Handbook on
Centre for Advanced Maintenance Technology Maharajpur, Gwalior
(M.P.) Pin Code – 474 005
End user: SSE, JE & Maintainer of S&T deptt.
i
ii
CAMTECH/S/PROJ/2020-21/SP1/1.0 April 2020
iii
iv
Foreword
The long distance underground cables are the nerves of a Railway
Signalling or Telecom system. If the cables connected with the
system are healthy and free from any defect, it will run smoothly
and efficiently. Any fault in the cable may affect the connected
circuit or equipment and paralyze the train operation. Locating the
cable fault by conventional methods and repairing thereafter are
time consuming and require substantial manpower. The repercussions
for these failures may be in the form of punctuality losses and
high maintenance cost to the Railways. To save time, manpower and
at the same time reduce cost and downtime, Railways need to adopt
innovative techniques in cable fault localization. With the advent
of advanced Electronics and Communication technology, equipments
have been developed over the years which can accurately locate
faults in underground cables.
CAMTECH has prepared this handbook for S&T Supervisors and
Technicians to get them acquainted with modern techniques in cable
fault localization. I hope that this handbook shall guide them in
the process of locating cable fault with the help of equipments
designed for this purpose.
CAMTECH Gwalior Jitendra Singh Date: 30.04.2020 Principal Executive
Director
v
vi
Preface
Underground cables play an important role in keeping the S&T
system operational by carrying different circuits through them.
Although every safety precaution is taken for the safety of cable
while laying it underground, unpredictable faults in a cable due to
various reasons are not ruled out. The type of fault for example
earth, open, short or low insulation fault in underground cables
can be detected easily with the help of a megger. But finding the
exact location of the cable fault needs special techniques. CAMTECH
has prepared this handbook to introduce S&T personnel with the
modern techniques of cable fault localization in less time and
minimum manpower. The handbook covers procedure for locating fault
in underground cables with the help of equipments using TDR and
other techniques. We are sincerely thankful to M/s Andig Systems,
Bangalore and M/s Aishwarya Technogies & Telecom Ltd.,
Hyderabad who helped us in preparing this handbook. If some
addition/modification is needed in this handbook please mail us on
[email protected] or write to us at Indian Railways Centre
for Advanced Maintenance Technology, In front of Adityaz Hotel,
Airport Road, Maharajpur, Gwalior (M.P.) 474005. CAMTECH Gwalior
Dinesh Kumar Kalame Date:30.04.2020 Joint Director (S&T)
Cable Fault Localization
...................................................... 1 1.1
Introduction
.......................................................................
1
1.2 Type of Cables carrying S&T circuits
................................ 1
1.3 Major causes of cable fault
................................................ 2
1.4 Types of cable faults
.......................................................... 2
1.5 Need for cable fault localization
........................................ 4
1.6 Advantages of cable fault localization
................................ 6
1.7 Techniques used for cable fault localization
........................12
1.8 Time Domain Reflectometer (TDR)
....................................12
1.9 General Precautions for Underground S&T cables
..................15
ANDIG Model 5289M Digital Cable Fault
Locator................................................ 17
2.1 Introduction
..........................................................................17
2.5.3 To measure Insulation Resistance
....................................29
2.5.4 To measure Foreign
potential..........................................31
2.6 Menu Flowchart
.....................................................................32
3.1 Introduction
..........................................................................34
3.2 Specifications
........................................................................35
3.5 Pulse Reflection Testing
......................................................38
3.6.2 Megameter and Ohmmeter
..............................................44
3.7 Charging
.............................................................................46
ISSUE OF CORRECTION SLIPS
The correction slips to be issued in future for this report will be
numbered as follows:
CAMTECH/S/PROJ/2020-21/SP1/1.0# XX date .......
Where “XX” is the serial number of the concerned correction slip
(starting from 01 onwards).
CORRECTION SLIPS ISSUED
Remarks
xi
DISCLAIMER It is clarified that the information given in this
handbook does not supersede any existing provisions laid down in
the Signal Engineering Manual, Telecom Engineering Manual, Railway
Board and RDSO publications. This document is not statuary and
instructions given are for the purpose of guidance only. If at any
point contradiction is observed, then Signal Engineering Manual,
Telecom Engineering Manual Railway Board/RDSO guidelines may be
referred or prevalent Zonal Railways instructions may be
followed.
