code no: r41022 high voltage engineering · pdf file4 draw the marx circuit arrangement for...

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IV B.Tech I Semester Supplementary Examinations, Feb/Mar - 2015

HIGH VOLTAGE ENGINEERING

(Electrical and Electronics Engineering)

Time: 3 hours Max. Marks: 75

Answer any FIVE Questions

All Questions carry equal marks

*****

1 a) Explain how the electric stress can be estimated and controlled. [8]

b) Explain what types of improvements are done for protecting the apparatus from

surge voltages. [7]

2 Explain the process of ionization by collision in gaseous discharge. [15]

3 a) Explain thermal breakdown in solid dielectrics and its significance. [8]

b) A specimen of solid dielectric has a dielectric constant of 5.5, and tan δ = 0.002

at a frequency of 50 Hz. If it is subjected to an alternating field of 55 KV/cm,

calculate the heat generated in the specimen due to the dielectric loss. [7]

4 Draw the Marx circuit arrangement for multistage impulse generators. How is

the basic arrangement modified to accommodate the wave time control

resistances? [15]

5 a) Explain the relative advantages and disadvantages of using a series resistance

micro ammeter and a potential divider with an electrostatic voltmeter for

measuring high d.c. voltages? [10]

b) Explain the conditions to be satisfied by a potential divider to be used for

impulse work? [5]

6 a) Why are the earthing and shielding arrangements needed in the Schering bridge

measurements? [8]

b) Explain the method of balanced detection for locating partial discharges in

electrical equipment. [7]

7 a) Explain the significances of power factor tests and partial discharge tests on

bushings? [8]

b) Explain the importance of Radio interference voltage measurements for EHV

power apparatus. [7]

8 Write short notes on the following:

a) Electrostatic copying

b) Breakdown in composite dielectrics

c) Measurement of DC resistivity [15]

Code No: R41022 Set No. 1 R10

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Time : 3 hours Max. Marks: 75



*****

1 a) Explain the importance of air as an insulating material with necessary properties. [8]

b) Explain the effect of transient voltages on the power apparatus.

[7]

2 Explain Photo ionization and secondary ionization processes in gases.

[15]

3 a) Explain the different mechanisms by which breakdown occurs in solid dielectrics

in practice.

[8]

b) Explain the broad classification of insulating materials used in the electrical

equipment and support them with proper examples.

[7]

4 a) With a neat sketch, explain the working of Van de Graff generator and what are

the factors that limit the maximum voltage obtained?

[10]

b) What is a Tesla Coil and explain its significance.

[5]

5

Explain how a sphere gap can be used to measure the peak value of voltages, and

illustrate it with a neat sketch. What are the parameters and factors that influence

such voltage measurement?

[15]

6 a) Define complex permittivity, relative permittivity and loss factor with respect to

lossy dielectric.

[8]

b) Explain the methods used for calibrating the partial discharge detectors.

[7]

7 a) Explain the terms i) Withstand voltage ii) Flash over voltage iii) 50 % flash over

voltage with respect to high voltage testing.

[7]

b) Explain the phenomena of partial discharge tests on high voltage cables.

[8]

8

Write short notes on the following:

a) Electrostatic coating

b) Generation of impulse currents

c) Liquid as an insulator

[15]


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*****

1 a) Explain the electrical field stresses in an insulating material. [8]

b) Explain the Electric field in mixed dielectrics.

[7]

2

Explain Townsend’s current growth equation with proper procedure. [15]

3 a) What is a composite dielectric and further explain its properties. [8]

b) Explain how the temperature and moisture effect the breakdown strength of solid

dielectrics?

[7]

4 a) Derive the expression for ripple and regulation in voltage multiplier circuits. [8]

b) How ripples and regulation can be minimized in voltage multiplier circuits.

[7]

5

Explain the principle of operation of an electrostatic voltmeter for very high

voltages with neat construction. What are its merits and demerits for high voltage

a.c measurements?

[15]

6 a) Explain Mole’s arrangement for measuring high Dissipation factors in the low

frequency range.

[8]

b) Explain how partial discharges in an insulation system or equipment can be

detected and displayed.

[7]

7

Explain the different electrical tests done on isolators and circuit breakers. [15]

8


a) Electrostatic separator

b) Pure and commercial liquids

c) Applications of insulating materials in rotating machines

[15]


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*****

1 a) Explain the common causes of insulation failure in high voltage cables. [8]

b) Explain the electric field in a single Dielectric medium.

[7]

2 a) What are the factors that influence conduction in pure liquid dielectrics and in

commercial liquid dielectrics?

[8]

b) What is paschen’s law? and explain its importance.

[7]

3 a) How does the internal discharge phenomenon lead to break down in solid

dielectrics?

[8]

b) Explain the different insulating materials used in circuit breakers and cables.

[7]

4

Explain Cockcroft – Walton circuit for voltage multiplier with a neat schematic

diagram.

[15]

5 a) Why are capacitance voltage dividers preferred for high ac voltage

measurements?

[8]

b) What are the requirements of an oscillograph for impulse and high frequency

measurements in high voltage test circuits?

[7]

6

Explain with a neat sketch, the high voltage Schering bridge for the tanδ and

capacitance measurement of insulators or bushings.

[15]

7 a) What is the significance of impulse tests? Briefly explain the impulse testing of

insulators.

[8]

b) Explain why synthetic testing is advantageous over the other testing methods

for short circuit tests?

[7]

8


a) Electrostatic precipitator

b) Numerical methods for electric field computation.

c) Tripping and control of impulse generators

[15]


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