1. Which of the following component is usually fabricated out of silicon steel ?
Correct : C. Statorcore
2. The frame of an induction motor is usually made of
Correct : B. cast iron
3. The shaft of an induction motor is made of
Correct : A. stiff
4. The shaft of an induction motor is made of
Correct : C. carbon steel
5. In an induction motor, no-load the slip is generally
Correct : A. less than 1%
6. In medium sized induction motors, the slip is generally around
Correct : C. 4%
7. In squirrel cage induction motors, the rotor slots are usually given slight skew in order
to
Correct : D. reduce magnetic hum
8. In case the air gap in an induction motor is increased
Correct : B. the power factor will decrease
9. Slip rings are usually made of
Correct : C. phospor bronze
10. A 3-phase 440 V, 50 Hz induction motor has 4% slip. The frequency of rotor e.m.f. will
be
Correct : C. 2 Hz
11. In Ns is the synchronous speed and s the slip, then actual running speed of an
induction motor will be
Correct : C. (l-s)Ns
12. The efficiency of an induction motor can be expected to be nearly
Correct : B. 80 to 90%
13. The number of slip rings on a squirrel cage induction motor is usually
Correct : D. none
14. The starting torque of a squirrel-cage induction motor is
Correct : A. low
15. A double squirrel-cage induction motor has
Correct : C. two parallel windings in rotor
16. Star-delta starting of motors is not possible in case of
Correct : A. single phase motors
17. The term 'cogging' is associated with
Correct : D. induction motors
18. In case of the induction motors the torque is
Correct : D. directly proportional to slip
19. An induction motor with 1000 r.p.m. speed will have
Correct : B. 6 poles
20. The good power factor of an induction motor can be achieved if the average flux
density in the air gap is
Correct : B. small
21. An induction motor is identical to
Correct : D. asynchronous motor
22. The injected e.m.f. in the rotor of induction motor must have
Correct : B. the same frequency as the slip fre-quency
23. Which of the following methods is easily applicable to control the speed of the
squirrel-cage induction motor ?
Correct : A. By changing the number of stator poles
24. The crawling in the induction motor is caused by
Correct : C. harmonics develped in the motor
25. The auto-starters (using three auto transformers) can be used to start cage induction
motor of the following type
Correct : C. (a) and (b) both
26. The torque developed in the cage induction motor with autostarter is
Correct : C. K2 x torque with direct switching
27. When the equivalent circuit diagram of doouble squirrel-cage induction motor is
constructed the two cages can be considered
Correct : B. in parallel
28. It is advisable to avoid line-starting of induction motor and use starter because
Correct : A. motor takes five to seven times its full load current
29. Stepless speed control of induction motor is possible by which of the following
methods ?
Correct : B. Changing the number of poles
30. Rotor rheostat control method of speed control is used for
Correct : B. slip ring induction motors only
31. In the circle diagram for induction motor, the diameter of the circle represents
Correct : B. rotor current
32. For which motor the speed can be controlled from rotor side ?
Correct : B. Slip-ring induction motor
33. If any two phases for an induction motor are interchanged
Correct : A. the motor will run in reverse direction
34. An induction motor is
Correct : C. self-starting with low torque
35. The maximum torque in an induction motor depends on
Correct : D. all of the above
36. In three-phase squirrel-cage induction motors
Correct : B. rotor conductors are short-circuited through end rings
37. In a three-phase induction motor, the number of poles in the rotor winding is always
Correct : D. equal to number of poles in stator
38. DOL starting of induction motors is usually restricted to
Correct : A. low horsepower motors
39. The speed of a squirrel-cage induction motor can be controlled by all of the following
except
Correct : C. changing winding resistance
40. The 'crawling" in an induction motor is caused by
Correct : D. harmonics developed in the motor
41. The power factor of an induction motor under no-load conditions will be closer to
Correct : A. 0.2 lagging
42. The 'cogging' of an induction motor can be avoided by
Correct : D. having number of rotor slots more or less than the number of stator slots (not equal)
43. If an induction motor with certain ratio of rotor to stator slots, runs at 1/7 of the
normal speed, the phenomenon will be termed as
Correct : C. crawling
44. Slip of an induction motor is negative when
Correct : C. rotor speed is more than the syn-chronous speed of the field and are in the same direction
45. Size of a high speed motor as compared to low speed motorfor the same H.P. will be
Correct : B. smaller
46. A 3-phase induction motor stator delta connected, is carrying full load and one of its
fuses blows out. Then the motor
Correct : A. will continue running burning its one phase
47. A 3-phase induction motor delta connected is carrying too heavy load and one of its fuses blows out. Then the motor
Correct : C. will stop and carry heavy current causing permanent damage to its winding
48. Low voltage at motor terminals is due to
Correct : C. any one of the above
49. In an induction motor the relationship between stator slots and rotor slots is that
Correct : C. stator slots are not exact multiple of rotor slots
50. Slip ring motor is recommended where
Correct : D. all above features are required
51. As load on an induction motor goes on increasing
Correct : D. its power factor goes on increasing upto full load and then it falls again
52. If a 3-phase supply is given to the stator and rotor is short circuited rotor will move
Correct : B. in the same direction as the direction of the field
53. It is advisable to avoid line starting of induction motor and use starter because
Correct : C. motor takes five to seven times its fullload current
54. The speed characteristics of an induction motor closely resemble the speedload
characteristics of which of the following machines
Correct : B. D.C. shunt motor
55. Which type of bearing is provided in small induction motors to support the rotor shaft
?