OUR OBJECTIVE
To upgrade Maintenance Technologies and Methodologies and achieve
improvement in Productivity and Performance of all Railway assets
and manpower which inter-alia would cover Reliability, Availability
and Utilisation. If you have any suggestion & any specific
comments, please write to us: Contact person :Jt. Director (Signal
& Telecommunication) Postal Address : Centre for Advanced
Maintenance
Technology, Maharajpur, Gwalior (M.P.) Pin Code – 474 005
Phone : 0751 - 2470185 Fax : 0751 – 2470841 Email :
[email protected]
CAMTECH Publications CAMTECH is continuing its efforts in the
documentation and up- gradation of information on maintenance
practices of Signalling & Telecom assets. Over the years a
large number of publications on Signalling & Telecom subjects
have been prepared in the form of handbooks, pocket books,
pamphlets and video films. These publications have been uploaded on
the internet as well as railnet. For downloading these publications
On Internet: Visit www.rdso.indianrailways.gov.in Go to
Directorates → CAMTECH Gwalior → Other Important links →
Publications for download - S&T Engineering On Railnet: Visit
RDSO website at 10.100.2.19 Go to Directorates → CAMTECH →
Publications → S&T Engineering A limited number of publications
in hard copy are also available in CAMTECH library which can be got
issued by deputing staff with official letter from controllong
officer. The letter should be addressed to Director (S&T),
CAMTECH, Gwalior. For any further information regarding
publications please contact:
Director (S&T) – 0751-2470185 (O)(BSNL) SSE/Signal - 7024141046
(CUG) Or Email at
[email protected] Or FAX to 0751-2470841
(BSNL) Or Write at Director (S&T) Indian Railways Centre for
Advanced Maintenance Technology, In front of Hotel Adityaz, Airport
Road, Maharajpur, Gwalior (M.P.) 474005
Cable Fault Localization
1.1 Introduction There are hundreds of trains which run daily on
Indian Railways and the various systems which are involved in the
operation of trains are Track, Rolling stock, Loco, Electrical
Traction, Signalling and Telecom and traffic control systems.
Railway Signalling and Telecom circuits run on hundreds of
kilometers of underground cables. Although adequate precautions are
taken in lying of cables beneath the ground and underground cables
are not affected by any adverse weather condition like pollution,
heavy rainfall, snow and storm etc. there are other factors which
may cause faults in the cables.
1.2 Type of Cables carrying S&T circuits (i) Signalling
cables
PVC insulated PVC sheathed and armoured signalling cables.
Generally, used copper conductor core sizes are 1.5 sq.mm. and
2.5sq.mm. Most commonly used cores are 2C, 4C, 6C, 8C, 9C, 12C,
19C, 20C, 24C & 30C.
(ii) Telecom cables Polyethylene Insulated Jelly Filled (PIJF)
cables 4 or 6 Quad cables (Core size 0.9 mm) Co-Axial Cables
CAMTECH/S/PROJ/2020-21/SP1 2
Cable Fault Localization April 2020
1.3 Major causes of cable fault Some of the causes of cable faults
are as given below: Ageing. Corrosion of sheath. Moisture in the
insulation. Heating of cable. Fire and lightning surges. Electrical
puncture Damage during laying. Damage while in use due to
excavation works.
1.4 Types of cable faults The common faults which develop in the
conductors of
multi-core cables are:
Earth fault When any of the conductors of the cable comes in
contact with the earth, it is called an earth fault. This type of
fault allows the current, carried by the conductor to leak to the
earth directly or indirectly instead of going to the apparatus to
which the conductor is connected. This usually occurs when the
outer sheath is damaged due to chemical reactions with soil or due
to vibrations and mechanical crystallization.
Fig.1: Earth fault
Conductor Insulation
CAMTECH/S/PROJ/2020-21/SP1 3
Cable Fault Localization April 2020
Short circuit fault When two or more conductors of a multi-core
cable come in contact with each other, then this is called a short
circuit fault. A short-circuit fault occurs when the individual
insulation of the conductor core is damaged.
Fig.2: Short Circuit fault
Open circuit fault As the name suggests, this fault involves an
open circuit in the conductors. When one or more cable conductors
(cores) break, it leads to discontinuity. This discontinuity also
occurs when the cable comes out of its joint due to mechanical
stress. This is known as Open circuit fault..
