Discussion
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- Question
Assertion (A): When an SCR is conducting, the voltage drop across is about 1 V.
Reason (R): When an SCR is conducting, the junction temperature is about 200°C.
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 correct but R is wrong
ExplanationJunction temperature is about 120°C. Hence R is wrong.
Power Electronics problems
Search Results
- 1. When the core of a saturable reactor is saturated, the inductance is high.
Options- A. True
- B. False Discuss
Correct Answer: False
Explanation:
Since core is saturated, change of flux is small and inductance is low.- 2. The symbol in figure is for
Options- A. DIAC
- B. P-N junction diode
- C. Schottky diode
- D. None of the above Discuss
Correct Answer: Schottky diode
- 3. A 3 phase semiconverter when supplying a certain load has a rectification efficiency of 0.6 and transformer utilisation factor of 0.35. When a 3 phase full converter is supplying the same load
Options- A. rectification efficiency will be more than 0.6 and TUF will be more than 0.35
- B. rectification efficiency will be more than 0.6 but TUF will be less than 0.35
- C. rectification efficiency will be less than 0.6 and TUF will be less than 0.35
- D. rectification efficiency will be less than 0.6 but TUF will be more than 0.35 Discuss
Correct Answer: rectification efficiency will be more than 0.6 and TUF will be more than 0.35
- 4. An SCR has a turn on time of 4 ?s. The gate pulse should have a duration of about
Options- A. 2 ?s
- B. 5 ?s
- C. 20 ?s
- D. 50 ?s Discuss
Correct Answer: 5 ?s
Explanation:
Duration of gate pulse should be slightly more than turn time of SCR.- 5. In a semi converter feeding a resistive load, the firing angle is a. Each thyristor conducts for
Options- A. p radians
- B. (p - a) radians
- C. (p + a) radians
- D. (p - 0.5 a) radians Discuss
Correct Answer: (p - a) radians
Explanation:
The conduction is from a to p.- 6. A single phase full wave regulator feeds R-L load. The best gating signal is
Options- A. short duration pulses
- B. long duration pulses
- C. pulse train
- D. either (a) or (b) Discuss
Correct Answer: pulse train
Explanation:
To ensure proper triggering pulse train in necessary because load is R - L.- 7. A cycloconverter cannot give a frequency higher than input frequency.
Options- A. True
- B. False Discuss
Correct Answer: False
Explanation:
Step up cycloconverter can give a frequency higher than input frequency.- 8. A 3 phase induction motor is fed by a 3 phase ac regulator to change the stator voltage. The variation in speed will be more if
Options- A. load torque is constant
- B. load torque increases with increase in speed
- C. load torque decreases with increase in speed
- D. either (a) or (b) Discuss
Correct Answer: load torque increases with increase in speed
Explanation:
If load torque is constant, the change in speed is very small.- 9. Assertion (A): A cycloconverter may be line commutated or forced commutated
Reason (R): A step up cycloconverter requires forced commutation.
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: Both A and R are correct and R is correct explanation of A
- 10. Present day HVDC converters are all
Options- A. 3 pulse converters
- B. 6 pulse converters
- C. 12 pulse converters
- D. either 6 pulse or 12 converters Discuss
Correct Answer: 12 pulse converters
Explanation:
To reduce ripple 12 pulse converters are used.
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