Only 60 MCQs on 3-Phase Induction Motor (Helpful)

MCQs on 3-Phase Induction Motor

Hi Learners, in this article we have listed 60+ important MCQs on 3-Phase Induction Motor which will be useful for your competitive exams, various interviews, viva, and other exams. The questions and answers are all collected from different exams and interviews of previous years.

Also, you need to know: 60+ Important MCQs on DC Motor

These listed MCQs will be helpful for your conceptual clarity and preparation about the 3-Phase Induction Motor.

1. An induction motor works with

a) DC only
b) AC Only
c)  Both AC & DC
d)  None of these

Answer: b

2. The stator frame in an induction motor is used to

a) Hold the armature stampings in position
b) Ventilate the armature
c)  Protect the whole machine
d)  Provide a return path for the flux

Answer: a

3. The frame of an induction motor is made of

a) Aluminum
b) Silicon steel
c) Closed-grained cast iron
d)  Stainless steel

Answer: c

4. The stator core of a 3- phase induction motor is laminated in order to reduce the

a) Eddy’s current loss
b) Hysteresis loss
c)  Both eddy current and hysteresis I loss
d)  Weight of the stator

Answer: a

5. Use of fractional pitch winding

a) Results in the reduced leakage reactance
b) Results in reduced axial length of the machine
c) Makes it stiffer
d) All of the above

Answer: d

6. If all the stator coils of an induction motor are connected for the same magnetic polarity, there will be formed an equal number of

a) Rotor poles with the same polarity
b) Rotor poles with opposite polarity
c)  Consequent pole with opposite polarity
d)  Consequent poles with the same polarity

Answer: c

7. The induction motor shaft should be

a) Hollow
b) Stiff
c)  Flexible
d)  Any of these

Answer: b

8. The induction motor shaft is made of

a) Mild steel
b) Cast iron
c) High-speed steel
d)  Stainless steel

Answer: a

9. Induction motors normally use die-cast aluminum rotors because aluminum is

a) Cheaper in cost
b) Lighter in weight
c)  Easy to cast owing to its low melting point and is easily available
d)  Of low resistivity

Answer: c

10. In a 3-phase squirrel cage induction motor

a) Rotor conductors are short-circuited through end rings
b) Rotor conductor ends are short-circuited through slip rings
c)  Rotor conductors are kept open
d)  None of the above

Answer: a

11. The squirrel cage rotor of a 6-pole induction motor can be used for ______induction motor

a) Only 6-pole
b) 6 or 12 poles
c)  Any number of poles in an
d)  None of the above

Answer: c

12. The squirrel cage induction motors are provided with blades in order to

a) Facilitate cooling of the rotor
b) Balance the rotor dynamically
c) Eliminate noise
d) None of these

Answer: a

13. The rotor of a 3-phase wound rotor induction motor is provided with

a) Single-phase winding
b) Three-phase winding
c)  Heavy copper or aluminum bars placed in rotor slots
d)  Heavy short-circuited end rings

Answer: b

14. In a 3-phase slip ring induction motor, the rotor winding terminals are brought out through slip rings to

a) Connect extra resistance across them during starting
b) Connect them either in star or in delta as per need
c)  Connect to 3-phase ac supply
d)  Close the rotor circuit externally

Answer: a

15. The rotor winding for a 3-phase slip ring induction motor having delta connected stator must be connected in

a) Delta
b) Star
c) Delta or star according to need
d) None of the above

Answer: b

16. In a 3-phase slip ring induction motor, brushes are connected to

a) External star-connected resistors
b) DC supply
c) 3-Phase AC supply
d) Equalizing coils

Answer: a

17. In a 3-phase wound rotor induction motor, the short circuit gear is used to short-circuit the

 a) Stator phases of the motor
b) Rotor at slip rings
c) Starting resistance in the starter
d) None of the above

Answer: b

18. An uneven gap in an induction motor is likely to cause

a) Heating of motor
b) Unbalancing of the motor shaft
c) Both (a) and (b)
d) None of these

Answer: c

19. A smaller air gap in a poly-phase induction motor helps to

a) Reduce the chance of crawling
b) Increase the starting torque
c) Reduce the chance of cogging
d) Reduce the magnetizing current

Answer: d

20. In an induction motor, if the air gap is increased

a) Its speed will reduce
b) Its efficiency will improve
c) Its power facts will reduce
d) Its breakdown torque will reduce

Answer: c

21. In an induction motor, the air gap flux density is usually kept low so as to

a) Improve efficiency
b) Improve power factor
c)  Reduce machine cost
d)  None of the above

