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

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Electrical Machines
In a dc generator operating on load with its brushes on the geometrical neutral axis (GNA), the magnetic neutral axis (MNA) is shifted in the direction of rotation. Now, if the brushes are given a lead of 90° (electrical), then the MNA will

 coincide with the GNA
 shift forward by 90°
 shift forward by more than 90°
 shift forward by less than 90°

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