Electrical Machines
Cogging in induction motor occurs when

 number of stator teeth - number of rotor teeth = negative number.
 number of stator teeth - number of rotor teeth = odd number.
 number of stator teeth - number of rotor teeth = 0.
 number of stator teeth - number of rotor teeth = even number.

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Electrical Machines
A dc shunt generator, when commissioned after a major repair of the field system, failed to build Up voltage. It was because

 field winding was wrongly connected
 there was a break in the armature circuit
 field system lost residual magnetism
 field resistance was higher than critical resistance

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Electrical Machines
Two of supply terminals to a 3 - Φ induction motor get interchanged during re-connection after normal maintenance. When switched on the supply, the motor will

  rotate in direction opposite to that before maintenance.
  get heated and damaged.
  rotate in the same direction as before maintenance.
  not start at all.

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