Exercise: Power Electronics

Questions for: Power Electronics

A high frequency series inverter consists of
A:
a number of series inverters in series
B:
a number of series inverters in parallel
C:
a number of parallel inverters in parallel
D:
a number of parallel inverters in series
Answer: B

A high frequency series inverter has many series inverters in parallel. Only one inverter operates at one time and they operate in fixed sequence.

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In a 3 phase semiconverter, the dc output voltage for a certain firing angle is 50% of the maximum possible value. The firing angle is
A:
30°
B:
60°
C:
90°
D:
120°
Answer: C

Vdc ∝ (1 + cos a). Maximum possible output voltage occurs when a = 0.

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In a multiphase chopper, the different choppers operate in
A:
series and all simultaneously
B:
parallel and one at a time
C:
parallel and simultaneously
D:
either (b) or (c)
Answer: B

Only one chopper operates at one time.

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An SCR has a turn on time of 4 Ξs. The gate pulse should have a duration of about
A:
2 Ξs
B:
5 Ξs
C:
20 Ξs
D:
50 Ξs
Answer: B

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

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A Shockley diode can be used
A:
in place of SCR
B:
as a trigger switch for SCR
C:
in place of UJT
D:
both in place of SCR and as a trigger switch for SCR
Answer: B

It is a four layered PNPN device without a gate terminal. Its characteristics is similar to that of SCR with zero gate current. It is acting as a trigger switch for Thyristor.

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