New project report

UNDERGROUND CABLE FAULT DETECTION
UNDER ESTEEM GUIDANCE
BY
Er. Vishal mohindra
Electrical & Electronic Engineering
SUBMITTED BY :
ABHILASH TIWARY 1152724
AJITESH KR. TIWARI 1152728
AMAN KR. SINGH 1152730
MEGHA KRITI 1152747

PREFACE
Life is a long journey where in each of us
crosses number of milestones. Every stoppage teaches us a
lot. I am being the student of engineering. Learnt a plethora
of things and was being bombarded with lots of learning,
events projects and seminars. The three year half time
programme of engineering course helped in lots of
learning.Such has been the presentations and projects which
enhanced our learning by adding on to our world of
knowledge
Project is one the part to enhance our learning
and technical skills. it was alife time experience for which i
thank to HOD sir and my dear Sir Vishal of “ EEE” branch ,
and administration of the college ( Swami Parmanand College
of Engineering and Technology ) .
Abhilash Tiwary
Ajitesh Tiwari
Aman kr. Singh
Megha Kriti
EEE / 7thSem.

Acknwoledgement
Project as learning is an essential part of individuals
future carrier. The “ Teach while you learn” attitude is a very
practical touch in the complete tenure of personal life.
Project bridges the gap between the learnt and the
happening.
We would like to put forth our regardful thanks to all
those who have and are making a remarkable attempt in
guiding us and making us learn the most during a short
period of our project.
We also put our special thanks to our HOD Er. A.K
Chopra who cared to give out an ample amount of time to
our regardless of being extremely busy in their work.
Ahead we put our special regards to Er. Vishal
Mohindra at SPCET. Who has always been so supporting ,
loving and always ready to help.
Thankful,
Abhilash Tiwary / 1152724
Ajitesh Tiwari / 1152728
Aman kr. Singh / 1152730
Megha Kriti / 1152747

Abstract
In this paper, the analisys of underground
power cable is performed using timer & counter and op
amp’s with the objective of detecting fault and the
average life of the cable. Three types of cables are used
in this project (red,yellow &blue respectively). Various
windowing techniques are applied to the experimental
data to eliminate any interface . This analysis reveales
differences in the frequency responce of the three
different types of cable and eventually can be used as
measure for fault detection.
Preliminary results reveal the differences
in the frequency responce. Accordingly this type of
method can be effectively used as low cost and vaible
solutions to identify and detect the fault in underground
cables.

Content:-
1 Introduction 1
2 Cable types 2
2.1 Cable Faults 4
3. Our project working model 5
3.1 Working 5
3.2 Equipments used 6
4 Cable Fault Location Procedure 7
5 Cable Fault Prelocation 7
5.1 Overview 9
6 Cable Route Tracing 10
6.1 Signal detection 11
6.2 Selection of Audio Frequency 13
7 Cable Fault Pin-Pointing 14
7.1 Pin-pointing of cable faults in pipe 17
arrangements
8 Cable identification 19
9 Cable Fault location in High Voltage 24
cables e.g. 115kV
10 Conclusion 28

INTRODUCTION:-
Power supply networks are growing continuously and
their reliability is getting more important than ever.The
complexity of the whole network comprises numerous
components that can fail and interrupt the power supply
for the end user. For most of the worldwide operated low
voltage and medium voltage distribution lines
underground cables have been used for many decades.
During the last years, also high voltage lines have been
developed to cables. To reduce the sensitivity of
distribution networks to environmental influences
underground high voltage cables are used more and
more. They are not influenced by weather conditions,
heavy rain, storm, snow and ice as well as pollution.
Even the technology used in cable factories is improving
steadily certain influences may cause cables to fail
during operation or test. Cables have been in use for
over 80years. The number of different designs as well
as the variety of cable types and accessories used in a
cable network is large. The ability to determine all kind
of different faults with widely different fault
characteristics is turning on the suitable measuring
equipment as well as on the operator’s skills. The right
combination enables to reduce the expensive time that
is running during a cable outage to a minimum.

Cable types :-
Cable types are basically defined as low-, medium- and
high voltage cables. The most common designs of
medium- and high voltage cables are shown below.
According to the cable type, different requirements to
cable testing, cable fault location as well as
maintenance strategy are defined. Three-conductor
cables have been in use in the lower voltage ranges.
The tendency of the last years show the shifting to
single-core systems as they are lower in price, lower in
weight and cheaper in regards to repair costs.
Furthermore oil impregnated or oil filled cables are used
less and less, as the environmental sustainability can
not be guaranteed. Especially in industrialized countries,
these cable types have been replaced and are no more
installed. On the other hand a high demand for
maintenance of those cables is given as the installed oil-insulated
networks do show up a lifetime of 50 years
and more. Today mainly XLPE insulated cables are
used. The improvement of the XLPE insulation material
combined with the modern design of the cable enable to
manufacture cables even for the extra high voltage level.

