# Download VTU BE 2020 Jan [folder1] 3rd Sem 18EC36 Power Electronics and Instrumention Question Paper

Download Visvesvaraya Technological University (VTU) BE-B.Tech (Bachelor of Engineering/ Bachelor of Technology) 2020 January [folder1] 3rd Sem 18EC36 Power Electronics and Instrumention Previous Question Paper

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Time: 3 hrs.
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Third Semester B.E. Degree Examination, Dt0109/.1aif.2020
Power Electronics and Instrumention
Max. Marks: 100
18EC36
Note: Answer any FIVE full questions, choosing ONE full question from each module.
Module-1
I a. Name the power semiconductor devices along their circuit symbols and maximum Ratings.
(04 Marks)
b. Explain the operation of SCR, interms of two transistor model and derive anode current and
gate currents relation. Discuss how a small gate current can trigger the device into condition.
(08 Marks)
C.
The latching current of a thyristor circuit is 60m Amp. The duration of the firing pulse is
50gsec. Given V, = 100V. R = 20Q and L = 0.5H are connected in series.
i) Derive the expression for circuit current i(t)
ii) Draw variation of current i(t) with reference to time
iii) Will the thyristor device gets turned ON?
(08 Marks)
OR
2 a. Enumerate the applications of power electronics. (04 Marks)
b. Explain the operation of self commutation by resonating load [class A] with relevant circuit
and waveforms. (08 Marks)
c. Wha.t are the gate triggering schemes? Explain with circuit diagram.' and wave forms, now
RC triggering circuit turns ON (triggers) SCRs. (08 Marks)
Module-2
3 a. Explain the control strategies used to operate choppers. (06 Marks)
b. Explain with the help of neat circuit diagram and waveformS, the operation of a single phase
half wave controlled rectifiers with resistive load. Derive an expression for the :
c. For the ideal type A [step down] chopper circuit, following conditions are given : V = 220V,
Duty cycle = 0.3, Chopping frequency f = 500Hz, R = 1Q, L = 3mH and Eb = 23 volts.
Determine the following :
i) Minimum value of output current (load)
iii Maximum value of output current (load)
iii) Average output (load) current. (06 Marks)
OR
4 a. Explain the effect of free wheeling diode used in controlled rectifiers. (04 Marks)
b. With the circuit diagram and circuit waveforms, explain the principle of operation of step-up
chopper. (08 Marks)
c. A single phase fully controlled bridge rectifier is feeding to a RL load, to obtain a regulated
DC output voltage. The RMS value of the AC voltage is 230V, at 50Hz and the firing angle
is maintained at 1113, so that the load current is 4Amp.
i) Calculate the DC average output voltage
ii) Active power and reactive power input
iii) Assuming the load resistance remains the same, determine DC average output voltage. If
a freewheeling diode is used at output with all the conditions remains same. (08 Marks)
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