Why the Rotor of Induction Motor is Skewed? Need of Skewing

The Rotor of the Induction Motor is skewed to prevent the Cogging Phenomenon. This is the main reason. For the skewing of the rotor of the induction motor, there are also some additional advantages. In this article, we will discuss what is skewing, how skewing of the rotor prevents Cogging, and the additional advantages of skewing. So let's discuss it in detail.

What is Skewing of Rotor?

In the induction motor rotor, the slots for the placement of conductors are not made exactly in parallel with the rotor shaft. A slight angle is maintained which means the rotor slots are made at some angle with the rotor shaft. This is called the Skewing of the rotor or Skewed Rotor.

In the above figure, you can see there are two types of the rotor are shown, the left side rotor is the unskewed rotor which means the slots are made exactly in parallel with the rotor shaft. The right side rotor is the skewed rotor. Here you can see the slots are made maintaining a slight angle. So the right-side skewed rotor is used in the Induction motor.

What is Cogging?

The main reason for using a skewed rotor is to prevent the Cogging. So let's discuss what is Cogging in an Induction Motor. In simple words, Cogging is the phenomenon of the magnetic locking between the Stator and Rotor of the Induction Motor. This magnetic locking occurs when the number of stator slots is equal to the number of rotor slots.

How Skewing of Rotor Eliminate the Cogging?

When the rotor is skewed or the slots are made at some angle, the magnetic locking between the stator and rotor is eliminated. As the slots are made at some angle, that means the aluminum bars (Which are used as conductors) are also placed at some angle. So when the magnetic flux is produced by the stator winding, the rotor bars cut the flux uniformly. The next bar starts cutting the magnetic flux before finishing the cutting of flux by the previous bar. So this continuous flux cutting creates a continuous torque on the rotor and eliminates the chance of magnetic locking.

Advantages of Skewing of Rotor in Induction Motor

1. The first and main advantage is the elimination of Cogging or magnetic locking.

2. As the skewing of the rotor is to reduce the magnetic locking, so the magnetic hum (vibration and sound) is also reduced.

3. It causes the production of uniform flux in the rotor, for this reason, the induction motor runs uniformly.

4. It increases the effective coupling between Rotor and Stator fluxes.

5. It also helps to reduce the Crawling in Induction Motor.

6. As the conductors are placed at some angle, the length of the conductor's increases, therefore the effective rotor resistance increases which helps to create more torque on the rotor.

 Read Also:

• Why DC is used not AC for excitation of Synchronous Alternator and Motor?
• Why Three Phase Induction Motor Self-Starting but Synchronous Motor not?
• Actual Difference Between Synchronous Motor and Induction Motor

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