21. Calculate the value of the fundamental displacement factor for 1-Φ Full wave bridge rectifier if the firing α=17°.
A. .98
B. .19
C. .56
D. .95
Answer: D
The fundamental displacement factor is the cosine of angle difference between the fundamental voltage and fundamental current.
D.F=cos(∝)=cos(17°)=0.95.
22. Calculate the value of the fundamental displacement factor for a 1-Φ Full-wave semi-converter if the firing angle value is 95o.
A. .60
B. .68
C. .62
D. .67
Answer: D
The fundamental displacement factor is the cosine of angle difference between the fundamental voltage and fundamental current. The fundamental displacement factor for 1-Φ Full-wave semi-converter is cos(∝÷2)=cos(47.5o)=.67.
23. Which one of the following loads is suitable for lagging power factor load in a Single-phase Half-bridge inverter?
A. C load
B. R-L-C overdamped
C. R-L-C underdamped
D. L-C load
Answer: B
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.
24. Which one of the following loads is suitable for the leading power factor load in a Single-phase Half-bridge inverter?
A. C load
B. R-L-C overdamped
C. R-L-C underdamped
D. L-C 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.
25. A step-down chopper has an input voltage of .1 V and output voltage of .01 V. Calculate the value of the duty cycle.
A. 0.1
B. 0.2
C. 0.3
D. 0.5
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 .01÷.1=.1.
26. Calculate the De-rating factor if the string efficiency is 98%.
A. .04
B. .02
C. .05
D. .03
Answer: B
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-.98=.02.
27. Calculate the string efficiency if the de-rating factor is .50.
A. 28 %
B. 42 %
C. 80 %
D. 50 %
Answer: D
The string efficiency is calculated for the series and parallel connection of SCRs. The value of string efficiency is 1-(De-rating factor)=1-.50=50 %.
28. 70 V rated 6 SCRs are connected in series. The operation voltage of the string is 130. Calculate the De-rating factor.
A. .70
B. .73
C. .78
D. .74
Answer: A
The string efficiency can be calculated using the formula operation voltage÷(Number of SCRs×Rated voltage)
=130÷(70×6)=.30.
The De-rating factor value is 1-.30=.70.
29. d(v)÷d(t) is more reliable for SCR triggering.
A. True
B. False
Answer: B
Gate triggering is more reliable than any other triggering method. The risk of false triggering of SCR increases in the case of the d(v)÷d(t) triggering.
30. Calculate the output voltage of the Buck converter if the supply voltage is 13 V and the duty cycle value is .16.
A. 2.08 V
B. 2.24 V
C. 2.58 V
D. 2.54 V
Answer: A
The output voltage of the buck converter is Vo = Vin×(D.=13×.16=2.08 V. The value of the duty cycle is less than one which makes the Vo < Vin. The buck converter is used to step down the voltage.