MCQOPTIONS
Saved Bookmarks
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.
| 1. |
While starting a salient pole synchronous motor by induction motor action and connecting field discharge resistance across field, starting and accelerating torque is produced by_____________? |
| A. | induction motor torque in field winding |
| B. | induction motor torque in damper winding |
| C. | eddy current and hysteresis torque in pole faces |
| D. | reHetance motor torque due to saliency of the rotor |
| E. | all of the above methods |
| Answer» F. | |
| 2. |
While starting a synchronous motor by induction motor action, field winding is usually_____________? |
| A. | connected to D.C. supply |
| B. | short-circuited by low resistance |
| C. | kept open-circuited |
| D. | none of the above |
| Answer» C. kept open-circuited | |
| 3. |
Which of the following motors will be used in electric clocks? |
| A. | D.C. shunt motor |
| B. | D.C. series motor |
| C. | A.C. induction motor |
| D. | A.C. synchronous motor |
| Answer» E. | |
| 4. |
Which of the following methods is used to start a synchronous motor? |
| A. | Damper winding |
| B. | Star-delta starter |
| C. | Damper winding in conjunction with star-delta starter |
| D. | Resistance starter in the armature circuit |
| Answer» D. Resistance starter in the armature circuit | |
| 5. |
Which of the following losses is not dissipated by the stator core surface in a synchronous motor? |
| A. | Eddy current losses in the conductors |
| B. | Iron losses in the stator |
| C. | Copper losses in the slot portion of the conductors |
| D. | Windage losses |
| E. | None of the above |
| Answer» E. None of the above | |
| 6. |
When V is the applied voltage, then the breakdown torque of a synchronous motor varies as_________? |
| A. | V |
| B. | V312 |
| C. | V2 |
| D. | 1/V |
| Answer» B. V312 | |
| 7. |
When the voltage applied to a synchronous motor is increased, which of the following will reduce? |
| A. | Stator flux |
| B. | Pull in torque |
| C. | Both A. and (b) |
| D. | None of the above |
| Answer» E. | |
| 8. |
When the stator windings are connected in such a fashion that the number of poles are made half, the speed of the rotor of a synchronous motor___________? |
| A. | remains same as the original value |
| B. | decreases to half the original value |
| C. | tends to becomes zero |
| D. | increases to two times the original value |
| Answer» E. | |
| 9. |
When the rotor speed, in a synchronous machine, becomes more than the synchronous speed during hunting, the damper bars develop_________________? |
| A. | inductor motor torque |
| B. | induction generator torque |
| C. | synchronous motor torque |
| D. | d.c. motor toque |
| E. | none of the above |
| Answer» C. synchronous motor torque | |
| 10. |
When the excitation of an unloaded salient pole synchronous motor suddenly gets disconnected______________? |
| A. | the motor stops |
| B. | it runs as a reluctance motor at the same speed |
| C. | it runs as a reluctance motor at a lower speed |
| D. | none of the above |
| Answer» B. it runs as a reluctance motor at the same speed | |
| 11. |
When the field of a synchronous motor is under-excited, the power factor will be____________? |
| A. | leading |
| B. | lagging |
| C. | unity |
| D. | zero |
| Answer» C. unity | |
| 12. |
When load on an over-excited or under excited synchronous*motor is increased, rate of change of its armature current as compared with that of power factor is___________? |
| A. | more |
| B. | less |
| C. | equal |
| D. | twice |
| Answer» C. equal | |
| 13. |
Under which of the following conditions hunting of synchronous motor is likely to occur? |
| A. | Periodic variation of load |
| B. | Over-excitation |
| C. | Over-loading for long periods |
| D. | Small and constant load |
| Answer» B. Over-excitation | |
| 14. |
To limit the operating temperature an electrical machine should have proper____________? |
| A. | voltage rating |
| B. | current rating |
| C. | power factor |
| D. | speed |
| Answer» C. power factor | |
| 15. |
The working of a synchronous motor is similar to_____________? |
| A. | gear train arrangement |
| B. | transmission of mechanical power by shaft |
| C. | distribution transformer |
| D. | turbine |
| E. | none of the above |
| Answer» C. distribution transformer | |
| 16. |
The torque angle, in a synchronous motor, is the angle between_______________? |
