in induction motor.

You can also read: What Causes an Intermittent Power Outage and How to Solve It?

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Md. Nazmul Islam
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