Single core, XLPE insulated medium voltage cables 6kV up to 36kV
3-core EPR, incl. 3-core XLPE 11kV 1-core XLPE 115kV
Data line, radial type
All kind of low-, medium- and high voltage cables are
delivered and stored on cable drums. The maximum
available cable length is mainly specified by the
diameter (1-core ore 3-core cable) and the voltage level
of the cable.
Overview of Pulse Velocity v/2 for different cable types: Cable Type Remark Average
Propagation Time Velocity:-

CABLE TYPES REMARKS Average Propagation
Time Velocity v/2 [m/μs]
PLIC Impregnated paper
Dry paper 75-85
108-132
XLPE 78-87
PE Approx. 100
PVC 76-87
EPR 68-83
Propagation Velocity V/2 For Different Types Of Cables
Cable Faults:-
A cable fault can be defined as any defect,
inconsistency, weakness or non-homogeneity that
affects the performance of a cable. All faults in
underground cables are different and the success of a
cable fault location depends to a great extent on
practical aspects and the experience of the operator. To
accomplish this, it is necessary to have personnel
trained to test the cables successfully and to reduce
their malfunctions. The development of refined
techniques in the field of high voltage testing and
diagnosis, in addition to the variety of methods for
locating power cable faults, makes it imperative that
qualified and experienced engineers and service
operators be employed. In addition, it is important for the
trained personnel to be thoroughly familiar with the
fundamentals of power cable design, operation and the
maintenance. The purpose of this document is therefore
to be an additional support to the user manuals of the
different equipments concerning all aspects of the fault

location in order to make up a volume of reference
which will hopefully be useful for operators and field
engineers. The technology used and the experience that
can be shared is based on the BAUR expertise collected
over more than 60 years.
OUR PROJECT WORKING MODEL :
WORKING :-
Power is stepped down by a step down
transformer and the output is conneted with 12v
relay now ac is converted to dc power by full wave
rectifier and the dc power is smoothen by the use
of a power filter. Power is filtered and the supply is
passed to timer and counter chip ic. We have used
6 led’s mainly 3 green and 3 red. These led’s are

connected to op amps, 3 pipe lines are used
representing the three cables red yellow and blue
and a switch is connected to trip the supply which
symbolise short circuit
When supply is given all the 3 red led
glow one by one with the help of counter ic. The 3
green led keeps glowing until the power is
interrupted. In case of short circuit in any cable
there is interruption in power in the cable with fault
this interruption is read by the op amp as a result
the green led blows off and the led glows for the
fault carrying cable and finally we find which cable
is faulty.
EQUIPMENTS USED:-
1. Step down transformer
2. Relay
3. Full wave rectifier
4. Timer and counter
5. Diode & Resistor
6. Led’s & IC’s
7. Plastic pipe for UG cables
8. Power filter
9. SPST switches
Cable Fault Location Procedure:-

Cable fault location as such has to be considered as a
procedure covering the following steps and not being
only one single step.

Fault Indication.
Disconnecting and Earthing.
Fault Analyses and Insulation Test.
Cable Fault Pre-location.
Cable Route Tracing.
Precise Cable Fault Location (Pinpointing).
Cable Identification.
Fault Marking and Repair.
Cable Testing and Diagnosis.
Switch on Power.
Cable Fault Types:-
1. Fault between core-core and/or core - sheath:-

Low resistive faults (R < 100 - 200 Ω)
o short circuit
High resistive faults (R > 100 - 200 Ω)
o Intermittent faults (breakdown or flash faults)
o Interruption (cable cuts)
2. Defects on the outer protective shield (PVC, PE):-

Cable sheath faults-

Most of the cable faults occur between cable
core and sheath. Furthermore, very frequently blown up
open joint connections or vaporized cable sections can
cause the core to be interrupted. To figure out whether
such a fault is present, the loop resistance test shall be
done. By using a simple multi-meter, the continuity in
general can be measured. The easiest way to perform
this test is to keep the circuit breaker at the far end
grounded. Corrosion of the cable sheath may increase
the line resistance. This is already an indication for
possible part reflections in the TDR result. As a rough
guidance, a line resistance of 0.7 Ohm/km can be
considered as normal condition. In dependence of the
fault characteristic, the suitable cable fault pre-location
and pinpointing methods need to be selected by the
operator.
Cable Fault Pre-location:-
 Overview:-
1.Low voltage method
 Impulse Reflection Method TDR for:
o Low resistive faults.
o Determination of the cable length.
o Localisation of cable interruptions.
o Detection of joints along the cable.
2.High voltage methods

