250+ TOP MCQs on Solid-State Switching Circuits – Three Phase, Full-Wave, AC/DC Conversion and Answers

Electric Drives Multiple Choice Questions & Answers on “Solid-State Switching Circuits – Three Phase, Full-Wave, AC/DC Conversion”.

1. For α > 90°, 3-Φ Full wave bridge rectifier acts as a natural commutated inverter.
A. True
B. False
Answer: A
Clarification: The output voltage of 3-Φ Full wave bridge rectifier is 3V_ml(cos(∝))÷π. For α > 90° the output voltage becomes negative. The power flows from DC to the AC side.

2. What is the formula for output voltage for 3-Φ Full wave bridge rectifier for R-L load?
A. 3V_ml(cos(∝))÷2π
B. 3V_ml(cos(∝))÷π
C. 2V_ml(cos(∝))÷π
D. 6V_ml(cos(∝))÷π
Answer: B
Clarification: The output voltage of 3-Φ Full wave bridge rectifier for R-L load is 3V_ml(cos(∝))÷π. The net area of the output voltage for R-L load remains zero.

3. The output voltage of 3-Φ Full wave bridge rectifier is six times of 3-Φ Half-wave rectifier.
A. True
B. False
Answer: B
Clarification: The output voltage of 3-Φ Full wave bridge rectifier is 3V_ml(cos(∝))÷π. The output voltage of 3-Φ Half wave rectifier is 3V_ml(cos(∝))÷2π.

4. What is the formula for output voltage for 3-Φ Full wave bridge rectifier for R load for α < 60°?
A. 2V_ml(cos(∝))÷π
B. 3V_ml(cos(∝))÷2π
C. 3V_ml(cos(∝))÷π
D. 6V_ml(cos(∝))÷π
Answer: C
Clarification: The output voltage of 3-Φ Full wave bridge rectifier for R load is 3V_ml(cos(∝))÷π for α < 60°. Conduction will only remain from 60°+α to 120°+α.

5. ____________ is the boundary for C.C.M and D.C.M mode in 3-Φ Full wave bridge rectifier for R load.
A. 60°
B. 10°
C. 80°
D. 50°
Answer: A
Clarification: 60° is the boundary for C.C.M and D.C.M mode in 3-Φ Full wave bridge rectifier for R load. Conduction will only remain from 60°+α to 120°+α.

6. What is the formula for output voltage for 3-Φ Full wave bridge rectifier for R load for α > 60°?
A. 2V_ml(1+cos(∝+60°))÷π
B. 3V_ml(1+cos(60°+∝))÷2π
C. 3V_ml(1+cos(60°+∝))÷π
D. 6V_ml(cos(∝))÷π
Answer: C
Clarification: The output voltage of 3-Φ Full wave bridge rectifier for R load is 3V_ml(1+cos(60°+∝))÷π for α > 60°. Conduction will only remain from 60°+α to 180°.

7. Calculate the r.m.s value of thyristor current in 3-Φ Full wave converter for the load current=4 A and α=12°.
A. 2.3 A
B. 2.5 A
C. 2.7 A
D. 2.9 A
Answer: A
Clarification: The r.m.s value of thyristor current in 3-Φ Full wave converter is I_o√1÷3. It is the r.m.s value of the thyristor current. I_(r.m.s) = I_o√1÷3 = 2.3 A.

8. Calculate the average value of thyristor current in 3-Φ Full wave converter for the load current=9 A and α=26°.
A. 4 A
B. 5 A
C. 7 A
D. 3 A
Answer: D
Clarification: The average value of thyristor current in 3-Φ Full wave converter is I_o÷3. It is the average value of the thyristor current. I_(r.m.s) = I_o÷3 = 3 A.

9. Calculate the De-rating factor if the string efficiency is 16 %.
A. .84
B. .44
C. .5
D. .6
Answer: A
Clarification: De-rating factor is used to measure the reliability of a string. The value of the De-rating factor is 1-(string efficiency)=1-.16=.84.

10. Full form of MOSFET is ___________
A. Metal oxide silicon field effect transistor
B. Metal oxide semiconductor field effect transistor
C. Metal oxide settle field effect transistor
D. Metal oriented silicon field effect transistor
Answer: B
Clarification: MOSFET stands for Metal oxide semiconductor field effect transistor. It is a three terminal device consists of source, drain, gate. It is a high switching device.

11. Full form of FET is ___________
A. Field effect transistor
B. Field engage transistor
C. Field effect terminal
D. Fire engage transistor
Answer: A
Clarification: FET stands for Field effect transistor. It is a transistor that depends upon the electric field to control the conductivity of the channel.

12. Calculate the compensator rating required for sin(Φ)=.13.
A. 0.45 P.U
B. 0.12 P.U
C. 0.13 P.U
D. 0.82 P.U
Answer: C
Clarification: The compensator rating can be calculated using the relation Q_P.U=√1-cos²(∅)=sin(∅)=.13. This per unit value VAR compensator is required to improve the power factor of the system.

13. Full form of DIAC is ___________
A. Digital Alternating current
B. Discrete Alternating current
C. Diode for Alternating current
D. Digital Alternating counter
Answer: C
Clarification: DIAC stands for Diode Alternating current. It is a bipolar switch. It will conduct when the voltage across it becomes greater than the breakover voltage.

14. Which harmonic is not present in 3-Φ fully controlled rectifier?
A. 81_st harmonic
B. 15^th harmonic
C. 17^th harmonic
D. 11^th harmonic
Answer: A
Clarification: Triplen harmonics are absent in the case of 3-phase fully controlled rectifier. Because of the absence of triplen harmonics THD of the rectifier 31%.

15. Fifth lowest order harmonic present in 3-Φ fully controlled rectifier is __________
A. 15^th
B. 17^th
C. 13^th
D. 12^th
Answer: B
Clarification: Only 6k±1 order harmonics are present in 3-Φ fully controlled rectifier. The fifth lowest order harmonic is 17^th harmonic for k=3. Third order harmonics are absent in 3-Φ fully controlled rectifier.