When thyristors are connected in series and parallel, it may be necessary to hav

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Question
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

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.

Power Electronics problems

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1. 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

3. 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

4. A single phase series converter is used for
Options
A. high voltage output
B. high current output
C. high voltage and high current output
D. improving the circuit efficiency

5. Assertion (A): An inverter does not require forced commutation
Reason (R): A series inverter is a forced commutation inverter.
Options
A. Both A and R are correct and R is correct explanation of A
B. Both A and R correct but R is not correct explanation of A
C. A is correct but R is wrong
D. A is wrong but R is correct

6. 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. 152 A
C.
D. 30 A

7. 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)

8. In dielectric heating, the thyristor circuits consist of
Options
A. rectifier-chopper combination
B. controlled rectifier
C. ac regulator
D. rectifier-inverter combination

9. 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

10. 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

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