MCQOPTIONS
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MCQOPTIONS
This section includes 97 Mcqs, each offering curated multiple-choice questions to sharpen your Electrical Engineering Questions knowledge and support exam preparation. Choose a topic below to get started.
| 51. |
Mostly, synchronous motors are of_____________? |
| A. | alternator type machines |
| B. | induction type machines |
| C. | salient pole type machines |
| D. | smooth cylindrical type machines |
| Answer» D. smooth cylindrical type machines | |
| 52. |
In which of the following motors the stator and rotor magnetic field rotate at the same speed? |
| A. | Universal motor |
| B. | Synchronous motor |
| C. | Induction motor |
| D. | Reluctance motor |
| Answer» C. Induction motor | |
| 53. |
In which of the following motors the stator and rotor fields rotate simultaneously? |
| A. | D.C. motor |
| B. | Reluctance motor |
| C. | Universal motor |
| D. | Synchronous motor |
| E. | Induction motor |
| Answer» E. Induction motor | |
| 54. |
In case one phase of a three-phase synchronous motor is short-circuited the motor will____________? |
| A. | not start |
| B. | run at 2/3 of synchronous speed |
| C. | run with excessive vibrations |
| D. | take less than the rated load |
| Answer» B. run at 2/3 of synchronous speed | |
| 55. |
In a synchronous motor, V-curves represent relation between____________? |
| A. | armature current and field current |
| B. | power factor and speed |
| C. | field current and speed |
| D. | field current and power factor |
| Answer» B. power factor and speed | |
| 56. |
In a synchronous motor, the armature current has large values for____________? |
| A. | high excitation only |
| B. | low excitation only |
| C. | both high and low excitation |
| D. | none of the above |
| Answer» D. none of the above | |
| 57. |
In a synchronous motor, the maximum power developed depends on all of the following except: |
| A. | rotor excitation |
| B. | maximum value of coupling angle |
| C. | direction of rotation |
| D. | supply voltage |
| Answer» D. supply voltage | |
| 58. |
In a synchronous motor, the magnitude of stator back e.m.f. & depends on_______________? |
| A. | d.c. excitation only |
| B. | speed of the motor |
| C. | load on the motor |
| D. | both the speed and rotor flux |
| Answer» B. speed of the motor | |
| 59. |
In a synchronous motor, the magnitude of stator back e.m.f. Eb depends on___________? |
| A. | load on the motor |
| B. | d.c. excitation only |
| C. | both the speed and rotor flux |
| D. | none of the above |
| Answer» C. both the speed and rotor flux | |
| 60. |
In a synchronous motor, the damping winding is generally used to______________? |
| A. | reduce noise level |
| B. | reduce the eddy currents |
| C. | provide starting torque only |
| D. | prevent hunting and provide the starting torque |
| E. | none of the above |
| Answer» E. none of the above | |
| 61. |
In a synchronous motor, the breakdown torque is__________? |
| A. | directly proportional to the square of the applied voltage |
| B. | directly proportional to applied voltage |
| C. | inversely proportional to applied voltage |
| D. | none of the above |
| Answer» C. inversely proportional to applied voltage | |
| 62. |
In a synchronous motor, damper windings are provided on____________? |
| A. | stator frame |
| B. | rotor shaft |
| C. | pole faces |
| D. | none of the above |
| Answer» D. none of the above | |
| 63. |
In a 3-phase synchronous motor, the negative phase sequence exists when the motor is_______________? |
| A. | supplied with unbalanced voltage |
| B. | under-loaded |
| C. | over-loaded |
| D. | none of the above |
| Answer» B. under-loaded | |
| 64. |
In a 3-phase, 4-pole, 50 Hz synchronous motor, the frequency, pole number and load torque all are halved. The motor speed will be____________? |
| A. | 3000 r.p.m. |
| B. | 1500 r.p.m. |
| C. | 750 r.p.m. |
| D. | none of the above |
| Answer» C. 750 r.p.m. | |
| 65. |
If the synchronous motor, properly synchronised to the supply is running on no load and is having negligible loss then_____________? |
| A. | the stator current will be zero |
| B. | the stator current will be very small |
| C. | the stator current will be very high |
