1. For 3phase I.M,the synchronous speed of rotating magnetic field is 1000 rpm,speed of rotor is 970 rpm ,then slip is
Correct : C. 0.03
2. For 3phase I.M,the synchronous speed of rotating magnetic field is 1500 rpm,speed of rotor is 1440 rpm ,then slip is
Correct : D. 0.04
3. For 3phase I.M,the synchronous speed of rotating magnetic field is 750 rpm, speed of rotor is 731.25 rpm ,then slip is
Correct : A. 0.025
4. For 3phase I.M.,the synchronous speed of rotating magnetic field is 1000 rpm, slip is 3% ,speed of rotor is----------
Correct : A. 970rpm
5. For 3phase I.M,the synchronous speed of rotating magnetic field is 750 rpm, slip is 2.5% ,speed of rotor is----------
Correct : B. 731.25rpm
6. For I.M. running with 731.25rpm with slip of 2.5%, the synchronous speed of rotating magnetic field
Correct : A. 750
7. For I.M. running with 1440rpm with slip of 4% the synchronous speed of rotating magnetic field
Correct : C. 1500
8. For I.M. running with 970rpm with slip of 3%, the synchronous speed of rotating magnetic field
Correct : B. 1000
9. A 6pole ,3 phase 50Hz I.M is running with 970 rpm. The slip of I.M is
Correct : A. 0.03
10. A 8 pole ,50Hz ,3phase I.M ,If full load slip is 2.5%. Rotor speed is
Correct : B. 731
11. A 8pole ,3 phase 50Hz I.M is running with 731.25 rpm. The slip of I.M is
Correct : C. 0.025
12. A 6pole ,3 phase 50Hz I.M is running with s=3%,runs with
Correct : D. 970
13. A 3-phase slip-ring induction motor has ……………… rotor.
Correct : B. wound
14. A wound rotor induction motor can be distinguished from a squirrel cage induction motor by
Correct : A. presence of slip-rings.
15. The operation of an induction motor is based on
Correct : C. principle of mutual induction
16. The rotating magnetic field produced by stator currents rotates at
Correct : A. synchronous speed , ns
17. The relative speed between stator flux and rotor is equal to
Correct : D. ns - n
18. Two of the supply terminals to a 3-phase induction motor get interchanged during reconnection after normal maintenance. When switched on to supply, the motor will
Correct : B. rotate in a direction opposite to that before maintenance.
19. The direction of rotation of a 3-phase induction motor can be reversed by
Correct : A. interchanging any two leads from supply.
20. The speed of rotor of an induction motor is always ………………… synchronous speed.
Correct : C. less than
21. Synchronous speed is defined as the speed at which the
Correct : A. stator magnetic field rotates.
22. A 3-phase, 4-pole induction motor has a no-load slip of 2% when connnected to a 25 Hz source, the no-load speed in rpm is
Correct : B. 735
23. A 4-pole, 3-phase induction motor is running at 4 percent slip at full load. If the speed of the motor is 720 rpm, the supply frequency is
Correct : B. 25hz
24. The speed of rotating field due to rotor currents relative to rotor surface in an induction motor is
Correct : B. s.n
25. The speed of rotating field due to rotor currents relative to stator core in an induction motor is
Correct : B. ns
26. A 3-phase ,400 V, 4-pole induction motor is fed from a 3-phase, 400V, 50 Hz supply and runs at 1440 rpm. The frequency of rotor emf is
Correct : A. 2hz
27. In a 3-phase induction motor, the mechanical power developed, in terms of air rotor input P2 is
Correct : D. (1 - s) p2
28. An induction motor employs a starting device to restrict………….. at start
Correct : B. line current
29. High starting torque can be produced by induction motor if
Correct : D. a slip-ring induction motor is started with rotor resistance starter
