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

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Electrical Machines
In a star - delta starting of an IM

  resistance is inserted in the rotor.
  applied voltage per stator phase is 57.7 % of a line volt
  reduced voltage is applied to the stator.
  line voltage is 57.7 % of stator voltage.

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