Fig.3: Open Circuit fault
Low insulation fault Sometimes when the cable core insulation
material is deteriorated by ageing, moisture, excessive heating or
dirt the insulation resistance is dropped to very low value
(several hundred to several kilo ohms) it is called as low
insulation fault. But if the insulation resistance is of the order
of mega ohms and less than 2 Mega Ohms it is
1
2
Short
1
2
1
2
Break
1
2
Cable Fault Localization April 2020
termed as high resistance fault or bad insulation. In both the
cases, the quality of communication or flow of current through the
cable is badly affected and the cable needs replacement.
1.5 Need for cable fault localization Whenever a fault occurs in
one or more conductors of underground cable, be it an earth fault,
open/short circuit fault or low insulation fault, the circuit
completing through the conductor or conductors is interrupted which
in turn affects the functioning of connected equipments. In a
railway signalling system the operation of signals or its
associated equipments is badly affected due to cable fault.
Similarly if a cable fault occurs in a telecom cable, the circuits
associated with Block working, Control or other communication
systems may not work. Unless the fault is identified and rectified,
the train movement is badly disrupted.
(i) Detection of type of fault The type of cable faults mentioned
in section 1.4 cannot be detected visually as these are buried
underground. However all the above type of faults can be detected
with the help of a Megger. Usually 500 V megger is used for testing
insulation resistance of Signalling cables whereas 100 V megger is
used for Telecom cables
CAMTECH/S/PROJ/2020-21/SP1 5
Fig.4: Analog Megger Fig.5: Digital Megger
An open circuit fault is characterized by infinite resistance.
Hence when the resistance between conductor which is break at some
point and the earth is measured using a megger it will read
infinite resistance.
A short-circuit is characterized by zero resistance. If the
resistance between any two conductors which are shorting each other
at some point is measured using a megger it will read zero
resistance. If the resistance between any two conductors is low,
the megger may show reading between several hundred ohms to less
than 2 Mega Ohms. An earth fault is somewhat similar to a short
circuit fault as the current again takes the least resistive path
and flows through the earth. The megger is connected between the
faulty conductor and the ground. If an earth fault is present, the
megger will show nearly zero reading.
CAMTECH/S/PROJ/2020-21/SP1 6
Cable Fault Localization April 2020
The above tests are performed on the portion of cable between two
junctions where the fault is suspected. If it is not certain that
in which patch of cable route the cable is faulty then the cable is
disconnected at each junction and tested to find the faulty
patch.
By above testing one can detect only the type of fault and the
portion of cable between two junctions in which the fault exists.
To restore the circuit either the circuit is transferred in spare
conductors if available or a new cable has to be laid between the
junctions containing faulty part of cable.
(ii) Detection of location of fault Finding the type of a fault in
underground cables using a megger may not be a difficult task. But
it is very difficult to locate and repair the fault. For detecting
the exact location of cable fault special techniques are
required.
1.6 Advantages of cable fault localization Detecting the cable
faults and pinpointing the fault location makes task faster and
easier for the site engineers through modern Cable Fault
Localization techniques. Fast and precise fault location plays a
significant role in speeding up system renovation, diminishing
great financial loss and operating cost thereby minimizing down
time and most importantly ensuring system availability and
performance.
CAMTECH/S/PROJ/2020-21/SP1 7
(i) Reduction in cost
There is a huge saving in cost if we use cable fault localization
techniques instead of conventional methods. We can take the example
of Signalling cable which is used to carry circuits for Signal lamp
and control, points operation and detection, track repeater relay
circuits etc. In reference to RVNL Standard bill of quantities for
S&T Works March 2018, the approximate cost of a signalling
cable including laying is summarized below: Description of
item/work Unit Rate/Km Approximate cost of Jelly Filled 0.9 mm dia
6 Quad Cable
Kms Rs 350000.00
Approximate cost of excavation of trenches at a depth of 1.2 Mtr.
deep and 300 mm wide and back filling the trench after laying of
cable along with supply and fixing of Cable route marker.
Kms Rs 100000.00
Rs 450000.00
Rs 450.00
Suppose a 6 Quad cable becomes faulty between two junctions which
are 600 mtrs. apart. If we don't know the location of fault, the
whole 600 mtr. cable is to be laid which shall cost 600 X 450 =
Rs.270000.00 approx.
