MCQOPTIONS
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MCQOPTIONS
This section includes 19 Mcqs, each offering curated multiple-choice questions to sharpen your Electrical Engineering Mcqs knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
Synchronous motors are generally not self-starting because: |
| A. | The direction of rotation is not fixed |
| B. | The direction of instantaneous torque reverses after half cycle |
| C. | Startes cannot be used on these machines |
| D. | Starting winding is not provided on the machines |
| Answer» C. Startes cannot be used on these machines | |
| 2. |
If the field circuit of an unloaded salientpole synchronous motor gets suddenly open-circuited, then |
| A. | It runs at a slower speed |
| B. | The motor stops |
| C. | It continues to run at the same speed |
| D. | It runs at a very high speed |
| Answer» C. It continues to run at the same speed | |
| 3. |
A synchronous motor is running with normal excitation. When the load is increased, the armature current drawn by it increases because |
| A. | Speed of the motor is reduced |
| B. | Power factor is decreased |
| C. | Eb (back e.m.f.) becomes less than V (applied voltage) |
| D. | Er (net resultant voltage) in armature is increased |
| Answer» E. | |
| 4. |
Stability of a synchronous machine: |
| A. | Decreases with increase in its excitation |
| B. | Increases with increase in its excitation |
| C. | Remains unaffected with increase in excitation |
| D. | Any of the above |
| Answer» C. Remains unaffected with increase in excitation | |
| 5. |
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 | |
| 6. |
Slip rings are usually made of__________? |
| A. | Carbon or graphite |
| B. | Brass or steel |
| C. | Silver or gold |
| D. | Copper or aluminium |
| Answer» C. Silver or gold | |
| 7. |
Synchronous motors are_____________? |
| A. | Not-self starting |
| B. | Self-starting |
| C. | Essentially self-starting |
| D. | None of the above |
| Answer» B. Self-starting | |
| 8. |
Synchronsizing power of a synchronous machine is_____________? |
| A. | Direcly proportional to the synchronous reactance |
| B. | Inversely proportional to the synchronous reactance |
| C. | Equal to the synchronous reactance |
| D. | None of the above |
| Answer» C. Equal to the synchronous reactance | |
| 9. |
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 | |
| 10. |
Synchronous motor always runs at______________? |
| A. | The synchronous speed |
| B. | Less than synchronous speed |
| C. | More than synchronous speed |
| D. | None of the above |
| Answer» B. Less than synchronous speed | |
| 11. |
Which of the following motors is non-self starting ? |
| A. | D.C. series motor |
| B. | Synchronous motor |
| C. | Squirrel cage induction motor |
| D. | Wound round induction motor |
| Answer» C. Squirrel cage induction motor | |
| 12. |
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 | |
| 13. |
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 | |
| 14. |
Slip-rings in a synchronous motor carry____________? |
| A. | Direct current |
| B. | Alternating current |
| C. | No current |
| D. | All of the above |
| Answer» B. Alternating current | |
| 15. |
The power factor of a synchronous motor is better than that of induction motor because |
| A. | Stator supply is relieved of responsibility of producing magnetic field |
| B. | Mechanical load on the motor can be adjusted |
| C. | Synchronous motor runs at synchronous speed |
| D. | Synchronous motor has large air gap |
| Answer» B. Mechanical load on the motor can be adjusted | |
| 16. |
. In a synchronous motor which loss varies with load ? |
| A. | Windage loss |
| B. | Bearing friction loss |
| C. | Copper loss |
| D. | Core loss |
| Answer» D. Core loss | |
| 17. |
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 | |
| 18. |
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. | |
| 19. |
Which of the following losses, in a synchronous motor, does not vary with load? |
| A. | Windage loss |
| B. | Copper losses |
| C. | Any of the above |
| D. | None of the above |
| Answer» B. Copper losses | |