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

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Electrical Machines
Cogging and crawling are phenomena associated with

 the former during starting and the latter at a fraction of its rated speed.
 any of the above.
 cage induction machines and they are essentially the same.
 the former at a fraction of its rate speed and the latter during starting.

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