Power Electronics 2

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Electronic Engineering MCQ Question Papers: ENTC, IT Interview Placement

Subject: Power Electronics 2

Part 2: List for questions and answers of Power Electronics


Q1. The typical value of SCR for modern alternator is?

a) 1.5

b) 0.5

c) 1.0

d) 1.2


Q2. An SCR has half cycle surge current rating of 3000 A for 50 Hz supply. One cycle surge current will be?

a) 1500 A

b) 6000 A

c) 2121.32 A

d) 4242.64 A


Q3. An SCR is considered to be a semi controlled device because ?

a) It can be turned OFF but not ON with a gate pulse

b) It conducts only during one half cycle of an alternating current wave

c) It can be turned ON but not OFF with a gate pulse

d) It can be turned ON only during one half cycle of an AC


Q4. A single phase full bridge inverter can operated in load commutation mode in case load consist of ?

a) RL

b) RLC underdamped

c) RLC overdamped

d) RLC critically damped


Q5. A step up chopper has input voltage 110 V and output voltage 150 V. The value of duty

cycle is?

a) 0.32

b) 0.67

c) 0.45

d) 0.27


Q6. Which statement is true for latching current ?

a) It is related to turn off process of the device

b) It is related to conduction process of device

c) It is related to turn on process of the device

d) Both C and D 


Q7. If holding current of a thyristor is 2 mA then latching current should be?

a) 0.01 A

b) 0.002 A

c) 0.009 A

d) 0.004 A


Q8. Leakage current flows through the thyristor in?

a) Forward blocking mode

b) Reverse blocking mode

c) Both forward and reverse blocking mode

d) Forward conduction mode


Q9. Which triggering is the most reliable?

a) Forward voltage triggering

b) Gate triggering

c) dV / dt triggering

d) Thermal triggering


Q10. Light triggering mainly used in?

a) Low – voltage direct current transmission

b) Medium voltage direct current transmission

c) High voltage direct current transmission

d) All of these


Q11. The latching current of SCR is 20 mA. Its holding current will be?

a) 23 mA

b) 40 mA

c) 10 mA

d) 60 mA


Q12. Thyristor can be protected from over voltages by using?

a) Voltage clamping device

b) Fuse

c) Heat sink

d) Snubber circuit


Q3. Example of a voltage clamping device?

a) Fast acting fuse

b) Snubber circuit

c) Metal oxide varistor

d) Aluminium block 


Q14. Under over voltage condition impedance offered by the voltage clamping device is?

a) High

b) Low

c) Moderate

d) Infinity


Q15. Under normal operating condition voltage clamping device offers impedance of?

a) High value

b) Low value.

c) Zero value

d) Moderate value


Q16. What is used to protect the SCR from over current ?

a) CB and fuse

b) Heat sink

c) Snubber circuit

d) Voltage clamping device


Q17. CB used for over current protection of thyristor operates when the fault current is?

a) of long period

b) of short duration

c) Both (A) and (B)

d) Neither (A) nor (B)


Q18. When a large surge current of very short duration flows through a thyristor then which one of the following device will operate to protect the thyristor ?

a) CB

b) Snubber circuit

c) Voltage clamping device

d) Fast acting current limiting device (FACL fuse)


Q19. How can we protect SCR from thermal conditions ?

a) Use of snubber circuit

b) Using heat sink

c) Using CB and fuse

d) Using equalizing circuit 


Q20. Which of the following is used in heat sink?

a) Iron

b) Aluminium

c) Carbon

d) Silver 


Part 2: List for questions and answers of Power Electronics


Q1. Answer: b


Q2. Answer: c


Q3. Answer: c


Q4. Answer: b


Q5. Answer: b


Q6. Answer: c


Q7. Answer: d


Q8. Answer: c


Q9. Answer: c


Q10. Answer: c


Q11. Answer: c


Q12. Answer: a


Q13. Answer: c


Q14. Answer: b


Q15. Answer: a


Q16. Answer: a


Q17. Answer: a


Q18. Answer: d


Q19. Answer: b


Q20. Answer: c