 Multiple Impulse Method SIM/MIM.
 Impulse Current Method ICM.
 Decay Method.
o High resistive faults.
o Breakdown / intermittent faults.
3.Bridge method
o Low and high resistive cable faults.
o Low and high resistive cable sheath faults.
o Core to core faults in unshielded cables.
o faults in pilot cables and signal lines
o faults in unshielded cores to ground
Cable Route Tracing:-
Cable route tracing is applied to determine the exact
route of the underground cable. Depending on the
availability of cable laying maps, route tracing is of very
high importance as prior step to cable fault pin-pointing.
Route tracing can be performed either active or
passive. At live cables the harmonics of the mains
frequency can be heard as ‘mains hum’. However, all
grounded conductors, water pipes and parallel running
cables which are connected to the 50Hz mains system
also have this ‘mains hum’. To avoid confusion, it is
recommendable to disconnect the conductor and feed
the cable with an audio frequency to perform an active
cable route tracing.

Signal detection:-
Above the ground, the electromagnetic signal
transmitted via the audio frequency generator can be
measured along the cable trace. Depending on the pick-up
coil direction, the signal can be coupled differently.
1.Maximum method
The detecting coil is horizontal to path of line. Maximum
audio signal is directly above the line. The maximum
method is used for cable routing as well for terrain
examination.
2.Minimum method
The detecting coil is vertical to the path of the line. The
minimum audio frequency signal is directly above line.
The minimum method is used for depth determination
measurement as well for exact cable tracing and
pinpointing.
Depth Measurement according to the Minimum
Method
For the depth determination with a simple surge coil, the
characteristic of an isosceles triangle
- first determine the exact position of the cable.
- subsequently, the coil has to be rotated to 45°
- The minimum audio-frequency signal is heard at the
depth “d” at a corresponding distance from the path of
the cable. Instruments designed specifically for route
tracing are operated with two integrated antenna
covering the functions of minimum and maximum
method as well as depth determination.

Terrain examination
Another application where the cable
locating set can be applied is the so called terrain
examination. The signal is injected into the soil via two
earth spikes. In case there is any metallic conductor, the
signal will return along the conductor. The
electromagnetic signal along the conductor can be
detected and the conductor can be found. To examine a
particular area for existing cable/pipes system, the follow
procedure is recommended:
- dividing the area into squares of approx. 25x25 m
- the audio frequency generator has to be set up in the
centre of the cable run
- the ground rods need to be set into the ground to the
left and right of the generator at approx. 12 to 15m
- the output power of the generator is kept low
If there is a metallic conductor within the set out area, it
will propagate a magnetic field in its vicinity. The
magnetic field has in most cases the shape of a single
sided maximum; e.g. with a steep edge to the audio
frequency waveform.
Selection of Audio Frequency:-
Every audio frequency generator is offering the
possibility to select different signal output frequencies.

The different characteristic of the frequencies is the
induction effect. The induction of a signal into a
neighbouring metal conductor is increasing with the
frequency.
- The higher the frequency, the higher the inductive
coupling effect
Basically the frequency has to be selected as following:
Low frequency e.g. 2kHz:
- for galvanic signal coupling
- the signal induction to other cables and pipes can be
minimized
High frequency e.g. 10kHz:
- for inductive signal coupling with current clamp or
frame antenna
- high inductive coupling effect is required to couple the
signal into the cable
Cable Fault Pin-Pointing:-
 Acoustic Fault Location
1. Acoustic Fault Location in direct buried cables
For pin-pointing of high resistive and
intermittent faults in buried cables the acoustic method
is used to pin-point the exact fault location. As signal
source, a surge generator is used in repetitive pulsing
mode. High energy pulses which are released by a

surge generator (SSG) force a voltage pulse to travel
along the cable. At the fault the flashover happens. This
causes a high acoustic signal that is locally audible.
Depending on the pulse energy, the intensity of the
acoustic signal varies. These noises are detected on
the ground surface by means of a ground microphone,
receiver and headphone. The closer the distance from
the fault to the microphone, the higher is the amplitude
of flashover noise. At the fault position the highest level
of flashover noise can be detected.

