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

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Electrical Machines
The damper windings also called the squirrel cage windings or damper grids

  both (A) and (B).
  consists of short-circuited copper bars embedded in the field pole faces.
  are provided on the stator for improving power factor.
  are provided in a synchronous motor to make it self starting.

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