CAMTECH/S/PROJ/2020-21/SP1 8
Cable Fault Localization April 2020
Whereas, in a working cable even if approximate location of fault
is detected, the whole cable need not be replaced or circuit
transferred to spare conductors. Only a cable piece of few meters
is to be laid which will be less costlier including the junctions
to be provided. For new works also, before laying of cable if a
fault is located, the part containing the fault can be cut and the
remaining good portion of cable can be used by jointing it or as
separate pieces as per the requirement
(ii) Saving of manpower To detect a fault in an underground cable
by disconnecting at each junction/joint manually and testing from
both ends is time consuming and requires manpower. We can take the
example of quad cable in block sections which run continuously from
one station to other with a number of joints buried underground.
Communication with Level Crossing Gate if situated in the section
may be of some help; otherwise it is difficult to predict the
location of fault. When exact location of fault is not known, each
underground cable joint is required to be opened and joined one by
one, which require at least 5 to 6 persons at site and minimum 2
persons at the station end. The task becomes more difficult when
cable markers are not available along the route. Similarly in case
of fault in a signalling cable in station yard, termination in each
location box or junction box coming in the route has to be
disconnected and tested with megger.
CAMTECH/S/PROJ/2020-21/SP1 9
Cable Fault Localization April 2020
If cable is tested with equipment like Cable Fault Locator the
joints need not be disconnected. Suppose the total length of a 6
Quad cable between two stations A and B is 8 Kms. The cable is
first disconnected at Station A and tested with all
joints/junctions intact upto station B. The distance of fault from
station A is located, say at 4880 mtr. The cable is then tested
from station B in a similar manner. Now the distance to fault from
station B comes out to be say 3125 mtr. By comparing both the
results it is confirmed that the fault is within 4875 to 4880 mtr
from station A or within 3120 to 3125 mtr from station B. Thus
exact location of fault can be arrived at in just two rounds
testing with minimum staff and in this case only a specified 5 mtr
portion of cable has to be replaced. Fig.6: Locating fault distance
between two points
(iii) Reduction in breakdown time When there is a fault in
underground cable carrying signalling or block circuits, the
equipments connected to it do not respond and as a result a part or
whole signalling system becomes inoperative. Trains are piloted and
despatched on paper authority until cable fault is identified and
restored. Suppose a cable is cut by miscreants in a block section
of 8 km length, then in the absence of any fault locator the only
means to locate the fault/damage is foot by foot inspection. This
means that
Station A
Station B
Cable Fault Localization April 2020
the downtime will be more. In such cases sometimes it takes one or
more days to identify and restore the fault. Examples of two cable
cut/theft cases are given below (Ref.: Railway Board Failure
data):
Sr. No.
detained
Remarks
1 22419 (30) 13258 (55) 14617 (35) 14227 (17) 22355 (10) 12317 (55)
Total - 6
Pakhrauli- Sultanpur,
29/30.5.19,
725
UP SSDAC with SLN Failed after 13237UP .B/Instt with (Dn Line)
FaileI. SE/E/SLN- 21.05,SSE/SLN-21.10,T/R at 21.15,6 quad cable
burnt by outsider at km no. 911/27-29, new 6 quad cable about 15
metres provided, jointed & put right by SSE/T/SLN
2 11014 (151) 11312 (49) 12627 (118) 12786 (100) 12684 (28) 16232
(112) 16520 (95) 16521 (18) 16522 (58) 16526 (63) Total -10
Kadlimatti KJM,
01.05.19,
260
Point No.71 failed for normal, Slot failed bet KJM- CSDR &
KJM-BPHI, due to 19C cable cut & theft by unknown person. New
19C cable laid and restored to normal. Failed after cable
restoration since newly laid cable conductor No.10 defective.
Conductor changed over to spare conductor No.11 and restored.
In the first case the breakdown time is about 12 hrs. in which 6
trains detained. The downtime in second case is less (4 hrs) but
total 10 trains are detained for longer periods. The breakdown time
can be reduced drastically
CAMTECH/S/PROJ/2020-21/SP1 11
Cable Fault Localization April 2020
if Cable Fault Locator is used for detecting the fault as explained
in para (ii) above.