The acoustic fault location set comprising the
receiver UL30 and the ground microphone BM 30 offers
the special feature of digital propagation time – distance
measurement.
Firstly, the ground microphone is measuring
the electromagnetic signal that can be recorded all
along the cable where the HV impulse is travelling

before finally flashing over at the faulty position. As this
signal is available all along the cable trace towards
the fault, it can further be used to make sure that the
“cable trace” is followed. The maximum signal confirms
to be directly above the cable.
Secondly the ground microphone will receive
the flashover noise next to the fault on the ground
surface as soon as the very close area around the fault
is reached.
Schematic Connection And Shape Of
Acoustic Signal – Acoustic Fault Location
Cable Fault,1-Core 11kv XLPE Cable

Therefore, every flashover activates two trigger
situations. – magnetic trigger and acoustic trigger
The two signals are of different propagation velocity.
Further the distance to the fault influences the difference
in trigger of acoustic trigger compared to the trigger of
the electromagnetic signal. As soon as the magnetic
trigger is reacting on the bypassing HV impulse in the
cable underneath, a timer is started. When the ground
microphone receives the delayed acoustic signal, the
measuring cycle is stopped. The receiver UL
automatically indicates the measured time distance
(propagation time) to the fault via a digital meter
indication. According to the meter indication, the faulty
position, where the distance indication is lowest, can be
found. By means of the audible acoustic signal the final
exact location of the cable fault can be determined. This
special feature increases the performance compared to
convenient acoustic pick-up sets, as the magnetic
indication offers an integrated tracing feature.
2. Pin-Pointing Of Cable Faults In Pipe
Arrangements
When cables are laid in pipes the acoustic signal is no
more audible right above the cable fault. The acoustic
signal in that case is travelling through the air in the pipe
and therefore only audible at both ends of the pipe or
on the manhole covers.
By means of the previously carried out cable
fault pre-location, the section of pipe can be determined.
Up to today, the final step to determine the exact fault
position in the pipe was very difficult or by most pick-up

sets impossible. The latest model of pick-up set UL/BM
therefore uses a special feature to determine the exact
fault position also in manhole
arrangements.
Manhole Arrangement, Cable Laid
In Pvc Pipe, Acoustic Signal Only Audible
On Manhole Cover
Acoustic Fault Location at Manholes
For this method, no additional instrument is
requested. Every latest UL receiver offers the mode of
pinpointing in manhole arrangement.
In a first step, the ground microphone is
placed on the first manhole cover, where the acoustic
signal and the magnetic signal are shown up in a certain
propagation time value. By confirming the signal, this
value is stored in the receiver.
In a second step, the ground microphone is
placed on the second manhole cover. Also at this
location, the ground microphone can pick-up an acoustic
signal and the magnetic signal that is showing up in a

second propagation time value. By entering the distance
between the manholes, via the propagation time ratio
over the distance, the direct distance to the fault in
the pipe is indicated.
UL30 Display, Manhole Mode,
Display Of Two Propagation Time Values Used
For Distance Calculation
3. Fault pin-pointing of low resistive
cable faults
Cable faults that are showing up in a solid grounded
condition do not enable to create a flashover at the
faulty point by means of a surge generator. Therefore
also no acoustic signal is audible and the cable fault
pinpointing according to the acoustic fault location is not
possible. This condition is mainly resulting from a
completely burnt cable fault that is furthermore also
low resistive to the surrounding soil. These kinds of
cable faults can be pinpointed by means of the step
voltage method explained below. Faults in low voltage
cables as well as pilot cables (signal lines) are often
difficult to be pin-pointed, because the maximum
voltage that may be applied to these cables does not
enable to force sufficient surge energy to create a
strong flashover that can be pinpointed by means of the
acoustic method. As these cables are mainly

unshielded, the fault in most cases also appears
towards the surrounding soil. Also here, the step
voltage method is the suitable pin-pointing method.
Another difficult fault condition to pin-point in low voltage
cables is if the fault is not related to ground and
therefore only showing up between two cores. For
these conditions, the Twist Method enables successful
pointing out the fault. The 3rd fault type showing similar
conditions is the cable sheath fault. A fault in the outer
protective PVC insulation of a XLPE cable can not be
located via the acoustic method, as no defined
potential point, where the flashover can take place, is
given. Here, also the step voltage method enables the
localisation. This method also enables to locate several
sheath fault locations along a cable.
 Step voltage method Pinpointing of:-
- Any earth contacting low resistive faults
- Cable Sheath Fault
As a signal source, a high voltage impulse sequence or
impulse block sequence is sent into the cable under test.
The HV pulse is discharged via the resistive fault to
the surrounding soil without a flashover. The voltage
drop into the soil at the fault location results in a voltage
funnel, which can be measured by means of the step
voltage method. By using two earth probes, the voltage
distribution field is indicated. The multifunctional receiver
UL indicates the positive or negative voltage (left or right
side from the fault location) via a bar graph as well as an
acoustic tone. As soon as the earth sticks are placed

