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

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Electrical Machines
For a given torque, reducing diverter resistance of a DC series motor causes

 decrease in speed demanding less armature current.
 decrease in speed but armature current remains the same.
 increase in speed but armature currnet remains the same.
 increase in speed demanding more armature current.

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