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Power Electronics problems

1. In a single phase full wave converter (M-2 connection) feeding on R - L load, the input voltage is v = V_m sin ?t. The expression for dc output voltage is
Options
A.
B.
C.
D.

2. An SCR is triggered at 40� in the positive half cycle only. The average anode current is 50 A. If the firing angle is changed to 80�, the average anode current is likely to be
Options
A. 50 A
B. 25 A
C. less than 50 A but more than 25 A
D. less than 25 A

3. Assertion (A): The surge current which an SCR can withstand is much higher than rms on state current.
Reason (R): The duration of surge current is very small.
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

4. A single phase half wave controlled rectifier circuit has a free wheeling diode. The load is a combination of R and L. The firing angle is a. The period of conduction of SCR and free wheeling diode respectively are
Options
A. a < ?t < p and p < ?t < (2p + a)
B. a < ?t < p and p < ?t < 2p
C. a < ?t < (p + a) and (p + a) < ?t < 2p
D. a < ?t < p and p < ?t < (2p - a)

5. A thyristor has a turn on time of 6 ?s. If the anode circuit is inductive, the turn on time will be
Options
A. 6 ?s
B. less than 6?s
C. more than 6 ?s
D. either 6 ?s or less

7. The value of capacitor C for dynamic equalising circuit of series connected thyristors is determined by
Options
A. forward characteristics of thyristors
B. reverse recovery characteristics of thyristors
C. both forward and reverse recovery characteristics of thyristors
D. none of the above

8. An electric heater is controlled by thyristors through on-off control. If a = 0.4, the heating is
Options
A. 16% maximum
B. 40% of maximum
C. 60% of maximum
D. 84% of maximum

9. A single phase half wave rectifier is feeding a resistive load. When a = 0, dc output voltage is 127 V. When a = 30�, the dc output voltage will be about
Options
A. 127 V
B. 120 V
C. 110 V
D. 100 V

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