(iv) Reduction in maintenance Although every precaution is observed
while laying of the cable and periodical meggering is done as per
the annual programme, unpredictable faults in an underground cable
due to various reasons are not ruled out. Sometimes the cable
sheath is damaged due to excavation works and gone unnoticed. In RE
area due to traction currents there is spark in the armour under
damaged sheath which results in deterioration of conductors coming
in contact with it. Over a period of time the other conductors also
come in contact and the cable becomes faulty. In other cases,
sometimes the moisture enters the damaged sheath and the low
insulation fault is developed in the cable. All these types of
faults can be prevented if a quick test is performed with Cable
Fault Locator within specified periods. Thus, cable fault
localization with special techniques avoid wastage of cable which
in turn cuts cost, ease of operation requires less manpower, quick
fault localization reduces downtime and can be better utilized for
preventive maintenance. In view of the above, apart from detection
of fault type, cable fault localization is needed before laying of
cable or at the time of cable fault. Note: Apart from Signal &
Telecom cables, cable fault localization techniques can be utilized
for electrical cables also
CAMTECH/S/PROJ/2020-21/SP1 12
Cable Fault Localization April 2020
1.7 Techniques used for cable fault localization There are
different technique for locating faults in underground cables
namely: (i) Murray loop test (ii) Varley loop test (iii) Cable
Thumping (iv) Time Domain Reflectometer (TDR) (v) High Voltage
Radar method (vi) Intelligent Bridge Testing
All the above techniques have some advantages and disadvantages.
There is no single method or combination of methods which can be
considered as best. However employing a technique which can
efficiently locate fault without causing damage or degradation of
cable is the key to safety of the system. The most popular
technique among the above is TDR which is explained below.
1.8 Time Domain Reflectometer (TDR) A Time Domain Reflectometer
(TDR) sends a short- duration low energy signal (of about 50 V) at
a high repetition rate into the cable. This signal reflects back
from the point of change in impedance in the cable (such as a
fault). TDR works on the similar principle as that of a RADAR. A
TDR measures the time taken by the signal to reflect back from the
point of change in impedance (or the point of fault). The TDR uses
Velocity of propagation (VOP) to calculate cable length.
CAMTECH/S/PROJ/2020-21/SP1 13
Cable Fault Localization April 2020
Velocity of propagation (VOP) Velocity of propagation is a cable
specification indicating the speed at which a signal travels down
the cable. A VOP of 66 means the signal travels at 66% of the speed
of light. The tester uses VOP to calculate cable length. Different
cables have different VOP settings. Using the VOP specified for a
cable ensures the most accuracy in fault location and length
measurement.
Suppose the Velocity of propagation (VOP) of pulse transmission in
a cable is V, the time taken by the signal to travel and reflect
back from the point of fault is T and the distance of fault is L
then
2L = VT L = VT/2
Thus if VOP and total time of to and fro travel of pulse
transmission is known, the distance to the fault can be found. The
reflections are traced on a graphical display with amplitude on
y-axis and the elapsed time on x-axis. The elapsed time is directly
related to the distance to the fault location. If the injected
signal encounters an open circuit (high impedance), it results in
high amplitude upward deflection on the trace. While in case of a
short-circuit fault, the trace will show a high amplitude negative
deflection.
CAMTECH/S/PROJ/2020-21/SP1 14
Fig.7: Graphical representation of pulse transmission
and reflection in open and short circuit faults Advantages and
disadvantages of TDR As a TDR sends a low energy signal into the
cable, it causes no degradation of the cable insulation. This is a
major advantage of using TDR to find the location of a fault in an
underground cable. A TDR works well for open-circuit faults as well
as conductor to conductor shorts. A weakness of TDR is that it
cannot pinpoint the exact location of faults. It gives an
approximate distance to the location of fault. Sometimes, this
information alone is sufficient and other times it is required to
be used in conjunction with other technique. In the following
sections details of Cable Fault locating equipments using TDR are
given.
Cable pair open
Cable pair shorted
Cable Fault Localization April 2020
1.9 General Precautions for Underground S&T cables Insulation
resistance for a new cable should not be
less than 200 Mega Ohms/Km at 20°C. First measurement of insulation
resistance of cable
should be carried out after laying of cable and after first monsoon
for all the conductors.
Thereafter the periodical testing of insulation should be carried
out once in 12 months for main cables and once in months for tail
cables. Circuits of low insulation conductors should be transferred
to healthy conductors in time.
If during periodical testing, the insulation resistance of cable is
found between 5 and 1 Mega Ohms/Km at buried temperature, the
subject cable should be programmed for replacement.
All defective tail cables should be replaced before monsoon. All
tail cables at entry of junction boxes, location boxes, signal
posts should be checked for breakage of insulation. All earth
faults should be removed beforehand.