Correct : A. Ball bearings
56. 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
Correct : D. get heated and subsequently get damaged
57. 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 ?
Correct : A. 730 r.p.m.
58. A 3-phase slip ring motor has
Correct : B. wound rotor
59. The starting torque of a 3-phase squirrel cage induction motor is
Correct : B. 1.5 times the full load torque
60. Short-circuit test on an induction motor cannot be used to determine
Correct : A. windage losses
61. In a three-phase induction motor
Correct : D. iron losses in stator will be more than that in rotor
62. In case of 3-phase induction motors, plugging means
Correct : D. interchanging two supply phases for quick stopping
63. Which is of the following data is required to draw the circle diagram for an induction
motor ?
Correct : D. Block rotor test, no-load test and stator resistance test
64. In three-phase induction motors sometimes copper bars are placed deep in the rotor
to
Correct : A. improve starting torque
65. In a three-phase induction motor
Correct : B. power factor at starting is low as compared to that while running
66. The vafcie of transformation ratio of an induction motor can be found by
Correct : B. short-circuit test only
67. The power scale of circle diagram of an induction motor can be found from
Correct : C. short-circuit test only
68. The shape of the torque/slip curve of induction motor is
Correct : C. rectangular parabola
69. A change of 4% of supply voltage to an induction motor will produce a change of
appromimately
Correct : D. 16% in the rotor torque
70. The stating torque of the slip ring induction motor can be increased by adding
Correct : B. external resistance to the rotor
71. A 500 kW, 3-phase, 440 volts, 50 Hz, A.C. induction motor has a speed of 960 r.p.m. on
full load. The machine has 6 poles. The slip of the machine will be
Correct : D. 0.04
72. The complete circle diagram of induetion motor can be drawn with the help of data
found from
Correct : D. all of the above
73. In the squirrel-cage induction motor the rotor slots are usually given slight skew
Correct : A. to reduce the magnetic hum and locking tendency of the rotor
74. The torque of a rotor in an induction motor under running condition is maximum
Correct : C. at the value of the slip which makes rotor reactance per phase equal to the resistance per phase
75. What will happen if the relative speed between the rotating flux of stator and rotor of
the induction motor is zero ?
Correct : B. The rotor will not run
76. The circle diagram for an induction motor cannot be used to determine
Correct : A. efficiency
77. Blocked rotor test on induction motors is used to find out
Correct : D. all of the above
78. Lubricant used for ball bearing is usually
Correct : B. grease
79. An induction motor can run at synchronous speed when
Correct : D. e.m.f. is injected in the rotor circuit
80. Which motor is preferred for use in mines where explosive gases exist ?
Correct : A. Air motor
81. The torque developed by a 3-phase induction motor least depends on
Correct : D. shaft diameter
82. In an induction motor if air-gap is increased
Correct : A. the power factor will be low
83. In induction motor, percentage slip depends on
Correct : C. copper losses in motor
84. When /?2 is tne rotor resistance, .X2 the rotor reactance at supply frequency and s the slip, then the condition for maximum torque under running condi-tions will be
Correct : C. R2 = sX2 i
85. In case of a double cage induction motor, the inner cage has
Correct : A. high inductance arid low resistance
86. The low power factor of induction motor is due to
Correct : D. all of the above
87. Insertion of reactance in the rotor circuit
Correct : A. reduces starting torque as well as maximum torque
88. Insertion of resistance in the rotcir of an induction motor to develop a given torque
Correct : D. rotor current rernains same
89. For driving high inertia loods best type of induction motor suggested is
Correct : A. slip ring type
90. Temperature of the stator winding of a three phase induction motor is obtained by
Correct : D. all above methods
91. The purpose of using short-circuit gear is
Correct : A. to short circuit the rotor at slip rings
92. In a squirrel cage motor the induced e.m.f. is
Correct : C. slip times the stand still e.m.f. induced in the rotor
93. Less maintenance troubles are experienced in case of
Correct : B. squirrel cage induction motor
94. A squirrel cage induction motor is not selected when
Correct : C. higher starting torque is the main consideration
95. Reduced voltage starter can be used with
Correct : C. squirrel cage as well as slip ring induction motor
96. Slip ring motor is preferred over squirrel cage induction motor where
Correct : A. high starting torque is required
97. In a star-delta starter of an induction motor
Correct : D. applied voltage per1 stator phase is 57.7% of the line voltage
98. The torque of an induction motor is
Correct : A. directly proportional to slip
99. The rotor of an induction motor runs at
Correct : B. below synchronous speed
100. The starting torque of a three phase induction motor can be increased by