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.
| 451. |
The operating speed of a synchronous motor can be changed to new fixed value by$? |
| A. | changing the load |
| B. | changing the supply voltage |
| C. | changing frequency |
| D. | using brakes |
| Answer» D. using brakes | |
| 452. |
As the load is applied to a synchronous motor, the motor takes more armature current because$? |
| 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 causing more motor current |
| Answer» C. The back e.m.f. decreases causing an increase in motor current | |
| 453. |
In a synchronous motor, the maximum power developed depends on all of the following except$? |
| A. | rotor excitation |
| B. | maximum value of coupling angle |
| C. | direction of rotation |
| D. | supply voltage |
| Answer» D. supply voltage | |
| 454. |
A synchronous machine with low value of short-circuit ratio has$? |
| A. | lower stability limit |
| B. | high stability limit |
| C. | good speed regulation |
| D. | good voltage regulation |
| Answer» B. high stability limit | |
| 455. |
Riunting in a synchronous motor takes place$? |
| A. | When supply voltage fluctuates |
| B. | When load varies |
| C. | When power factor is unity |
| D. | Motor is under loaded |
| Answer» C. When power factor is unity | |
| 456. |
To limit the operating temperature an electrical machine should have proper$? |
| A. | voltage rating |
| B. | current rating |
| C. | power factor |
| D. | speed |
| Answer» C. power factor | |
| 457. |
The maximum power developed in a synchronous motor will depend on$? |
| A. | the rotor excitation only |
| B. | the supply voltage only |
| C. | the rotor excitation and supply volt-age both |
| D. | the rotor excitation, supply voltage and maximum value of coupling angle (90°) |
| Answer» E. | |
| 458. |
When the excitation of an unloaded salient pole synchronous motor suddenly gets disconnected$? |
| 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 | |
| 459. |
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$? |
| A. | become more |
| B. | become less |
| C. | remain constant |
| D. | none of the above |
| Answer» C. remain constant | |
| 460. |
Under which of the following conditions hunting of synchronous motor is likely to occur ?$? |
| A. | Periodic variation of load |
| B. | Over-excitation |
| C. | Over-loading for long periods |
| D. | Small and constant load |
| Answer» B. Over-excitation | |
| 461. |
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. | |
| 462. |
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 | |
| 463. |
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 | |
| 464. |
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 causing more motor current |
| Answer» C. The back e.m.f. decreases causing an increase in motor current | |
| 465. |
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 | |
| 466. |
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 |
| Answer» B. high stability limit | |
| 467. |
A synchronous motor develops maximum power when load angle is? |
| A. | 45° |
| B. | 60° |
| C. | 90° |
| D. | 120° |
| Answer» D. 120¬¨‚àû | |
| 468. |
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 | |
| 469. |
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°) |
| Answer» E. | |
| 470. |
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 | |
| 471. |
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 | |
| 472. |
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. | |
| 473. |
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 | |
| 474. |
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 | |
| 475. |
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 | |
| 476. |
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. | |
| 477. |
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. | |
| 478. |
Which of the following resistances can be measured by conducting insulation resistance test on a synchronous motor ? |
| A. | Phase to phase winding resistance |
| B. | Stator winding to earthed frame |
| C. | Rotor winding to earthed shaft |
| D. | All of the above |
| Answer» E. | |
| 479. |
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. | |
| 480. |
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 | |
| 481. |
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 | |
| 482. |
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 | |
| 483. |
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. | |
| 484. |
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. | |
| 485. |
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 | |
| 486. |
The shaft of synchronous motor is made of |
| A. | mild steel |
| B. | chrome steel |
| C. | alnico |
| D. | stainless steel |
| Answer» B. chrome steel | |
| 487. |
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 | |
| 488. |
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. | |
| 489. |
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 | |
| 490. |
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 | |
| 491. |
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. | |
| 492. |
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 | |
| 493. |
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 | |
| 494. |
The armature current of the synchronous motor |
| A. | has large values for low excitation i niy |
| B. | has large values for high excitation only |
| C. | has large values for low and high excitation |
| D. | any of the above |
| Answer» D. any of the above | |
| 495. |
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. | |
| 496. |
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¬¨‚àû | |
| 497. |
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 | |
| 498. |
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 | |
| 499. |
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 | |
| 500. |
The angle between the rotating stator flux and rotor poles is called _____ angle. |
| A. | torque |
| B. | obtuse |
| C. | synchronizing |
| D. | power factor |
| Answer» B. obtuse | |