Electrical Machines
The armature resistance of a permanent magnet dc motor is 0.8 Ohm. At no load, the motor draws 1.5 A from a supply voltage of 25 V and runs at 1500 rpm. The efficiency of the motor while it is operating on load at 1500 rpm drawing a current of 3.5 A from the same source will be

 59.2%.
 88.8%.
 57.1%.
 48.0%.

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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.
  locking of rotor due to harmonics.
  starting the motor on load which is more than the rated load.

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