Electrical Machines
A dc shunt generator, when commissioned after a major repair of the field system, failed to build Up voltage. It was because

 field winding was wrongly connected
 field resistance was higher than critical resistance
 there was a break in the armature circuit
 field system lost residual magnetism

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Electrical Machines
Armature reaction in a DC machine

 makes an angle with the main pole axis which is load dependent.
 is in the same direction as the main poles.
  makes an angle of 90° with the main pole axis.
 is in direct opposition to the main poles.

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