Yashwantrao Chavan Maharashtra Open University 2006 Certification TES Power Electronics - I - Question Paper

TES101/EE/20070811
Power Electronics - I
Time : 180 minutes Marks : 100
Instructions for the students :
1. All ques. are compulsory.
2. “Long ans kind ques. (LAQ)” is a supply kind ques. of 20 marks, which
require typical ans of about 60-80 lines in about 32-40 minutes.
3. “Short ans kind ques. (SAQ)” is a supply kind ques. of five marks, which
require typical ans of about 15-20 lines in about 08-10 minutes.
4. Use of non-programmable kind of scientific calculator is allowed.
5. Draw neat diagrams wherever necessary.
6. presume suitable data if necessary.


Long ans kind ques. (LAQ’s)
1. (a) elaborate the different thyristorised power controllers ?
(b) Draw and discuss the gate characteristics of SCR in details.
(c) If the Vg-Ig characteristics of an SCR is presumed to be a straight
line passing through the origin with a gradient of three x 103, compute
the needed gate source resistance. provided Egs = 10 V and
allowable Pg = 0.012
.

2. (a) discuss with a neat diagram and associated waveforms; the
operation of resistance firing circuit.
(b) Draw the circuit of static and dynamic equalizing network for
series connected SCRs. Derive the relation to obtain the values
of R and C.


3. (a) Derive an expression for the
i) avg. load voltage
ii) avg. load current and
iii) RMS load voltage for single phase half controlled converter
fore relative load.
(b) define the working of single phase controlled bridge converter
with inductive load and draw its waveforms.


4. (a) Develop a µp based scheme for three-phase fully controlled bridge
circuit.
(b) Write a short note on :
i) SMPS
ii) Arc welding using SCR

Short ans kind ques. (SAQ’s)
5. describe :
i) Holding Current ii) Latching Current
iii) Gate Current iv) di/dt rating
v) dv/dt rating
5
6.
Derive an expression for the period time ? ?
?
?
? ??
?
-
=
1 ?
1
e T RCLog for UJT
relaxation oscillator.

7. A three-phase half wave controlled rectifier has a supply of 200 V phase.
Determine the avg. load voltage for firing angle of 00, 300 and 600.
Assuming a thyristor voltage drop of 1.5 V and continuous load current.

8. Draw and discuss the over voltage protection circuit for an SCR.

Earning:   Approval pending.