symmetrical above the fault, the resulting voltage is
zero and the fault position is determined.
Useable HV signal sources:
- SSG / STG surge generators function
Useable receivers:-
- UL of latest version in combination with cable sheath
fault location accessories
- KMF 1 in combination with cable sheath fault location
accessories In case of multiple sheath faults, e.g. 3
faults, all faults can be located as explained above
during one passage over the cable route. This requires
appropriate practice and one should know that the step
voltage shows several passing through zero
position that might irritate (5 passing through zero).
 Twist method
The twist method can be applied for pin-pointing of low
resistive faults in twisted cables. In this method, the
effect that the cores are longitudinally turned-in is used.
The basic signal used is a high frequency audio signal
causing equivalent signals like used for cable route
tracing. Differing to route tracing, where the signal is
sent through a healthy core, for this method the signal
is forced over the fault. Therefore the application is
depending on the fault resistance. Higher resistive faults
request a very powerful audio frequency generator.
The audio frequency signal is passing back and forth in
the same cable up to the fault where the signal faces the
return point. Due to the twist, what means the steadily

change of geometrical position of the cores in the cable,
the maxima and minima of signal resulting can be
followed on the surface. The twist length in the cable is
depending on the type of cable but is roughly 1meter.
According to this, the point where the signal ends can
be determined as the cable fault.
Cable identification:-
Cable identification is the most critical and safety
related sequence during all the procedure of cable fault
location. The correct identification of a cable out of a
bundle of cables, where most of them can be cables in
service, has to be carried out not only carefully, but also
by means of an instrument widely eliminating the
possibility of human error or misinterpretation.
Additionally, it is highly recommended to use cable
cutters according to EN 50340 and / or a cable shooting
devices. The local safety and accident precaution
instructions are always applicable, and mandatory. The
BAUR cable identification system KSG 100 was
designed to fulfil these most important safety
aspects.
Principle of operation of the KSG 100
The transmitter of the KSG contains a capacitor that is
charged and then discharged into the target cable.
During this process the test sample must be connected
in such a way that current can flow through it. The
flexible coupler is used to couple the current pulse at the
target cable. The direction of flow of the current

pulse and its amplitude are indicated on the display of
the receiver. The amplitude of the current pulse is
dependent on the loop resistance. To be able to clearly
determine the direction of current flow, the positive
output is colour-coded red and the flexible coupler
marked with an arrow. The current difference that is
calibrated can be measured very accurately. As there
are no relevant losses, the displayed current is nearly
equivalent to the calibration signal.
Pulse Signal Flow Scheme
Field Application Of Cable Identification
Depending on the cable arrangement, the signal loop is
changing. The application of cable identification can be

carried out on any cable arrangement. Before the
actual process of cable identification begins, the
instrument is performing a self calibration whereby the
target cable is analysed. During this sequence the
receiver analyses the test sample for interference and
the amplitude of the pulse. As the signal amplitude is
dependent on the loop resistance, the receiver
automatically sets the internal amplifier to 100% output
amplitude. In this way it is ensured that not only the
direction in which the current pulse flows, but also the
amplitude is used for the evaluation. In the final
calibration step, the transmitter is synchronised to the
receiver using a defined cycle time. This
synchronisation is performed because during the
subsequent cable identification the receiver will only
evaluate the pulses during a period of 100 ms (Phase).
This impulse is not affected by any magnetic field, as a
high current impulse is used. Finally there is only one
single core fulfilling all the calibrated values with positive
direction on site, independent how many cables are
faced in the tray or manhole. These relevant signal
characteristics mentioned above can be mentioned
shortly as
ATP - signal acquisition:
A … Amplitude and direction of signal;
T … Time interval of released signals synchronized with
transmitter;
P … Phase: same signal direction in the correct cable,
all neighbouring cables are used as return wire or do not
carry any signal.
The BAUR KSG 100 is the only instrument available
providing such high safety certainty. The fully automatic

