Electrical Machines
Two mechanically coupled alternators deliver power at 50 Hz and 60 Hz respectively. The highest speed of the alternators is

  3000 rpm.
  500 rpm.
  600 rpm.
  3600 rpm.

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

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

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