Sunday, September 13, 2020

Chapter 8: Induction Motor-Page 5

  Chapter 8: Induction Motor

41. Short-circuit test on an induction motor cannot be used to determine
A. windage losses
B. copper losses
C. transformation ratio
D. power scale of circle diagram


... Answer is (A)

 

 
 

42. In a three-phase induction motor
A. iron losses in stator will be negligible as compared to that in rotor
B. iron losses in motor will be negligible as compared to that in rotor
C. iron losses in stator will be less than that in rotor
D. iron losses in stator will be more than that in rotor

... Answer is (D)

 
 
 

43. In case of 3-phase induction motors, plugging means
A. pulling the motor directly on line without a starter
B. locking of rotor due to harmonics
C. starting the motor on load which is more than the rated load
D. interchanging two supply phases for quick stopping

... Answer is (D)

 

 
 

44. Which is of the following data is required to draw the circle diagram for an induction motor?
A. Block rotor test only
B. No load test only
C. Block rotor test and no-load test
D. Block rotor test, no-load test and stator resistance test

  ... Answer is (D)

 

 
 
45. In three-phase induction motors sometimes copper bars are placed deep in the rotor to
A. improve starting torque
B. reduce copper losses
C. improve efficiency
D. improve power factor
  ...
Answer is (A)

 
 
 

46. In a three-phase induction motor
A. power factor at starting is high as compared to that while running
B. power factor at starting is low as compared to that while running
C. power factor at starting in the same as that while running
D. power factor remains through out constant

  ... Answer is (B)

 

 
 

47. The value of transformation ratio of an induction motor can be found by
A. open-circuit test only
B. short-circuit test only
C. stator resistance test
D. none of the above

... Answer is (B)

 
 

48. The power scale of circle diagram of an induction motor can be found from
A. stator resistance test
B. no-load test only
C. short-circuit test only
D. none of the above

... Answer is (C)

 
 

49. The shape of the torque/slip curve of induction motor is
A. parabola
B. hyperabola
C. rectangular parabola
D. straight line

 
  ... Answer is (C)

 
 

50. A change of 4% of supply voltage to an induction motor will produce a change of approximately
A. 4% in the rotor torque
B. 8% in the rotor torque
C. 12% in the rotor torque
D. 16% in the rotor torque

  ... Answer is (D)

 

 

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