MCQOPTIONS
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MCQOPTIONS
This section includes 120 Mcqs, each offering curated multiple-choice questions to sharpen your Electrical Machines knowledge and support exam preparation. Choose a topic below to get started.
| 51. |
A 3-phase induction motor delta connected is 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 winding |
| D. | Will continue running without any harm to the winding |
| Answer» D. Will continue running without any harm to the winding | |
| 52. |
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» B. Will continue running burning its two phases | |
| 53. |
Blocked rotor test on induction motors is used to find out |
| A. | Leakage reactance |
| B. | Power factor on short circuit |
| C. | Short-circuit current under rated voltage |
| D. | All of the above |
| Answer» E. | |
| 54. |
In medium sized induction motors, the slip is generally around |
| A. | 0.04 % |
| B. | 0.4 % |
| C. | 4 % |
| D. | 14 % |
| Answer» D. 14 % | |
| 55. |
The term 'cogging' is associated with |
| A. | Three-phase transformers |
| B. | Compound generators |
| C. | D.C. series motors |
| D. | Induction motors |
| Answer» E. | |
| 56. |
A double squirrel-cage induction motor has |
| A. | Two rotors moving in opposite direction |
| B. | Two parallel windings in stator |
| C. | Two parallel windings in rotor |
| D. | Two series windings in stator |
| Answer» D. Two series windings in stator | |
| 57. |
The efficiency of an induction motor can be expected to be nearly |
| A. | 60 to 90 % |
| B. | 80 to 90 % |
| C. | 95 to 98 % |
| D. | 99 % |
| Answer» C. 95 to 98 % | |
| 58. |
The torque developed in the cage induction motor with auto-starter is |
| A. | k/torque with direct switching |
| B. | K × torque with direct switching |
| C. | K2 × torque with direct switching |
| D. | k2/torque with direct switching |
| Answer» D. k2/torque with direct switching | |
| 59. |
Insertion of resistance in the rotor of an induction motor to develop a given torque |
| A. | Decreases the rotor current |
| B. | Increases the rotor current |
| C. | Rotor current becomes zero |
| D. | Rotor current remains same |
| Answer» E. | |
| 60. |
Which of the following component is usually fabricated out of silicon steel? |
| A. | Bearings |
| B. | Shaft |
| C. | Stator core |
| D. | None of the above |
| Answer» D. None of the above | |
| 61. |
In Ns is the synchronous speed and s the slip, then actual running speed of an induction motor will be |
| A. | Ns |
| B. | s.N |
| C. | (l-s) Ns |
| D. | (Ns-l) s |
| Answer» D. (Ns-l) s | |
| 62. |
The rotor of an induction motor runs at |
| A. | Synchronous speed |
| B. | Below synchronous speed |
| C. | Above synchronous speed |
| D. | Any of the above |
| Answer» C. Above synchronous speed | |
| 63. |
The good power factor of an induction motor can be achieved if the average flux density in the air gap is |
| A. | Absent |
| B. | Small |
| C. | Large |
| D. | Infinity |
| Answer» C. Large | |
| 64. |
The torque developed by a 3-phase induction motor least depends on |
| A. | Rotor current |
| B. | Rotor power factor |
| C. | Rotor e.m.f. |
| D. | Shaft diameter |
| Answer» E. | |
| 65. |
Slip of an 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» D. None of the above | |
| 66. |
If any two phases for an induction motor are interchanged |
| A. | The motor will run in reverse direction |
| B. | The motor will run at reduced speed |
| C. | The motor will not run |
| D. | The motor will burn |
| Answer» B. The motor will run at reduced speed | |
| 67. |
The injected e.m.f. in the rotor of induction motor must have |
| A. | Zero frequency |
| B. | The same frequency as the slip frequency |
| C. | The same phase as the rotor e.m.f. |
| D. | High value for the satisfactory speed control |
| Answer» C. The same phase as the rotor e.m.f. | |
| 68. |
The low power factor of induction motor is due to |
| A. | Rotor leakage reactance |
| B. | Stator reactance |
| C. | The reactive lagging magnetizing current necessary to generate the magnetic flux |
| D. | All of the above |
| Answer» E. | |
| 69. |
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» D. Reducing supply voltage | |
| 70. |
Reduced voltage starter can be used with |
| A. | Slip ring motor only but not with squirrel cage induction motor |
| B. | Squirrel cage induction motor only but not with slip ring motor |
| C. | Squirrel cage as well as slip ring induction motor |
| D. | None of the above |
| Answer» D. None of the above | |
| 71. |
In induction motor, percentage slip depends on |
| A. | Supply frequency |
| B. | Supply voltage |
| C. | Copper losses in motor |
| D. | None of the above |
| Answer» D. None of the above | |
| 72. |
DOL starting of induction motors is usually restricted to |
| A. | Low horsepower motors |
| B. | Variable speed motors |
| C. | High horsepower motors |
| D. | High speed motors |
| Answer» B. Variable speed motors | |
| 73. |
A 3-phase 440 V, 50 Hz induction motor has 4% slip. The frequency of rotor e.m.f. will be |
| A. | 200 Hz |
| B. | 50 Hz |
| C. | 2 Hz |
| D. | 0.2 Hz |
| Answer» D. 0.2 Hz | |
| 74. |