Answer: b

22. A wound rotor induction motor can be distinguished from a squirrel cage induction motor by

a) Presence of slip rings
b) Size of frame
c)  Shaft diameter
d)  Any of the above

Answer: a

23. Induction motors normally

a) The stator winding is connected to ac supply and the rotor winding is short-circuited
b) The rotor winding is connected to ac supply and the stator winding is short-circuited
c)  Both the stator and rotor windings are connected to ac supply
d)  Stator winding is connected to ac supply and rotor winding to dc supply

Answer: a

24. A 3-phase, 4-squirrel cage induction motor has 36 stator and 28 rotor slots. The number of phases in the rotor is

a) 3
b) 9
c)  7
d)  8

Answer: a

25. The rotor slots are slightly skewed in the squirrel cage induction motor to

a) Increase the strength of rotor bars
b) Reduce the magnetic hum and locking tendency of rotor
c) Economize on the copper to be used
d) Provide case of fabrication

Answer: b

26. Skewing of the rotor in a three-phase squirrel cage induction motor reduces

a) Nose parasitic torque, starting torque, and pull-out torque
b) Noise and parasitic toque, but increases starting torque and pull-out torque
c)  Noise and pull-out torque, but increases parasitic torque ad starting torque
d)  Noise, parasitic torque, and starting torque, but increases

Answer: a

27. The principle of operation of a 3-phase induction motor is almost similar to a

a) Synchronous motor
b) Repulsion start induction motor
c)  Transformer with a shorted secondary
d)  Capacitor start induction motor

Answer: c

28. The rotor of a 3-phase induction motor rotates in the same direction as that of a stator rotating field. This can be explained by

a) Faraday’s laws of electromagnetic induction
b) Lens’s law
c)  Newton’s law of motion
d)  Fleming’s right-hand rule

Answer: b

29. Stator flux induces emf in the rotor bar

a)Rotating at synchronous speed around the stator
b) Constant in magnitude
c) Magnitude depending upon the load on the motor
d)  None of the above

Answer: c

30. The rotor circuit of an induction motor under operating conditions is

a)Always closed
b) Always open
c) May be open or closed depending upon the loading conditions
d)  None of the above

Answer: a

31. The 3-phase induction motor with the rotor circuit open will

a) Run normally
b) Get overheated
c)  Not run
d)  Make noise

Answer: c

32. If any two leads from slip rings are interchanged in a 3-phase induction motor the motor will

a) Continue running in the same direction as before
b) Run in a direction opposite to the previous one
c) Not run
d) Get damaged

Answer: a

33. Two of the supply terminals to a 3-phase induction motor get interchanged during reconnection after normal maintenance, when switched on to supply the motor will

a) Rotate in the same direction as before maintenance
b) Rotate in a direction opposite to that before maintenance
c)  Not start at all
d)  get heated and damaged

Answer: b

34. The direction of rotation of a 3-phase induction motor can be reversed by

a) Transposing any two leads from the supply
b) Transposing any two leads from slip rings
c)  Transposing all three leads from the supply
d)  Disconnecting any one phase

Answer: a

35. The rotor of an induction motor rotates in the direction of the rotation of the stator field in order to

a) Reduce the relative speed between the rotating stator field and the stationary rotor conductors
b) Oppose the rotor current
c) Increase the relative speed between the rotating stator field and stationary rotor conductors
d) None of the above

Answer: a

36. The rotor of an induction motor never runs at synchronous speed because then the relative speed between the rotating flux and rotor will be

a) Maximum and hence, torque will be maximum
b) Maximum and hence, torque will be zero
c) Zero and hence, torque will be maximum
d) Zero and hence torque will be zero

Answer: d

37. The voltage actually used for the setting of the useful flux in the air gap of a 3-phase induction motor is

a) Equal to the applied voltage
b) > applied voltage
c) < applied voltage
d) = rotor-induced emf

Answer: a

38. Synchronous speed is defined as the speed at which the

a) Stator magnetic field rotates
b) Rotor rotates on no load
c) Rotor rotates on full load
d) None of the above

Answer: a

39. The maximum possible speed of a 3-phase squirrel cage induction motor running at a slip of 4% is

a) 2,880 rpm
b) 3,000 rpm
c) 1,440rpm
d) 960rpm

Answer: a

Also Read: 130+ Polyphase Induction Motors MCQs and Answers [Top100+ Hitlist]

