MCQOPTIONS
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MCQOPTIONS
This section includes 34 Mcqs, each offering curated multiple-choice questions to sharpen your Power Electronics knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
In a 3-phase converter circuit, during commutation when one SCR in one phase is turned on, turning of an SCR in another phase results is: |
| A. | Voltage sag |
| B. | harmonic distortion |
| C. | voltage notching |
| D. | voltage swell |
| Answer» D. voltage swell | |
| 2. |
In a 3-phase half wave rectifier the dc output voltage is 230 V. The peak inverse voltage across each diode is |
| A. | 481.7 V |
| B. | 460 V |
| C. | 345 V |
| D. | 360 V |
| Answer» B. 460 V | |
| 3. |
For an SCR, di/dt protection is achieved through the use of |
| A. | R in series with SCR |
| B. | L in series with SCR |
| C. | RL in series with SCR |
| D. | RLC in series with SCR |
| Answer» C. RL in series with SCR | |
| 4. |
A delayed full-wave rectified sinusoidal current has an average value equal to half its maximum value. Find the delay angle θ. |
| A. | \(\theta = {\cos ^{ - 1}}\left( {\frac{\pi }{2} - \frac{1}{2}} \right)\;\;\) |
| B. | \(\theta = {\cos ^{ - 1}}\left( {\frac{\pi }{2} + 1} \right)\) |
| C. | \(\theta = {\cos ^{ - 1}}\left( {\frac{\pi }{2} - 1} \right)\) |
| D. | \(\theta = {\cos ^{ - 1}}\left( {\frac{\pi }{2}} \right)\) |
| Answer» D. \(\theta = {\cos ^{ - 1}}\left( {\frac{\pi }{2}} \right)\) | |
| 5. |
For a 3-ϕ, 50 Hz supply, calculate the ratio of output voltage ripple frequency to the supply voltage frequency of 6 pulse diode bridge rectifier. |
| A. | 3 |
| B. | 12 |
| C. | 2 |
| D. | 6 |
| Answer» E. | |
| 6. |
A fully controlled rectifier operates in the _______ quadrant. |
| A. | First |
| B. | Second |
| C. | First and second |
| D. | First and fourth |
| Answer» E. | |
| 7. |
Consider the following statements:Phase controlled converters at small values of output voltage have1. Large harmonics in utility system2. Poor power factor3. High efficiency4. Notches in line voltage waveformWhich of the above statements are correct? |
| A. | 1 and 2 only |
| B. | 1, 2 and 4 |
| C. | 2, 3 and 4 |
| D. | 1 and 4 only |
| Answer» C. 2, 3 and 4 | |
| 8. |
Distortion factor (DF) and total harmonic distortion (THD) are related by. |
| A. | \(DF = \sqrt {\frac{1}{{1 - TH{D^2}}}} \) |
| B. | \(THD = \sqrt {\frac{1}{{2 + D{F^2}}}} \) |
| C. | \(THD = \sqrt {\frac{1}{1} - D{F^2}} \) |
| D. | \(THD = \sqrt {\frac{1}{{D{F^2}}} - 1} \) |
| Answer» E. | |
| 9. |
In the circuit shown in the given figure, the SCR is fired at 45°. Which of the following statements is correct with respect to load voltage and current at ωt = π? |
| A. | Only load voltage is zero |
| B. | Both load voltage and load current are zero |
| C. | Only load current is zero |
| D. | Both load voltage and load current are non-zero |
| Answer» B. Both load voltage and load current are zero | |
| 10. |
A single-phase full-wave rectifier is constructed using thyristors. If the peak value of the sinusoidal input voltage is Vm and the delay angle is π/3 radian, then the average value of output voltage is |
| A. | 0.32 Vm |
| B. | 0.48 Vm |
| C. | 0.54 Vm |
| D. | 0.71 Vm |
| Answer» B. 0.48 Vm | |
| 11. |
A 3-phase, 4-wire ac is applied to the following rectifier. Determine the average value of the output voltage. Take Vp is the rms value of the phase voltage. |
| A. | \(\frac{{3\sqrt 6 }}{\pi }{V_p}\) |
| B. | \(\frac{{\sqrt 6 }}{{2\pi }}{V_p}\) |
| C. | \(\frac{{3\sqrt 2 }}{{2\pi }}{V_p}\) |
| D. | \(\frac{{3\sqrt 6 }}{{2\pi }}{V_p}\) |
| Answer» E. | |
| 12. |
