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BE- SEMESTER-V (NEW) EXAMINATION — WINTER 2020
Subject Code:2150903 Date:29/01/2021
Subject Name:Power Electronics — I
Time:10:30 AM TO 12:30 PM Total Marks: 56
Instructions:
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- Attempt any FOUR questions out of EIGHT questions.
- Make suitable assumptions wherever necessary.
- Figures to the right indicate full marks.
MARKS
Q.1 (a) Compare SCR with IGBTs. 03
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(b) Draw input voltage, output voltage and output current waveform of half wave diode 04 rectifier with RL load.
(c) Develop two transistor analogy model of SCR. Explain working principle of SCR 07 from it.
Q.2 (a) Explain construction of TRIACs. 03
(b) How SCRs can be used as bidirectional switch? 04
(c) Explain series and parallel operation of SCRs and problem associated with them. 07
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Q.3 (a) Explain the requirement of gate drive. 03
(b) Explain the term latching current and holding current of SCR. Compare them. 04
(c) Discuss RC triggering circuit. Explain its limitations. 07
Q.4 (a) Explain principle of natural commutation. 03
(b) Explain effect of gate current on V-I characteristics.of SCR. 04
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(c) With the necessary circuit diagram and waveforms explain the operation of UJT 07 triggering circuit.
Q.5 (a) Explain snubber circuit and its applications: 03
(b) Explain applications of pulse transformer and optocouplers. 04
(c) Sketch circuit diagram and waveform-of 3-phase full wave fully controlled converter. 07 Analyse its performance with RL load.
Q.6 (a) Explain requirement of di/dt and dv/dt protection of SCR. 03
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(b) Discuss need of freewheeling diode. 04
(c) Sketch circuit diagram and waveform of 1-phase full wave bridge converter. Analyse 07 its performance with' RLE load.
Q.7 (a) Compare voltage commutated, current commutated and load commutated chopper. 03
(b) Explain four quadrant operation of DC drives. 04
(c) Explain operation of 3-phase separately excited DC drive controlled by semi 07 converter.
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Q.8 (a) Explain working principle of boost converter. 03
(b) Explain four quadrant operation of chopper. 04
(c) Explain the concept of regenerative breaking. Explain chopper controlled DC drive 07 with regenerative breaking.
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