synchronous motors MCQs – Page 3

Practise focused synchronous motors questions with marked answers for exam preparation and subject revision.

synchronous motors Mcqs

41. An over-excited synchronous motor takes__________?
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A. leading current

B. lagging current

C. both A. and (b)

D. none of the above

42. Slip-rings in a synchronous motor carry____________?
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A. no current

B. direct current

C. alternating current

D. all of the above

43. Which of the following motors will be used in electric clocks?
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A. D.C. series motor

B. A.C. induction motor

C. A.C. synchronous motor

D. D.C. shunt motor

44. Hunting in a synchronous motor cannot be due to___________?
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A. variable frequency

B. variable supply voltage

C. windage friction

D. variable load

45. When the voltage applied to a synchronous motor is increased, which of the following will reduce?
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A. Stator flux

B. Pull in torque

C. Both A. and (b)

D. None of the above

46. A synchronous motor can be made self starting by providing?
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A. damper winding on rotor poles

B. damper winding on stator as well as rotor poles

C. damper winding on stator

D. none of the above

47. The operating speed of a synchronous motor can be changed to new fixed value by___________?
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A. changing the load

B. using brakes

C. changing frequency

D. changing the supply voltage

48. A synchronous motor connected to infinite bus-bars has at constant full load, 100% excitation and unity power factor. On changing the excitation only, the armature current will have_____________?
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A. lagging power factor with over-excitation

B. leading power factor with over-excitation

C. leading power factor with under-excitation

D. no change of power factor

49. The angle between the rotating stator flux and rotor poles is called _________ angle.
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A. torque

B. obtuse

C. power factor

D. synchronizing

50. In a synchronous motor, damper windings are provided on____________?
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A. rotor shaft

B. none of the above

C. pole faces

D. stator frame

51. An over excited synchronous motor is used for____________?
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A. variable speed loads

B. low torque loads

C. power factor corrections

D. fluctuating loads

52. While starting a synchronous motor by induction motor action, field winding is usually_____________?
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A. kept open-circuited

B. connected to D.C. supply

C. short-circuited by low resistance

D. none of the above

53. When V is the applied voltage, then the breakdown torque of a synchronous motor varies as_________?
0

A. V

B. V2

C. 1/V

D. V312

54. The shaft of synchronous motor is made of____________?
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A. alnico

B. mild steel

C. stainless steel

D. chrome steel

55. When a 3-phase synchronous generator is supplying a zero power factor lagging load, the armature field affects the main field in the following way
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A. augments it directly

B. none of the above

C. directly opposes it

D. cross-magnetises it

56. A synchronous motor has better power factor as compared to that of an equivalent induction motor. This is mainly because?
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A. mechanical load on the rotor remains constant

B. synchronous motor has large airgap

C. stator supply is not required to produce magnetic field

D. synchronous motor has no slip

57. The efficiency of a properly designed synchronous motor will usually fall in range___________?
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A. 99 to 99.5%

B. 75 to 80%

C. 85 to 95%

D. 60 to 70%

58. The working of a synchronous motor is similar to_____________?
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A. turbine

B. transmission of mechanical power by shaft

C. distribution transformer

D. none of the above

E. gear train arrangement

59. The armature current of the synchronous motor has higher values for_____________?
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A. high excitation only

B. low excitation only

C. both A. and (b)

D. none of the above

60. The back e.m.f. in the stator of a synchronous motor depends on____________?
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A. flux density

B. none of the above

C. rotor speed

D. number of poles

E. rotor excitation

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