| D. | the back e.m.f. will be more than the supply voltage |
| E. | none of the above |
| Answer» B. the stator current will be very small | |
| 66. |
If the field winding of an unloaded salient pole synchronous motor is open circuited, the motor will__________? |
| A. | stop |
| B. | run as induction motor |
| C. | function as static condenser |
| D. | burn with dense smoke |
| Answer» B. run as induction motor | |
| 67. |
If the field of a synchronous motor is underexcited, the power factor will be_____________? |
| A. | zero |
| B. | unity |
| C. | lagging |
| D. | leading |
| Answer» D. leading | |
| 68. |
If one-phase of a 3-phase synchronous motor is short-circuited, motor will ______________? |
| A. | will refuse to start |
| B. | will overheat in spots |
| C. | will not come upto speed |
| D. | will fail to pull into step |
| Answer» B. will overheat in spots | |
| 69. |
If load (or torque) angle of a 4-pole synchronous motor is 6° electrical, its value in mechanical degrees is__________? |
| A. | 2 |
| B. | 3 |
| C. | 4 |
| D. | 6 |
| Answer» C. 4 | |
| 70. |
If in a synchronous motor, driving mechanical load and drawing current at lagging power factor from constant voltage supply, its field excitation is increased, then its power factor__________? |
| A. | become more |
| B. | become less |
| C. | remain constant |
| D. | none of the above |
| Answer» C. remain constant | |
| 71. |
If excitation of a synchronous motor running with a constant load is decreased from its normal value, ignoring effects of armature reaction, it leads to____________? |
| A. | increase in both armature current and power factor angle |
| B. | increase in back e.m.f. but decrease in armature current |
| C. | increase in both armature current and power factor which is lagging |
| D. | increase in torque angle but decrease in back e.m.f. |
| Answer» B. increase in back e.m.f. but decrease in armature current | |
| 72. |
Hunting in a synchronous motor cannot be due to___________? |
| A. | windage friction |
| B. | variable load |
| C. | variable frequency |
| D. | variable supply voltage |
| Answer» B. variable load | |
| 73. |
For V-curves for a synchronous motor the graph is drawn between:_______________? |
| A. | armature current and power factor |
| B. | terminal voltage and load factor |
| C. | power factor and field current |
| D. | field current and armature current |
| Answer» E. | |
| 74. |
For power factor correction, synchronous motors operate at____________? |
| A. | no-load and greatly over-excited fields |
| B. | no-load and under-excited fields |
| C. | normal load with minimum excitation |
| D. | normal load with zero excitation |
| Answer» B. no-load and under-excited fields | |
| 75. |
Exciters of synchronous machines are______________? |
| A. | d.c. series machines |
| B. | d.c. shunt machines |
| C. | d.c. compound machines |
| D. | any of the above |
| Answer» C. d.c. compound machines | |
| 76. |
Change of D.C. excitation of a synchronous motor changes: |
| A. | applied voltage of the motor |
| B. | power factor of power drawn by the motor |
| C. | motor speed |
| D. | none of the these |
| E. | all of the these |
| Answer» C. motor speed | |
| 77. |
Armature of a synchronous machine is____________? |
| A. | of reducing number of slip rings on the rotor |
| B. | armature is associated with large power as compared to the field circuits |
| C. | of difficulty of providing high voltage insulation on rotor |
| D. | all of the above reasons |
| Answer» E. | |
| 78. |
An over-excited synchronous motor takes__________? |
| A. | leading current |
| B. | lagging current |
| C. | both A. and (b) |
| D. | none of the above |
| Answer» B. lagging current | |
| 79. |
An over excited synchronous motor is used for____________? |
| A. | fluctuating loads |
| B. | variable speed loads |
| C. | low torque loads |
| D. | power factor corrections |
| Answer» E. | |
| 80. |
A three-phase synchronous motor will have_____________? |
| A. | no slip-rings |
| B. | one slip-ring |
| C. | two slip-rings |
| D. | three slip-rings |
| Answer» D. three slip-rings | |
| 81. |
A synchronous motor working at leading power factor can be used as____________? |
| A. | voltage booster |
| B. | phase advancer |
| C. | noise generator |
| D. | mechanical synchronizer |
