Model Question Paper-I with effect from 2018-19

USN 15EE73

Seventh Semester B.E.(CBCS) Examination

High Voltage Engineering
(Core subject, E&EE)
Time: 3 Hrs Max.Marks: 80

Note: Answer any FIVE full questions, choosing at least ONE question from each
module.
Module-1
1. (a) What is paschen’s low ? How do you account for the minimum voltage for break down under
a given “p x d “condition? (06 Marks)

(b) Explain clearly the electromechanical breakdown in solid dielectric . (05 Marks)

(c) Explain the Bubbles theory of breakdown in liquid. (05 Marks)

OR
2. (a) Explain the supended particle theory of breakdown in liquid. (05 Marks)

(b) Explain the Townsends current growth equation. (05 Marks)

(c) In an experiment in a certain gas it was found that the steady state current is 5.5 x10-8
A at 8 KV at a distance of 0.4 cm between the plane electrode .keeping the field constant and
reducing the distance to 0.1 cm results in a current of 5.5x10-9 A .calculate Townsends primary
ionization coefficient α. (06 Marks)
Module-2

3. (a) With neat figure explain the construction and working of Marx Generator. (08 Marks)

(b) A 100 KVA ,400v/250kv testing transformer has 8 % leakage reactance 2 % resistance on 100
kva base .a cable has to be tested at 500 kv using the above transformer as a resonant transformer
at 50 Hz. If the charging current of the cable at 500 kV is 0.4 A .find the series inductance
required .Assume 2% resistance for the inductor to be used and the connecting leads .neglect
dielectric loss of the cable .what will be the input voltage to the transformer
(08 Marks)
OR

4 (a) With a neat diagram explain the three stage cascade transformer connection to produce high
Voltage at 50 Hz. (06 Mark)
(b) With a neat sketch explain the working of 4 stage cockroft-walton DC generator. (06 Mark)

(c) A 12 stage impulse generator has 0.126 µf capacitors .the wave front & wave tail resistance are
800Ω & 5k Ω respectively .if the load capacitor is 1000pf find the front & tail times of the impulse wave
produced (04 Mark)
 Module-3
5 (a) Explain the cathode ray oscilloscope with block diagram? (05 Marks)

(b) Explain the construction of sphere gap measurement. (05 Marks)

( c) Discuss in brief the method of measuring HVAC by chubb & fortescue method (06 Marks)

OR
6 . (a) Explain the various factors that affect the spark over voltage of sphere gap. (08 Marks)

(b) With the help of neat sketch explain the construction and working principle of generating voltmeter
and .bring out advantage and disadvantage. (08 Marks)

Module-4
7. (a) Explain the different theories of charge formation in cloud.
(08 Marks)
(b) Explain the control of overvoltage due to switching and power frequency.
(08 Marks)
OR
8.(a).Explain the principles of insulation coordination on HV and EHV power system. (08 Marks)
(b) Explain the surge arrester with neat diagram. (08 Marks)

Module-5
9. (a) Explain the operation of Schering bridge for three terminal measurement . (08 Marks)
(b) Explain discharge detection using straight detector for partial discharge measurement. (08 Marks)

OR
10. (a) What are the different type of test conducted on circuit breaker and explain (05 Marks)
(b) . Write a short note on testing of cables (05 Marks)

(C) A 33 KV ,50 Hz high voltage shearing bridge used to test a sample of insulation .the various arm
of bridge at balance are :standard capacitor 500 pf; resistive branch is 800 ohm ;branch with parallel
combination of resistor and capacitor has values 318 ohm and 0.0.35 µf .determine the value of the
capacitance ,its parallel equivalent loss resistance and the power factor of test object .
(06 Marks)
*******
 15EE73

m
USN

1a
Seventh Semester B.E. Degree Examination, Dec.2018/Jan.2019
High Voltage Engineering

7:3
:3
Time: 3 hrs. Max. Marks: 80
Note: Answer any FIVE full questions, choosing one full question from each module.

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08
2. Any revealing of identification, appeal to evaluator and /or equations written eg, 42+8 = 50, will be treated as malpractice.

