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Power Electronics
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Question
A single phase fully controlled bridge rectifier is fed by a source having inductance. The output voltage during overlap period is
Options
A. V
m
B. 0.5 V
m
C. zero
D. 0.5 V
m
- voltage drop across inductance
Correct Answer
zero
Explanation
During the period of overlap all the four thyristors conduct and load is effectively short-circuited. Output voltage is zero.
Power Electronics problems
Search Results
1. In a 3 phase semiconverter, the firing frequency is
Options
A. equal to line frequency
B. 3 times the line frequency
C. 6 times the line frequency
D. 12 times the line frequency
Show Answer
Scratch Pad
Discuss
Correct Answer: 3 times the line frequency
Explanation:
Since the circuit has 3 thyristors, firing frequency is three times the line frequency.
2. In dielectric heating, the thyristor circuits consist of
Options
A. rectifier-chopper combination
B. controlled rectifier
C. ac regulator
D. rectifier-inverter combination
Show Answer
Scratch Pad
Discuss
Correct Answer: rectifier-inverter combination
Explanation:
Input ac is rectified and then converted to high frequency ac.
3. In a multiphase chopper, the different choppers operate in
Options
A. series and all simultaneously
B. parallel and one at a time
C. parallel and simultaneously
D. either (b) or (c)
Show Answer
Scratch Pad
Discuss
Correct Answer: parallel and one at a time
Explanation:
Only one chopper operates at one time.
4. In the below figure, the average value of load current is 15 A. The load is highly inductive. The peak value of thyristor current is
Options
A. 15 A
B. 15
2
A
C.
D. 30 A
Show Answer
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Discuss
Correct Answer: 15 A
Explanation:
Because of highly inductive load, output current is nearly constant.
5. When thyristors are connected in series and parallel, it may be necessary to have :
Options
A. current derating
B. voltage derating
C. both current and voltage derating
D. none of the above
Show Answer
Scratch Pad
Discuss
Correct Answer: both current and voltage derating
Explanation:
Thyristors in series do not share the voltage equally and require voltage derating. Thyristors in parallel need current derating.
6. A thyristor has its gate current zero. To start conduction the forward voltage must exceed
Options
A. about 0.5 V
B. forward breakover voltage
C. on state voltage
D. peak working off state forward voltage
Show Answer
Scratch Pad
Discuss
Correct Answer: forward breakover voltage
Explanation:
With zero gate current, conduction can be started only if forward voltage exceeds breakover voltage.
7. In the below figure the rms voltage across each half of secondary is 200 V. The peak inverse voltage across each of thyristor is
Options
A. 200 V
B.
2
(200) V
C.
2
(400) V
D. 800 V
Show Answer
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Discuss
Correct Answer:
2
(400) V
Explanation:
PIV =
2
(2 x 200).
8. In a dual converter both converters work as rectifiers.
Options
A. True
B. False
Show Answer
Scratch Pad
Discuss
Correct Answer: False
Explanation:
One operators as rectifier and the other as inverter.
9. The waveshape of output voltage of half bridge inverter is
Options
A. sinusoidal
B. square
C. triangular
D. either (a) or (b)
Show Answer
Scratch Pad
Discuss
Correct Answer: square
10. In an SCR, the anode current consists of
Options
A. only holes
B. only electrons
C. both electrons and holes
D. either electrons or holes
Show Answer
Scratch Pad
Discuss
Correct Answer: both electrons and holes
Explanation:
Both electrons and holes contribute to current.
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