| A. | the supply voltage and the back e.m.f. |
| B. | magnetising current and back e.m.f. |
| C. | the rotating stator flux and rotor poles |
| D. | none of the above |
| Answer» D. none of the above | |
| 17. |
The synchronous motor is not inherently self-starting because_______________? |
| A. | the force required to accelerate the rotor to the synchronous speed in an instant is absent |
| B. | the starting device to accelerate the rotor to near synchronous speed is absent |
| C. | a rotating magnetic field does not have enough poles |
| D. | the rotating magnetic field is produced by only 50 Hz frequency currents |
| Answer» B. the starting device to accelerate the rotor to near synchronous speed is absent | |
| 18. |
The standard full-load power factor ratings for synchronous motors are___________? |
| A. | zero or 0.8 leading |
| B. | unity or 0.8 lagging |
| C. | unity or 0.8 leading |
| D. | unity or zero |
| Answer» D. unity or zero | |
| 19. |
The speed regulation of a synchronous motor is always___________? |
| A. | 1% |
| B. | 0.5% |
| C. | positive |
| D. | zero |
| Answer» E. | |
| 20. |
The speed of a synchronous motor: |
| A. | increases as the load increases |
| B. | decreases as the load decreases |
| C. | always remains constant |
| D. | none of the above |
| Answer» D. none of the above | |
| 21. |
The size of a synchronous motor decreases with the increase in___________? |
| A. | flux density |
| B. | horse power rating |
| C. | speed |
| D. | all of the above |
| Answer» B. horse power rating | |
| 22. |
The shaft of synchronous motor is made of____________? |
| A. | mild steel |
| B. | chrome steel |
| C. | alnico |
| D. | stainless steel |
| Answer» B. chrome steel | |
| 23. |
The rotor copper losses, in a synchronous motor, are met by____________? |
| A. | d.c. source |
| B. | armature input |
| C. | motor input |
| D. | supply lines |
| Answer» B. armature input | |
| 24. |
The ratio of starting torque to running torque in a synchronous motor is____________? |
| A. | zero |
| B. | one |
| C. | two |
| D. | infinity |
| Answer» B. one | |
| 25. |
The power developed by a synchronous motor will be maximum when the load angle is____________? |
| A. | zero |
| B. | 45° |
| C. | 90° |
| D. | 120° |
| Answer» D. 120° | |
| 26. |
The percentage slip in case of a synchronous motor is____________? |
| A. | 1% |
| B. | 100% |
| C. | 0.5% |
| D. | zero |
| Answer» E. | |
| 27. |
The oscillations in a synchronous motor can be damped out by_______________? |
| A. | maintaining constant excitation |
| B. | running the motor on leading power factors |
| C. | providing damper bars in the rotor pole faces |
| D. | oscillations cannot be damped |
| Answer» D. oscillations cannot be damped | |
| 28. |
The operating speed of a synchronous motor can be changed to new fixed value by___________? |
| A. | changing the load |
| B. | changing the supply voltage |
| C. | changing frequency |
| D. | using brakes |
| Answer» D. using brakes | |
| 29. |
The net armature voltage of a synchronous motor is equal to the_______________? |
| A. | vector sum of Eb and V |
| B. | arithmetic sum of Eb and V |
| C. | arithmetic difference of Eb and V |
| D. | vector difference of Eh and V |
| Answer» E. | |
| 30. |
The minimum armature current of the synchronous motor corresponds to operation at______________? |
| A. | zero power factor leading |
| B. | unity power factor |
| C. | 0.707 power factor lagging |
| D. | 0.707 power factor leading |
| Answer» C. 0.707 power factor lagging | |
| 31. |
The mechanical displacement of the rotor with respect to the stator, in polyphase multipolar synchronous motors running at full load, is of the order of_____________? |
| A. | zero degree |
| B. | two degrees |
| C. | five degrees |
| D. | ten degrees |
| Answer» D. ten degrees | |
| 32. |
The maximum value of torque that a synchronous motor can develop without losing its synchronism, is known as_____________? |
| A. | slip torque |
| B. | pull-out torque |
| C. | breaking torque |
| D. | synchronising torque |
| Answer» E. | |
| 33. |
The maximum torque which a synchronous motor will develop at rest for any angular position of the rotor, at rated stator supply voltage and frequency, is known as__________? |
| A. | locked-rotor torque |
| B. | synchronous torque |
| C. | pull up torque |