Module-1

-T
1 a. Explain the current growth in the presence of secondary processes. (08 Marks)

8
b. Classify the breakdown mechanism in liquids and explain any one mechanism. (08 Marks)

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01

-T
-2 OR
2 a. Classify the breakdown mechanism in solids and explain any one mechanism. (10 Marks)
Important Note : 1. On completing your answers, compulsorily draw diagonal cross lines on the remaining blank pages.

b. In an experiment in a certain gas it was found that the steady state current is 5.5 × 10-8 A at a

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12

distance of 0.4cm between the plane electrodes. Keeping the field constant and reducing the

-T
distance to 0.1cm result in a current of 5.5 × 10-9 A. Calculate Townsend’s primary
9-

ionization coefficient α. (06 Marks)

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-2

-T
Module-2
U

3 a. What are the different forms of high voltage and mention their applications. (06 Marks)
VT

b. Explain with schematic diagram the Marx circuit of multistage impulse generator
am
-T

incorporating the series and wave tail resistances within the generator. (10 Marks)
OR
29

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4 a. With a neat sketch, explain Cockcroft Walton voltage multiplier circuit and also draw the
G

-T
voltage waveforms across the first and last capacitors of the cascaded voltage multiplier
-T

0:

circuit. (10 Marks)

b. How a full impulse wave is characterized? Explain. (06 Marks)
:5

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-T
08

Module-3
-T

5 a. What are the factors influencing the spark over voltage of spheregaps? Explain any two
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factors. (08 Marks)

8
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-T

b. Determine the breakdown voltage for air gaps 2mm and 15mm lengths under uniform field
01
-T

and standard atmospheric conditions. Also determine the voltage is the atmospheric pressure
is 750mm Hg and temperature 35°C (08 Marks)
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-2
TG

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OR
2

6 a. Draw Chubb – Fortescue circuit for measurement of peak value of a.c voltages. Discuss its
-1

advantages over other methods.

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(08 Marks)
29

b. What is Rogowski coil? Explain with a neat diagram its principle of operation for
-T

measurement of high impulse currents. (08 Marks)

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Module-4
-T

7 a. Explain the different theories of charge formation in the clouds. (08 Marks)
b. What are the different methods employed for lighting protection of over head lines? Explain
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them. (08 Marks)

-T

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-T
TG
 15EE73

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1a
OR
8 a. A 3-phse single circuit transmission line is 400km long. If the line is rated for 220kV and

:3
has parameters, R = 0.1/km, L = 1.26mH/km, C = 0.009, μF/km and G = 0. Find
(i) The surge impedance and (ii) The velocity of propagation neglecting the resistance of the

7
line if a surge of 150kV and infinitely long tail strikes at one end of the line, what is the time

:3
taken for the surge to travel to the other end of the line? (08 Marks)

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08
b. Write a note on surge diverters. (08 Marks)

-T
Module-5

8
9 a. With a neat circuit diagram, explain the balanced detection method using Schering bridge.

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01
(08 Marks)

-T
b. Explain the operation of Schering bridge for three terminal measurements with Wagner’s
-2
earthling device. (08 Marks)

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12

-T
OR
10 a. A 33 kV, 50Hz, high voltage Schering bridge is used to test a sample of insulation. The
9-

various arms have the following parameters on balance. The standard capacitance 500pF, the
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-2

resistive branch 500 ohms and branch with parallel combination R and C, has 180 and
-T
0.15μF. Determine the value of capacitance of this sample, its parallel equivalent loss
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resistance, The pF and power loss under these conditions. (08 Marks)
VT

b. Explain the methods to determine the large capacitance using shunt arrangement. (08 Marks)
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*****
29

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0:
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08
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TG

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 10EE73

m
USN

3a
Seventh Semester B.E. Degree Examination, Dec.2018/Jan.2019

:5
High Voltage Engineering

8
:4
Time: 3 hrs. Max. Marks:100
Note: Answer any FIVE full questions, selecting

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08
at least TWO questions from each part.
2. Any revealing of identification, appeal to evaluator and /or equations written eg, 42+8 = 50, will be treated as malpractice.

-T
PART – A

9
1 a. Discuss the important applications of high voltages.

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01
(06 Marks)
b. Explain the need for generating high voltages in the laboratory. (06 Marks)

-T
c. What is electrostatic precipitator? Explain the operating principle of electrostatic precipitator
-2
and electrostatic painting. (08 Marks)
Important Note : 1. On completing your answers, compulsorily draw diagonal cross lines on the remaining blank pages.

