August
V62/T04061/EE/20150811
2015
Power Electronics
Instructions:
Marks-80
Time: 3 Hrs
1. All questions are compulsory.
2. “Long Answer type Question (LAQ)” is a supply type
question of 15 marks which required a typical answer of about
60-80 lines in bout 32-40 minutes.
3. “Sort Answer type Question (SAQ)” is a supply type question
of 5 marks which required a typical answer of about 15-20 lines
in bout 08-10 minutes.
4. Figures to the right indicate marks allotted to the questions.
5. Assume suitable data if necessary
6. Use a nonprogrammable type of scientific calculator is
allowed
Marks
SECTION-A
Q.1 State four important Features of IGBT. Draw symbol & structure of
an IGBT. Explain principle of operation & function of each layer.
15
OR
Q.1 Explain SCR Rating with details of current rating & voltage rating.
What is the function of the drift layer in power BJT?
15
Q.2 Calculate the value of R1, R2 & C for com-mutating the main SCR
when it is conducting a full current of fifteen Amps. The minimum
time for which this SCR which to be reverse biased for proper
commutation is 30 microsecond .it is given that the complementary
SCR will undergo natural commutation when its forward current
falls below the holding current of 3mA in a class C commutation
circuit .assume supply voltage to be 100 Volts.
15
OR
Q.2 Explain how SCR can be turning off naturally? Draw & explain the
turn off characteristics of an SCR. In which factors the turn off time
depends.
15
Q.3 Compare GTO & IGBT. With respect to Basic construction,
working principle, rating &characteristics, Symbol & Application.
5
Q.4 Derive the expressions for commutating components used in
auxiliary voltage commutation.
5
SECTION-B
Q.5 Draw & explain symbol, block diagram of phase controlled
rectifier. What is the principle of phase angle control with concept
of firing & conduction angle?
15
OR
Q.5 Draw the three phase half wave controlled rectifier configuration
with inductive & purely resistive load .Draw & explain input output
waveform with modes of operation.
15
Q.6 State any six specification of inverter. List any five application of
inverter. Write classification of inverter based on nature of output
waveform.
OR
15
Q.6 Comparison between step up & step down choppers (any six
points). A first quadrant chopper is having a supply voltage of
200volts dc & operating at a frequency of 1kHz. Find out a) Duty
Cycle b) Average load voltage. If the on time of chopper is 500
microsec.
15
Q.7 Define the term controlled rectifier .why phase controlled rectifier
are called ac dc converters?
5
Q.8 Explain rectifying mode & inverting mode with reference to full
wave controlled rectifier.
5
Computer Generated Random Question Paper dated: 07-07-2015 15:22:21
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