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
The results of a slip test for determining direct axis (Xd) and quadrature axis (Xq) reactances of a star connected salient pole alternator are given below Phase values: Vmax = 108 V ; Vmin = 96 V Imax = 12 A ; Imin = 10 A Hence the two reactances will be

 Xd = 9Ω and Xq = 9.6Ω
 Xd = 9.6Ω and Xq = 9Ω
 Xd = 10.8Ω and Xq = 8Ω
 Xd = 8Ω and Xq = 10.8Ω

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