250+ TOP MCQs on Single Phase FW AC-DC-3 and Answers

Power Electronics Questions and Answers for experienced people on “Single-Phase FW AC-DC-3”.

1. A motor load is connected to a single-phase full converter B-2 type controlled rectifier. The net energy is transferred from ac source to the motor (dc loaD. when
A. π+α > 90
B. π-α > α
C. π+α > α
D. π-α > 90
Answer: B
Clarification: Converter will work as a line commuted inverter when π-α > α.

2. The below shown rectifier configuration has continues load current, find the expression for the average value of output voltage when the supply Vs = Vm sinωt is connected.

A. (Vm/π)cosα
B. (2Vm/π)cosα
C. (Vm/π) (1+cosα)
D. (2Vm/π) (1+cosα)
Answer: B
Clarification: Vo = 1/π x [∫ Vm sinωt d(ωt)] Where the integration runs from α to π+α.

3. Find the expression of the rms value of output voltage for a single-phase M-2 type rectifier with RL load and continues load current. Transformer ratio is 1:1 with supply voltage Vs = Vm sinωt
A. Vm/√2
B. Vs
C. 2Vs
D. Vs/√2
Answer: B
Clarification: Vor² = 1/π x [∫ Vm² sin²ωt d(ωt)], Where the integration runs from α to π+α
Vor = Vm²/2 = Vs.

4. A single-phase full controlled converted with RLE load will act like a line-commutated inverter when the firing angle α
A. α > 180°
B. α > 90°
C. α < 90°
D. α = 90°
Answer: B
Clarification: It will act like a inverter i.e. most of the current would flow from the battery or back emf E to the source. For α=90° it will not act like a converter nor an inverter.

5. In converter operation, with output voltage = Vo and RLE load.
A. Vo < E
B. Vo = E
C. Vo > E
D. None of the mentioned
Answer: C
Clarification: The output voltage obtained by a converter is always greater than the counter or back emf E.
Vo = IR + E.

6. In inverter operation, with output voltage = Vo and a RLE load connected
A. Vo < E
B. Vo = E
C. Vo > E
D. None of the mentioned
Answer: A
Clarification: In inverter operation Vo < E.

7. A motor load is connected to a single-phase full converter B-2 type controlled rectifier, the net energy is transferred from ac source to the motor (dc loaD. when
A. π+α > 90
B. π-α < α
C. π+α < α
D. π-α > α
Answer: B
Clarification: It works as a converter when π-α < α.

8. The below shown rectifier configuration has continues load current, find the expression of the RMS value of output voltage when the supply Vs = Vm sinωt
A. Vs²/2
B. 2Vs/π
C. Vs
D. √Vs/2
Answer: C
Clarification: Vor² = 1/π x [∫Vm² sin²ωt d(ωt)] Where the integration runs from α to π+α
Vor = Vm²/2 = Vs.

9. Choose the correct statement
A. M-2 type connection requires SCRs with higher PIV as compared to those in a B-2 type
B. M-2 type connection requires SCRs with lower PIV as compared to those in a B-2 type
C. The average output voltage in M-2 type is more than that obtained from a B-2 type configuration of the same rating
D. The average output voltage in M-2 type is less than that obtained from a B-2 type configuration of the same rating
Answer: A
Clarification: The PIV of diodes in M-2 is 2Vm, whereas that in B-2 type of connection is Vm.

10. An SCR has the peak forward voltage = 1000 V. Find the maximum voltage that the SCR can handle if employed in a M-2 type full controlled converter circuit. Use factor of safety (FOS) = 2.5
A. 500 V
B. 400 V
C. 200 V
D. 1000 V
Answer: C
Clarification: In M-2 type configuration maximum voltage handled is 2Vm
Therefore, 1000/2×2.5 = 200 V.

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