Electrical Machines
A single-phase transformer has its maximum efficiency at 60 percent of full load. At full load copper loss will be

 equal to core loss.
  more than core loss.
 less than core loss.
 zero.

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

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Electrical Machines
Armature reaction in a DC machine

 makes an angle with the main pole axis which is load dependent.
  makes an angle of 90° with the main pole axis.
 is in the same direction as the main poles.
 is in direct opposition to the main poles.

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