An SCR has a turn on time of 4 ?s. The gate pulse should have a duration of abou

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Question
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

Correct Answer

5 ?s

Explanation

Duration of gate pulse should be slightly more than turn time of SCR.

Power Electronics problems

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1. 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

2. 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

4. A dc chopper V = 500 V feeds an electric fraction dc series motor. The chopping frequency is 400 Hz. The series inductance required to limit the maximum current swing to 10 A is
Options
A. 20 mH
B. about 31 mH
C. about 51 mH
D. about 92 mH

5. In a single phase dual converter, a₁, and a₂ are firing angles of the two converters. Then
Options
A. a₁ - a₂ =
B. a₁ + a₂ = p
C. a₁ - a₂ = p
D. a₁ + a₂ =

6. 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

8. When the core of a saturable reactor is saturated, the inductance is high.
Options
A. True
B. False

9. 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

10. 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)

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