11. 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.
12. 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 %.
13. 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.
14. 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.
15. 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.
16. Calculate the Vo(avg) for the 3-Φ phase Half-wave uncontrolled rectifier if the supply value is 440 V.
A. 297.25 V
B. 298.15 V
C. 298.11 V
D. 300.15 V
Answer: A
The Vo(avg) for the 3-Φ phase Half-wave uncontrolled rectifier is 3Vml÷2π. The value of output voltage is
3Vml÷2π
=3×√2×440÷6.28=297.25 V.
17. Calculate the pulse number if the supply frequency is 2π and the output frequency is 2π÷3.
A. 4
B. 5
C. 6
D. 3
Answer: D
The pulse number can be calculated using the ratio of input frequency to the output frequency. The value of pulse number (P) is 2π÷(2π÷3)=3. It is a three-pulse converter or 3-Φ phase Half-wave uncontrolled rectifier.
18. Calculate the average value of current for the 3-Φ phase Half-wave uncontrolled rectifier if the supply value is 400 V and the resistive load value is 5 Ω.
A. 54.04 A
B. 57.26 A
C. 51.64 A
D. 58.15 A
Answer: A
The Io(avg) for the 3-Φ phase Half-wave uncontrolled rectifier is 3Vml÷2πR.
The value of output voltage is
3Vml÷2πR
=3×√2×440÷6.28×5=54.04 A.
19. In a 3-Φ Fully controlled rectifier calculate the average value of the voltage if the supply is 400 V and the firing angle is 45°.
A. 381.15 V
B. 382.16 V
C. 383.19 V
D. 384.25 V
Answer: B
In 3-Φ Fully controlled rectifier, the average value of the voltage is
3Vml(cos(∝))÷π
=3×400×√2(cos(45°))÷3.14=382.16 V.
20. Calculate the Vo(r.m.s) (Highly inductive load. for the 3-Φ phase Half-wave uncontrolled rectifier if the supply value is 441 V.
A. 297.25 V
B. 298.15 V
C. 298.11 V
D. 300.15 V
Answer: A
The Vo(r.m.s) for the 3-Φ phase Half-wave uncontrolled rectifier is 3Vml÷2π. The value of output voltage is
