Download PTU (I.K.Gujral Punjab Technical University (IKGPTU)) B-Tech (Bachelor of Technology) (AR)- Automation-And-Robotics 2020 December 4th Sem 63014 Power Electronics And Motors Previous Question Paper
Roll No.
Total No. of Pages : 02
Total No. of Questions : 18
B.Tech.(Automation & Robotics) (2012 & Onward) (Sem.?4)
POWER ELECTRONICS & MOTORS
Subject Code : BTAR-401
M.Code : 63014
Time : 3 Hrs. Max. Marks : 60
INST RUCT ION TO CANDIDAT ES :
1 .
SECT ION-A is COMPULSORY cons is ting of TEN questions carrying TWO marks
each.
2 .
SECT ION-B c ontains F IVE questions c arrying FIVE marks eac h and s tud ents
have to atte mpt any FOUR q ues tions.
3 .
SECT ION-C contains THREE questions carrying T EN marks e ach and s tudents
have to atte mpt any T WO questio ns.
SECTION-A
Answer briefly :
1.
Draw the symbol and V-I characteristics of a DIAC.
2.
What is the principle of operation for dual converter?
3.
Why equalizing networks are required in series connection of SCRs?
4.
Write two comparisons between transistors and thyristors.
5.
The reverse biased junction capacitance of an SCR is 40 picofarads. The device can be
turned on if the charging current flowing through the junction capacitor is 10 mA.
Calculate the dV/dt capability of the device.
6.
What are the causes of overvoltages in thyristors circuits?
7.
List the applications of cycloconverters.
8.
Discuss two disadvantages of harmonics present in the inverter system.
9.
Differentiate between voltage-fed and current-fed inverters.
10. Describe time - ratio control (TRC) method in choppers.
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SECTION-B
11. A thyristors string is formed by the series and parallel connection of thyristors. The voltage
and current ratings of the string are 5 kV and 1000 A respectively. Available thyristors
have the voltage and current ratings of 750 V and 225 A respectively. The string efficiency
is 80% for both the series and parallel connections. Calculate the number of thyristors to be
connected in series and parallel.
12. Explain the various types of triggering methods of SCR briefly. Which is the universal
method and why?
13. Explain in detail the operation of a single - phase full converter bridge rectifier with RLE
load. Describe with circuit diagram and appropriate waveforms.
14. Describe the working of type-C and type-D choppers along with their reliable waveforms.
15. Describe modified McMurray half - bridge single - phase inverter with relevant voltage and
current waveforms.
SECTION-C
16. a) What is impulse commutation? Describe it with a circuit diagram and appropriate
waveforms.
b) Draw and explain the switching characteristics of an SCR.
17. a) A chopper circuit is operating at a frequency of 1 kHz on a 220 V dc supply. If the load
voltage is 180 V, calculate the Ton and Toff of thyristors in each cycle.
b) Define firing angle, extinction angle, and conduction angle by showing in appropriate
waveform.
18. a) Discuss the principle of working of a three - phase bridge inverter with an appropriate
circuit diagram. Draw voltage waveforms on the assumption that each thyristor
conducts for 180? and the resistive load is star - connected. The sequence of firing of
various SCRs should also be indicated in the waveforms.
b) List the advantages and disadvantages of dual converter with circulating current mode.
NOTE : Disclosure of Identity by writing Mobile No. or Making of passing request on any
page of Answer Sheet will lead to UMC against the Student.
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This post was last modified on 13 February 2021