Discussion
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- Question
An SBS can conduct is one direction only.
Options- A. True
- B. False
- Correct Answer
- False
ExplanationIt is a bilateral switch.
Power Electronics problems
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- 1. 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.- 2. 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.- 3. 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 Discuss
Correct Answer: A is wrong but R is correct
Explanation:
Some inverters require forced commutation.- 4. 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%.- 5. 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.- 6. 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.- 7. 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.- 8. In the below figure, the average value of load current is 15 A. The load is highly inductive. The peak value of thyristor current is
Options- A. 15 A
- B. 152 A
- C.
- D. 30 A Discuss
Correct Answer: 15 A
Explanation:
Because of highly inductive load, output current is nearly constant.- 9. In a multiphase chopper, the different choppers operate in
Options- A. series and all simultaneously
- B. parallel and one at a time
- C. parallel and simultaneously
- D. either (b) or (c) Discuss
Correct Answer: parallel and one at a time
Explanation:
Only one chopper operates at one time.- 10. In dielectric heating, the thyristor circuits consist of
Options- A. rectifier-chopper combination
- B. controlled rectifier
- C. ac regulator
- D. rectifier-inverter combination Discuss
Correct Answer: rectifier-inverter combination
Explanation:
Input ac is rectified and then converted to high frequency ac.
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