Exercise: Power Electronics

Questions for: Power Electronics

In a single phase full wave regulator feeding R-L load, the minimum firing angle can be zero.
A:
True
B:
False
C:
D:
Answer: A

Range of control of a is 0 ≤ a ≤ p.

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A dc circuit breaker must use
A:
natural commutation
B:
forced commutation
C:
both natural and forced commutation
D:
either natural or forced commutation
Answer: B

Natural commutation is possible only in ac circuits.

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A single phase half wave rectifier is feeding a resistive load. When a = 0, dc output voltage is 127 V. When a = 30°, the dc output voltage will be about
A:
127 V
B:
120 V
C:
110 V
D:
100 V
Answer: B

Using Eq

= 0.933.

Hence Vdc for 30° firing angle = 0.933 x 127 = ≈ 120 V.

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Assertion (A): An ideal rectifier should have unity harmonic factor

Reason (R): An ideal rectifier should have unity displacement factor.

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
Answer: D

Ideal rectifier should have zero harmonic factor and unity displacement factor.

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Figure shows a chopper feeding RLE load, The free wheeling diode conducts when
A:
thyristor is on
B:
thyristor is off
C:
both when thyristor is on and thyristor is off
D:
partly when thyristor is off and partly when thyristor is on
Answer: B

FD is forward biased only when thyristor is off.

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