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

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Electrical Machines
Two of supply terminals to a 3 - Φ induction motor get interchanged during re-connection after normal maintenance. When switched on the supply, the motor will

  rotate in direction opposite to that before maintenance.
  rotate in the same direction as before maintenance.
  not start at all.
  get heated and damaged.

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Electrical Machines
An inverted V curve of synchronous motor shows variation of

  power factor and DC excitation at constant load.
 power factor and supply voltage during hunting.
 supply voltage and field current at constant excitation.
 supply voltage and excitation current at constant load.

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