71. 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.
72. 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.
73. 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.
74. 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.
75. 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.
76. 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.
77. 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 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.
78. 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.
79. 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.
80. 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.
