Three Phase Induction Motor MCQs

21. A 3-phase induction motor

  1. is self-starting with zero torque
  2. is self-starting with high torque
  3. is self-starting with low torque
  4. is not self-starting

Answer. c

22. To use an AC motor in a DC circuit, Which equipment would be required additionally?

  1. Capacitor
  2. Inductor
  3. Inverter
  4. Rectifier

Answer. c

23. Rotating magnetic field is produced in a

  1. Single-phase induction motor
  2. Three-phase induction motor
  3. D.C. series motor
  4. A.C. series motor

Answer. b

24. The output power of any electric motor is taken from

  1. frame
  2. commutator
  3. coupling mounted on shaft
  4. armature

Answer. c

25. The rotor power output of a 3 phase induction motor is 15 kW and the corresponding slip is 4%. The rotor copper losses will be

  1. 525 W
  2. 625 W
  3. 600 W
  4. 500 W

Answer. b

26. If the rotor circuit resistance of a 3-phase induction motor is increased, then

  1. The starting torque will increase but the maximum torque will remain unchanged
  2. Both the starting and the maximum torque will decrease
  3. The starting torque will decrease but the maximum torque will remain unchanged
  4. Both the starting and the maximum torque will increase

Answer. a

27. In the circle diagram for a 3 phase induction motor, the diameter of the circle is determined by?

  1. Rotor current
  2. Rotor current referred to stator
  3. Exciting current
  4. Total stator current

Answer. d

28. Which of the following motors can be used for unity power factor?

  1. Schrage motor
  2. Hysteresis motor
  3. Shaded pole motor
  4. Capacitor run motor

Answer. a

29. Motor operating at maximum power output has an efficiency of approximately

  1. 26.5 %
  2. 50 %
  3. 43 %
  4. 71 %

Answer. b

30. Slip of a 3 phase induction motor is 0.1. If the line frequency is 60 Hz, the rotor frequency will be

  1. 59.4 Hz
  2. 54 Hz
  3. 6 Hz
  4. 5.4 Hz

Answer. c

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