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

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

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Electrical Machines
Torque angle of a synchorous machine operating from a constant voltage bus is usually defined as the space angle between

  Rotor mmf wave and stator mmf wave.
 Stator mmf wave and resultant mmf wave.
 Stator mmf wave and resultant flux density.
 Rotor mmf wave and resultant flux density wave.

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