Electrical Machines
Short circuiting is caused in the armature winding due to

  failure of insulation between two turns of coil.
 failure of insulation between two commutator bars.
  any of above.
  grounding of two or more turns of the same coil.

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Electrical Machines
The synchronous reactance( Xs) is the

 reactance due to leakage flux
 combined reactance due to armature reaction and leakage flux
 reactance due to armature reaction of the machine
 reactance either due to armature reaction or leakage flux

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