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01

-T
2 a. Define townsends first and second ionization coefficient. Derive Townsend’s current in air
1-

gap considering secondary ionization process. (08 Marks)

b. State and explain Paschen’s law with necessary diagram. (06 Marks)
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-0

c. Explain breakdown mechanism in electronegative gases. (06 Marks)

-T
U

3 a. List the important properties of liquid dielectrics. (04 Marks)

VT

b. Explain cavitation and bubble mechanism of breakdown in liquid dielectrics.

am (06 Marks)
c. Explain the following breakdown mechanism in solid dielectrics:
-T

i) Avalanch breakdown
31

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ii) Thermal breakdown (10 Marks)
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-T
-T

3:

4 a. What is the necessity of cascade connection? With neat schematic diagram, explain cascade
connection of transformers for generation of high voltages ac. (06 Marks)
:5

b. What is Tesla coil? How are damped high frequency oscillations obtained from Tesla coil?
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-T

(06 Marks)
08
-T

c. A ten stage Cockroft-Walton circuit has all capacitors of 0.055 F the secondary voltage of
the supply is 125 KV at a frequency of 200 Hz. If the load current is 2 mA, determine:
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9
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i) The voltage regulation

-T
01

ii) The % ripple

-T

iii) The optimum number of stages for maximum output voltage

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-2

iv) The maximum output voltage (08 Marks)

TG

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1

PART – B
-0

5 a. Explain Marx circuit arrangement for multistage impulse generator. (07 Marks)
G

b. An 8-stage impulse generator has 0.12 F capacitors rated for 167 KV. What is the
01

-T

maximum discharge energy? If it has to produce a 1/50 sec waveform across a load
capacitor of 15000 PF, find the values of wave front and wave tail resistances. (06 Marks)
c. What is trigatron gap? Explain its function and operation.
G

(07 Marks)
-T

6 a. Explain with schematic diagrams, construction and working principle of generating

voltmeter. (08 Marks)
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b. Explain how peak value of high voltage AC is measured using Chubb and Fortescue
-T

method. (06 Marks)

c. Discuss the factors affecting the measurement of high voltage using sphere gap. (06 Marks)
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1 of 2
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TG
 10EE73

m
7 a. With the help of a neat schematic diagram describe how dielectric loss and capacitance of an
insulator can be measured using a high voltage Schering bridge. (08 Marks)

3a
b. Define partial discharge. Explain how it is measured using straight detection method.
(06 Marks)

:5
c. With the help of equivalent circuit describe resistance voltage divider for measurement of

8
fast rising voltages. (06 Marks)

:4

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08
8 a. What are the various power frequency and impulse tests done on insulator? Describe the

-T
procedure for impulse tests. (08 Marks)
b. Write short notes on the following:

9
i) High voltage tests on cables

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01
ii) Impulse current generator

-T
iii) Rogowski coils
-2 (12 Marks)

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*****
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VT

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3:
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SRI SAIRAM COLLEGE OF ENGINEERING
SRI SAIRAM COLLEGE OF ENGINEERING
 USN lOEE73

Seventh Semester B.E. Degree Examination, Dec.2015/Jan.2016

High Voltage Engineering
Time: 3 hrs. Max. Marks: 100
Note: Answer FIVE full questions, selecting
at least TWO questions from each part.
PART-A
1 a. Explain the need for generation of very high voltages in the laboratory. (06 Marks)
b. What are the advantages of transmitting electrical power at high voltages? (06 Marks)
c. Describe the various components of electrostatic precipitator (ESP) and its principle of
working. (08 Marks)

2 a. Write the preferred properties of gaseous dielectric for high voltage applications. Give any
three examples of gaseous dielectric. (06 Marks)
b. Explain the process of ionization by collision and hence obtain the Townsend's current
growth equation. (08 Marks)
c. In an experiment in a certain gas it was found that the steady state current is 5.5 x 10-8 A at
8 KV at a distance of 0.4 ern between the plane electrodes. Keeping the field constant and
reducing the distance to 0.1 em results in a current of 5.5 x 10-9 A. Calculate Townsend's
primary ionization coefficient o: (06 Marks)

3 a. State and explain Paschen's law. (06 Marks)

b. Explain the following breakdown mechanism in solid:
i) Streamer breakdown. ii) Electromechanical breakdown. (14 Marks)

4 a. Explain with a neat figure, how cascade transformers generate high ac voltages. (08 Marks)
b. Explain the principle of operation of a resonant transformer. (06 Marks)
c. A Cockcroft- Walton type voltage multiplier circuit has eight stages with capacitances all
equal to 0.05 IlF. The supply transformer secondary voltage is 125 KV at a frequency of
150 Hz. [fthe load current to be supplied is 5 mA. Find
i) The voltage drop and regulation.
ii) The optimum number of stages for minimum voltage drop. (06 Marks)

PART-B

5 a. Explain the Marx circuit arrangement for multistage impulse generator. (08 Marks)
b. Explain the operation of a trigatron gap. (06 Marks)
c. A 12-stage impulse generator has 0.126 IlF capacitors. The wavefront and wave tail
resistances connected are 800 ohms and 5000 ohms respectively. If the load capacitor is
1000 pF, find the front and tail lines of the impulse wave produced. (06 Marks)

6 a. With a schematic diagram, explain the principle of operation of a generating voltmeter.

