MCQOPTIONS
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MCQOPTIONS
This section includes 29 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. |
A full-wave rectifier uses 2 diodes. The internal resistance of each diode is 20 Ω. The transformer RMS secondary voltage from centre tap to each end of the secondary is 50 V and the load resistance is 980 Ω. Mean load current will be |
| A. | 45 A |
| B. | 4.5 A |
| C. | 45 mA |
| D. | 45 μA |
| Answer» D. 45 μA | |
| 2. |
It is required to control the speed and braking operation of a dc shunt motor in both the directions of rotation. The most suitable power electronic circuit will be |
| A. | A half-controlled converter |
| B. | A fully-controlled converter |
| C. | A diode-bridge converter |
| D. | A dual converter |
| Answer» E. | |
| 3. |
A half controlled single phase bridge rectifier is supplying on R-L load. If it is operated at a firing angle α and the load current is continuous. The fraction of the cycle freewheeling diode conducts is |
| A. | \(\frac{1}{2}\) |
| B. | \(\left( {1 - \frac{\alpha }{\pi }} \right)\) |
| C. | \(\frac{\alpha }{{2\pi }}\) |
| D. | \(\frac{\alpha }{\pi }\) |
| Answer» E. | |
| 4. |
A separately excited dc motor when fed from single phase full converter runs at a speed of 1200 rpm. Load current remains continuous. If one of the SCR gets open circuited, the motor speed will reduce to |
| A. | 900 rpm |
| B. | 800 rpm |
| C. | 600 rpm |
| D. | 400 rpm |
| Answer» D. 400 rpm | |
| 5. |
Compute the ripple factor of a single-phase full wave rectifier with load resistance RL = 10 kΩ. Forward bias dynamic resistance of didoes used is 100 Ω. The rms voltage across secondary winding is 330 V. |
| A. | 4.82 |
| B. | 1.21 |
| C. | 0.482 |
| D. | 0.812 |
| Answer» D. 0.812 | |
| 6. |
An AC voltage of maximum value equal to 100V is applied to a single-phase fully controlled bridge circuit. The peak inverse voltage rating of each SCR used will be ______. |
| A. | 141.4 V |
| B. | 200 V |
| C. | 70.7 V |
| D. | 100 V |
| Answer» E. | |
| 7. |
A single-phase, full-bridge diode rectifier fed from a 230 V, 50 Hz sinusoidal source supplies a series combination of finite resistance, R, and a very large inductance, L. The two most dominant frequency components in the source current are: |
| A. | 50 Hz, 0 Hz |
| B. | 50 Hz, 100 Hz |
| C. | 50 Hz, 150 Hz |
| D. | 150 Hz, 250 Hz |
| Answer» D. 150 Hz, 250 Hz | |
| 8. |
A single phase full bridge converter supplies a load drawing current (constant and ripple free) If the triggering angle is 30°, the input power factor will be |
| A. | 0.65 |
| B. | 0.78 |
| C. | 0.85 |
| D. | 0.866 |
| Answer» C. 0.85 | |
| 9. |
A signal phase full wave mid-point thyristor uses a 220 / 200 V transformer with central tap on the secondary side. The PIV per thyristor will be: |
| A. | 333.98 V |
| B. | 556.34 V |
| C. | 789.87 V |
| D. | 282.84 V |
| Answer» E. | |
| 10. |
In a dual converter, if the firing angle of one bridge is 30°, then the firing angle of second bridge is ______. |
| A. | 30° |
| B. | 180° |
| C. | 120° |
| D. | 150° |
| Answer» E. | |
| 11. |
A delayed full-wave rectified sinusoidal current has an average value equal to one – third its maximum value. Find the delay angle. |
| A. | cos-10.047 |
| B. | cos-10.678 |
| C. | cos-10.866 |
| D. | cos-10.386 |
| Answer» B. cos-10.678 | |
| 12. |
For a firing angle of 60° in respect of a single-phase half-wave controlled rectifier with resistive load supplied from a 230 V (rms), 50 Hz supply, the average output voltage would be |
| A. | 52 V |
| B. | 77.5 V |
| C. | 104 V |
| D. | 155 V |
| Answer» C. 104 V | |
| 13. |
A separately excited DC motor is energised from a 440 V, 50 Hz, 3 ϕ full converter. The input voltage to the motor for a firing angle of 45°, in volts, is: |
| A. | 420 |
| B. | 297 |
| C. | 390 |
| D. | 260 |
| Answer» B. 297 | |
| 14. |
A 3 – phase semi-converter is feeding a separately excited dc motor at constant field current. The motor can operate in the following condition: |
| A. | Speed positive, torque positive |
| B. | Speed positive or negative, torque positive |
| C. | Speed positive, torque positive or negative |
| D. | Speed positive or negative, torque positive or negative |
| Answer» B. Speed positive or negative, torque positive | |
| 15. |
A 3-phase semi-converter works as a six-pulse converter when the firing angle α is: |
| A. | between 60° to 120° |
| B. | between 0° to 60° |
| C. | between 90° to 150° |
| D. | between 120° to 180° |
| Answer» C. between 90° to 150° | |
| 16. |
A single-phase full wave bridge diode rectifier delivers a constant current of 10 A to the load. Average and RMS values of source current are |
