Sunday, September 13, 2020

Chapter 8: Induction Motor-Page 3

  Chapter 8: Induction Motor

31. Low voltage at motor terminals is due to
A. inadequate motor wiring
B. poorely regulated power supply
C. any one of the above
D. none of the above

... Answer is (C)



32. In an induction motor the relationship between stator slots and rotor slots is that
A. stator slots are equal to rotor slots
B. stator slots are exact multiple of rotor slots
C. stator slots are not exact multiple of rotor slots
D. none of the above

... Answer is (C)


33. Slip ring motor is recommended where
A. speed control is required
B. frequent starting, stopping and reversing is required
C. high starting torque is needed
D. all above features are required

... Answer is (D)



34. As load on an induction motor goes on increasing
A. its power factor goes on decreasing
B. its power factor remain constant
C. its power factor goes on increasing even after full load
D. its power factor goes on increasing upto full load and then it falls again

  ... Answer is (D)


35. If a 3-phase supply is given to the stator and rotor is short circuited rotor will move
A. in the opposite direction as the direction of the rotating field
B. in the same direction as the direction of the field
C. in any direction depending upon phase squence of supply
D. with synchronous speed
Answer is (B)


36. It is advisable to avoid line starting of induction motor and use starter because
A. it will run in reverse direction
B. it will pick up very high speed and may go out of step
C. motor takes five to seven times its full-load current
D. starting torque is very high

  ... Answer is (C)



27. The speed characteristic of an induction motor closely resemble the speedload characteristic of which of the following machines
A. D.C. series motor
B. D.C. shunt motor
C. universal motor
D. none of the above

... Answer is (B)


38. Which type of bearing is provided in small induction motors to support the rotor shaft?
A. Ball bearings
B. Cast iron bearings
C. Bush bearings
D.None of the above

... Answer is (A)


39. A pump induction motor is switched on to a supply 30% lower than its rated voltage. What will eventually happen? It will
A. start after sometime
B. start immediately
C. continue to run at lower speed without damage
D. get heated and subsequently get damaged

  ... Answer is (D)


40. 5 H.P., 50-Hz, 3-phase, 440 V, induction motors are available for the following r.p.m. Which motor will be the costliest?
A. 730 r.p.m.
B. 960 r.p.m.
C. 1440 r.p.m.
D. 2880 r.p.m.

  ... Answer is (A)



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