The frame of an induction motor is usually made of |
| A. | Silicon steel |
| B. | Cast iron |
| C. | Aluminium |
| D. | Bronze |
| Answer» C. Aluminium | |
| 75. |
As load on an induction motor goes on increasing |
| A. | Its power factor goes on decreasing |
| B. | Its power factor remains constant |
| C. | Its power factor goes on increasing even after full load |
| D. | Its power factor goes on increasing up to full load and then it falls again |
| Answer» E. | |
| 76. |
Less maintenance troubles are experienced in case of |
| A. | Slip ring induction motor |
| B. | Squirrel cage induction motor |
| C. | Both (A) and (B) |
| D. | None of the above |
| Answer» C. Both (A) and (B) | |
| 77. |
An induction motor with 1000 r.p.m. speed will have |
| A. | 8 poles |
| B. | 6 poles |
| C. | 4 poles |
| D. | 2 poles |
| Answer» C. 4 poles | |
| 78. |
The complete circle diagram of induction motor can be drawn with the help of data found from |
| A. | No-load test |
| B. | Blocked rotor test |
| C. | Stator resistance test |
| D. | All of the above |
| Answer» E. | |
| 79. |
An induction motor is identical to |
| A. | D.C. compound motor |
| B. | D.C. series motor |
| C. | Synchronous motor |
| D. | Asynchronous motor |
| Answer» E. | |
| 80. |
The vafcie 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» C. Stator resistance test | |
| 81. |
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» B. Cast iron bearings | |
| 82. |
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» E. | |
| 83. |
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» D. None of the above | |
| 84. |
The 'cogging' of an induction motor can be avoided by |
| A. | Proper ventilation |
| B. | Using DOL starter |
| C. | Autotransformer starter |
| D. | Having number of rotor slots more or less than the number of stator slots (not equal) |
| Answer» E. | |
| 85. |
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 |
| A. | Humming |
| B. | Hunting |
| C. | Crawling |
| D. | Cogging |
| Answer» D. Cogging | |
| 86. |
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» E. | |
| 87. |
Slip ring motor is preferred over squirrel cage induction motor where |
| A. | High starting torque is required |
| B. | Load torque is heavy |
| C. | Heavy pull out torque is required |
| D. | All of the above |
| Answer» B. Load torque is heavy | |
| 88. |
An induction motor can run at synchronous speed when |
| A. | It is run on load |
| B. | It is run in reverse direction |
| C. | It is run on voltage higher than the rated voltage |
| D. | e.m.f. is injected in the rotor circuit |
| Answer» E. | |
| 89. |
For driving high inertia loads best type of induction motor suggested is |
| A. | Slip ring type |
| B. | Squirrel-cage type |
| C. | Any of the above |
| D. | None of the above |
| Answer» B. Squirrel-cage type | |
| 90. |
In case the air gap in an induction motor is increased |
| A. | The magnetizing current of the rotor will decrease |
| B. | The power factor will decrease |
| C. | Speed of motor will increase |
| D. | The windage losses will increase |
| Answer» C. Speed of motor will increase | |
| 91. |
The crawling in the induction motor is caused by |
| A. | Low voltage supply |
| B. | High loads |
| C. | Harmonics developed in the motor |
| D. | Improper design of the machine |
| Answer» D. Improper design of the machine | |
| 92. |
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» E. | |
| 93. |
The torque of an induction motor is |
| A. | Directly proportional to slip |
| B. | Inversely proportional to slip |
| C. | Proportional to the square of the slip |
| D. | None of the above |
| Answer» B. Inversely proportional to slip | |
| 94. |
In case of the induction motors the torque is |
| A. | Inversely proportional to (V-slip) |
| B. | Directly proportional to (slip)2 |
| C. | Inversely proportional to slip |
| D. | Directly proportional to slip |
| Answer» E. | |
| 95. |
Temperature of the stator winding of a three phase induction motor is obtained by |
| A. | Resistance rise method |
| B. | Thermometer method |
| C. | Embedded temperature method |
| D. | All above methods |
| Answer» E. | |
| 96. |
In the squirrel-cage induction motor the rotor slots are usually given slight skew |
| A. | To reduce the magnetic hum and locking tendency of the rotor |
| B. | To increase the tensile strength of the rotor bars |
| C. | To ensure easy fabrication |
| D. | None of the above |
| Answer» B. To increase the tensile strength of the rotor bars | |
| 97. |
5 H.P., 50Hz, 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» B. 960 r.p.m. | |
| 98. |
For which motor the speed can be controlled from rotor side? |
| A. | Squirrel-cage induction motor |
| B. | Slip-ring induction motor |
| C. | Both (A) and (B) |
| D. | None of the above |
| Answer» C. Both (A) and (B) | |
| 99. |
Lubricant used for ball bearing is usually |
| A. | Graphite |
| B. | Grease |
| C. | Mineral oil |
| D. | Molasses |
| Answer» C. Mineral oil | |
| 100. |
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 sequence of supply |
| D. | None of these |
| Answer» C. In any direction depending upon phase sequence of supply | |