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MCQs

Total Questions : 473 | Page 5 of 48 pages
Question 41. In three-phase squirrel-cage induction motors
  1.    Rotor conductor ends are short-circuited through slip rings
  2.    Rotor conductors are short-circuited through end rings
  3.    Rotor conductors are kept open
  4.    Rotor conductors are connected to insulation
 Discuss Question
Answer: Option B. -> Rotor conductors are short-circuited through end rings
Question 42. In an induction motor if air-gap is increased
  1.    The power factor will be low
  2.    Windage losses will be more
  3.    Bearing friction will reduce
  4.    Copper loss will reduce in an induction motor
 Discuss Question
Answer: Option A. -> The power factor will be low
Question 43. A pump induction motor is switched on to a supply 30% lower than its rated voltage. The pump runs. What will eventually happen? It will
  1.    Stall after sometime
  2.    Stall immediately
  3.    Continue to run at lower speed without damage
  4.    Get heated and subsequently get damaged
 Discuss Question
Answer: Option D. -> Get heated and subsequently get damaged
Question 44. The circle diagram for an induction motor cannot be used to determine
  1.    Efficiency
  2.    Power factor
  3.    Frequency
  4.    Output
 Discuss Question
Answer: Option A. -> Efficiency
Question 45. What will happen if the relative speed between the rotating flux of stator and rotor of the induction motor is zero?
  1.    The slip of the motor will be 5%
  2.    The rotor will not run
  3.    The rotor will run at very high speed
  4.    The torque produced will be very large
 Discuss Question
Answer: Option B. -> The rotor will not run
Question 46. The torque of a rotor in an induction motor under running condition is maximum
  1.    At the unit value of slip
  2.    At the zero value of slip
  3.    At the value of the slip which makes rotor reactance per phase equal to the resistance per phase
  4.    At the value of the slip which makes the rotor reactance half of the rotor
 Discuss Question
Answer: Option C. -> At the value of the slip which makes rotor reactance per phase equal to the resistance per phase
Question 47. Short-circuit test on an induction motor cannot be used to determine
  1.    Windage losses
  2.    Copper losses
  3.    Transformation ratio
  4.    Power scale of circle diagram
 Discuss Question
Answer: Option A. -> Windage losses
Question 48. In three-phase induction motors sometimes copper bars are placed deep in the rotor to
  1.    Improve starting torque
  2.    Reduce copper losses
  3.    Improve efficiency
  4.    Improve power factor
 Discuss Question
Answer: Option A. -> Improve starting torque
Question 49. The speed characteristics of an induction motor closely resemble the speed-load characteristics of which of the following machines
  1.    D.C. series motor
  2.    D.C. shunt motor
  3.    Universal motor
  4.    None of the above
 Discuss Question
Answer: Option B. -> D.C. shunt motor
Question 50. Step-less speed control of induction motor is possible by which of the following methods?
  1.    e.m.f. injection in rotor eueuit
  2.    Changing the number of poles
  3.    Cascade operation
  4.    None of the above
 Discuss Question
Answer: Option B. -> Changing the number of poles

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