11. Which of the following is used to protect SCR from d(i)/d(t) condition?
A. Inductor
B. Capacitor
C. Heat sink
D. Fuse
Answer: A
Inductor is used to protect SCR from d(i)/d(t) condition. The inductor does not allow the sudden change in current.
12. Which of the following is used to protect SCR from d(v)/d(t) condition?
A. Capacitor
B. Fuse
C. Snubber circuit
D. Inductor
Answer: C
Snubber circuit is used to protect SCR from d(v)/d(t) condition. The snubber circuit consists of a capacitor and resistor. The capacitor does not allow the sudden change in voltage and the resistor resists the discharging of the capacitor.
13. A snubber circuit is used with thyristor in ____________
A. Parallel
B. Series
C. Anti-parallel
D. Series or Parallel
Answer: A
A snubber circuit is used with a thyristor in parallel. Snubber circuit is used to protect SCR from d(v)/d(t) condition. The snubber circuit consists of a capacitor and resistor.
14. When maximum power loss occurs?
A. Rise time
B. Delay time
C. Spread time
D. Rise time or Delay time
Answer: A
Rise time is very low (1-4 μseC. During rising, time anode voltage and anode current are very high.
Power loss(V×I) is very high.
15. Calculate the value of Vpeak if crest factor=47 and Vr.m.s=6 V.
A. 282 V
B. 300 V
C. 290 V
D. 286 V
Answer: A
The value of the crest factor is Vpeak÷Vr.m.s.
The value of Vpeak is
(crest factor) × Vr.m.s = 47×6 = 282 V.
It signifies the ratio of Vpeak and Vr.m.s.
16. Which one of the following loads is suitable for load commutation in a Single-phase Half-bridge inverter?
A. R-L load
B. R-L-C overdamped
C. R-L-C underdamped
D. L-load
Answer: C
R-L-C underdamped are leading power factor loads. They do not require any forced commutation technique. Anti-Parallel diodes help in the commutation process.
17. R-L-C overdamped loads are generally lagging power factor loads.
A. True
B. False
Answer: A
R-L-C overdamped loads are generally lagging power factor loads. They require forced commutation. Anti-Parallel diodes do not help in the commutation process.
18. A step-down chopper has an input voltage of 40 V and output voltage of 20 V. Calculate the value of the duty cycle.
A. 0.5
B. 0.2
C. 0.3
D. 0.4
Answer: A
The output voltage of the step-down chopper is Vo = Vin×(D).
The value of the duty cycle is less than one which makes the Vo < Vin. The step-down chopper is used to step down the voltage.
The value of the duty cycle is 20÷40 = .5.
19. Calculate the De-rating factor if the string efficiency is 20 %.
A. .8
B. .4
C. .5
D. .6
Answer: A
The de-rating factor is used to measure the reliability of a string. The value of the De-rating factor is 1-(string efficiency) = 1-.2 = .8.
20. Calculate the string efficiency if the de-rating factor is .48.
A. 48 %
B. 52 %
C. 50 %
D. 60 %
Answer: B
The string efficiency is calculated for the series and parallel connection of SCRs. The value of string efficiency is