(08 Marks)
b. Explain the Chubb and Forteswe method for measurement of peak value of an ac voltage
waveform. (06 Marks)
c. Explain the principle of operation of an electrostatic voltmeter for measurement of very high
d.)
de and ac voltages. (06 Marks)
o
z
c: 7 a. Explain the method of balanced detection for locating partial discharges in electrical
~ equipment. (10 Marks)
o
0..
E b. Explain how capacitance and tan 0 can be measured using a Schering bridge. (10 Marks)

8 a. Defme the following terminologies: i) Disruptive discharge voltage.

ii) Fifty percent Flashover voltage. iii) Impulse voltages. (06 Marks)
b. Write brief notes on: i) Testing on insulators. ii) Testing of cables. (14 Marks)
*****
SRI SAIRAM COLLEGE OF ENGINEERING
SRI SAIRAM COLLEGE OF ENGINEERING
SRI SAIRAM COLLEGE OF ENGINEERING
 USN l0EE73
&'\,,*.,. -l

{.'} ,, .
Seventh Semester B.E. xamination, June/July 2017
High Voltage Engineering
Time: 3 hrs. Max. Marks:100
Note: Answer any FIVE full questions, selecting
d
atleust TWO questions from each part.
o
!v

PART _ A

I a.
c6

o Explain the need for generation of high voltages in the laboratory. Mention its applications.
o (05 Marks)
3o b. What are the advantages of transmitting electrical power at high voltage? Mention the
.:' industrial applications of high voltage. (05 Marks)

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c. Describe the working principle of electrostatic precipitator and electrostatic painting.
-o (10 Marks)
bol
trca
.E c\
Hbo
tso
oE
2 a. Define Townsend's first and second ionization co-effrcient. Derive an expression for the
do
current growth in a gas discharge due to secondary mechanism. (10 Marks)
b. What are electronegative gases? Why is the breakdown strength of these gases higher
t,n compared to that of other gases? (05 Marks)
a:i c. A steady current of 600pA flows through the plane electrode separated by a distance of
o() 0.5cm, when a voltage of 10KV is applied. Determine the Townsends's first ionization co-
(!0
efficient if a current of 60ptA flows when the distance of separation is reduced to 0.lcm and
botr
the field is kept constant at the previous value. (05 N{arks)
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64

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a-d

='o
6; a. What is thermal breakdown in "solid dielectrics" and how it is practically morc significant
than other mechanisms? (06 Marks)
p.a
o'.
b. Explain briefly suspended particle theory of breakdown in liquid dielectrics. (06 Marks)
o; c. The following observations were made in an experiment for determination of dielectric
o=
ao
strength of transformer oil. Determine the power law equation :
4lE
ro Gap spacing (mm) 4 6 8 10
6.v
>,
ooe
!: Breakdown voltaee (KV) 88 135 165 2t2
iEo (08 Nllarks)
olE
p.ii
tr>
=o
eL
a-
tra 4 a. Describe thc working of a 3-stagc Cockcroft-Walton's cascadcd DC-gencrator. I)crivc thc
\J<
-i 6i cxprcssions for ripplc and output voltagc. (Ott Nlarks)
o b. With thc help of a ncat skctch, explain thc construction and working prinCiplc of cascading
z of transformers of three units, for producing very high'oAC" voltage. (06 Marks)

c. A ten-stage Cockcroft-Walton circuit has all capacitors of 0.06ptF. The secondary voltage of
o
o. the supply transformer is 100 KV at a fiequency of 150H2. If the load current is 1 mA
determine i) voltage regulation ii) the ripple iii) the optimum number of stages for maximum
(06 Marks)
output voltage.

1 of2
 10EE73

PART _ B
5a. Describe the method of generation of impulse currents. Derive the
related mathematical
formulae. How are capacitors arranged in such circuits?
(07 Marks)
b. Describe the Tesla coil with its equivalent circuit and output wavefbrms.
Give the
application ol'Tcsla coil. Show thar v2 = u,.f- with usual notations. (07 Marks)
V c:
c' An impulse generator has eight stages with each capacitor rated for 0.16 micro-farad
and
125 KV the load capacitor available is 1000 Pico-faiad. Find the series
resistance and the
damping resistance needed to produce 1.2150 micro-second impulse
wave. What is the
maximum output voltage of the generator if the charging voltage is tZO
fVZ (06 Marks)

