Electrical Machines
The rotor of a 3 - Φ wound induction motor is provided with

  heavy short-circuited end rings.
  heavy copper or aluminium bars placed in rotor slots.
  three phase winding.
  single phase winding.

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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

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

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