Electrical Machines
DC generator will not build up voltage

 if field resistance is more than critical resistance.
  if it has lost residual magnetism.
 due to wrong direction of rotation.
 any one of above.

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Electrical Machines
If two 8-pole dc machines of identical armature sare wound, one with lap winding and the other with wave winding, then

 lap-wound machine will have more rated voltage and more current
 lap-wound machine will have more rated voltage and less current
 wave-wound machine will have more rated current and more voltage
 wave-wound machine will have more rated voltage and less current

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