| A. | 5 A, 10 A |
| B. | 10 A, 10 A |
| C. | 10 A, 7.07 A |
| D. | 0 A, 10 A |
| Answer» E. | |
| 17. |
For the single-phase fully controlled rectifier shown in the given figure, if the SCR3 is damaged and gets open-circuited, calculate the average DC output voltage if a free-wheeling diode is connected and AC input voltage is 230 V. Firing angle is maintained at \(\dfrac{\pi}{3}\). |
| A. | 77.65 V |
| B. | 44.7 V |
| C. | 39 V |
| D. | 33.6 V |
| Answer» B. 44.7 V | |
| 18. |
A phase-controlled, single-phase, full bridge converter is supplying a highly inductive DC load. The converter is fed from a 230 V, 50 Hz AC source. The fundamental frequency in Hz of the voltage ripple on the DC side is |
| A. | 25 |
| B. | 50 |
| C. | 100 |
| D. | 300 |
| Answer» D. 300 | |
| 19. |
A six-pulse thyristor bridge rectifier is connected to a balanced three-phase, 50 Hz AC source. Assuming that the DC output current of the rectifier is constant, the lowest harmonic component in the AC input current is |
| A. | 100 Hz |
| B. | 150 Hz |
| C. | 250 Hz |
| D. | 300 Hz |
| Answer» D. 300 Hz | |
| 20. |
A single phase full converter is supplied from 230 V, 50 Hz source. Load is R-L load. At α = 60°, calculate the average dc voltage. |
| A. | 103.5 V |
| B. | 206 V |
| C. | 230 V |
| D. | 320 V |
| Answer» B. 206 V | |
| 21. |
A single phase fully controlled rectifier is supplying a load with an anti-parallel diode as shown in the figure. All switches and diodes are ideal. Which one of the following is true for instantaneous load voltage and current? |
| A. | \({v_0} \ge 0\;\& \;{i_0} < 0\) |
| B. | \({v_0} < 0\;\& \;{i_0} < 0\) |
| C. | \({v_0} \ge 0\;\& \;{i_0} \ge 0\) |
| D. | \({v_0} \le 0\;\& \;{i_0} \ge 0\) |
| Answer» D. \({v_0} \le 0\;\& \;{i_0} \ge 0\) | |
| 22. |
In a 3 phase semi-converter, firing angle = 120° and extinction angle = 110°. Each SCR and freewheeling diode conducts respectively for |
| A. | 60°, 50° |
| B. | 30°, 50° |
| C. | 60°, 10° |
| D. | 30°, 40° |
| Answer» B. 30°, 50° | |
| 23. |
For a total harmonic distortion of 0.1 with I1 = 4A and Rc = 8Ω, calculate total power |
| A. | 50 W |
| B. | 70 W |
| C. | 64.64 W |
| D. | 55.55 W |
| Answer» D. 55.55 W | |
| 24. |
In a center tap full wave rectifier, if the peak voltage applied between the center tap and one of the secondary 200 V, then the reverse biased diode is applied with a maximum voltage of: |
| A. | 200 V |
| B. | 100 V |
| C. | 200√2 V |
| D. | 400 V |
| Answer» E. | |
| 25. |
A single phase full converter feeds power to RLE load with R = 8Ω, L = 8 mH and E = 46.42 V, the ac source voltage is 230 V, 50 Hz, for continuous conduction. Find the average value of load current for a firing angle delay of 45° |
| A. | 12.5 A |
| B. | 25 A |
| C. | 8.75 A |
| D. | 20 A |
| Answer» B. 25 A | |
| 26. |
A three phase fully controlled bridge converter is feeding a load drawing a constant and ripple free load current of 10 A at a firing angle of 30° The approximate total harmonic Distortion (%THD) and the rms value of fundamental component of input current will respectively be_ |
| A. | 31% and 6.8 A |
| B. | 31% and 7.8 A |
| C. | 66% and 6.8 A |
| D. | 66% and 7.8 A |
| Answer» C. 66% and 6.8 A | |
| 27. |
A three phase converter feeds pure resistance load at a firing angle of α = 60°. The average value of current flowing in the loads is 10 A. If a very large inductance is connected in the load circuit, then the: |
| A. | Average value of current will remain as 10 A |
| B. | Trend of variation of current cannot be predicted unless the exact value of inductance connected is known |
| C. | Average value of current will become less than 10 A |
| D. | Average value of current will become greater than 10 A |
| Answer» B. Trend of variation of current cannot be predicted unless the exact value of inductance connected is known | |
| 28. |
In a three phase (50Hz) full converter, the ripple frequency in output voltage? |
| A. | 50 Hz |
| B. | 100 Hz |
| C. | 150 Hz |
| D. | 300 Hz |
| Answer» E. | |
| 29. |
Directions: It consists of two statements, one labelled as the ‘Statement (I)’ and the other as ‘Statement (II). Examine these two statements carefully and select the answer using the codes given below:Statement (I): For the same voltage output, the power factor of a single phase semi converter is better than a full converter.Statement (II): The single phase semi converter uses two diodes and two controlled switches. |
| 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» C. Statement (I) is true but Statement (II) is false | |