81. Calculate the Vo(avg) for the 3-Φ phase Half-wave controlled rectifier if the supply value is 364 V and the value of firing angle is 2°.
A. 247.62 V
B. 245.76 V
C. 214.26 V
D. 233.26 V
Answer: B
The Vo(avg) for the 3-Φ phase Half-wave controlled rectifier is 3Vmlcos(α)÷2π. The value of output voltage is
3Vmlcos(α)÷2π
= 3×√2×364×(.99)÷6.28 = 245.76 V.
82. Calculate the value of the Input power factor for a 3-Φ Fully controlled rectifier if the firing angle value is 16°.
A. .96
B. .91
C. .93
D. .94
Answer: B
The value of the input power factor for a 3-Φ Fully controlled rectifier is .95cos(16°) = .91. The input power factor is a product of the distortion factor and displacement factor.
83. In a 3-Φ semi-controlled rectifier calculate the average voltage value if the supply is 299 V and the firing angle is 56.15°.
A. 311.26 V
B. 304.26 V
C. 314.51 V
D. 312.45 V
Answer: C
In 3-Φ Semi-controlled rectifier, the average value of the voltage is
3Vml(1+cos(∝))÷2π
= 3×299×√2(1+cos(56.15°))÷6.28 = 314.51 V.
84. Calculate the circuit turn-off time for 3-Φ Fully controlled rectifier if the firing angle is 13° and the supply frequency is 49.5 Hz.
A. 730.2 msec
B. 740.8 msec
C. 754.5 msec
D. 755.1 msec
Answer: A
The circuit turn-off time for 3-Φ Fully controlled rectifier is (240°-α)÷ω.
The value of circuit turn-off time for ∝ < 60° is (240°-13°)÷6.28×49.5 = 730.2 msec.
85. Calculate the circuit turn-off time for 3-Φ Fully controlled rectifier if the firing angle is 170° and the supply frequency is 50.5 Hz.
A. 32.4 msec
B. 35.2 msec
C. 39.3 msec
D. 31.5 msec
Answer: D
The circuit turn-off time for 3-Φ Fully controlled rectifier is (180°-α)÷Ω.
The value of circuit turn-off time for ∝ ≥ 60° is (180°-170°)÷6.28×50.5 = 31.5 msec.
86. Calculate the form factor if V(r.m.s) = 45 V, V(avg) = 15 V.
A. 2
B. 5
C. 3
D. 8
Answer: C
The form factor is defined as the ratio of the Vr.m.s÷Vavg = 45÷15 = 3. The r.m.s value is three times of average value Vavg.
87. Calculate the Vo(avg) for the 3-Φ phase Half-wave controlled rectifier if the supply value is 480 V and the value of firing angle is 92°.
A. 264.02 V
B. 487.26 V
C. 858.26 V
D. 248.25 V
Answer: A
The Vo(r.m.s) for the 3-Φ phase Half-wave controlled rectifier is 3Vm(1+cos(α))÷2π.
The value of output voltage is
3Vm(1+cos(α+30))÷2π
= 3×480×√3×√2(1+cos(92))÷2π = 264.02 V.
88. Full form of SCR is ____________
A. Silicon-controlled rectifier
B. State-controlled rectifier
C. State cover rectifier
D. State-controlled reset
Answer: A
SCR stands for the silicon-controlled rectifier. It is a semi-controlled, bipolar, uni-directional switch. It is a high power-rating than other power electronic devices.
89. Full form of TRIAC is __________
A. Triode for Alternating current
B. Tri for Alternating current
C. Triode for Alternating counter
D. Tri for Alternating counters
Answer: A
TRIAC stands for Triode for Alternating current. It is a bipolar, bidirectional switch. It is used in fan regulators to control the speed of fans.
90. TRIAC is a unipolar switch.
A. True
B. False
Answer: B
TRIAC stands for Triode for Alternating current. It is a bipolar, bidirectional switch. It is used in fan regulators to control the speed of fans.
91. For α > 90°, 3-Φ Full wave bridge rectifier acts as a natural commutated inverter.
A. True
B. False
Answer: A
The output voltage of the 3-Φ Full wave bridge rectifier is 3Vml(cos(∝))÷π.
For α > 90° the output voltage becomes negative. The power flows from DC to the AC side.
92. What is the formula for output voltage for 3-Φ Full wave bridge rectifier for R-L load?
A. 3Vml(cos(∝))÷2π
B. 3Vml(cos(∝))÷π
C. 2Vml(cos(∝))÷π
D. 6Vml(cos(∝))÷π
Answer: B
The output voltage of the 3-Φ Full wave bridge rectifier for R-L load is 3Vml(cos(∝))÷π. The net area of the output voltage for the R-L load remains zero.
93. The output voltage of the 3-Φ Full wave bridge rectifier is six times of the 3-Φ Half-wave rectifier.
A. True
B. False
Answer: B
The output voltage of the 3-Φ Full wave bridge rectifier is 3Vml(cos(∝))÷π.
The output voltage of the 3-Φ Half wave rectifier is 3Vml(cos(∝))÷2π.
94. What is the formula for output voltage for 3-Φ Full wave bridge rectifier for R load for α < 60°?
A. 2Vml(cos(∝))÷π
B. 3Vml(cos(∝))÷2π
C. 3Vml(cos(∝))÷π
D. 6Vml(cos(∝))÷π
Answer: C
The output voltage of the 3-Φ Full wave bridge rectifier for R load is 3Vml(cos(∝))÷π for α < 60°. Conduction will only remain from 60°+α to 120°+α.
95. ____________ is the boundary for C.C.M and D.C.M mode in 3-Φ Full wave bridge rectifier for R load.
A. 60°
B. 10°
C. 80°
D. 50°
Answer: A
60° is the boundary for C.C.M and D.C.M mode in 3-Φ Full wave bridge rectifier for R load. Conduction will only remain from 60°+α to 120°+α.
96. What is the formula for output voltage for 3-Φ Full wave bridge rectifier for R load for α > 60°?
A. 2Vml(1+cos(∝+60°))÷π
B. 3Vml(1+cos(60°+∝))÷2π
C. 3Vml(1+cos(60°+∝))÷π
D. 6Vml(cos(∝))÷π
Answer: C
The output voltage of the 3-Φ Full wave bridge rectifier for R load is
3Vml(1+cos(60°+∝))÷π for α > 60°. Conduction will only remain from 60°+α to 180°.
97. Calculate the r.m.s value of thyristor current in 3-Φ Full-wave converter for the load current = 4 A and α = 12°.
A. 2.3 A
B. 2.5 A
C. 2.7 A
D. 2.9 A
Answer: A
The r.m.s value of thyristor current in a 3-Φ Full-wave converter is Io√1÷3. It is the r.m.s value of the thyristor current.
I(r.m.s) = Io√1÷3 = 2.3 A.
98. Calculate the average value of thyristor current in a 3-Φ Full-wave converter for the load current = 9 A and α = 26°.
A. 4 A
B. 5 A
C. 7 A
D. 3 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 = 3 A.
99. Calculate the De-rating factor if the string efficiency is 16 %.
A. .84
B. .44
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-.16 = .84.
100. Full form of MOSFET is ___________
A. metal oxide silicon field-effect transistor
B. metal oxide semiconductor field-effect transistor
C. Metal oxide settle field-effect transistor
D. Metal-oriented silicon field-effect transistor
Answer: B
MOSFET stands for Metal oxide semiconductor field-effect transistor. It is a three-terminal device consisting of a source, drain, and gate. It is a high switching device.
