Electrical Machines
A dc shunt generator, when driven without any excitation, showed an open circuit voltage of 12 V. When the field winding was excited, the voltage dropped to zero. It happened because

 field winding was wrongly connected
 there was a break in the armature circuit
 field resistance was higher than critical resistance
 there was no residual magnetism in the field circuit

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

ANSWER DOWNLOAD EXAMIANS APP