Electrical Machines
Synchronising power of a synchronous motor varies

 directly as Xs2
 directly as synchronous reactances Xs
All of these
 inversely as 1/Xs

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Electrical Machines
Armature reaction in a DC machine

 is in direct opposition to the main poles.
 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.

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