| D. | reluctance torque |
| Answer» B. synchronous torque | |
| 34. |
The maximum speed variation in a 3-phase synchronous motor is____________? |
| A. | 10 per cent |
| B. | 6 per cent |
| C. | 4 per cent |
| D. | per cent |
| E. | zero |
| Answer» F. | |
| 35. |
The maximum power developed in a synchronous motor occurs at a coupling angle of____________? |
| A. | 30° |
| B. | 60° |
| C. | 90° |
| D. | 180° |
| Answer» D. 180° | |
| 36. |
The maximum power developed in a synchronous motor will depend on__________? |
| A. | the rotor excitation only |
| B. | the supply voltage only |
| C. | the rotor excitation and supply volt-age both |
| D. | the rotor excitation, supply voltage and maximum value of coupling angle (90°) |
| E. | none of the above |
| Answer» E. none of the above | |
| 37. |
The maximum constant load torque under which a synchronous motor will pull into synchronism at rated rotor supply voltage and frequency is known as___________? |
| A. | pull-up torque |
| B. | pull-in torque |
| C. | pull-out torque |
| D. | none of the above |
| Answer» C. pull-out torque | |
| 38. |
The magnitude of field flux in a 3-phase synchronous motor? |
| A. | varies with power factor |
| B. | varies with speed |
| C. | varies with the load |
| D. | remains constant at all loads |
| Answer» E. | |
| 39. |
The induced e.m.f. in a synchronous motor working on leading power factor will be_____________? |
| A. | more than the supply voltage |
| B. | less than the supply voltage |
| C. | equal to the supply voltage |
| D. | None of these |
| Answer» B. less than the supply voltage | |
| 40. |
The efficiency of a properly designed synchronous motor will usually fall in range___________? |
| A. | 60 to 70% |
| B. | 75 to 80% |
| C. | 85 to 95% |
| D. | 99 to 99.5% |
| Answer» D. 99 to 99.5% | |
| 41. |
The effect of increasing the load on a synchronous motor running with normal excitation is to___________? |
| A. | decrease both armature current and power factor |
| B. | decrease armature current but increase power factor |
| C. | increase armature current but decrease power factor |
| D. | increase both its armature current and power factor |
| Answer» D. increase both its armature current and power factor | |
| 42. |
The duration of sudden snort-circuit test on a synchronous motor is usually about_____________? |
| A. | one hour |
| B. | one minute |
| C. | one second |
| D. | none of the above |
| Answer» D. none of the above | |
| 43. |
The coupling angle or load angle of synchronous motor is defined as the angle between the__________? |
| A. | rotor and stator teeth |
| B. | rotor and the stator poles of opposite polarity |
| C. | rotor and the stator poles of the same polarity |
| D. | none of the above |
| Answer» C. rotor and the stator poles of the same polarity | |
| 44. |
The construction of a synchronous motor resembles____________? |
| A. | a series motor |
| B. | an induction motor |
| C. | an alternator |
| D. | a rotary converter |
| Answer» D. a rotary converter | |
| 45. |
The back e.m.f. of a synchronous motor depends on______________? |
| A. | speed |
| B. | load |
| C. | load angle |
| D. | all of the above |
| Answer» D. all of the above | |
| 46. |
The back e.m.f. in the stator of a synchronous motor depends on____________? |
| A. | number of poles |
| B. | flux density |
| C. | rotor speed |
| D. | rotor excitation |
| E. | none of the above |
| Answer» E. none of the above | |
| 47. |
The armature current of the synchronous motor has higher values for_____________? |
| A. | high excitation only |
| B. | low excitation only |
| C. | both A. and (b) |
| D. | none of the above |
| Answer» D. none of the above | |
| 48. |
The angle between the rotating stator flux and rotor poles is called _________ angle. |
| A. | synchronizing |
| B. | obtuse |
| C. | torque |
| D. | power factor |
| Answer» D. power factor | |
| 49. |
Riunting in a synchronous motor takes place___________? |
| A. | when supply voltage fluctuates |
| B. | when load varies |
| C. | when power factor is unity |
| D. | motor is under loaded |
| Answer» C. when power factor is unity | |
| 50. |
Power factor of a synchronous motor is unity when_____________? |
| A. | the armature current is maximum |
| B. | the armature current is minimum |
| C. | the armature current is zero |
| D. | none of the above |
| Answer» C. the armature current is zero | |