The andlsquo;coggingandrsquo; of an induction motor can be avoided by:a)Proper ventilationb)Using DOL starterc)Auto-transformer starterd)Having number of rotor slots more or less than the number of stator slotsCorrect answer is option 'D'. Can you explain this answer?

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The ‘cogging’ of an induction motor can be avoided by:

a)
Proper ventilation
b)
Using DOL starter
c)
Auto-transformer starter
d)
Having number of rotor slots more or less than the number of stator slots

Correct answer is option 'D'. Can you explain this answer?

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The ‘cogging’ of an induction motor can be avoided by:a)Pr...

Sometimes induction motor refuses to start at all. Sometimes it happens because of the low supply voltage. But the main reason for starting problem in the motor is because of cogging in which the slots of the stator get locked up with the rotor slots.

As we know that there is a series of slots in the stator and rotor of the induction motor. When the slots of the rotor are equal in number with slots in the stator, they align themselves in such way that both face to each other and at this stage the reluctance of the magnetic path is minimum and motor refuse to start. This characteristic of the induction motor is called cogging.

Apart from this, there is one more reason for cogging. If the harmonic frequencies coincide with the slot frequency due to the harmonics present in the supply voltage then it causes torque modulation. As a result of it, cogging occurs. This characteristic is also known as magnetic teeth locking of the induction motor.

This problem can be easily solved by adopting several measures. These solutions are as follows:

1. The number of slots in the rotor should not be equal to the number of slots in the stator.
2. 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.

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The ‘cogging’ of an induction motor can be avoided by:a)Proper ventilationb)Using DOL starterc)Auto-transformer starterd)Having number of rotor slots more or less than the number of stator slotsCorrect answer is option 'D'. Can you explain this answer?

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