Design of Three Phase Induction Motor MCQ PDF

41. Current density in the rotor bars of an induction motor is taken

(a) 3 to 4 A/mm².
(b) 4 to 7 A/mm².
(c) 8 to 10 A/mm².
(d) 10 to 15 A/mm².

42. If the design of a 3-phase induction motor is done with a higher value of current density then

(a) weight of copper will be more.
(b) temperature rise would be less.
(c) copper losses would be more.
(d) winding resistance would be less.

43. In induction motors, the harmonic fields are produced due to

(a) saturation.
(b) slotting.
(c) windings.
(d) irregularities in the air gap.
(e) all of the above.

44. The value of operating power factor of a 3-phase induction motor is high when

(a) closed slots are used both on stator and rotor.
(b) semi-closed slots are used both on stator and rotor.
(c) open slots are used both on stator and rotor.
(d) open and closed slots are used on stator and rotor respectively.

45. In rotating machines, the harmonics are produced due to

(a) slotting of the stator core.
(b) non-sinusoidal form of field.
(c) both (a) and (b).
(d) none of these.

46. A 3 phase winding carrying sinusoidal currents produces harmonics of the order of

(a) n = 6N ± 3
(b) n = 6N ± 1.
(c) n = 8N ± 1.
(d) n = 8N ± 3.

47. A 5 hp, 400 V, 4-pole, 50 Hz induction motor having 36 slots in the stator and 40 slots in the rotor may crawl synchronously at

(a) 50 rpm.
(b) 150 rpm.
(c) 200 rpm.
(d) 750 rpm. [A.M.I.E. 1993]

48. If the number of slots selected for a 3-phase, 6-pole induction motor is 42, then it is possible to get

(a) balanced fractional slot winding.
(b) full pitch integral slot winding.
(c) short pitch integral slot winding.
(d) none of the above.

49. The effects of harmonics in rotating machines can be reduced/ eliminated by

(a) using distributed winding.
(b) skewing the poles.
(c) increasing air gap length.
(d) using short chord winding.
(e) all of the above.

50. For avoiding cogging in induction motor the difference between the number of stator slots and rotor slots should not be equal to

(a) 3 P
(b) P
(c) 5 P
(d) 7 P

51. Skewing of slots

(a) improves heat transfer.
(b) reduces noise.
(c) suppresses the undesirable harmonics.
(d) none of the above.

52. If the stator of a 4-pole, 3-phase induction motor has 24 slots then the order of tooth ripples produced are

(a) 5 and 7
(b) 6 and 8
(c) 9 and 11
(d) 11 and 13

53. Synchronous cusps in torque-speed curve of a 3-phase induction motor is due to

(a) even harmonics.
(b) odd harmonics.
(c) both odd and even harmonics.
(d) none of the above.

54. The ratio of magnetizing current to ideal short-circuit current is called the

(a) leakage coefficient.
(b) short-circuit ratio.
(c) dispersion coefficient.
(d) none of the above.

55. Dispersion coefficient is the ratio of

(a) magnetizing current to supply voltage.
(b) magnetizing current to ideal short-circuit current.
(c) magnetizing current to full load current.
(d) none of the above.

56. Maximum power factor is given as

(a) (1 – σ)/(1 + σ)
(b) (1 + σ)/(1 – σ)
(c) 1/(1 + σ)
(d) 1/(1 – σ)

57. If the frequency is changed without changing the number of poles, the dispersion coefficient will

(a) increase.
(b) decrease.
(c) remain unaffected.

58. A large value of short-circuit current is an indication of

(a) good pf.
(b) poor pf.
(c) zero pf.
(d) unity pf.

59. For a 20 kW, 3-phase, 400 V induction motor, the no load current is about

(a) 100 A
(b) 40 A
(c) 10 A
(d) 2 A

60. An induction motor of 75 kW, 1000 rpm will have………power factor and…………efficiency in comparison to those of 5 kW 1000 rpm motor.

(a) low, low
(b) high, high
(c) low, high
(d) high, low

61. An induction motor of 10 HP, 1500 rpm will have……….power factor and……..efficiency in comparison to those of 10 Hp; 750 rpm motor.

(a) low, high
(b) high, low
(c) high, high
(d) low, low

62. At s = 0, the torque of an induction motor is

(a) 0.
(b) equal to full-load torques.
(c) very high.
(d) very low.

 

1. Electrical Machine Design MCQ Part – 1
2. Electrical Machine Design MCQ Part – 2
3. Electrical Machine Design MCQ Part – 3

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