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
 there was no residual magnetism in the field circuit
 field winding was wrongly connected
 there was a break in the armature circuit

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Electrical Machines
In a stepper motor the detente torque means

  maximum of the static torque with the phase winding unexcited.
  minimum of the static torque with the phase winding unexcited.
  minimum of the static torque with the phase winding excited.
  maximum of the static torque with the phase winding excited.

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