30. A squirrel cage induction motor is favoured when ……………….. is the main consideration.
Correct : C. stator core and stator teeth
31. The torque developed by a 3-phase induction motor during starting
Correct : A. depends on rotor induced emf during starting
32. Condition for maximum torque developed during starting by a three phase induction motor is
Correct : A. r2 = x2
33. Condition for maximum torque developed during running by a three phase induction motor is
Correct : B. r2 =s x2
34. Starting torque depends on
Correct : C. both 1 and 2
35. Torque developed by three phase induction motor
Correct : D. both 1 and 2
36. The power factor of induction motor is during running condition
Correct : D. both b and c
37. The torque developed by three phase induction motor depends on following three factors
Correct : D. rotor emf, rotor current and rotor p.f
38. When load is placed in three phase induction motor, its speed
Correct : A. decreases
39. When load is connected to three phase induction motor is increased, then its slip
Correct : B. increases
40. When load is connected to three phase induction motor is increased, then its rotor induced emf
Correct : B. increases
41. When load is placed in three phase induction motor its current
Correct : B. increases
42. When load is placed in three phase induction motor, its torque
Correct : B. increases
43. Maximum torque during running condition developed by three phase induction motor can be obtained by changing rotor resistance
Correct : B. in slip ring type motor
44. There is no electrical connection between stator and rotor, still power is transffered from stator to rotor through
Correct : A. magnetic flux
45. At start , the slip of induction motor is
Correct : C. one
46. Under running condition, the rotor reactance is proportional to
Correct : C. slip
47. Under running condition , the rotor resistance is proportional to
Correct : D. none of these
48. At start the rotor power factor is
Correct : B. very low
49. Power factor of rotor of three phase induction motor depends on
Correct : D. all of these
50. The function of starter is
Correct : C. to limit the starting current
51. When three phase induction motor is started with star-delta starter, during starting stator is connected
Correct : A. in star
52. When three phase induction motor is started with star-delta starter, during normal running condition, stator is connected
Correct : B. in delta
53. The torque developed by three phase induction motor is approximately proportional to
Correct : A. square of applied voltage
54. The rotor of an induction motor can't run at synchronous speed, if it did so then
Correct : D. all of these
55. A 3-phase , 50 Hz , 4-pole squirrel cage induction motor has its stator rewound for 6 poles without any alternations in the rotor. The motor would now run at a speed
Correct : A. less than 1000 rpm
56. If the input voltage and the frequency of supply is halved, to the 3-phase induction motor
Correct : A. the maximum torque is halved
57. The speed of the slip ring induction motor can be easily controlled by
Correct : D. all of these
58. A 440V, 20HP, 3phase motor operates at full load, 88% efficiency and 0.65 power factor lagging, the current drawn by motor is
Correct : C. 34.22 a
59. A6 pole 3 phase 50Hz induction motor develops mechanical power of 40Hp and has mechanical losses of 1500W at a speed of 960rpm when connected to 500V. The output available at the shaft is (Take 1HP=746W)
Correct : D. 28340w
60. DOL starter is used for 3 phase I.M. motor having rating of
Correct : A. ≤5 h.p.
61. Thermal relays are used in DOL starter of Three Phase I.M. to
Correct : B. protect the motor from overloading
62. No. of contacts used in a contactor of DOL starter
Correct : C. 4
63. Q. In DOL starter NO(Normally open) contact is used as
Correct : A. start push button
64. In DOL starter NC(Normally closed) contact is used as
Correct : B. stop push button
65. The advantage of Autotransformer starter over stator resistance starter is
Correct : B. produces less losses
66. The rotor speed of a 6 pole 50Hz induction motor is 960 r.p.m. The percentage slip is ____.
Correct : B. 0.04
67. A 3 phase induction motor connected from a 3 pjhase, 50Hz AC supply runs at 720rpm and has slip 4%. The number of poles in motor are _____.
Correct : C. 8
68. The torque developed in an induction motor is nearly proportional to
Correct : C. v^2
69. The air gap between the stator and rotor of a 3 phase induction motor ranges from
Correct : B. 0.4mm to 4mm
70. An induction motor under full load has slip of about____.
Correct : A. 0.03
71. A 4 pole, 440V, 50Hz induction motor is running at a slip of 4%. The speed of motor is ____.
Correct : B. 1440rpm
72. A 4 pole, 50Hz induction motor runs at a speed of 1440rpm. The frequency of the rotor induced emf is _____.
Correct : C. 2hz
73. The value of slip is ___ at start.
Correct : D. 1
74. Slip rings are usually made up of ___.
Correct : D. phosphor-bronze
75. The rotor standstill resistance and reactance of an induction motor are 0.5Ω and 2.5Ω hence the rotor impedance at 5% slip is____.