Insulation of cables should be monitored with the help of Earth
Leakage Detector where provided. For effective monitoring, ELD data
may be linked to Data Logger.
Minimum 5% healthy spare conductors are to be made available in
each location/goomty/relay room and to be kept labelled /marked for
easy identification during emergency.
All supervisors shall familiarize themselves with the position of
spare conductors in their respective sections.
CAMTECH/S/PROJ/2020-21/SP1 16
Cable Fault Localization April 2020
Protective works provided for the cables at places like track
crossings, culverts, bridges etc. shall be inspected periodically
especially before and after monsoon.
Earthing of armour of all cables and continuity of cable armour be
ensured.
Quad cable meant for Block should be tested or their insulation
resistance, cross talk, loop resistance, db losses. Position of
cable joints should be known accurately and joints to be repaired
if required before onset of rains.
It is a good practice to provide Cable route markers along the
route of cable. Alternatively distance of cable route from OHE mast
to be recorded n cable route plan during cable laying.
CAMTECH/S/PROJ/2020-21/SP1 17
ANDIG Model 5289M Digital Cable Fault Locator
2.1 Introduction
ANDIG Model 5289M Digital Cable Fault Locator is manufactured and
supplied by of M/s Andig Systems, Bangalore. It is basically a
combination of Pulse Echo Meter (TDR) and High Resistance Fault
locator. It can locate break, short (loop) and low insulation
faults in underground copper cable. The distance to fault is
displayed directly in metres and there are no calculations
involved.
Fig.7:Andig Model 528M Digital Cable fault Locator
CAMTECH/S/PROJ/2020-21/SP1 18
Cable Fault Localization April 2020
2.2 Technical specifications Physical Dimension Width : 265 mm
Height : 195 mm Depth : 140 mm Weight : 3 Kgs (Approx.)
Power Battery : Internal Rechargable Li-Ion Battery Charging source
: External 16 V DC, 1A Adapter Operating time : 8 hours continuous
without Back light
Environment Operating temperature : 0 to 50° C
Display 240 X 128 dot-matrix Graphic, Liquid Crystal Display (LCD)
with Back light
Pulse Echo mode Max range : 10 Kms (0.9 to 1.5 mm) Accuracy :
Better than 1% of reading V.O.P.: Fixed for Standard cable or User
Programmable Waveform Storage : Upto 20 Waveform Low Insulation
Faults Mode Max. range : For open & Short Circuit faults - 5
Kms. For Low insulation faults - 15 Kms Accuracy : +/- 0.5% of
reading Output Connectors : 4 Front Panel Banana sockets Serial I/O
Ports : RS-232 Testable Low insulation Resistance : 2 Mega Ohms
Accessories Standard: Battery Adaptor, Operation Manual,
connectors,
carry bag
CAMTECH/S/PROJ/2020-21/SP1 19
Cable Fault Localization April 2020
2.3 Front Panel Description The front panel of Digital Cable Fault
Locator is given
below:
Fig.8: Front panel of Digital Cable fault Locator
Function of different keys SELECT : When Pressed selects
highlighted menu on
display screen MENU : When Pressed Main Menu is displayed
: Moves Up & Down the highlighted Menu : Moves Left or Right
the selected cursor or
increments/ decrements function selected in multifunction
box.
CAMTECH/S/PROJ/2020-21/SP1 20
Cable Fault Localization April 2020
RANGE : Display range status (RANGE 1 upto 1km, RANGE 2 upto 2km,
RANGE 3 upto 3.5km, & RANGE 4 upto 5km) Select range using Left
& Right arrow keys.
ZOOM : It displays current zoom status from zoom1- zoom5. At zoom 6
it displays maximum expanded waveform. (Select Zoom level Using
Left & Right arrow keys)
CUR : Selects Cursor 1 or Cursor 2 BACK : Not Used GAIN : Selects
Gain level (Default sets to Gain 1) &
displays status in multifunction box. START : When pressed starts
testing the Cable Pair
under test (Display Scanning) PRINT : Not Used B/L : Switches ON
Back Light LINE 1 : Socket pair for connecting faulty pair
under
test LINE 2 : Socket pair for connecting good reference pair
RS 232 : Connector for PC Interface PRINTER : not used DC Socket :
Socket for Ext DC & for battery charging (12 To 15 VDC)
Note: Following keys are used only in Pulse Reflection mode When
pulse (Waveform) is displayed on LCD.
a) RANGE, b) ZOOM, c) GAIN, d) CURSOR.
