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MCQs

Total Questions : 395 | Page 6 of 40 pages
Question 51. A synchronous motor will always stop when
  1.    supply voltage fluctuates
  2.    load in motor varies
  3.    excitation winding gets disconnected
  4.    supply voltage frequency changes
 Discuss Question
Answer: Option C. -> excitation winding gets disconnected
Question 52. Which of the following motors will be used in electric clocks ?
  1.    D.C. shunt motor
  2.    D.C. series motor
  3.    A.C. induction motor
  4.    A.C. synchronous motor
 Discuss Question
Answer: Option D. -> A.C. synchronous motor
Question 53. 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
  1.    augments it directly
  2.    directly opposes it
  3.    cross-magnetises it
  4.    none of the above
 Discuss Question
Answer: Option B. -> directly opposes it
Question 54. In a synchronous motor, damper windings are provided on
  1.    stator frame
  2.    rotor shaft
  3.    pole faces
  4.    none of the above
 Discuss Question
Answer: Option C. -> pole faces
Question 55. In a synchronous motor, the damping winding is generally used to
  1.    prevent hunting and provide the starting torque
  2.    reduce the eddy currents
  3.    provide starting torque only
  4.    reduce noise level
 Discuss Question
Answer: Option A. -> prevent hunting and provide the starting torque
Question 56. A synchronous motor has better power factor as compared to that of an equivalent induction motor. This is mainly because
  1.    synchronous motor has no slip
  2.    stator supply is not required to produce magnetic field
  3.    mechanical load on the rotor remains constant
  4.    synchronous motor has large airgap
 Discuss Question
Answer: Option B. -> stator supply is not required to produce magnetic field
Question 57. Under which of the following conditions hunting of synchronous motor is likely to occur ?
  1.    Periodic variation of load
  2.    Over-excitation
  3.    Over-loading for long periods
  4.    Small and constant load
 Discuss Question
Answer: Option A. -> Periodic variation of load
Question 58. The torque angle, in a synchronous motor, is the angle between
  1.    the supply voltage and the back e.m.f.
  2.    magnetising current and back e.m.f.
  3.    the rotating stator flux and rotor poles
  4.    none of the above
 Discuss Question
Answer: Option C. -> the rotating stator flux and rotor poles
Question 59. A synchronous motor is running with normal excitation. When the load is increased, the armature current drawn by it increases because
  1.    Speed of the motor is reduced
  2.    Power factor is decreased
  3.    Eb (back e.m.f.) becomes less than V (applied voltage)
  4.    Er (net resultant voltage) in armature is increased
 Discuss Question
Answer: Option D. -> Er (net resultant voltage) in armature is increased
Question 60. 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
 Discuss Question
Answer: Option A. -> stop

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