Figure shows 1-ϕ full converter feeding RLE load with XL = 3 Ω, R = 4 Ω, and E = 10 V. Determine the average value of load voltage for the average load current of ILo = 50 A. |
| A. | 150 |
| B. | 190 |
| C. | 110 |
| D. | 210 |
| Answer» E. | |
| 13. |
A single-phase fully controlled bridge is supplied at 120 V rms. What will be the average load voltage for a delay angle of 90° assuming continuous load current? |
| A. | 0 V |
| B. | 70.4 V |
| C. | 102 V |
| D. | 170 V |
| Answer» B. 70.4 V | |
| 14. |
Current-ripple factor (CRF), ripple current Ir and average load current Io are related by the expression. |
| A. | CRF = (Io)(Ir) |
| B. | CRF = Io + Ir |
| C. | Ir = (CRF)(Io) |
| D. | Io = (CRF)(Ir) |
| Answer» D. Io = (CRF)(Ir) | |
| 15. |
A semi-controlled rectifier operates in the _______ quadrant. |
| A. | First |
| B. | Second |
| C. | First and second |
| D. | First and fourth |
| Answer» B. Second | |
| 16. |
A single-phase semi-converter is operated form 120 V, 50 Hz AC supply at a firing angle of 30 degrees. The load is such that the load current is continuous and ripple-free. Displacement factor of the converter is: |
| A. | 0.77 |
| B. | 0.97 |
| C. | 0.67 |
| D. | 0.57 |
| Answer» C. 0.67 | |
| 17. |
For continuous conductions, in a single phase full converter each pair of SCRs conducts for |
| A. | (π – α) radians |
| B. | π radians |
| C. | α radians |
| D. | (π + α) radians |
| Answer» C. α radians | |
| 18. |
A 240 V single-phase AC supply is fed to a load resistor of 100 Ω through a thyristor. If the thyristor is fired at 90°, what is the power consumed by the load? |
| A. | 144 W |
| B. | 432 W |
| C. | 576 W |
| D. | 0 W |
| Answer» B. 432 W | |
| 19. |
For large power output, multiphase rectifiers are used along with filters to reduce level of harmonics by increasing the fundamental frequency in |
| A. | Diode rectifier |
| B. | Bridge rectifier |
| C. | Star rectifier |
| D. | Delta rectifier |
| Answer» D. Delta rectifier | |
| 20. |
In a 3-ϕ controlled bridge rectifier, the maximum conduction of each Thyristor is |
| A. | 60° |
| B. | 90° |
| C. | 120° |
| D. | 150° |
| Answer» D. 150° | |
| 21. |
Match List-I (1-ϕ Rectifier topology-feeding resistive load) with List-II (Average output voltage) and select the correct answer (α is firing angle)List-IA. Uncontrolled half waveB. Controlled half waveC. Controlled full waveD. Semi controlledList-II1. \(\frac{{{V_{peak}}}}{\pi }\left( {1 + \cos \alpha } \right)\)2. \(\frac{{2{V_{peak}}}}{\pi }\cos \alpha \)3. \(\frac{{{V_{peak}}}}{\pi }\)4. \(\frac{{{V_{peak}}}}{{2\pi }}\left( {1 + \cos \alpha } \right)\) |
| A. | A – 3, B – 2, C – 4, D – 1 |
| B. | A – 1, B – 4, C – 2, D – 3 |
| C. | A – 3, B – 4, C – 2, D – 1 |
| D. | A – 1, B – 2, C – 4, D – 3 |
| Answer» D. A – 1, B – 2, C – 4, D – 3 | |
| 22. |
A 3-ϕ full wave converter as shown in the figure is operated from a 3-ϕ Y-connected 208 V (line-line rms), 50 Hz supply and the load resistance is R = 10 Ω. If the delay angle α is 60°, find the average output voltage? |
| A. | 160.32 V |
| B. | 140.45 V |
| C. | 200.56 V |
| D. | 100 V |
| Answer» C. 200.56 V | |
| 23. |
In a three-phase full wave AC to Dc converter, the ripple frequency of the output is: |
| A. | 6 × supply voltage frequency |
| B. | 2 × supply voltage frequency |
| C. | 12 × supply voltage frequency |
| D. | 3 × supply voltage frequency |
| Answer» B. 2 × supply voltage frequency | |
| 24. |
A freewheeling diode in a phase-controlled rectifier: |
| A. | Is responsible for additional harmonics |
| B. | Is responsible for additional reactive power |
| C. | Enables the inverter operation |
| D. | Improves the line power factor |
| Answer» E. | |
