Electric Drives Questions and Answers – Solid-State Switching Circuits – Single Phase, Half-Wave, AC/DC Conversion for Inductive Loads With Freewheeling Diode

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This set of Electric Drives MCQs focuses on “State Switching Circuits – Single Phase, Half-Wave, AC/DC Conversion for Inductive Loads With Freewheeling Diode”.

1. Calculate the voltage across the freewheeling diode when the output voltage is 24 V.
a) -15 V
b) -24 V
c) 28 V
d) 39 V
View Answer

Answer: b
Explanation: The freewheeling diode is used to provide a freewheeling path. It is connected in the anti-parallel direction of the load. The voltage across the diode is -Vo=-24 V.
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2. Calculate the value of the conduction angle for SCR for R-L load with a freewheeling diode if the value of β and α are 65° and 12°.
a) 168°
b) 170°
c) 130°
d) 180°
View Answer

Answer: a
Explanation: The conduction angle for SCR for R-L load with a freewheeling diode is π-α=180°-12°=168°. R-L load is a current stiff type of load. The current in the SCR only flows from α to π.

3. Calculate the value of the conduction angle for diode for R-L load with a freewheeling diode if the value of α is 45°. (Continous conduction mode)
a) 220°
b) 225°
c) 230°
d) 280°
View Answer

Answer: b
Explanation: The conduction angle for diode for R-L load with a freewheeling diode is π+α=180°+45°=225°. R-L load is a current stiff type of load.

4. Calculate the value of the conduction angle for diode for R-L load with a freewheeling diode if the value of β is 226°. (Discontinuous conduction mode)
a) 40°
b) 45°
c) 50°
d) 46°
View Answer

Answer: b
Explanation: The conduction angle for diode for R-L load with a freewheeling diode is β-π=226°-180°=45°. R-L load is a current stiff type of load.

5. Calculate the value of the conduction angle for R-L load if the value of β and α are 56° and 18°.
a) 48°
b) 38°
c) 57°
d) 15°
View Answer

Answer: b
Explanation: The conduction angle for R-L load is β-α=56°-18°=38°. R-L load is a current stiff type of load. The current in the circuit only flows from α to β.
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6. Calculate the value of the fundamental displacement factor for 1-Φ Full wave bridge rectifier if the firing α=17°.
a) .98
b) .19
c) .56
d) .95
View Answer

Answer: d
Explanation: Fundamental displacement factor is the cosine of angle difference between the fundamental voltage and fundamental current. D.F=cos(∝)=cos(17°)=0.95.

7. Calculate the value of the fundamental displacement factor for 1-Φ Full wave semi-converter if the firing angle value is 95o.
a) .60
b) .68
c) .62
d) .67
View Answer

Answer: d
Explanation: Fundamental displacement factor is the cosine of angle difference between the fundamental voltage and fundamental current. The fundamental displacement factor for 1-Φ Full wave semi-converter is cos(∝÷2)=cos(47.5o)=.67.

8. Which one of the following load is suitable for lagging power factor load in Single phase Half-bridge inverter?
a) C load
b) R-L-C overdamped
c) R-L-C underdamped
d) L-C load
View Answer

Answer: b
Explanation: R-L-C overdamped loads are generally lagging power factor loads. They require forced commutation. Anti-Parallel diodes do not help in the commutation process.

9. Which one of the following load is suitable for leading power factor load in Single phase Half-bridge inverter?
a) C load
b) R-L-C overdamped
c) R-L-C underdamped
d) L-C load
View Answer

Answer: c
Explanation: R-L-C underdamped are leading power factor loads. They do not require any forced commutation technique. Anti-Parallel diodes help in the commutation process.
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10. A step-down chopper has input voltage .1 V and output voltage .01 V. Calculate the value of the duty cycle.
a) 0.1
b) 0.2
c) 0.3
d) 0.5
View Answer

Answer: a
Explanation: The output voltage of the step-down chopper is Vo = Vin×(D). The value of the duty cycle is less than one which makes the Vo < Vin. The step-down chopper is used to step down the voltage. The value of the duty cycle is .01÷.1=.1.

11. Calculate the De-rating factor if the string efficiency is 98%.
a) .04
b) .02
c) .05
d) .03
View Answer

Answer: b
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-.98=.02.

12. Calculate the string efficiency if the de-rating factor is .50.
a) 28 %
b) 42 %
c) 80 %
d) 50 %
View Answer

Answer: d
Explanation: The string efficiency is calculated for series and parallel connection of SCRs. The value of string efficiency is 1-(De-rating factor)=1-.50=50 %.

13. 70 V rated 6 SCRs are connected in series. The operation voltage of the string is 130. Calculate the De-rating factor.
a) .70
b) .73
c) .78
d) .74
View Answer

Answer: a
Explanation: The string efficiency can be calculated using the formula operation voltage÷(Number of SCRs×Rated voltage)=130÷(70×6)=.30. The De-rating factor value is 1-.30=.70.
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14. d(v)÷d(t) is more reliable for SCR triggering.
a) True
b) False
View Answer

Answer: b
Explanation: Gate triggering is more reliable than any other triggering method. The risk of false triggering of SCR increases in the case of the d(v)÷d(t) triggering.

15. Calculate the output voltage of the Buck converter if the supply voltage is 13 V and duty cycle value is .16.
a) 2.08 V
b) 2.24 V
c) 2.58 V
d) 2.54 V
View Answer

Answer: a
Explanation: The output voltage of the buck converter is Vo = Vin×(D)=13×.16=2.08 V. The value of the duty cycle is less than one which makes the Vo < Vin. The buck converter is used to step down the voltage.

Sanfoundry Global Education & Learning Series – Electric Drives.

To practice MCQs on all areas of Electric Drives, here is complete set of 1000+ Multiple Choice Questions and Answers.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He is Linux Kernel Developer & SAN Architect and is passionate about competency developments in these areas. He lives in Bangalore and delivers focused training sessions to IT professionals in Linux Kernel, Linux Debugging, Linux Device Drivers, Linux Networking, Linux Storage, Advanced C Programming, SAN Storage Technologies, SCSI Internals & Storage Protocols such as iSCSI & Fiber Channel. Stay connected with him @ LinkedIn