POWER ELECTRONICS QUIZ

How can we protect SCR from thermal conditions ?

Using CB and fuse.

Using heat sink.

Use of snubber circuit.

Using equalizing circuit.

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IGBT combines the advantages of

None of these.

BJTs and MOSFETs.

SITs and MOSFETs.

BJTs and SITs.

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The capacitance of reversed bised junction J2 in a thyristor is CJ2 = 20 pF and can be assumed to be independant of the off state voltage. The limiting value of the charging current to turn on the thyristor is 16 mA. What is the critical value of dv/dt?

1200 V/µs.

1000 V/µs.

800 V/µs.

600 V/µs.

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

of short duration.

both (A) and (B).

of long period.

neither (A) nor (B).

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During gate recovery time

charge carriers of J2 junction is swept out.

charge carriers of J3 junction is removed.

charge carriers of J2 junction recombined.

charge carrier of J1 junction removed.

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Under normal operating condition voltage clamping device offers impedance of

low value.

zero value.

high value.

moderate value.

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

2121.32 A.

1500 A.

4242.64 A.

6000 A.

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Light triggering mainly used in

low - voltage direct current transmission.

high voltage direct current transmission.

medium voltage direct current transmission.

all of these.

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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

6, 4.

5, 7.

4, 6.

7, 5.

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BCT is used for

High power current control.

High power phase control.

Low power phase control.

Low power current control.

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