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- Question
Assertion (A): An inverter does not require forced commutation
Reason (R): A series inverter is a forced commutation inverter.
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
- Correct Answer
- A is wrong but R is correct
ExplanationSome inverters require forced commutation.
Power Electronics problems
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- 1. A dc separately excited motor has a constant field current. The armature is fed from a single phase supply through a semi-converter. When a = 0, speed is 600 rpm. If a = 90°, the speed is likely to be
Options- A. about 300 rpm
- B. about 150 rpm
- C. about 75 rpm
- D. about zero Discuss
Correct Answer: about 300 rpm
Explanation:
Average output voltage is reduced to 50% if a = 90°. Hence speed is also reduced to 50%.- 2. HVDC transmission systems generally use
Options- A. 12 pulse converters
- B. 6 pulse converters
- C. 3 pulse converters
- D. either 12 or 6 pulse converters Discuss
Correct Answer: 12 pulse converters
Explanation:
To reduce ripple, 12 pulse converters are used in HVDC.- 3. A 3 phase ac regulator uses
Options- A. 3 thyristors
- B. 6 thyristors
- C. 9 thyristors
- D. 12 thyristors Discuss
Correct Answer: 6 thyristors
Explanation:
Two thyristors for each phase.- 4. In a single phase full wave ac regulator the rms value of load current is 20 A load is purely resistive. Then
Options- A. average thyristor current will be less than 20 A but rms thyristor current will be more than 20 A
- B. both the average and rms thyristor currents will be less than 20 A
- C. both the average and rms thyristor currents will be more than 20 A
- D. rms thyristor current will be 20 A and average thyristor current will be 10 A Discuss
Correct Answer: both the average and rms thyristor currents will be less than 20 A
Explanation:
Each thyristor conducts for 50% of time.- 5. An RC snubber circuit is used to protect a thyristor against :
Options- A. false triggering
- B. failure to turn on
- C. switching transients
- D. failure to commutate Discuss
Correct Answer: switching transients
Explanation:
Especially high
during switching.
- 6. A single phase series converter is used for
Options- A. high voltage output
- B. high current output
- C. high voltage and high current output
- D. improving the circuit efficiency Discuss
Correct Answer: high voltage output
Explanation:
Series connection increases the voltage.- 7. The average load current supplied by a thyristor depends on
Options- A. firing angle
- B. firing frequency
- C. magnitude of gate current
- D. all of the above Discuss
Correct Answer: firing angle
Explanation:
The firing angle controls the period of conduction and hence average load current.- 8. An SBS can conduct is one direction only.
Options- A. True
- B. False Discuss
Correct Answer: False
Explanation:
It is a bilateral switch.- 9. A high frequency series inverter consists of
Options- A. a number of series inverters in series
- B. a number of series inverters in parallel
- C. a number of parallel inverters in parallel
- D. a number of parallel inverters in series Discuss
Correct Answer: a number of series inverters in parallel
Explanation:
A high frequency series inverter has many series inverters in parallel. Only one inverter operates at one time and they operate in fixed sequence.- 10. When thyristors are connected in series and parallel, it may be necessary to have :
Options- A. current derating
- B. voltage derating
- C. both current and voltage derating
- D. none of the above Discuss
Correct Answer: both current and voltage derating
Explanation:
Thyristors in series do not share the voltage equally and require voltage derating. Thyristors in parallel need current derating.
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