2.4 Powering On On powering on the instrument performs self check
and on completion will display Main Menu.
CAMTECH/S/PROJ/2020-21/SP1 21
Fig.9: Main Menu
Use UP & DOWN arrow keys to select one from following:
1.Pulse Echo Reflection : for Open & Short Faults 2. Low
Insulation Faults : for Low Insulation Faults 3. Insulation
Resistance : for measuring Insulation Resistance 4. Foreign
Potential : for measuring Foreign Voltage on Cables
2.5 Operating Instructions In this section the operating
instructions for detection and localization of different types of
faults in underground cables through digital fault locator are
given.
2.5.1 To Locate Open/Short circuit faults Select Pulse Echo
Reflection, it displays
PULSE ECHO REFLECTION 1. Normal Scan (L1 Scan) 2. L2-L20 Scan 3. L1
& L2-L20 Scan 4. Differential Scan 5. Settings
Software Version....................................
1. Pulse Echo Reflection 2. Low Insulation Faults 3.Insulation
Resistance 4.Foreign Potential Press Select key to enter Battery
Level
CAMTECH/S/PROJ/2020-21/SP1 22
Go to Settings and press Select. It displays
By default instrument sets to 0.5mm gauge and cable type jelly
filled. To change gauge & type of the cable go to settings and
do changes as given below: Go to Cable Type and press Select. It
displays
Go to required cable type and press Select Press Menu key to
exit.
Go to Guage and press Select. It displays
TDR SETTINGS 1. Cable Type 2. Gauge
CABLE TYPE 1. Jelly 2. Paper 3. Co-Axial 4. Others 5. PVC
GAUGE SELECTION 1. 0.4 mm 2. 0.5 mm 3. 0.63 mm 4. 0.9 mm 5. 1.5
mm
CAMTECH/S/PROJ/2020-21/SP1 23
Cable Fault Localization April 2020
Go to required gauge and press Select Press Menu key to exit.
Connect pair under test to LINE1 Terminals on the top right corner
of front panel.
There is no need to disconnect the pair at the other end.
An electrical pulse of 30V amplitude is sent along the cable ,
which will be reflected back from the point of fault. The signal
propagation time is calculated and the distance arrived at based on
the velocity of propagation based on the medium involved. Go to
Normal Scan (L1 Scan) and press Select. Both Incident and reflected
pulse appear on the LCD screen. For open circuit fault the incident
and reflected waveform will be
Fig.10: Incident and reflected waveform for open
circuit fault
CAMTECH/S/PROJ/2020-21/SP1 24
Cable Fault Localization April 2020
For short circuit fault the incident and reflected waveform will
be
Fig.11: Incident and reflected waveform for short
circuit fault. If the fault is at less than 1 km distance, use Zoom
4, Zoom 3 to check whether reflected pulse appears within the
screen along with incident pulse. If reflected pulse is not
displayed clearly in zoom 5, zoom 4, zoom 3 then Press Range -
Using Left & Right Arrow Keys Select range depending on the
distance to fault. Range 1 upto 1 Km, Range 2 upto 2km, Range 3
upto 3 km, & Range 4 upto 5km. Press Start : Both incident
& reflected Pulse appears on screen. If reflected pulse is not
seen press range & select next range Press Gain : Select Gain
1, Gain 2, for amplifying reflected pulse & Press Start Press
Cur : Displays Cursor 1 or Cursor 2 in the multifunction box. Using
Left & Right Arrow keys adjust Cursor 1 to the starting point
of incident pulse (The Point from Where
CAMTECH/S/PROJ/2020-21/SP1 25
Cable Fault Localization April 2020
incident pulse starts rising) & Cursor 2 to starting point of
reflected pulse. After aligning cursors to the incident and
reflected pulse distance to fault is displayed in distance
box.
N o t e : F For better accuracy at different fault distances select
Range, Zoom & Gain positions. For faster cursor movements you
can use zoom facilities.
2.5.2 To Locate Low Insulation faults (i) To locate Low Insulation
faults using Good pair Basic requirement to conduct this
test.
A Good (Reference) pair preferably in the same cable in which
faulty pair exists is to be tested.
Insulation Resistance (Megger Value) between Limb A & B and
between each Limb to Earth should be more than 5 Mega Ohms.
