MCQOPTIONS
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MCQOPTIONS
This section includes 517 Mcqs, each offering curated multiple-choice questions to sharpen your Electrical Engineering knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
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 | |
| 2. |
A synchronous motor is running on a load with normal excitation. Now if the load on the motor is increased |
| A. | power factor as well as armature current will decrease |
| B. | power factor as well as armature current will increase |
| C. | power factor will increase but armature current will decrease |
| D. | power factor will decrease and armature current will increase |
| Answer» E. | |
| 3. |
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 | |
| 4. |
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 | |
| 5. |
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. | |
| 6. |
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 |
| Answer» E. | |
| 7. |
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 | |
| 8. |
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 | |
| 9. |
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 | |
| 10. |
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 | |
| 11. |
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 | |
| 12. |
A 3-phase synchronous motor is running clockwise. If the direction of its field current is reversed |
| A. | the motor will stop |
| B. | the motor continue to run in the same direction |
| C. | the winding of the motor will burn |
| D. | the motor will run in the reverse direction |
| Answer» C. the winding of the motor will burn | |
| 13. |
By which of the following methods the constant speed of a synchronous motor can be changed to new fixed value ? |
| A. | By changing the supply frequency |
| B. | By interchanging any two phases |
| C. | By changing the applied voltage |
| D. | By changing the load. |
| Answer» B. By interchanging any two phases | |
| 14. |
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. | |
| 15. |
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 | |
| 16. |
An important advantage of a synchronous motor over wound round induction motor is that |
| A. | its power factor may be varied at will |
| B. | its speed is independent of supply frequency |
| C. | its speed may be controlled more easily |
| D. | none of the above |
| Answer» B. its speed is independent of supply frequency | |
| 17. |
In a synchronous motor running with fixed excitation, when the load is increased three times, its torque angle becomes approximately |
| A. | one-third |
| B. | twice |
| C. | thrice |
| D. | six times |
| Answer» D. six times | |
| 18. |
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 | |
| 19. |
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 | |
| 20. |
When a 3-phase synchronous generator is supplying a zero power factor lagging load, the armature field affects the main field in the following way |
| A. | augments it directly |
| B. | directly opposes it |
| C. | cross-magnetises it |
| D. | none of the above |
| Answer» C. cross-magnetises it | |
| 21. |
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 | |
| 22. |
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. | |
| 23. |
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 | |
| 24. |
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. | |
| 25. |
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 | |
| 26. |
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 | |
| 27. |
In a synchronous motor it the back e.m.f. generated in the armature at noload is approximately equal to the applied voltage, then |
| A. | the motor is said to be fully loaded |
| B. | the torque generated is maximum |
| C. | the excitation is said to be zero per cent |
| D. | the excitation is said to be hundred per cent |
| Answer» E. | |
| 28. |
As the load is applied to a synchronous motor, the motor takes more armature current because |
| A. | the increased load has to take more current |
| B. | the rotor by shifting its phase backward causes motor to take more current |
| C. | the back e.m.f. decreases causing an increase in motor current |
| D. | the rotor strengthens the rotating field casuing more motor current |
| Answer» C. the back e.m.f. decreases causing an increase in motor current | |
| 29. |
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 | |
| 30. |
When V is the applied voltage, then the breakdown torque of a synchronous motorvaries as |
| A. | V |
| B. | V312 |
| C. | V2 |
| D. | 1/V |
| Answer» B. V312 | |
| 31. |
The power developed by a synchronous motor will be maximum when the load angleis |
| A. | zero |
| B. | 45° |
| C. | 90° |
| D. | 120° |
| Answer» D. 120° | |
| 32. |
The maximum value of torque that a synchronous motor can develop without losingits synchronism, is known as |
| A. | slip torque |
| B. | pull-out torque |
| C. | breaking torque |
| D. | synchronising torque |
| Answer» E. | |
| 33. |
By which of the following methods the constant speed of a synchronous motor can bechanged to new fixed value ? |
| A. | By changing the supply frequency |
| B. | By interchanging any two phases |
| C. | By changing the applied voltage |
| D. | By changing the load. |
| Answer» B. By interchanging any two phases | |
| 34. |
The coupling angle or load angle of synchronous motor is defined as the anglebetween 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 | |
| 35. |
When the voltage applied to a synchronous motor is increased, which of the followingwill reduce ? |
| A. | Stator flux |
| B. | Pull in torque |
| C. | Both (a) and (b) |
| D. | None of the above |
| Answer» E. | |
| 36. |
If in a synchronous motor, driving mechanical load and drawing current at laggingpower 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 | |
| 37. |
In a synchronous motor it the back e.m.f. generated in the armature at noload isapproximately equal to the applied voltage, then |
| A. | the motor is said to be fully loaded |
| B. | the torque generated is maximum |
| C. | the excitation is said to be zero per cent |
| D. | the excitation is said to be hundred per cent |
| Answer» E. | |
| 38. |
A synchronous motor is running on a load with normal excitation. Now if the load onthe motor is increased |
| A. | power factor as well as armature current will decrease |
| B. | power factor as well as armature current will increase |
| C. | power factor will increase but armature current will decrease |
| D. | power factor will decrease and armature current will increase |
| Answer» E. | |
| 39. |
Due to which of the following reasons a synchronous motor fails to pull into synchronism after applying D.C. field current ? |
| A. | High field current |
| B. | Low short circuit ratio |
| C. | High core losses |
| D. | Low field current |
| Answer» E. | |
| 40. |
If excitation of a synchronous motor running with a constant load is decreased fromits 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 | |
| 41. |
In a 3-phase, 4-pole, 50 Hz synchronous motor, the frequency, pole number and loadtorque 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. | |
| 42. |
The maximum torque which a synchronous motor will develop at rest for anyangular 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 | |
| 43. |
A synchronous motor running with normal excitation adjusts to load increasesessentially by increase in |
| A. | back e.m.f. |
| B. | armature current |
| C. | power factor |
| D. | torque angle |
| Answer» C. power factor | |
| 44. |
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 | |
| 45. |
The effect of increasing the load on a synchronous motor running with normalexcitation 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 | |
| 46. |
An important advantage of a synchronous motor over wound round induction motoris that |
| A. | its power factor may be varied at will |
| B. | its speed is independent of supply frequency |
| C. | its speed may be controlled more easily |
| D. | none of the above |
| Answer» B. its speed is independent of supply frequency | |
| 47. |
A 3-phase synchronous motor is running clockwise. If the direction of its field currentis reversed |
| A. | the motor will stop |
| B. | the motor continue to run in the same direction |
| C. | the winding of the motor will burn |
| D. | the motor will run in the reverse direction |
| Answer» C. the winding of the motor will burn | |
| 48. |
When the stator windings are connected in such a fashion that the number of polesare 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. | |
| 49. |
A synchronous motor has better power factor as compared to that of an equivalentinduction 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 | |
| 50. |
The mechanical displacement of the rotor with respect to the stator, in polyphasemultipolar 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 | |