MCQOPTIONS
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MCQOPTIONS
This section includes 657 Mcqs, each offering curated multiple-choice questions to sharpen your Testing Subject knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
The phenomenon of overlap in converter operation due to |
| A. | source resistance |
| B. | source inductance |
| C. | both source resistance and source inductance |
| D. | high value of firing angle |
| Answer» C. both source resistance and source inductance | |
| 2. |
A dc circuit breaker must use |
| A. | natural commutation |
| B. | forced commutation |
| C. | both natural and forced commutation |
| D. | either natural or forced commutation |
| Answer» C. both natural and forced commutation | |
| 3. |
A fully controlled bridge converter is feeding an RLE load. The load current is I0. The input voltage is Vm sin ωt. The KVL equation to find firing angle a is |
| A. | cos a = E + I0R |
| B. | cos a = E + I0R |
| C. | cos a = E - I0R |
| D. | cos a = E - I0R |
| Answer» D. cos a = E - I0R | |
| 4. |
A chopper cannot be line commutated. |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» B. False | |
| 5. |
In a step down chopper using pulse width modulation, Ton = 3 x 10¯³ and Toff = 1 x 10¯³ s. The chopping frequency is |
| A. | 333.33 |
| B. | 250 |
| C. | 500 |
| D. | 1000 |
| Answer» C. 500 | |
| 6. |
Which of these commutation methods uses an external pulse for commutation? |
| A. | Class A |
| B. | Class C |
| C. | Class E |
| D. | Class F |
| Answer» D. Class F | |
| 7. |
In a single phase full wave ac regulator using two thyristors only, the gate circuits of the two thyristors |
| A. | must be isolated |
| B. | may or may not be isolated |
| C. | should be preferably, isolated |
| D. | should not be isolated |
| Answer» B. may or may not be isolated | |
| 8. |
Thyristors connected in series need : |
| A. | static equalizing circuit |
| B. | dynamic equalizing circuit |
| C. | both static and dynamic equalizing circuits |
| D. | none of the above |
| Answer» D. none of the above | |
| 9. |
A load commutated chopper circuit has |
| A. | one thyristor |
| B. | two thyristors |
| C. | four thyristors |
| D. | six thyristors |
| Answer» D. six thyristors | |
| 10. |
A full bridge inverter is fed by a battery of 30 V. The rms value of output voltage is |
| A. | 15 V |
| B. | 15√2 V |
| C. | 30 V |
| D. | 30√2 V |
| Answer» D. 30√2 V | |
| 11. |
Thyristors are suitable for dc circuit breakers but not for ac circuit breakers. |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» C. May be True or False | |
| 12. |
The stud in a stud mounted SCR acts as |
| A. | anode |
| B. | cathode |
| C. | gate |
| D. | anode or cathode |
| Answer» B. cathode | |
| 13. |
A half bridge inverter |
| A. | needs a 3 wire dc supply |
| B. | may use a two wire or 3 wire dc supply |
| C. | has higher output voltage if fed from 3 wire dc supply |
| D. | has higher efficiency if fed from 3 wire dc supply |
| Answer» B. may use a two wire or 3 wire dc supply | |
| 14. |
In a 3 phase full converter the average load current is 150 A. The average thyristor current is |
| A. | 150 A |
| B. | 75A |
| C. | 50 A |
| D. | 25 A |
| Answer» D. 25 A | |
| 15. |
In a 3 phase full wave regulator feeding a star connected resistance load, firing angle is 75°. Then the number of thyristors conducting at one time is |
| A. | 1 |
| B. | 2 |
| C. | 3 |
| D. | 4 |
| Answer» C. 3 | |
| 16. |
Which of the following devices has two gates? |
| A. | SCR |
| B. | SCS |
| C. | SUS |
| D. | SBS |
| Answer» C. SUS | |
| 17. |
A thyristor is reverse biased. A positive gate pulse is applied. The thyristor |
| A. | will be turned on |
| B. | may or may not turn on |
| C. | will not turn on |
| D. | will turn on after sometime |
| Answer» D. will turn on after sometime | |
| 18. |
If 4 quadrant operation is required we need |
| A. | dual converter |
| B. | full converter |
| C. | semi converter |
| D. | none of the above |
| Answer» B. full converter | |
| 19. |
The use of free wheeling diode in controlled rectifier improves the waveshape of load current. |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» B. False | |
