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

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Electrical Machines
Short circuit test is performed on a transformer with a certain impressed voltage at rated frequency. If the short circuit test is now performed with the same magnitude of impressed voltage, but at frequency higher than the rated frequency then

 The magnitude of current will decrease but the power factor will increase.
 The magnitude of circuit as well as the power factor will decrease.
 The magnitude will both increase.
 The magnetude of current will increase, but power factor will decrease.

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Electrical Machines
Skewing of the rotor in a 3 - Φ squirrel cage induction motor reduces

  noise, parasitic and starting torque, but increase pull out torque.
  noise and parasitic torque, but increase starting and pull-out torque.
  noise, parasitic torque, starting torque and pull out torque.
  noise and pullout torque, but increase parasitic and starting torque.

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