The term 'cogging' is associated with
A. Three-phase transformers
B. Compound generators
C. D.C. series motors
D. Induction motors
Answer: Option D
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Which is of the following data is required to draw the circle diagram for an induction motor?
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A. Increasing slip
B. Increasing current
C. Both (A) and (B)
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Sometimes, the rotor of a squirrel cage induction motor refuses to start at all, particularly if the supply voltage is low. This happens especially when number of rotor teeth is equal to number of stator teeth, because of magnetic locking between the stator teeth and the rotor teeth. When the rotor teeth and stator teeth face each other, the reluctance of the magnetic path is minimum, that is why the rotor tends to remain fixed. This phenomenon is called cogging or magnetic locking of induction motor.