Power Electronics - Section 1

Directions to Solve

Power Electronics - Section 1

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: Option B

Explanation:

Using Eq 286-233-2

286-233-1

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

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: Option D

Explanation:

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

Figure shows a chopper feeding RLE load, The free wheeling diode conducts when

280-323-1

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: Option B

Explanation:

FD is forward biased only when thyristor is off.

A semi converter operates in two quadrants.

A.	True
B.	False

Answer: Option B

Explanation:

It operates only in quadrant.

If V_dc1 is the dc output voltage in half wave controlled rectifier circuit feeding resistive load and V_dc2 is the dc output voltage in full wave controlled rectifier circuit (M - 2 connection) feeding resistive load, then

A.	Vdc1 = 0.5 Vdc2 for all values of firing angle
B.	Vdc1 = Vdc2 for all values of firing angle
C.	Vdc1 ≤ 0.5 Vdc2 for all values of firing angle
D.	Vdc1 ≥ 0.5 Vdc2 for all values of firing angle

Answer: Option A

Explanation:

286-233-2 and V_dc = 267-52-2 (1 + cos a).

Assertion (A): A TRIAC is a bidirectional SCR.

Reason (R): A TRIAC is a four layers 3 terminal device and can conduct in both directions.

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: Option A

Explanation:

Since a TRIAC can conduct in both directions it is bi directional SCR.

The total number of leads in reverse conducting thyristor is

A.	2
B.	3
C.	1
D.	4

Answer: Option B

Explanation:

286-145-1

A thyristor has a turn on time of 6 μs. If the anode circuit is inductive, the turn on time will be

A.	6 μs
B.	less than 6μs
C.	more than 6 μs
D.	either 6 μs or less

Answer: Option C

Explanation:

Inductive load increases the turn on time.

Power Electronics - Section 1

Power Electronics - Section 1

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