1. Calculate the output frequency for the two-pulse converter if the supply frequency is 20 Hz.
A. 40 Hz
B. 20 Hz
C. 60 Hz
D. 90 Hz
Answer: A
The output of a two-pulse converter consists of two pulses in one cycle. The output frequency of the two pulse converters is
2×supply frequency=2×20=40 Hz.
2. Calculate the pulse number if the supply frequency is 2π and the output frequency is π÷3.
A. 4
B. 2
C. 6
D. 8
Answer: C
The pulse number can be calculated using the ratio of input frequency to the output frequency.
The value of pulse number (P) is 2π÷π÷3=6. It is a six-pulse converter.
3. 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 15°.
A. 521.2 V
B. 522 V
C. 523 V
D. 524 V
Answer: B
In 3-Φ Fully controlled rectifier, the average value of the voltage is
3Vml(cos(∝))÷π
=3×400×√2(cos(15°))÷3.14=522 V.
4. Calculate the value of the Input power factor for a 3-Φ Fully controlled rectifier if the firing angle value is 70°.
A. .32
B. .38
C. .31
D. .33
Answer: A
The value of the input power factor for a 3-Φ Fully controlled rectifier is
.95cos(70°)=.32.
The input power factor is a product of the distortion factor and displacement factor.
5. Calculate the value of THD value for a 3-Φ Fully controlled rectifier.
A. 48.43 %
B. 47.25 %
C. 39.26 %
D. 31 %
Answer: D
The value of the distortion factor is .95. The value of THD value for a 3-Φ Fully controlled rectifier is
√(1÷.95)2-1=31 %.
THD measures the amount of harmonic distortion.
6. In a 3-Φ semi-controlled rectifier calculate the average value of the voltage if the supply is 440 V and the firing angle is 22°.
A. 571.5 V
B. 572.8 V
C. 548.3 V
D. 524.1 V
Answer: B
In 3-Φ Semi-controlled rectifier, the average value of the voltage is
3Vml(1+cos(∝))÷2π
=3×440×√2(1+cos(22°))÷6.28=572.8 V.
7. Calculate the circuit turn-off time for 3-Φ Fully controlled rectifier if the firing angle is 20° and the supply frequency is 60 Hz.
A. 8.8 msec
B. 7.4 msec
C. 10.1 msec
D. 6.5 msec
Answer: C
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°-20°)÷6.28×60=10.1 msec.
8. Calculate the circuit turn-off time for 3-Φ Fully controlled rectifier if the firing angle is 110° and the supply frequency is 50 Hz.
A. 3.8 msec
B. 5.2 msec
C. 9.3 msec
D. 8.7 msec
Answer: A
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°-110°)÷6.28×50=3.8 msec.
9. Calculate peak-peak voltage if Vmax=80 V and Vmin=20 V.
A. 60 V
B. 50 V
C. 70 V
D. 10 V
Answer: A
Peak-Peak voltage is equal to the difference between the maximum
and minimum voltage. It is mathematically represented as
Vp-p=Vmax-Vmin=80-20=60 V.
10. Calculate the value of the Crest factor if Vpeak=12 V and Vr.m.s=24 V.
A. .2
B. .3
C. .4
D. .5
Answer: D
The value of the crest factor is Vpeak÷Vr.m.s=12÷24=.5. It signifies the peak value is .5 times the r.m.s value.
