Electrical Machines
Commutator in DC generator is used for

 reduce losses
 collecting of current
 convert AC armature current in to DC
 increase efficiency

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

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

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