11. Thyristors are used in series to complete ________
A. High voltage demand
B. High current demand
C. Low voltage demand
D. Low current demand
Answer: C
Thyristors are used in series to complete high voltage demand. In series voltage across the components can be the same or different but the value of current remains the same.
12. Thyristors are used in parallel to complete ________
A. High voltage demand
B. High current demand
C. Low current demand
D. Low voltage demand
Answer: C
Thyristors are used in parallel to complete high current demand. In parallel current in the components can be the same or different but the value of voltage remains the same.
13. Calculate peak-peak voltage if Vmax=200 V and Vmin=190 V.
A. 20 V
B. 10 V
C. 60 V
D. 80 V
Answer: B
Peak-Peak voltage is equal to the difference between the maximum and minimum voltage. It is mathematically represented as
Vp-p=Vmax-Vmin=200-190=10 V.
14. Which harmonic is not present in 3-Φ fully controlled rectifier?
A. 27th harmonic
B. 15th harmonic
C. 17th harmonic
D. 12th harmonic
Answer: A
Triple harmonics are absent in the case of a 3-phase fully controlled rectifier. Because of the absence of triple harmonics, the THD of the rectifier is 31%.
15. Third lowest order harmonic present in 3-Φ fully controlled rectifier is __________
A. 11th
B. 17th
C. 13th
D. 22nd
Answer: A
Only 6k±1 order harmonics are present in 3-Φ fully controlled rectifiers. The lowest order harmonic is the 11th harmonic for k=2. Third-order harmonics are absent in 3-Φ fully controlled rectifier.
16. Calculate the value of output r.m.s voltage for a Single-phase Half-bridge inverter if the DC supply is 80 V.
A. 40 V
B. 20 V
C. 10 V
D. 60 V
Answer: A
The output voltage of a single-phase half-bridge inverter is a square wave with an amplitude equal to vD.C÷2.
The r.m.s value of output voltage is
vD.C÷2=80÷2=40 V.
17. High d(i)÷d(t) causes _______________
A. Local hotspots
B. Breakdown
C. High cost
D. Low cost
Answer: A
High d(i)÷d(t) causes local hotspots. Local hotspots are small areas with high temperatures due to overcrowdedness of charge generation. This causes high heat generation.
18. Calculate the value of output r.m.s voltage for a Single-phase Full-bridge inverter if the DC supply is 25 V.
A. 26 V
B. 25 V
C. 27 V
D. 28 V
Answer: B
The output voltage of a single-phase full-bridge inverter is a square wave with an amplitude equal to vD.C.
The r.m.s value of output voltage is vD.C=25 V.
19. High d(v)÷d(t) causes _______________
A. Local hotspots
B. False triggering
C. High cost
D. High-speed operation
Answer: B
High d(v)÷d(t) causes false triggering. The high value of d(v)÷d(t) causes the breakdown of junction J2. The thyristor will trigger automatically.
20. A step-down chopper has an input voltage of 12 V and output voltage of 2 V. Calculate the value of the duty cycle.
A. 0.26
B. 0.16
C. 0.33
D. 0.41
Answer: B
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 2÷12=.16.
