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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Electrical Machines
A bipolar dc machine with interpoles has a main-pole flux of ф per pole and an interpole flux of Фᵢ per pole. The yoke of the machine is devide into four quadrants by the main-pole axis and The commutation axis. The flux-distribution in the quadrants will be

 ½ ( ф + фᵢ ) in two adjacent quadrants and ½ ( ф - фᵢ ) in the remaining two quadrants
 ½ ( ф - фᵢ ) in all the four quadrants
 ½ ( ф + фᵢ ) in all the four quadrants
 ½ ( ф + фᵢ ) in two diametrically opposite quadrants and ½ ( ф - фᵢ ) in the remaining two Quadrants

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