power-electronics electronics-and-communication-engineering question and answers -Page 12

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Power Electronics problems

2. In an SCR, the anode current consists of
Options
A. only holes
B. only electrons
C. both electrons and holes
D. either electrons or holes

4. 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 =

5. 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

7. 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

8. 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

9. 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

10. 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

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