Correct : C. 0.5154Ω
76. The torque of 3 phase induction motor depends on__.
Correct : D. all of these
77. The constant 'k' in the torque equation of a 3 phase induction motor depends
Correct : C. synchronous speed
78. A 3 phase indution motor is running with slip of 4% hving synchronous speed of 1500rpm. If rotor induced emf per phase in standstill condition is 115.47V and rotor impedance in standstill condition is 0.1+j1 Ω then torque developed ia____.
Correct : B. 87.81
79. A 3 phase induction motor running with full load slip of 1.2% and its rotor impedance per phase on standstill is 0.016+j0.265Ω then the ratio of full load torque to maximum torque is
Correct : A. 0.382
80. A 3 phase induction motor is running with full load slip of 1.2% and its rotor impedance per phase is 0.06+j0.265Ω then ratio of starting torque to maximum torque is
Correct : C. 0.123
81. A 3 phase I.M. is running with full load slip of 1.2% and its rotor impedance per phase on standstill is 0.016+j0.265Ω then ratio of full load torque to starting torque is _____.
Correct : B. 3.16
82. A 4 pole, 50Hz , 3 phase I M is running at 1425rpm on full load having rotor impedance per phase on standstill as 0.4+j2Ω. If voltage between the slip rings on open circuit is 520V then the torque developed on full load is ___ Nm.
Correct : A. 202.52
83. A 4 pole, 50Hz , 3 phase I M is running at 1425rpm on full load having rotor impedance per phase on standstill as 0.4+j2Ω. If voltage between the slip rings on open circuit is 520V then the maximum torque developed is ___ Nm.
Correct : C. 430.36
84. A 4 pole, 50Hz , 3 phase I M is running at 1425rpm on full load having rotor impedance per phase on standstill as 0.4+j2Ω. The ratio of full load torque to maximum torque is ___.
Correct : D. 0.4705
85. A 4 pole, 50Hz , 3 phase I M is running at 1425rpm on full load having rotor impedance per phase on standstill as 0.4+j2Ω. The external resistance required in the rotor per phase to get maximum torque at start is ___.
Correct : B. 1.6
86. A 3 phase I.M. has rotor impedance on standstill as 0.8+j3.8Ω. Then the maximum torque will occur at slip of ____%
Correct : A. 21.05
87. A 50Hz, 8 pole, 3 phase I.M. has a full load slip of 4%. Its rotor impedance per phase on standstill is 0.01+j0.005 ohms. Then the speed at maximum torque is ____.
Correct : D. 600
88. A 50Hz 20 poles 3 phase I.M. has a full load slip 1.33%. Its rotor impedance per phase on standstill is 0.02+j0.3ohms. Then the ratio of starting torque to the maximum torque is____.
Correct : C. 0.132
89. The external resistance added in the rotor circuit at start _____.
Correct : D. all of these
90. A 3 phase induction motor is running with 4% slip. Its rotor input is 10kW then rotor copper losses are
Correct : C. 400w
91. A 3 phase I.M. is running with slip 5%. Its air gap power is 12kW then total mechanical power developed is____.
Correct : A. 11.4kw
92. A 3 phase I.M. running with slip 5%. Its rotor input is 20kW then its power output is ____ if frictional losses are 1kW.
Correct : C. 18kw
93. A 3 phase I.M. is running with 5% slip. Its rotor input is 20kW and its synchronous speed is 1500rpm then its shaft torque is ___ if frictional losses are 1kW.
Correct : B. 120.62nm
94. A 3 phase I.M. is running with 5% slip. Its rotor input is 20kW then its rotor efficiency is ____.
Correct : A. 0.95
95. A 25kW, 3 phase I.M. is running with 6% slip. Its rotor copper losses are ____ if frictional losses are 850W.
Correct : B. 1650
96. A 25kW, 3 phase I.M. is running with 6% slip. Its rotor resistance per phase is____ if frictional losses are 850W and rotor current per phase is 65A.
Correct : C. 0.13
97. A 4 pole, 3 phase I.M. is running with a slip of 4% producing shaft torque of 300Nm then its output power is ____ kW.
Correct : D. 45.23
98. For a 3 phase I.M. running at 1440 rpm the torque lost in friction is 50Nm then its frictional losses are____.
Correct : A. 7.54
99. A 3 phase I.M. is running with speed 1455 rpm on full load then its synchronous speed must be ____ rpm.
Correct : B. 1500
100. An induction motor is
Correct : C. self starting with small torque as compared to rated torque