40. A three-phase 6 poles, 50 Hz, an induction motor is running at 5% slip. What is the speed of the motor?

a) 850 rpm
b) 900 rpm
c) 950 rpm
d) 1000 rpm

Answer: c

41. The no-load current in an induction motor is ____in comparison to that of a power transformer

a)  Much lower
b) Much higher
c) Slightly less
d)  Slightly more

Answer: b

42. In a 3-phase induction motor, the variable mechanical load is represented electrically by a variable ____only

 a) Inductance
b) Capacitance
c)  Resistance
d)  Any of these

Answer: c

43. If the load on an induction motor is increased from no load to full load, its slip and the power factor will, respectively

a) Decrease, decrease
b) Decrease, increase
c)  Increase, decrease
d)  Increase, increase

Answer: d

44. The output power of a 3-phase induction motor will be maximum when the equivalent load resistance is equal to the standstill leakage _____of the motor

a) Impedance  Z
b) Reactance  X
c)  Resistance
d)  Capacitance

Answer: a

45. The power factor of an induction motor operating at no load will have a value of around

a) 0.9 lag
b) 0.2 lead
c) 0.2 lag
d) 0.9 lead

Answer: c

46. The power factor of an induction motor at full load is likely to be

a) Unity
b) 85 lead
c)  0.85 lag
d)  0.5 lag

Answer: c

47. The power factor of a 3-phase induction motor is likely to be maximum when it will operate at

a) Full load
b) No-load
c)  Maximum slip
d)  Maximum torque

Answer: a

48. The power factor of a lightly loaded induction motor is quite low because

a) The current drawn is largely a magnetizing current due to the air gap
b) Of the current due to air gap
c)  The current drawn is largely a magnetizing component due to the laminated core
d)  The current drawn is largely an energy component due to the laminated core

Answer: a

49. When the load is increased from light load in a 3-phase induction motor

a)Rotor pf increases but stator pf decreases
b) Stator pf increases but the rotor pf decreases
c) Both stator and rotor pf increase
d)  Both stator and rotor pf decrease

Answer: b

50. An induction motor always operators on lagging power factor this is due to

a)Stator reactance
b) Rotor leakage reactance
c) The large reactive lagging magnetizing current essential to produce the magnetic flux
d)  All of the above

Answer: d

51. Open circuit test is usually conducted on which type of induction motor?

a) Slip-ring motors
b) Wound rotor motors
c) Either of (a) and (b)
d) None of these

Answer: c

52. In which of the following tests to be conducted on induction motors, reduced voltage is applied

a) Blocked rotor test
b) No load test
c) Both (a) and (b)
d) None of these

Answer: a

53. The blocked rotor test of an induction motor corresponds, incase of a transformer to

a) Full load
b) Half-full load
c)  No load
d)  Short circuit operation

Answer: d

54. What is the shunt resistance component in an equivalent circuit obtained by the no-load test of an induction motor representative of?

a) Windage and frictional losses only
b) Core losses only
c)  Core, windage and frictional losses
d)  Copper losses

Answer: b

55. Under the no-load conditions, if the applied voltage to an induction motor is reduced from the rated voltage to half the rate value

a) The speed decrease and the stator current increases
b) Both the speed and the stator current decrease
c) The speed and the stator current remain practically constant
d) There are negligible changes in the speed but the stator current decreases

Answer: b

56. The core losses, and friction and windage losses in case of an induction motor are determined from the _____test

a) No load
b) Blocked rotor
c) Load
d) Stator resistance

Answer: a

57. A short circuit test is performed on an induction motor to determine

a) Short-circuit current under rated voltage
b) Equivalent resistance and reactance
c) Transformation ratio and Power factor on short circuit
d) All of the above

Answer: d

58. A circle diagram is employed to determine the performance of a

a) Synchronous motor
b) Induction motor
c) DC motor
d) Transformer

Answer: b

59. The power scale of the circle diagram of an induction motor is determined from ____test data only

a) Open circuit
b) Stator resistance
c) Short circuit
d) Slip

Answer: c

60. In the circle diagram of an induction motor, the diameter of the circle represents the

a) Rotor current
b) Line voltage
c) Operating torque
d) Maximum torque

Answer: a

Did you know?? 8 Facts and Reasons Behind this Electrical Equipment at our Home

If you find this article helpful, share this article with your friends who are also Electrical and electronics engineers. Lastly, if you have any questions ask feel free to comment down below, and we will reply to you back right away.

LEAVE A REPLY

Please enter your comment!
Please enter your name here