Question 71 : Consider the following statements regarding phase controlled converters:
i) They do not provide smooth variation of output voltage.
ii) They inject harmonics into the power system.
iii) They draw non-unity power factor current for finite firing angles.
Which of the above statements are correct?
1. All the three
2. i and ii only
3. i and iii only
4. ii and iii only
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Question 72 : In a single-phase half-wave circuit with RL load and a freewheeling diode, the freewheeling period is
1. 0 to π
2. α to π+α
3. π to 2π+α
4. π/2 to 2π-α
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Question 73 : A single full converter alone can given a
1. four quadrant operation
2. three quadrant operation
3. two quadrant operation
4. none of the mentioned
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Question 74 : If in the below given converter configuration, any 3 of the 4 SCRs are replaced by diodes
1. the average output voltage would increase
2. the average output voltage would decrease
3. the average output voltage would not change
4. the circuit would malfunction
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Question 75 : A 3-phase full converter delivers a ripple free load current of 10 A with a firing angle delay of 45°. Find the DF (distortion factor).
1. 1.414
2. 0
3. 0.707
4. 0.569
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Question 76 : A 3-phase full converter has an average output voltage of 365 V for zero degree firing and resistive load. For a firing angle of 90 degree, the output voltage would be
1. 125 V
2. 569 V
3. 365 V
4. zero
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Question 77 : In converter operation, with output voltage = Vo and RLE load.
1. Vo < E
2. Vo = E
3. Vo > E
4. None of the mentioned
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Question 78 : In a single-phase half-wave circuit with RL load and a freewheeling diode, the load voltage during the freewheeling period will be
1. zero
2. positive
3. negative
4. positive than negative
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Question 79 : In any AC-DC circuit, the freewheeling action
1. improves the power handling capabilities
2. increases the THD
3. improves CDF
4. all of the mentioned
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Question 80 : A single phase full converter has discontinues load current. The converter is supplying a dc shunt motor (R-L-E) load. When the current falls to zero the output voltage is
1. Zero
2. Vo
3. Vm
4. E
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