| Answer» C. noise generator | |
| 82. |
A synchronous motor will always stop when:______________? |
| A. | supply voltage fluctuates |
| B. | load in motor varies |
| C. | excitation winding gets disconnected |
| D. | supply voltage frequency changes |
| Answer» D. supply voltage frequency changes | |
| 83. |
A synchronous motor which works on a leading power factor and does not drive a mechanical load is called as_________? |
| A. | static condenser |
| B. | condenser |
| C. | synchronous condenser |
| D. | none of the above |
| Answer» D. none of the above | |
| 84. |
A synchronous motor running with normal excitation adjusts to load increases essentially by increase in______________? |
| A. | back e.m.f. |
| B. | armature current |
| C. | power factor |
| D. | torque angle |
| Answer» C. power factor | |
| 85. |
A synchronous motor installed at the receiving end substation operates with such an excitation that it takes power at lagging power factor. Now if the applied voltage of the synchronous motor goes down, the power factor of the synchronous motor will___________? |
| A. | remain same |
| B. | go down |
| C. | improve |
| D. | none of the above |
| Answer» D. none of the above | |
| 86. |
A synchronous motor has better power factor as compared to that of an equivalent induction motor. This is mainly because? |
| A. | synchronous motor has no slip |
| B. | stator supply is not required to produce magnetic field |
| C. | mechanical load on the rotor remains constant |
| D. | synchronous motor has large airgap |
| Answer» C. mechanical load on the rotor remains constant | |
| 87. |
A synchronous motor develops maximum power when load angle is____________? |
| A. | 45° |
| B. | 60° |
| C. | 90° |
| D. | 120° |
| Answer» D. 120° | |
| 88. |
A synchronous motor connected to infinite bus-bars has at constant full load, 100% excitation and unity power factor. On changing the excitation only, the armature current will have_____________? |
| A. | no change of power factor |
| B. | lagging power factor with over-excitation |
| C. | leading power factor with under-excitation |
| D. | leading power factor with over-excitation |
| Answer» E. | |
| 89. |
A synchronous motor can operate at____________? |
| A. | lagging power factor only |
| B. | leading power factor only |
| C. | unity power factor only |
| D. | lagging, leading and unity power factors |
| Answer» E. | |
| 90. |
A synchronous motor can develop synchronous torque: |
| A. | when under loaded |
| B. | while over-excited |
| C. | only at synchronous speed |
| D. | below or above synchronous speed |
| Answer» D. below or above synchronous speed | |
| 91. |
A synchronous motor can be used as a synchronous capacitor when it is____________? |
| A. | under-loaded |
| B. | over-loaded |
| C. | under-excited |
| D. | over-excited |
| Answer» E. | |
| 92. |
A synchronous motor can be started by________? |
| A. | pony motor |
| B. | D.C. compound motor |
| C. | providing damper winding |
| D. | any of the above |
| Answer» E. | |
| 93. |
A synchronous motor can be made self starting by providing? |
| A. | damper winding on rotor poles |
| B. | damper winding on stator |
| C. | damper winding on stator as well as rotor poles |
| D. | none of the above |
| Answer» E. | |
| 94. |
A synchronous machine with low value of short-circuit ratio has___________? |
| A. | lower stability limit |
| B. | high stability limit |
| C. | good speed regulation |
| D. | good voltage regulation |
| E. | none of the above |
| Answer» B. high stability limit | |
| 95. |
A synchronous machine with large air gap has______________? |
| A. | a higher value of stability limit |
| B. | a small value of inherent regulation |
| C. | a higher synchronizing power which makes the machine less sensitive to load variations |
| D. | all of the above |
| Answer» E. | |
| 96. |
A rotory converter can also be run as a___________? |
| A. | d.c. shunt motor |
| B. | d.c. series motor |
| C. | d.c. compound motor |
| D. | induction motor |
| E. | synchronous motor |
| Answer» F. | |
| 97. |
A pony motor is basically a_________? |
| A. | small induction motor |
| B. | D.C. series motor |
| C. | D.C. shunt motor |
| D. | double winding A.C./D.C. motor |
| Answer» B. D.C. series motor | |