Electrical Machines
The synchronous reactance( Xs) is the

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

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Electrical Machines
In case of 3 - Φ IM, plugging means

  pulling the motor directly on line without a rotor.
  locking of rotor due to harmonics.
  interchanging two supply phases for quick stopping.
  starting the motor on load which is more than the rated load.

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