| 20. |
Assertion (A): An ac regulator uses natural commutationReason (R): An ac regulator can be used for static on load tap changing of transformer. |
| A. | Both A and R are correct and R is correct explanation of A |
| B. | Both A and R correct but R is not correct explanation of A |
| C. | A is correct but R is wrong |
| D. | A is wrong but R is correct |
| Answer» C. A is correct but R is wrong | |
| 21. |
In a single phase full wave ac regulator the firing angles during both half cycles are equal. |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» B. False | |
| 22. |
Which converter is used in HVDC transmission? |
| A. | 3 pulse |
| B. | 6 pulse |
| C. | 12 pulse |
| D. | 24 pulse |
| Answer» D. 24 pulse | |
| 23. |
Current chopping leads to |
| A. | over voltage |
| B. | over current |
| C. | both over voltage and over current |
| D. | either over voltage or over current |
| Answer» B. over current | |
| 24. |
A class E chopper |
| A. | can operate in second quadrant only |
| B. | can operate in first or third quadrant |
| C. | can operate in all the four quadrants |
| D. | can operate in either second or third quadrant |
| Answer» D. can operate in either second or third quadrant | |
| 25. |
A 3 phase fully controlled converter is a |
| A. | 3 pulse converter |
| B. | 6 pulse converter |
| C. | 2 pulse converter |
| D. | 12 pulse converter |
| Answer» C. 2 pulse converter | |
| 26. |
Which of these devices is used in relaxation oscillator? |
| A. | UJT |
| B. | SCR |
| C. | DIAC |
| D. | TRIAC |
| Answer» B. SCR | |
| 27. |
A single phase full bridge inverter for R-L loads needs |
| A. | 4 thyristors |
| B. | 4 thyristors and 4 diodes |
| C. | 4 thyristors and 2 diodes |
| D. | 8 thyristors |
| Answer» C. 4 thyristors and 2 diodes | |
| 28. |
The terminals of a power MOSFET are called |
| A. | emitter, base, collector |
| B. | source, gate, drain |
| C. | source, base, drain |
| D. | emitter, gate, drain |
| Answer» C. source, base, drain | |
| 29. |
In a series inverter |
| A. | the commutating elements L and C are in parallel |
| B. | the commutating elements L and C are in series with load |
| C. | the commutating L and C may be in series or parallel with the load |
| D. | none of the above |
| Answer» C. the commutating L and C may be in series or parallel with the load | |
| 30. |
Assertion (A): Chopper always requires forced commutationReason (R): Morgan chopper uses a saturable reactor. |
| A. | Both A and R are correct and R is correct explanation of A |
| B. | Both A and R correct but R is not correct explanation of A |
| C. | A is correct but R is wrong |
| D. | A is wrong but R is correct |
| Answer» C. A is correct but R is wrong | |
| 31. |
As regards single phase dual converter |
| A. | the change in operation from one quadrant to the other is faster in non-circulating current mode |
| B. | the change in operation from one quadrant to the other is faster in circulating current mode |
| C. | the time response to change in operation from one quadrant to other is the same in both the modes |
| D. | the time response to change in operation from one quadrant to the other may be faster in any of the two modes |
| Answer» C. the time response to change in operation from one quadrant to other is the same in both the modes | |
| 32. |
The amount of dielectric heating is inversely proportional to frequency. |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» C. May be True or False | |
| 33. |
In a single phase full wave converter (M - 2 connection) feeding a highly inductive load, the firing angle for each thyristor is a in the respective half cycle. The period of conduction of each thyristor is |
| A. | π - a |
| B. | π |
| C. | π + a |
| D. | π - 2a |
| Answer» C. π + a | |
| 34. |
In pulse width modulation of chopper |
| A. | T is kept constant and Ton is varied |
| B. | Ton is kept constant T is varied |
| C. | both T and Ton are varied |
| D. | either T or Ton is varied |
| Answer» B. Ton is kept constant T is varied | |
| 35. |
