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Visvesvaraya Technological University (VTU) 2007 B.E Electrical and Electronics Engineering 7th SEM HIGH VOLTAGE ENGINEERING - Question Paper

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Seventh Semester B.E. Degree Examination, May 2007 Electrical and Electronics Engineering

High Voltage Engineering Time: 3 hrs.]    [Max. Marks: 100

Note : Answer any FIVE full questions.

\. a, List the advantages of HVDC bulk power transmission over HVAC bulk power transmission.    (04 Marks)

b.    Discuss the need of generating high voltages in a laboratory.    (03 Marks)

c.    Mention the important applications of high voltage.    (05 Marks)

d.    Write the preferred properties of a gaseous dielectric for high voltage applications. Give any four examples of gaseous dielectric.    (08 Marks)

I a. Write about CORONA discharges in non-uniform fields.    (10 Marks)

b.    Briefly write about Paschens law.    (05 Marks)

c.    Explain the time lags for breakdown with a diagram for step function voltage pulse.

(05 Marks)

t a. Explain the suspended particle theory of breakdown in commercial liquids. (05 Marks)

b. Explain the 3 stage cascade connection of transformers for generation of HVAC with a schematic diagram.    (15 Marks)

a. Describe the Tesla coil with its equivalent circuit and output waveform. Give the

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application of the Tesla coil. Show that V2 = V, /r) with usual notations.

(10 Marks)

b. A ten stage Cockraft-Watton generator circuit has all capacitors of 0.06 jiF. The secondary voltage of the supply transformer is 100 kV peak at a frequency of 150 Hz. If the load current is 1 mA, determine

i)    Voltage regulation

ii)    Percentage ripple

iii)    The optimum number of stages for maximum output voltage

iv)    Maximum output voltage.    (10 Marks)

5 a. Draw the lightning impulse voltage and both the components in the same graph of V = V0(e"at -e-pi) and comment on a and p.    (05 Marks)

b.    Draw the exact equivalent circuit of an impulse generator, single stage. (03 Marks)

c.    Discuss the components of a multistage impulse generator of less than 1 MV.

(12 Marks)

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6 a. Mention the advantages and limitations of generating voltmeter.    (06 Marks)

b.    Explain the series resistance microammeter used in HVDC measurement. Write the limitations of the method.    (10 Marks)

c.    A generating voltmeter has to be designed so that it can have a range from 20 kV to 200 kV dc. If the indicating meter reads a minimum current of 2 A and maximum current of 25 (iA, what should be the capacitance of the generating voltmeter be? The driving motor has a synchronous speed of 1500 rpm.    (04 Marks)

7    a. Discuss the various factors that affect the spark over voltage of a sphere gap.

(12 Marks)

b. Discuss the diy and wet flashover tests on an insulator.    (08 Marks)

8    a. Obtain an expression for the dielectric power loss P interms of voltage V

capacitance C, frequency f and loss angle S.    (04 Marks)

b.    A 20 kV, 50 Hz schering bridge has a standard capacitance of 106 F. In a test on a bakeiite sheet, balance was obtained with a capacitance of 0.35 fxF in parallel with a non-inductive resistance of 318 Q, the non-inductive resistance in the remaining arm of the bridge being 130 Q. Determine the equivalent

i)    Series resistance and capacitance and the power factor of the test specimen.

ii)    Parallel resistance and capacitance and the power factor of test specimen.

(12 Marks)

c.    Draw the basic circuit for measuring narrow band partial discharge.    (04 Marks)

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