21. 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.
22. 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.
23. In a 3-Φ semi-controlled rectifier calculate the average value of the voltage 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.
24. 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.
25. 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.
26. 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.
27. 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.
28. 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.
29. 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.
30. 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.