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Power Electronics Question Paper - Dec 17 - Electrical And Electronics (Semester 5) - Visveswaraya Technological University (VTU)
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Power Electronics - Dec 17
Electrical And Electronics (Semester 5)
Total marks: 80
Total time: 3 Hours
Note: Answer any FIVE full questions choosing one full question from each module.
1.a.
With the help of circuit diagram, input and output waveform explain working of different types of power electronic converters.
(8 marks)
00
1.b.
The reverse recovery time of a diode $\mu$s and rate of fall of Diode current is 80A/$\mu$s.
(4 marks)
00
Calculate : i) the storage charge ii) peak reverse current
1.c.
List the parameters on which the performance of rectifier is evaluated.
(4 marks)
00
OR
2.a.
Briefly explain different types of power diodes.
(6 marks)
00
2.b.
Explain the peripheral effects of power electronic equipments.
(6 marks)
00
2.c.
The bridge rectifier has an AC source with =100V at 60Hz and a series load (RL) with R= 10$\OHM$ and L= 10mH. Calculate:
i) average current in the load.
ii) average current in the diodes.
(4 marks) 00
Module-2
3.a
Explain the switching characteristics of MOSFET.
(5 marks)
00
3.b.
Explain the anti-stauration control of BJT.
(5 marks)
00
3.c.
The $\beta$ of bipolar transistor varies from 12 ti 75. The load resistance is 1.5 ohm. The supply voltage Vcc
(6 marks)
00
OR
4.a.
List and explain the switching limits of power BJT.
(8 marks)
00
4.b.
TYPE_QUESTION_HERE
(8 marks)
00
Module-3
5.a.
Explain the VI characteristics of SCR. Also define : i) holding current and ii) latching current.
(6 marks)
00
5.b.
Explain different methods of turning on of thyristor.
(6 marks)
00
5.c.
For the SCR shown in fig.Q.5(c) , has a latching current of 20mA and is fixed by a pulse width of 50$\mu$s . Determine whether the SCR turn on as not and comment on the result obtained.
(5 marks)
00
OR
6.a.
With the help of two transistor model , derive an expression for anode current of a thyristor and explain why gate looses its control over the device once thyristor its turned on
(8 marks)
00
6.b.
A string of STRs ate connected in the series to withstand a DC voltage of 15KV. The maximum leakage current and recovery charge difference of thyristor are 10mA and 150$\mu$C respectively. A derating factor of 20% is applied for steady state and transient stage voltage sharing's of thyristor ms. If the maximum steady state voltage sharing is 1000v. Calculate:
(8 marks)
00
i) steady state voltage Sharing resistance R for each thyristor
ii) transient voltage capacitance c1 and
iii) string efficiency.
Module-4
7.a.
With the help of circuit diagram and waveform explain the working of single-phase full converter with R-L load.
(8 marks)
00
7.b.
A single-phase full wave AC voltage controller has an input voltage of 150V (rms) and a load of 8 ohm. The firing angle of thyristor is 60 degree. Find :i) average output voltage ii) rms output voltage iii) output power and iv) input P.F.
(8 marks)
00
OR
8.a.
Explain the working of single-phase full wave AC voltage controller with resistive load. Draw relevant circuit, waveform. Derive
(5 marks)
00
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