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.
| 401. |
*/*_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 | |
| 402. |
*/*_Synchronsizingpower 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 | |
| 403. |
*/*_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 | |
| 404. |
*/*_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 | |
| 405. |
*/*_The magnitude of field flux in a 3-phase synchronous motor? |
| A. | remains constant at all loads |
| B. | varies with speed |
| C. | varies with the load |
| D. | varies with power factor |
| Answer» B. varies with speed | |
| 406. |
*/*_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 | |
| 407. |
%_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 | |
| 408. |
%_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 | |
| 409. |
%_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 | |
| 410. |
%_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 the above |
| Answer» B. less than the supply voltage | |
| 411. |
%_The magnitude of field flux in a 3-phase synchronous motor_% |
| A. | remains constant at all loads |
| B. | varies with speed |
| C. | varies with the load |
| D. | varies with power factor |
| Answer» B. varies with speed | |
| 412. |
%_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 | |
| 413. |
%_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 | |
| 414. |
_ Synchronsizingpower of a synchronous machine is$? |
| A. | direcly proportional to the synchronous reactance |
| B. | inversely proportional to the synchronous reactance |
| C. | equal to the synchronous reactance |
| D. | none of the above |
| Answer» C. equal to the synchronous reactance | |
| 415. |
_ Synchronous motor always runs at$? |
| 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 | |
| 416. |
_ A synchronous motor is running with normal excitation. When the load is increased, the armature current drawn by it increases because$? |
| A. | Speed of the motor is reduced |
| B. | Power factor is decreased |
| C. | Eb (back e.m.f.) becomes less than V (applied voltage) |
| D. | Er (net resultant voltage) in armature is increased |
| Answer» E. | |
| 417. |
_ In a synchronous motor, damper windings are provided on$? |
| A. | stator frame |
| B. | rotor shaft |
| C. | pole faces |
| D. | none of the above |
| Answer» D. none of the above | |
| 418. |
_ Exciters of synchronous machines are$? |
| A. | d.c. shunt machines |
| B. | d.c. series machines |
| C. | d.c. compound machines |
| D. | any of the above |
| Answer» B. d.c. series machines | |
| 419. |
_ In a synchronous motor, the magnitude of stator back e.m.f. Eb depends on$? |
| 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 | |
| 420. |
_ The speed regulation of a synchronous motor is always$? |
| A. | 1% |
| B. | 0.5% |
| C. | positive |
| D. | zero |
| Answer» E. | |
| 421. |
_ In which of the following motors the stator and rotor magnetic field rotate at the same speed ?$? |
| A. | Universal motor |
| B. | Synchronous motor |
| C. | Induction motor |
| D. | Reluctance motor |
| Answer» C. Induction motor | |
| 422. |
_ An over-excited synchronous motor takes$? |
| A. | leading current |
| B. | lagging current |
| C. | both (A) and (B) |
| D. | none of the above |
| Answer» B. lagging current | |
| 423. |
_ The mechanical displacement of the rotor with respect to the stator, in polyphase multipolar synchronous motors running at full load, is of the order of$? |
| A. | zero degree |
| B. | two degrees |
| C. | five degrees |
| D. | ten degrees |
| Answer» D. ten degrees | |
| 424. |
_ Which of the following losses, in a synchronous motor, does not vary with load?$? |
| A. | Windage loss |
| B. | Copper losses |
| C. | Any of the above |
| D. | None of the above |
| Answer» B. Copper losses | |
| 425. |
_ When the rotor speed, in a synchronous machine, becomes more than the synchronous speed during hunting, the damper bars develop$? |
| A. | inductor motor torque |
| B. | induction generator torque |
| C. | synchronous motor torque |
| D. | d.c. motor toque |
| Answer» C. synchronous motor torque | |
| 426. |
_ In a synchronous motor, the armature current has large values for$? |
| A. | high excitation only |
| B. | low excitation only |
| C. | both high and low excitation |
| D. | none of the above |
| Answer» D. none of the above | |
| 427. |
_ Synchronous motors are generally not self-starting because$? |
| 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 | |
| 428. |
_The rotor copper losses, in a synchronous motor, are met by$? |
| A. | d.c. source |
| B. | armature input |
| C. | motor input |
| D. | supply lines |
| Answer» B. armature input | |
| 429. |
_By which of the following methods the constant speed of a synchronous motor can be changed to new fixed value ?$? |
| 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 | |
| 430. |
_The power factor of a synchronous motor is better than that of induction motor because$? |
