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

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Electrical Machines
Cogging in induction motor occurs when

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

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