# Electric Drives Questions and Answers – Solid-State Switching Circuits – Three Phase, Full-Wave, AC/DC Conversion

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This set of Electric Drives Multiple Choice Questions & Answers focuses 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

Explanation: The output voltage of 3-Φ Full wave bridge rectifier is 3Vml(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) 3Vml(cos(∝))÷2π
b) 3Vml(cos(∝))÷π
c) 2Vml(cos(∝))÷π
d) 6Vml(cos(∝))÷π

Explanation: The output voltage of 3-Φ Full wave bridge rectifier for R-L load is 3Vml(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

Explanation: The output voltage of 3-Φ Full wave bridge rectifier is 3Vml(cos(∝))÷π. The output voltage of 3-Φ Half wave rectifier is 3Vml(cos(∝))÷2π.

4. What is the formula for output voltage for 3-Φ Full wave bridge rectifier for R load for α < 60°?
a) 2Vml(cos(∝))÷π
b) 3Vml(cos(∝))÷2π
c) 3Vml(cos(∝))÷π
d) 6Vml(cos(∝))÷π

Explanation: The output voltage of 3-Φ Full wave bridge rectifier for R load is 3Vml(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°

Explanation: 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) 2Vml(1+cos(∝+60°))÷π
b) 3Vml(1+cos(60°+∝))÷2π
c) 3Vml(1+cos(60°+∝))÷π
d) 6Vml(cos(∝))÷π

Explanation: The output voltage of 3-Φ Full wave bridge rectifier for R load is 3Vml(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

Explanation: The r.m.s value of thyristor current in 3-Φ Full wave converter is Io√1÷3. It is the r.m.s value of the thyristor current. I(r.m.s) = Io√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

Explanation: The average value of thyristor current in 3-Φ Full wave converter is Io÷3. It is the average value of the thyristor current. I(r.m.s) = Io÷3 = 3 A.

9. Calculate the De-rating factor if the string efficiency is 16 %.
a) .84
b) .44
c) .5
d) .6

Explanation: 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

Explanation: 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

Explanation: 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

Explanation: The compensator rating can be calculated using the relation QP.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

Explanation: 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) 81st harmonic
b) 15th harmonic
c) 17th harmonic
d) 11th harmonic

Explanation: 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) 15th
b) 17th
c) 13th
d) 12th 