| A. | stator supply is relieved of responsibility of producing magnetic field |
| B. | mechanical load on the motor can be adjusted |
| C. | synchronous motor runs at synchronous speed |
| D. | synchronous motor has large air gap |
| Answer» B. mechanical load on the motor can be adjusted | |
| 431. |
_When the field of a synchronous motor is under-excited, the power factor will be$? |
| A. | leading |
| B. | lagging |
| C. | unity |
| D. | zero |
| Answer» C. unity | |
| 432. |
_In a synchronous motor which loss varies with load ?$? |
| A. | Windage loss |
| B. | Bearing friction loss |
| C. | Copper loss |
| D. | Core loss |
| Answer» D. Core loss | |
| 433. |
_A synchronous motor connected to infinite bus-bars has at constant full load, 100% excitation and unity power factor. On changing the excitation only, the armature current will have$? |
| 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. | |
| 434. |
_The minimum armature current of the synchronous motor corresponds to operation at$? |
| A. | zero power factor leading |
| B. | unity power factor |
| C. | 0.707 power factor lagging |
| D. | 0.707 power factor leading |
| Answer» C. 0.707 power factor lagging | |
| 435. |
_Armature of a synchronous machine is$? |
| 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. | |
| 436. |
_The effect of increasing the load on a synchronous motor running with normal excitation is to$? |
| A. | decrease both armature current and power factor |
| B. | decrease armature current but increase power factor |
| C. | increase armature current but decrease power factor |
| D. | increase both its armature current and power factor |
| Answer» D. increase both its armature current and power factor | |
| 437. |
_The torque angle, in a synchronous motor, is the angle between$? |
| 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 | |
| 438. |
_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$? |
| A. | augments it directly |
| B. | directly opposes it |
| C. | cross-magnetises it |
| D. | none of the above |
| Answer» C. cross-magnetises it | |
| 439. |
_The maximum value of torque that a synchronous motor can develop without losing its synchronism, is known as$? |
| A. | slip torque |
| B. | pull-out torque |
| C. | breaking torque |
| D. | synchronising torque |
| Answer» E. | |
| 440. |
_In a synchronous motor, the magnitude of stator back e.m.f. £& depends on$? |
| A. | d.c. excitation only |
| B. | speed of the motor |
| C. | load on the motor |
| D. | both the speed and rotor flux |
| Answer» B. speed of the motor | |
| 441. |
_If the synchronous motor, properly synchronised to the supply is running on no load and is having negligible loss then$? |
| 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 |
| Answer» B. the stator current will be very small | |
| 442. |
_The speed of a synchronous motor$? |
| A. | increases as the load increases |
| B. | decreases as the load decreases |
| C. | always remains constant |
| D. | none of the above |
| Answer» D. none of the above | |
| 443. |
Slip-rings in a synchronous motor carry$? |
| A. | direct current |
| B. | alternating current |
| C. | no current |
| D. | all of the above |
| Answer» B. alternating current | |
| 444. |
Which of the following losses is not dissipated by the stator core surface in a synchronous motor ?$? |
| A. | Eddy current losses in the conductors |
| B. | Iron losses in the stator |
| C. | Copper losses in the slot portion of the conductors |
| D. | Windage losses |
| Answer» E. | |
| 445. |
Which of the following motors is non-self starting ?$? |
| A. | D.C. series motor |
| B. | synchronous motor |
| C. | Squirrel cage induction motor |
| D. | Wound round induction motor |
| Answer» C. Squirrel cage induction motor | |
| 446. |
Due to which of the following reasons a synchronous motor fails to pull into synchronism after applying D.C. field current?$? |
| A. | High field current |
| B. | Low short circuit ratio |
| C. | High core losses |
| D. | Low field current |
| Answer» E. | |
| 447. |
The maximum torque which a synchronous motor will develop at rest for any angular position of the rotor, at rated stator supply voltage and frequency, is known as$? |
| A. | locked-rotor torque |
| B. | synchronous torque |
| C. | pull up torque |
| D. | reluctance torque |
| Answer» B. synchronous torque | |
| 448. |
If in a synchronous motor, driving a given mechanical load and drawing current at a leading power factor from constant voltage supply its field excitation is increased, its power factor$? |
| A. | will become more |
| B. | will become less |
| C. | will remain unchanged |
| D. | none of the above. |
| Answer» C. will remain unchanged | |
| 449. |
A synchronous motor develops maximum power when load angle is$? |
| A. | 45° |
| B. | 60° |
| C. | 90° |
| D. | 120° |
| Answer» D. 120¬¨‚àû | |
| 450. |
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 | |