6a. Discuss how resistance potential dividers are used to mesure high
voltages. Explain the
effect of stray capacitances on such measurements and also suggest
suitable remedial
measure.
(10 Marks)
b. Describe with a neat sketch the working of a generating voltmeter
used to measure hieh
lg DC
vo ltages.
(06 Marks)
L. An absolute electrostatic voltmeter has a moveable circular plate gcms
in diameter. If the
distance between the plates during a measurement is 4mm and
the applied voltage is I KV.
calculate the force on the plate fAssume medium as having E.: 1]. (04 Marks)

7a. What are partial discharges? Explain with a neat diagram the principle
of pulse current
technique.-
measurement of partial discharges by straight detection
e7 Marks)
b. Describe the Schering bridge method of determining the capacitance
dielectric specimen. Derive the relevant - r and loss angle of a
formulae. (07 Marks)
c. A 33KV, 50Hz high Schering bridge is used to test a sample of insulation. The
Yo-Iug:
various arms have the following parameters on balance. The
standard capacitance 500pF the
resistive branch 800ohm and branch with parallel combination
of resistance and capacitance
has valued 180 ohms and 0.l5prF. Determine the value of
the capacitance of this sample its
parallel equivalent loss resistance the power factor and the power
loss under these test
conditions. (06 Marks)

8a. With a neat diagram, explain the impulse testing of transforrcers. How
are the faults detected
and located?
b. Mention the different power frequency tests that are carried out practicp
Explain the procedure of conducting each ur
in on HV tf:#rilXl
of these Ltrsrs'
trrE.tr tests.
\ 'i
Exptaln any one method of testing Jables.
[3:ffi113

****r<

2 of2
 I
USN 10EE73

Seventh Semester B.E. ination, Dec.2016 I Jan.2|l7

High ineering
Time:3 hrs.
Max. Marks:100
Note: Answer FIVEfuU questions, selecting
at least TWO qaestionsfrom each part
PART _ A
1 a' What are the advantages and timitations of transmitting power at high voltages? Explain
D
O
brieflv. --
( lo Marks)
o
!
c.
b' With; neat sketch explain the principle and working of electrostatic painting
and coating.
(10 Marks)
a
2 a. Derive the criterion for breakdown in electronegative gases and discuss
the importance of
=a) e lectro-negative gases.
o (10 Marks)
b. Explain the streamer theory of breakdown in air at atmospheric pressure.
l.o (10 Marks)
3a. Explain the various theories that explain the breakdown in commercial
liquid dielectrics.
=^.
b. Briefly explain electromechanical break down and thermal breakdown in solid
_3
aq materials. i[ffirl?
-i (10 Marks)
4a. Explain the schemes for cascade connection of transformers for producing
voltages. ' Qvery high a.c
(o6Marks)
b. What is tesla coil? How are the damped high frequency oscillations
obtained from of tesla
a>
?t coil? (06 Marks)
c. A cockraft-Waltons type voltage multiplier has eight stages with capacitance
all are equal
to 0.'05pF. The supply transformer secondary voltge is tzstV at a ilequency
!,
the load current to be supplied is 5mA, find: i) the
of l50Hz, if
fercentage ripple ii) RegLriatiolo,
50a *r*,
=.
)7
f,a. WithneatsketchexplaintheMarx.ffiementformuItistageimpulsegenerator.
z,a
b. w!1 is trigatron gap? Explain its tunction and operation.
c. A 12 stage impulse generator has capacito..u.h rated at 0.3pF, [:ffi:[:]
l50kv. The capacitance of
test specimen is 400pF. Determine the wave front and wave
tail resistances to produces a
-= 1.2/50pF. (04 Marks)
i=
a, t: 6a. With neat sketch explain principle, working and construction of electrostatic
voltmeter.
=!
LO
b. Briefly explain the factors affecting measurement of voltages using
.'; sphere gap. [}:ffi13
c0_ c. A resistance divider of 1400kv (impulse) has a high ,Jltug"
arm of l6ko and L.v arm
consisting of 16 members of 250Q, 2watt resistors ii parallei.
The divider is connected to a
F> CRO through a cable of surge impedances 75Q and is terminated
oI at the other end though
75Q resistor. calculate the exact divider ratio.
o< 7a. Explain method of measurement of capacitance and tan 6 using
(04 Marks)
H.V Schering bridge.

Z
b' Explain the transformer ratio arm bridge for audio frequency range
measurements. [:ffiili
c' Discuss the method of discharge dJtection using straigirt defectors
for locating partial
E discharges in electrical equipment.
a- (06 Marks)
E a' What are the different power frequencies and impulse tests done
on insulators? Mention the
procedure for testing.
(10 Marks)
b' E'xplain the method of impulse testing of high voltage. Transformers.
what is the procedure
adopted for locating the failure?
(r0 Marks)
*{<*x*