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

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

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Electrical Machines
In large sized DC machines the compensating windings are provided to

  neutralize voltage induced in coil due to fluctuation of l
 compensate for the decrease in speed due to increase of load.
 reduce eddy current losses by providing local short circuits.
None of these

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