| 25. |
A single-phase fully controlled rectifier has an average voltage of ‘P’ volts when α = 0°. Its output voltage when α = 30° is: |
| A. | 0.5 P volts |
| B. | 0.707 P volts |
| C. | P volts |
| D. | (√3/2) P volts |
| Answer» E. | |
| 26. |
A single-phase half wave controlled rectifier, operating at 120 V rms and 60 Hz ac supply, has a firing angle of 60°. The average value of its output voltage is |
| A. | \(\frac {45\sqrt 2}{\pi} V\) |
| B. | \(\frac {45\sqrt 3}{\pi} V\) |
| C. | \(\frac {90\sqrt 2}{\pi} V\) |
| D. | \(\frac {90\sqrt 3}{\pi}V\) |
| Answer» D. \(\frac {90\sqrt 3}{\pi}V\) | |
| 27. |
A 1-phase SCR based ac regulator is feeding power to a load consisting of 5 Ω resistance and 16mH inductance. The input supply is 230 V, 50 Hz. The maximum firing angle at which the voltage across the device becomes zero all throughout and the rms value of current through SCR, under the operating condition are |
| A. | 30° and 46 A |
| B. | 30° and 23 A |
| C. | 45° and 23 A |
| D. | 45° and 32 A |
| Answer» D. 45° and 32 A | |
| 28. |
A freewheeling diode in a phase-controlled rectifier |
| A. | improves the line power factor |
| B. | is responsible for additional reactive power |
| C. | prevents inverse operation |
| D. | is responsible for additional harmonics |
| Answer» B. is responsible for additional reactive power | |
| 29. |
For controlling the speed of dc motor 200 hp rating, the following type of converter is normally used: |
| A. | Single-phase full converter |
| B. | Single-phase dual converter |
| C. | Three-phase full converter |
| D. | Three-phase dual converter |
| Answer» D. Three-phase dual converter | |
| 30. |
Direction: The following item consists of two statements, one labelled as ‘Statement (I)’ and the other as ‘Statement (II)’. Examine these two statements carefully and select the answers to these items using the code given below:Statement (I): The main function of a freewheeling diode in Rectifier circuits is to prevent the reversal of load voltage.Statement (II): The freewheeling diode is never connected across the load. |
| A. | Both Statement I and Statement II are individually true and Statement II is the correct explanation of Statement I |
| B. | Both Statement I and Statement II are individually true but Statement II is not the correct explanation of Statement I |
| C. | Statement I is true but Statement II is false |
| D. | Statement I is false but Statement II is true |
| Answer» D. Statement I is false but Statement II is true | |
| 31. |
In a zero current switching resonant converter, the switching loss and noise are increased due to presence of capacitive coupling called |
| A. | Miller capacitor |
| B. | Series-resonant capacitor |
| C. | Parallel resonant capacitor |
| D. | Switch capacitor |
| Answer» B. Series-resonant capacitor | |
| 32. |
In a 3-phase half wave rectifier, each diode is subjected to a PIV of |
| A. | Vm |
| B. | \(\frac{{{V_m}}}{{\sqrt 2 }}\) |
| C. | √2 Vm |
| D. | √3 Vm |
| Answer» E. | |
| 33. |
An SCR has an anode supply of sine voltage 200 Vr.m.s., 50 Hz applied through a 100 Ω resistor and fired at an angle of 60°. Assuming no voltage drop the r.m.s. value of the output voltage is nearly |
| A. | 90 V |
| B. | 126 V |
| C. | 166 V |
| D. | 200 V |
| Answer» C. 166 V | |
| 34. |
For a three-phase, half-wave AC to DC converter, VDC is given by |
| A. | \(\frac{{3\sqrt 3 {V_m}}}{{2\pi }}\cos \alpha \) |
| B. | \(\frac{{3\sqrt 3 {V_m}}}{\pi }\cos \alpha\) |
| C. | \(\frac{{{V_m}}}{{2\pi }}\left( {1 + \cos \alpha } \right)\) |
| D. | \(\frac{{2{V_m}}}{\pi }\cos \alpha\) |
| Answer» B. \(\frac{{3\sqrt 3 {V_m}}}{\pi }\cos \alpha\) | |