Discussion
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- Question
The symbol in figure is for
Options- A. DIAC
- B. P-N junction diode
- C. Schottky diode
- D. None of the above
- Correct Answer
- Schottky diode
- 1. 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
- 2. 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
- 3. 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
- 4. The gate current required to turn on an SCR is
Options- A. few amperes
- B. a few mA
- C. almost equal to anode current
- D. about 50% of anode current Discuss
- 5. Between which points does UJT exhibit negative resistance characteristics
Options- A. between peak and valley points
- B. before peak point
- C. after peak point
- D. after valley point Discuss
- 6. When the core of a saturable reactor is saturated, the inductance is high.
Options- A. True
- B. False Discuss
- 7. 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 Discuss
- 8. 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
- 9. A cycloconverter cannot give a frequency higher than input frequency.
Options- A. True
- B. False Discuss
- 10. 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
Power Electronics problems
Search Results
Correct Answer: rectification efficiency will be more than 0.6 and TUF will be more than 0.35
Correct Answer: 5 ?s
Explanation:
Duration of gate pulse should be slightly more than turn time of SCR.
Correct Answer: (p - a) radians
Explanation:
The conduction is from a to p.
Correct Answer: a few mA
Explanation:
Only a very small gate current is required to trigger SCR into conduction.
Correct Answer: between peak and valley points
Correct Answer: False
Explanation:
Since core is saturated, change of flux is small and inductance is low.
Correct Answer: A is correct but R is wrong
Explanation:
Junction temperature is about 120°C. Hence R is wrong.
Correct Answer: pulse train
Explanation:
To ensure proper triggering pulse train in necessary because load is R - L.
Correct Answer: False
Explanation:
Step up cycloconverter can give a frequency higher than input frequency.
Correct Answer: load torque increases with increase in speed
Explanation:
If load torque is constant, the change in speed is very small.
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