setting adjustment and calibration minimizes the risk of
operating error. The signal coupling can be done on
either dead cables as well as on live cables: On dead
cables, the direct coupling can be performed to the core
of the cable. In such arrangements, where the core is
used as the conductor, there is no limitation in regards
to voltage rating or diameter of the cable. The flexible
Rogowski coil can loop a diameter of 200mm and
therefore is applicable even on high voltage cables.
Full cable not accessible,
application of Expert mode enables
the safe cable identification.
For the application on live cables, it is independent
whether the load rating is high or low or whether the line
voltage is low voltage or even high voltage. As the
coupling in that case is done via a current clamp, the
restriction is given by the diameter of the clamp only.
KSG 100 Expert Mode
Certain substation arrangements in
combination with 3-core cables do not allow an access
to the full diameter of the cable in the substation. The

calibration as explained above can not be done similar.
The Rogowski coil has to be connected around the core
without the sheath involved. Therefore the calibration
signal is not equal to the signal that is measured on the
whole cable diameter on site. For these arrangements
the KSG 100 is equipped with an Expert mode that
enables to adjust the gain of the received signal. The
indication of direction as well as the phase
synchronisation is still corresponding to the calibration
performed in the substation. Therefore, it is enabled to
perform the safe cable identification even on very
difficult arrangement. The application of cable
identification in PILC cables may be influenced by the
characteristic that the outer protective layer is
conductive and therefore the cable sheath is also
conductive to soil. If the signal return path is defined via
the cable sheath, a certain amount of signal may be
leaking and travelling via surrounding conductors. These
so called vagabonding currents are then no more routed
along a defined path. This effect is the reason, why on
such arrangement not the full signal value may be
available on site.
By using the KSG 100 in the Expert
mode, also the effect of vagabonding currents can be
considered. As long as possible, the forward and return
path of the signal should be defined via the cable cores.
Like this, the effect of vagabonding currents in PILC
cables can be eliminated.
Cable Fault location in High Voltage cables e.g. 115kV:-

High voltage cables such as e.g. 115kV cables, 230kV
cables or similar are mainly operated at high load. In
case of a cable fault the flash over energy is very
high.
XLPE cables:
In XLPE cables most often a big explosion is happening
and the cable parts around the fault are burnt and/or
vaporized completely. Also the other cores as well as
neighbouring cables are very often damaged beside.
Due to this reason cable fault location can be carried out
easily with basic cable fault location equipment used
for medium voltage cables. A fault location system
based on a surge generator up to 32kV is mostly fully
sufficient to pre-locate these cable faults. The
comparison of TDR graphs of a healthy core in
comparison with the faulty phase leads to precise cable
fault pre-location graphs in low resistive fault conditions.
Depending on the current load of the cable at the
moment of flash over the conditions may also remain
high resistive or intermittent. In general the 32kV surge
generator combined with the SIM/MIM or ICM method
can cover these fault conditions. If the fault condition
shows solid grounded conditions the pin pointing may
not be possible by means of the acoustic fault location
method as no flash over can take place at a short circuit
fault. In such a case the step voltage method is the
only method to perform the cable fault pin pointing in 1-
core cables.

Vaporized Core After Cable Fault, 132kv XLPE
In 3-core cables, which are used rarely,
also the Twist Method can be used for pin pointing.
PILC cables: High voltage PILC cables are more
resistant to the flash over. In these cables the remaining
fault condition may be an intermittent fault with a certain
breakdown voltage possibly higher than 32kV. To pre-locate
such faults the Decay method based on a HV DC
or VLF instrument that is covering the breakdown
voltage is required. Basically all these available HV
instruments enable to be used in burn mode. Most of the
fault conditions can be changed by application of the
burn mode over a certain time.
During this fault burning the paper insulation is
carbonizing and the break down voltage of the fault
can be reduced.

Cable Fault In A 132kv PILC Cable
Finally for pin pointing a surge
generator with a maximum output voltage of 32kV can
be applied. Only very seldom it is required to use a
surge generator with higher output voltage.
Advantages:-
 Less maintainance
 Higher efficiency

 Easy cable fault location
DISADVANTAGES
 Cost, must consider life time costs not just
initial
 Cost differential decreasing with time
 Fault location instantaneous, can have
longer repair time
CONCLUSION:-

Further this project can be enhanced by using
capacitor in an AC circuits to measure the impedance which
can even locate the open circuited cable, unlike the short
circuited fault only using resistor in AC circuit as followed in
the above proposed project

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