# PTU B.Tech Electrical Engineering 6th Semester May 2019 72789 POWER ELECTRONICS Question Papers

PTU Punjab Technical University B-Tech May 2019 Question Papers 6th Semester Electrical and Electronics Engineering (EEE)-EE-Electrical Engineering

Roll No.
Total No. of Pages : 02
Total No. of Questions : 09
B.Tech. (EE) PT (Sem.?6)
POWER ELECTRONICS
Subject Code : BTEE-504
M.Code : 72789
Time : 3 Hrs. Max. Marks : 60
INSTRUCTIONS TO CANDIDATES :
1.
SECTION-A is COMPULSORY consisting of TEN questions carrying T WO marks
each.
2.
SECTION-B contains FIVE questions carrying FIVE marks each and students
have to attempt any FOUR questions.
3.
SECTION-C contains T HREE questions carrying T EN marks each and students
have to attempt any T WO questions.

SECTION-A
1.

a. What is light triggering? Discuss.

b. Draw and explain why snubber circuit is required?

c. Why Germanium is not used for controlled rectification? Explain.

d. What do you mean by power dissipation? Explain.

e. Differentiate between AC and DC choppers.

f. Draw the Symbol and characteristics of UJT.

g. Differentiate between forced and natural commutation.

h. What is an inverter? List different requirements of a good inverter.

j. Draw the Symbol and characteristics of SUS.

1 | M-72789

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SECTION-B
2.
SCR with a rating of 1000V and 200A are available to be used in a string to handle 6kV
and lkA. Calculate the number of series and parallel units required in case derating factor
is (a) 0.1 and (b) 0.2.
3.
Describe the working of a single phase half bridge inverter. What is its main drawback?
Explain how this drawback can be taken care off.

4.
Explain the operating principle of single phase to single-phase step down cycloconverter
with the help of midpoint configuration for discontinuous load current.
5.
Discuss with the relevant waveforms, Class F type of commutation employed for
thyristor circuits.

6.
A single phase full converter is operated from 230V, 50Hz source and the load consists of
R=10 and a large inductance so as to render the load current constant. For a firing angle
delay of 30 degree, determine :

a. Average output voltage

b. Average output current

c. Average and rms values of thyristor currents

d. Power factor

SECTION-C
7.
Describe in detail the current commutated chopper with relevant current and voltage
waveforms as a function of time.

8.
Draw and explain the static VI characteristics of a thyristor. List the various turn on
methods of the thyristor and explain in detail gate triggering and dv/dt triggering.
9.
Discuss :

a. Dual Converter

b. Reverse Conducting thyristors

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