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Posted By: prashanth beerelli Member Level: Diamond Posted Date: 04 Sep 2008
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2006 Jawaharlal Nehru Technological University Electrical and Electronics Engineering III B.Tech I Semester Regular Examinations, November 2006 POWER ELECTRONICS Question paper
Code No: RR310204 Set No. 3
III B.Tech I Semester Regular Examinations, November 2006
POWER ELECTRONICS
(Electrical & Electronic Engineering)
Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
? ? ? ? ?
1. The voltage and current ratings of a particular circuit are 3.3KV and 750 amps.
SCRs with rating of 800V and 175 amps are available. The recommended minimum
derating factor is 15%. Calculate min. series and parallel units required. Also
calculate the values of resistance and capacitance to be used in the static and
dynamic equalizing circuits if the max. forward blocking current for the SCRs is
25mA and Qmax is 50µC. Where Qmax is max. charge stored in thyristor. [16]
2. Explain the operation of a singe phase half wave converter for R-load with neat
circuit diagram and necessary waveforms. Also derive the output average voltage
and current for a = 300. [12+4]
3. A three phase, fully controlled bridge converter is supplying dc load of 400V, 60A
from a three phase 50Hz, 660V (line) supply. If the thyristors have a voltage drop
of 1.2V when conducting, then neglecting overlap, compute
(a) firing angle of thyristor
(b) RMS value of thyristor currents
(c) mean power loss in thyristors [6+5+5]
4. Derive the output rms voltage, output rms current and source power factor for a
single phase ac voltage controller fed to R-L load. [6+4+6]
5. Explain the operation of single phase midpoint cyclo converter with R-L load s for
continuous conduction with relevant circuit diagram nd necessary output waveforms
for f0 = 1/3 fs. [4+6+6]
6. Explain the operation of DC Morgan’s Chopper for resistive load with neat circuit
diagram and output voltage and current waveforms. [4+7+5]
7. Draw and explain the simple SCR series inverter circuit employing class A type
commutation. With the help of important waveforms. State the limitations of this
inverter. [8+4+4]
8. A single PWM inverter feeds an RL load with R = 10 ohms, and L = 20mH. If the
Vs = 120 V, find out the total harmonic distortion in the load current. The width
of each pulse is 1200 and the output frequency is 50Hz.
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