In a multiphase chopper, all choppers operate together. |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» C. May be True or False | |
| 36. |
In a half bridge inverter each thyristor is gated at a frequency f. The output frequency is |
| A. | 2 f |
| B. | f |
| C. | 0.5 f |
| D. | 0.25 f |
| Answer» C. 0.5 f | |
| 37. |
In a thyristors are i = kvᵃ. The value of a is |
| A. | about 0.5 |
| B. | about 2 |
| C. | about 5 |
| D. | about 20 |
| Answer» D. about 20 | |
| 38. |
A 3 phase bridge inverter is fed by 400 V battery. The load is star connected and has a resistance of 10 Ω per phase. The peak value of thyristor current is |
| A. | 400/10 A |
| B. | 400/15 A |
| C. | 400/20 A |
| D. | 400/30 A |
| Answer» C. 400/20 A | |
| 39. |
The output frequency of a cycloconverter can be changed by changing the firing angle. |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» C. May be True or False | |
| 40. |
A NAND gate has 3 inputs and one output. The number of thyristors required for this gate are |
| A. | 1 |
| B. | 2 |
| C. | 3 |
| D. | 3 or 4 |
| Answer» D. 3 or 4 | |
| 41. |
The difference between resonant commutation and self commutation is |
| A. | both these methods are based on entirely different principles |
| B. | in resonant commutation, the commutating elements carry load current but in self commutation, the commutating elements do not carry load current |
| C. | resonant commutation uses L and C but self commutation uses only capacitor |
| D. | none of the above |
| Answer» B. in resonant commutation, the commutating elements carry load current but in self commutation, the commutating elements do not carry load current | |
| 42. |
A 3 phase induction motor is fed by a 3 phase ac regulator to change the stator voltage. The variation in speed will be more if |
| A. | load torque is constant |
| B. | load torque increases with increase in speed |
| C. | load torque decreases with increase in speed |
| D. | either (a) or (b) |
| Answer» C. load torque decreases with increase in speed | |
| 43. |
The static equalisation circuit for thyristors connected in series is |
| A. | one resistor in series with each thyristor |
| B. | one resistor in parallel with each thyristor |
| C. | one resistor and one capacitor in parallel with each thyristor |
| D. | none of the above |
| Answer» C. one resistor and one capacitor in parallel with each thyristor | |
| 44. |
In integral cycle control the period of on-off control should be more than mechanical time constant of load. |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» C. May be True or False | |
| 45. |
In a series inverter supplying a load resistance R, the commutating elements L and C should be such that |
| A. | R² = 4L/C |
| B. | R² < 4L/C |
| C. | R² > 4L/C |
| D. | R² < 2L/C |
| Answer» C. R² > 4L/C | |
| 46. |
A single phase cycloconverter feeds a resistance heating load. The heating power is provided by |
| A. | only the fundamental component of output wave |
| B. | only higher harmonics in the output wave |
| C. | both fundamental and higher harmonics in the output wave |
| D. | either (a) or (b) |
| Answer» D. either (a) or (b) | |
| 47. |
For a 12 pulse operation, the two 6 pulse units are fed by |
| A. | Y - Y and Y - Y transformers |
| B. | Δ - Δ and Δ - Δ transformers |
| C. | Y - Y and Y - Δ transformers |
| D. | Y - Δ and Y - Δ transformers |
| Answer» D. Y - Δ and Y - Δ transformers | |
| 48. |
When thyristors are connected in series and parallel, it may be necessary to have : |
| A. | current derating |
| B. | voltage derating |
| C. | both current and voltage derating |
| D. | none of the above |
| Answer» D. none of the above | |
| 49. |
The rated current of a thyristor is 40 A. The holding current will be about : |
| A. | 20 A |
| B. | 1 A |
| C. | 100 mA |
| D. | 10 mA |
| Answer» E. | |
| 50. |
A single phase half wave converter is feeding a resistive load. Just before triggering, the voltage across thyristor is |
| A. | zero |
| B. | about 1 V |
| C. | same as input voltage |
| D. | twice the input voltage |
| Answer» D. twice the input voltage | |