power electronics MCQs – Page 2

Practise focused power electronics questions with marked answers for exam preparation and subject revision.

power electronics Mcqs
21. Which of the following is disadvantage of fast recovery diodes?
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A. Doping is carried out

B. Recovery is only 50 s

C. Recovery is only 5 s

D. None of these

22. 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 ___________?
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A. Snubber circuit

B. Voltage clamping device

C. Fast acting current limiting device (FACL fuse)

D. CB

23. n a phase controlled 3 phase ac voltage controller, the harmonic present is__________?
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A. 2nd

B. 7th

C. 3rd

D. 5th

24. Dynamic equalizing circuit is used for________________?
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A. equal division of voltage across each thyristor in parallel

B. equal division of current through each thyristor in parallel

C. equal division of current through each thyristor in series

D. equal division of voltage across each thyristor
25. Which statement is true ?
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A. Reverse recovery time ( trr ) > gate recovery time (tgr)

B. Device turn OFF time ( tq ) > reverse recover time (trr)

C. All of these

D. Circuit turn OFF time > device turn OFF time ( tq )

26. Under over voltage condition impedance offered by the voltage clamping device is__________?
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A. moderate

B. low

C. infinity

D. High

27. A string of n parallel SCRs is operated at 72 KA, the rating of each SCR is 1 KA. If derating factor of the string is 0.1. value of n will be___________?
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A. 60

B. 70

C. 80

D. 90

28. A combination of synchronized leading edge and trailing edge modulation has also been used to control a____________?
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A. Boost single phase power factor converter

B. A buck dc dc converter to reduce ripple in the intermediate dc bus capacitor

C. Both A. and B.

D. None f these

29. Which triggering is the most reliable____________?
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A. Thermal triggering

B. Forward voltage triggering

C. Gate triggering

D. dV / dt triggering

30. Electrical power output in a D.C. generator is equal to_____________?
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A. Mechanical power input iron and friction losses copper losses

B. Electrical power developed in armature iron and copper losses

C. Electrical power developed in armature copper losses

D. Mechanical power input iron and friction losses

31. The most suited gate pulses given to the AC regulator with R L load can be in the form of____________?
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A. None of these

B. Continuous signal

C. A train of pulses

D. Large isolating pulse transformer

32. COOLMOS device can be used in application up to power range of___________?
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A. 500 VA

B. 1 KVA

C. 2 KVA

D. 100 KVA

33. LISN is a device used to measure conducted emissions. LISN stands for_____________?
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A. Line integrated stored network

B. Line impedance stabilization network

C. Line integrated stabilization network

D. Laser integrated stabilization networking

34. Unipolar modulation is generally used in____________?
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A. DC DC converters

B. AC AC converters

C. AC DC converters

D. DC AC converters

35. Thyristor is nothing but a____________?
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A. Controlled switch

B. Controlled transistor

C. Amplifier with higher gain

D. Amplifier with large current gain

36. The reverse recovery time of diode is trr = 3 Is and the rate off all of the diode current is di/dt = 30 A/Is. The storage charge current QRR is___________?
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A. 140 Is

B. 130 Is

C. 135 Is

D. 145 Is

37. The Graetz bridge makes excellent use of ______________?
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A. SCR

B. Power transformer

C. Potential transformer

D. Current transformer

38. In constant frequency PWM, at perturbation the amplitude of the sinusoidal component is a___________?
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A. Linear function

B. Non linear function

C. None of these

D. Constant function

39. In commutation PAC stands for_______?
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A. Phase and commutation

B. Phase angle commutation

C. Phase angle converter

D. Permanent angle converter

40. A thyristor string is made of a no. of SCR connected in series and parallel. The string have volume and current of 11 KV and 4 KA. The voltage and current rating of available SCRs are 1800 V and 1000 A. For a string efficiency of 90 % let the number of SCRs in series and parallel are a and b respectively. Then the value of a and b will be_____________?
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A. 4, 6

B. 5, 7

C. 7, 5

D. 6, 4