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

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Electrical Machines
Which of the following is done in speed control of DC motor by field flux control?

 Inserting resistance to armature circuit and field circuit.
 Any of above.
 Inserting an additional resistance in the field circuit.
 Inserting an additional resistance in the armature circuit.

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

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

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Electrical Machines
Compensating windings are used in DC generators

  mainly to reduce the eddy currents by providing local short circuit.
None of these
  to provide path for the circulation of cooling air.
  to neutralize the cross magnetizing effect of the armature reaction.

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