Exercise: Power Electronics

Questions for: Power Electronics

A cycloconverter is
A:
ac-dc converter
B:
dc-ac converter
C:
dc-dc converter
D:
ac-ac converter
Answer: D

It changes ac at frequency f into ac at a frequency different from f.

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The rated current of a thyristor is 40 A. The holding current will be about :
A:
20 A
B:
1 A
C:
100 mA
D:
10 mA
Answer: D

The holding current is much less then 1% of rated current.

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In an SCR, the anode current is controlled by
A:
gate current only
B:
external circuit only
C:
both gate current and external circuit
D:
none of the above
Answer: B

Once SCR has been triggered the gate has no control. Only external resistance controls the anode current.

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A 3 phase bridge inverter is fed by 400 V battery. The load is star connected and has a resistance of 10 Ω per phase. The peak value of load current is
A:
40 A
B:
20 A
C:
10 A
D:
5 A
Answer: B

Two resistances are in series at any time.

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Current chopping leads to
A:
over voltage
B:
over current
C:
both over voltage and over current
D:
either over voltage or over current
Answer: A

e = L . In current chopping is high. Hence e is high.

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