111. ____________ is the boundary for C.C.M and D.C.M mode in 3-Φ Half wave bridge rectifier for R load.
A. 60°
B. 10°
C. 80°
D. 30°
Answer: D
30° is the boundary for C.C.M and D.C.M mode in 3-Φ Half wave bridge rectifier for R load. Conduction will only remain from 30°+α to 150°+α.
112. Buck-Boost acts as Buck converter for duty cycle is equal to _________
A. .9
B. .7
C. .6
D. .4
Answer: D
The output voltage of the buck-boost converter is Vo = D×Vin ÷ (1-D). It can step up and step down the voltage depending upon the value of the duty cycle.
If the value of the duty cycle is less than .5 it will work as a buck converter. The answer is .4.
113. Buck-Boost acts as Boost converter for duty cycle is equal to _________
A. .8
B. .1
C. .2
D. .4
Answer: A
The output voltage of the buck-boost converter is Vo = D×Vin ÷ (1-D). It can step up and step down the voltage depending upon the value of the duty cycle.
If the value of the duty cycle is more than .5 it will work as a boost converter. The answer is .8.
114. Inductor and Capacitor in Buck converter are used to ___________
A. Increase the cost
B. Decrease the cost
C. Filter out the harmonics
D. Increase the harmonics
Answer: C
Inductor and capacitor in Buck converter are used to filter out the harmonics. They remove the ripple from the output voltage.
115. Calculate peak-peak voltage if Vmax = 1 V and Vmin = -1 V.
A. 6 V
B. 2 V
C. 3 V
D. 1 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 = 1+1 = 2 V.
116. Calculate the value of the Crest factor if Vpeak = 0 V and Vr.m.s = 24 V.
A. 0
B. 3
C. 5
D. 8
Answer: A
The value of the crest factor is Vpeak÷Vr.m.s = 0÷24 = 0 V. It signifies the peak value is 0 times the r.m.s value.
117. Calculate the output voltage of the Buck converter if the supply voltage is 789 V and the duty cycle value is .9.
A. 711.1 V
B. 710.1 V
C. 722.2 V
D. 713.2 V
Answer: B
The output voltage of the buck converter is
Vo = Vin×D = 789×.9 = 710.1 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.
118. Calculate the average value of thyristor current in a 3-Φ Full-wave converter for the load current = 27 A and α = 6°.
A. 9 A
B. 4 A
C. 5 A
D. 9 A
Answer: D
The average value of thyristor current in a 3-Φ Full-wave converter is Io÷3. It is the average value of the thyristor current.
I(r.m.s) = Io÷3 = 9 A.
119. Calculate the output voltage of the Boost converter if the supply voltage is 156 V and the duty cycle value is .4.
A. 260 V
B. 264 V
C. 261 V
D. 268 V
Answer: A
The output voltage of the boost converter is
Vo = Vin×(1-D). = 156×1.66 = 260 V.
The value of the duty cycle is less than one which makes the Vo > Vin. The boost converter is used to step up the voltage.
120. Inverters are used to convert DC power into variable AC power.
A. True
B. False
Answer: A
Inverters are used to convert DC power into variable AC power. The variable AC power means variable frequency and variable voltage level.
121. The short circuit problem is severe in the case of the Voltage source inverter.
A. True
B. False
Answer: A
Short-circuit problem is severe in the case of voltage source inverter. The output voltage of VSI is fixed but the output current depends upon the load. When Z = 0, I = V÷Z = ∞.
123. Switches used in VSI are ___________
A. Unipolar & Unidirectional
B. Bipolar & Bidirectional
C. Unipolar & Bidirectional
D. Unidirectional
Answer: C
Switches used in VSI are unipolar and bidirectional. MOSFET and BJT are examples of switches used in VSI. The output voltage of VSI is fixed but the output current depends upon the load.
124. Switches used in CSI are ____________
A. Bipolar & Unidirectional
B. Bipolar & Bidirectional
C. Unipolar & Unidirectional
D. Bidirectional
Answer: A
Switches used in CSI are bipolar and unidirectional in nature. GTO and thyristors are examples of switches used in CSI. The output voltage of CSI is variable but the output current is fixed.
125. Full form of VSI is ___________
A. Voltage source inverter
B. Volume source inverter
C. Voltage severe inverter
D. Voltage source inserter
Answer: A
VSI stands for Voltage source inverter. The output voltage of VSI is fixed but the output current depends upon the load. Switches used in VSI are unipolar and bidirectional in nature.
126. Full form of CSI is ___________
A. Counter source inverter
B. Counter severe inverter
C. Current source inverter
D. Current severe inverter
Answer: C
CSI stands for Current source inverter. The output voltage of CSI is variable but the output current is fixed.
127. Number of switches turned on in 3-phase 180° VSI at a single time are __________
A. 3
B. 2
C. 1
D. 4
Answer: B
In 3-phase 180° VSI each phase conducts for 180° and only two switches from different phases conduct at a single time.
128. Number of switches turned on in 3-phase 120° VSI at a single time are __________
A. 2
B. 4
C. 5
D. 3
Answer: D
In 3-phase 120° VSI each phase conducts for 120° and only three switches from different phases conduct simultaneously.
129. Calculate the phase voltage for 3-∅ 180° VSI if the value of the DC supply is 20 V.
A. 9.40 V
B. 9.42 V
C. 9.18 V
D. 9.78 V
Answer: B
The phase voltage for 3-∅ 180° VSI is
(√2÷3)×VDC = .471×20 = 9.42 V.
In 3-phase 180° VSI each phase conducts for 180° and only two switches from different phases conduct simultaneously.
130. Calculate the line voltage for 3-∅ 180° VSI if the value of the DC supply is 22 V.
A. 18.52 V
B. 18.12 V
C. 17.96 V
D. 15.48 V
Answer: C
The line voltage for 3-∅ 180° VSI is
(√2÷√3)×VDC
= .81×22 = 17.96 V.
In 3-phase 180° VSI each phase conducts for 180° and only two switches from different phases conduct simultaneously.
