Sunday, September 13, 2020

Chapter 8: Induction Motor-Page 3

  Chapter 8: Induction Motor-

21. In a three-phase induction motor, the number of poles in the rotor winding is always
A. zero
B. more than the number of poles in stator
C. less than number of poles in stator
D. equal to number of poles in stator


... Answer is (D)

 

 
 

22. The speed of a squirrel-cage induction motor can be controlled by all of the following except
A. changing supply frequency
B. changing number of poles
C. changing winding resistance
D. reducing supply voltage

... Answer is (C)

 
 
 

23. The 'crawling' in an induction motor is caused by
A. high loads
B. low voltage supply
C. improper design of machine
D. harmonics developed in the motor

... Answer is (D)

 

 
 

24. The power factor of an induction motor under no-load conditions will be closer to
A. 0.2 lagging
B. 0.2 leading
C. 0.5 leading
D. unity

  ... Answer is (A)

 

 
 
25. The `cogging' of an induction motor can be avoided by
A. proper ventilation
B. using DOL starter
C. auto-transformer starter
D. having number of rotor slots more or less than the number of stator slots (not equal)
  ...
Answer is (D)

 
 
 

26. If an induction motor with certain ratio of rotor to stator slots, runs at of the normal speed, the phenomenon will be termed as
A. humming
B. hunting
C. crawling
D. cogging

  ... Answer is (C)

 

 
 

27. Slip of a induction motor is negative when
A. magnetic field and rotor rotate in opposite direction
B. rotor speed is less than the synchronous speed of the field and are in the same direction
C. rotor speed is more than the synchronous speed of the field and are in the same direction
D. none of the above

... Answer is (C)

 
 

28. Size of a high speed motor as compared to low speed motor for the same H.P. will be
A. bigger
B. smaller
C. same
D. any of the above

... Answer is (B)

 
 

29. A 3-phase induction motor stator delta connected, is carrying full load and one of its fuses blows out. Then the motor
A. will continue running burning its one phase
B. will continue running burning its two phases
C. will stop and carry heavy current causing permanent damage to its winding
D. will continue running without any harm to the winding

 
  ... Answer is (A)

 
 

30.  A 3-phase induction motor delta connected in carrying too heavy load and one of its fuses blows out. Then the motor
A. will continue running burning its one phase
B. will continue running burning its two phase
C. will stop and carry heavy current causing permanent damage to its windig
D. will continue running without any harm to the winding

  ... Answer is (C)

 

 

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