Most Synchronous Motors

41. If the field of a synchronous motor is underexcited, the power factor will be

  1. zero
  2. unity
  3. lagging
  4. leading

Correct answer: (C)
lagging

42. If the field winding of an unloaded salient pole synchronous motor is open circuited, the motor will

  1. stop
  2. run as induction motor
  3. function as static condenser
  4. burn with dense smoke

Correct answer: (A)
stop

43. If the synchronous motor, properly synchronised to the supply is running on no load and is having negligible loss then

  1. the stator current will be zero
  2. the stator current will be very small
  3. the stator current will be very high
  4. the back e.m.f. will be more than the supply voltage

Correct answer: (A)
the stator current will be zero

44. In a 3-phase synchronous motor, the negative phase sequence exists when the motor is

  1. supplied with unbalanced voltage
  2. under-loaded
  3. over-loaded
  4. none of the above

Correct answer: (A)
supplied with unbalanced voltage

45. In a 3-phase, 4-pole, 50 Hz synchronous motor, the frequency, pole number and load torque all are halved. The motor speed will be

  1. 3000 r.p.m.
  2. 1500 r.p.m.
  3. 750 r.p.m.
  4. none of the above

Correct answer: (B)
1500 r.p.m.

46. In a synchronous motor it the back e.m.f. generated in the armature at noload is approximately equal to the applied voltage, then

  1. the motor is said to be fully loaded
  2. the torque generated is maximum
  3. the excitation is said to be zero per cent
  4. the excitation is said to be hundred per cent

Correct answer: (D)
the excitation is said to be hundred per cent

47. In a synchronous motor running with fixed excitation, when the load is increased three times, its torque angle becomes approximately

  1. one-third
  2. twice
  3. thrice
  4. six times

Correct answer: (C)
thrice

48. In a synchronous motor which loss varies with load ?

  1. Windage loss
  2. Bearing friction loss
  3. Copper loss
  4. Core loss

Correct answer: (C)
Copper loss

49. In a synchronous motor, damper windings are provided on

  1. stator frame
  2. rotor shaft
  3. pole faces
  4. none of the above

Correct answer: (C)
pole faces

50. In a synchronous motor, the armature current has large values for

  1. high excitation only
  2. low excitation only
  3. both high and low excitation
  4. none of the above

Correct answer: (C)
both high and low excitation

Previous
Page 5 of 13
Next
Copyright © EngineeringMCQ.com