Electrical Machines
For satisfactory parallel operation of two transformers which of the following conditions is most essential,

 percentage impedance of all transformers must be same.
 MVA rating of all transformer inversely proportional to impedance.
  polarities of all transformers must be same.
 voltage ratio of all transformers must be same.

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Electrical Machines
An alternator is feeding an infinite busbar. Its prime mover is suddenly shutdown. The alternator will

 continue to work as synchronous motor with same direction of rotation.
 continue to work as alternator but the direction of rotation will reverse.
 start working as induction motor.
 come to stand still.

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

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