Electrical Machines
The residual magnetism of a self-excited dc generator is lost. To build up its emf again

 the armature connection must be reversed
 field winding must be excited by low voltage dc supply
 the field winding must be replaced
 the field winding connection must be reversed

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Electrical Machines
The coil spam

 can never be equal to pole pitch.
  may or may not be exactly equal to people pitch.
 none of above.
 must be exactly equal to people pitch.

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