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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
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Code No: RR310204 Set No. 2
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. Explain the V-I Characteristics of Thyristors with elaborating the following :
(a) Latching current
(b) holding current
(c) on-state and off-state condition
(d) turn-on and turn-off times
(e) finger voltage [6+10]
2. Single phase dual converter is operated from 230V, 50Hz supply and the load re-
sistance 10 ohms. The circulating inductance is LC = 40mH, firing angles are a1
= 600 and a2 = 1200. Calculate the peak circulating current, peak currents of
converter 1 and converter 2. Also compute the load current. [8+4+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. A single phase full wave ac voltage controller has a resistance load of
(a) 10 ohms and
(b) 5 ohms.
The input ac voltage is 230V, 50Hz. For a delay angle of 900, determine the
rms load voltage, rms load current, rms thyristor current and input power
factor for above two loads. [8+8]
5. Explain the operation of single phase bridge type cyclo converter when fed form
230V, 50Hz source and controlling power to resistive load with the help of neat
circuit diagram and output voltage and current waveforms for a = 450 and a =
1600 for f0 = 1/5 fs. [4+6+6]
6. A load commutated chopper, fed from a 230V dc source has a constant load current
of 50A. For a duty cycle of 0.4 and a chopping frequency of 2 KHz, Calculate
(a) the value of commutating capacitance
(b) average output voltage
(c) circuit turn-off time for one SCR pair
(d) total commutation interval [4+4+4+4]
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) What are the different pulse width modulation techniques used for inverters.
(b) Which of the schemes gives better quality of voltage and current.
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