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Power Electronics
Comments
Question
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)
Correct Answer
parallel and one at a time
Explanation
Only one chopper operates at one time.
Power Electronics problems
Search Results
1. 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
Scratch Pad
Discuss
Correct Answer: 15 A
Explanation:
Because of highly inductive load, output current is nearly constant.
2. 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.
3. A high frequency series inverter consists of
Options
A. a number of series inverters in series
B. a number of series inverters in parallel
C. a number of parallel inverters in parallel
D. a number of parallel inverters in series
Show Answer
Scratch Pad
Discuss
Correct Answer: a number of series inverters in parallel
Explanation:
A high frequency series inverter has many series inverters in parallel. Only one inverter operates at one time and they operate in fixed sequence.
4. An SBS can conduct is one direction only.
Options
A. True
B. False
Show Answer
Scratch Pad
Discuss
Correct Answer: False
Explanation:
It is a bilateral switch.
5. The average load current supplied by a thyristor depends on
Options
A. firing angle
B. firing frequency
C. magnitude of gate current
D. all of the above
Show Answer
Scratch Pad
Discuss
Correct Answer: firing angle
Explanation:
The firing angle controls the period of conduction and hence average load current.
6. 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.
7. 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.
8. 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
Show Answer
Scratch Pad
Discuss
Correct Answer: zero
Explanation:
During the period of overlap all the four thyristors conduct and load is effectively short-circuited. Output voltage is zero.
9. 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.
10. 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
Scratch Pad
Discuss
Correct Answer:
2
(400) V
Explanation:
PIV =
2
(2 x 200).
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