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

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

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Electrical Machines
In a dc generator operating on load with its brushes on the geometrical neutral axis (GNA), the magnetic neutral axis (MNA) is shifted in the direction of rotation. Now, if the brushes are given a lead of 90° (electrical), then the MNA will

 shift forward by 90°
 shift forward by less than 90°
 shift forward by more than 90°
 coincide with the GNA

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