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
View Answer
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
View Answer
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
View Answer
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
View Answer
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°
View Answer
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
View Answer
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
View Answer
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
View Answer
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
View Answer
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
View Answer
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
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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
View Answer
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
View Answer
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
View Answer
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
View Answer
Explanation: Only 6k±1 order harmonics are present in 3-Φ fully controlled rectifier. The fifth lowest order harmonic is 17th harmonic for k=3. Third order harmonics are absent in 3-Φ fully controlled rectifier.
Sanfoundry Global Education & Learning Series – Electric Drives.
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