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- Question
A dc circuit breaker must use
Options- A. natural commutation
- B. forced commutation
- C. both natural and forced commutation
- D. either natural or forced commutation
- Correct Answer
- forced commutation
ExplanationNatural commutation is possible only in ac circuits.
Power Electronics problems
Search Results
- 1. The number of doped regions in a SCR is
Options- A. 2
- B. 3
- C. 4
- D. 5 Discuss
Correct Answer: 4
Explanation:
p = n = p = n.- 2. A single phase step up cycloconverter changes 50 Hz to 100 Hz. Then one half wave of input will give rise to
Options- A. one half wave of output
- B. one full wave of output
- C. two full waves of output
- D. either (b) or (c) Discuss
Correct Answer: one full wave of output
Explanation:
Since output frequency is 2f, one half wave of input must equal one full wave of output.- 3. The two modes of operation of three phase bridge inverters are known as
Options- A. 60° mode and 120° mode
- B. 90° mode and 120° mode
- C. 120° mode and 180° mode
- D. 120° mode and 240° mode Discuss
Correct Answer: 120° mode and 180° mode
Explanation:
In 180° mode each thyristor conducts for 180° and in 120° mode each thyristor conducts for 120°.- 4. Assertion (A): A dual converter may be circulating current type or non circulating current type.
Reason (R): In circulating current dual converter only one converter can be operated at one time.
Options- A. Both A and R are correct and R is correct explanation of A
- B. Both A and R correct but R is not correct explanation of A
- C. A is correct but R is wrong
- D. A is wrong but R is correct Discuss
Correct Answer: A is correct but R is wrong
Explanation:
In circulating current dual converter both converters operate together.- 5. All inverters use forced commutation.
Options- A. True
- B. False Discuss
Correct Answer: False
Explanation:
Line commutated inverters are also used especially in HVDC.- 6. In a full wave converter (M - 2 connection) feeding an RLE load, the peak thyristor current is 15 A. For fully controlled bridge circuit and same load current, the peak thyristor current will be
Options- A. 30 A
- B. 152 A
- C. 15 A
- D.
Discuss
Correct Answer: 15 A
Explanation:
In both the connections the output voltage and peak thyristor current are the same. Both are full wave rectifiers.- 7. If ton and toff are the turn on and turn off times of a thyristor, then
Options- A. ton and toff are almost equal
- B. ton >> toff
- C. toff >> ton
- D. ton is about twice toff Discuss
Correct Answer: toff >> ton
Explanation:
Turn on time is less than 3 ?s while turn off time is between 10-300 ?s.- 8. In 180° mode of operation of a 3 phase bridge inverter, two thyristors conduct at one time.
Options- A. True
- B. False Discuss
Correct Answer: False
Explanation:
In 180° mode three thyristors conduct simultaneously.- 9. Which of these commutation methods uses an auxiliary SCR?
Options- A. Class A
- B. Class B
- C. Class C
- D. Class D Discuss
Correct Answer: Class C
Explanation:
Class C commutation uses an auxiliary SCR and it is also called auxiliary commutation.- 10. In an SCR, the anode current is controlled by
Options- A. gate current only
- B. external circuit only
- C. both gate current and external circuit
- D. none of the above Discuss
Correct Answer: external circuit only
Explanation:
Once SCR has been triggered the gate has no control. Only external resistance controls the anode current.
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