Electrical Machines
A 250 V DC generator in run at rated speed with no excitation. The open circuit voltage will be

  zero.
  very small, say about 2 or 3 V.
 about 100 V.
  250 V.

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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

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

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