Power Electronics Questions and Answers – Single Phase FW AC-DC-2

This set of Power Electronics Interview Questions and Answers for experienced people focuses on “Single-Phase FW AC-DC-2”.

1. For the below given circuit,

a) T2 and T3 are gated together
b) T1 and T4 are gated together
c) T1 and T3 are gated together
d) T1 and T2 are gated together

Explanation: T1-T2 are gated together at a time and T3-T4 are gated together at a time.

2. With respect to the below given circuit, from ωt = 0 to α, ____ thyristor(s) block the forward voltage

a) T1 and T2
b) T2
c) T3 and T4
d) T4

Explanation: T1 and T2 are not yet gated, hence they block the forward voltage.

3. With respect to the below given circuit, from ωt = 0 to α,

a) voltage across all the thyristors is zero
b) negative voltage appears across T1 and T2
d) voltage across T3 and T4 is zero

Explanation: T1 and T2 are not yet gated, hence they block the forward voltage where as no voltage exists across T3 and T4.

4. For the below given circuit, when the devices T1 and T2 are conducting from ωt = α till they are naturally commutated at π voltage across the other two pair of devices is

a) zero
b) positive (forward voltage)
c) negative (reverse voltage)
d) none of the mentioned

Explanation: When T1 and T2 are conducting they act like S.C’s and the other pair of devices i.e. T3 and T4 has to take care of the reverse voltage.

5. A single-phase full converter B-2 type connection has a RLE type of motor load connected. The minimum requirement to turn-on the device is
a) α > 30°
b) Vm sinα > E
c) Vm sinα < E
d) α < 30°

Explanation: Device will not turn on until the supply voltage exceeds the motor back emf E.
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6. For the below shown circuit with continuous load current.

Each thyristor pair conducts for

Explanation: As the load current is continuous each pair conducts from π to π+α i.e π radians.

7. For the below given circuit

a) all the devices are gated together
b) T3 and T4 are gated together
c) T3 and T1 are gated together
d) T3 and T2 are gated together

Explanation: T1-T2 are gated together at a time and T3-T4 are gated together at a time.

8. For the below shown circuit has dis-continuous load current waveform.

Each thyristor pair conducts for

Explanation: Load current is discontinues than SCR pair conducts for less than 90° depending on the value of the inductor L.

9. A single-phase full converter with B-2 type of connection has a continuous load current waveform. The thyristor pairs T3, T4 is triggered at ωt =
a) 0
b) α
c) π+α
d) π-α

Explanation: First, at α T1-T2 conduct, then after π+α the next pair is excited i.e. T3-T4 and likewise.

10. The PIV for each diode in a single-phase, full converter with B-2 type of controlled rectifier is
Consider supply voltage as Vs = Vm sinωt.
a) 2Vm
b) Vm
c) Vm/2
d) Vm/√2

Explanation: The peak inverse voltage handled by each device is Vm in case of B-2 type of configuration.

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