Faulty pair should have less than 2 Mega Ohms Insulation
Resistance.
Distance of fault
CAMTECH/S/PROJ/2020-21/SP1 26
Cable Fault Localization April 2020
Testing setup Measure the Good pair insulation resistance and
Faulty pair insulation resistance as per procedure given in section
2.5.3. Loop the Good pair and extend it to one limb of Faulty pair.
(refer Fig.13). Connect the Faulty pair to Line 1. The extended
limb of faulty pair must be connected to Black terminal of Line 1
in the instrument and the other limb to Red terminal. Connect Good
pair to Line 2 Ensure that the connections are perfect. Check the
resistance between limb to limb of good pair using multi meter to
ensure it is properly looped at the far end (say it reads 500
Ohms). Check the resistance between any one limb of good pair to
faulty pair limb, it should read the same resistance as good pair.
If fault is between Limb to Earth, connect Red terminal of Line 1
to Earth
Fig.13: Setup to locate Low Insulation faults using Good pair
CAMTECH/S/PROJ/2020-21/SP1 27
Cable Fault Localization April 2020
Using Up & Down arrow keys, Go to Low Insulation Faults. Press
Select. It displays:
Using Up & Down arrow keys highlight Setting and Press Select
Key. Select the ambient Temperature and Gauge of cable under test.
By default instrument sets to temp 27 Degree Centigrade and gauge
0.5 mm. Press Menu key, the Main Menu is displayed. Using Up &
Down arrow keys, again Go to Low Insulation Faults. Press Select,
the LOW INSULATION FAULTS menu is displayed as above. Go to Double
Limb Scan and Press Select.
LOW INSULATION FAULTS 1. Double Limb Scan 2. Mixed Gauge Scan 3.
Settings 4. Mixed Gauge Settings 5. Single Limb Scan
Temperature Gauge
LOW INSULATION FAULTS 1. Double Limb Scan 2. Mixed Gauge Scan 3.
Settings 4. Mixed Gauge Settings 5. Single Limb Scan
CAMTECH/S/PROJ/2020-21/SP1 28
Cable Fault Localization April 2020
After 30 seconds the result will be displayed as shown below: All
the distances are in Metre.
(ii) To locate Low Insulation faults using only one good Limb
Verify good Limb for more than 5M ohms insulation resistance.
Short Red & Black terminal of Line 2 & connect to good
Limb.
Loop good Limb to faulty limb at the far end. Connect Black
terminal of Line 1 to faulty Limb, which
is looped to good Limb. Connect Red terminal of Line 1 to 2nd Limb
of faulty
pair if the fault is between Limb to Limb. Connect Red terminal of
Line 1 to Earth if the fault is
between Limb to Earth.
Fig.14: Setup to locate Low Insulation faults using only one
Good limb
Distance to Loop : 540 Mts. Distance to Fault : 210 Mts.
CAMTECH/S/PROJ/2020-21/SP1 29
Cable Fault Localization April 2020
Select Low Insulation Fault & then Select Single Limb Scan from
Menu. (Available in Software version 1.1/171103)
If the Menu for Single Limb Scan is not available then the fault
distance displayed should be multiplied by 2 for actual distance to
fault.
2.5.3 To measure Insulation Resistance Test for Good pair
In the Main Menu, using Up & Down arrow keys, Go to Insulation
Resistance.
Press Select. It displays Connect Limb A & Limb B to Line 1 Go
to Scan & press Select After few seconds it display resistance
value in K ohms: --- Connect Limb A & Ground to Line 1 &
Press Start After few seconds it display resistance value in K
ohms: ---
1. Pulse Echo Reflection 2. Low Insulation Faults 3.Insulation
Resistance 4.Foreign Potential
RESISTANCE MODE Scan
Cable Fault Localization April 2020
Connect Limb B & Ground to Line 1 & Press Start After few
seconds it display resistance value in K ohms: --- In all the above
cases Insulation resistance should be more than 5000 K ohms for a
good pair. Test for Faulty pair Similar to the test procedure for
Good pair.
Connect Limb A & Limb B to Line 1 Go to Scan & press
Select
After few seconds it display resistance value in K ohms, less than
2 M ohms for fault between limbs.
Connect Limb A & Ground to Line 1 & Press Start After few
seconds it display resistance value in K ohms,
less than 2 M ohms for fault between limb A to Earth.
Connect Limb B & Ground to Line 1 & Press Start After few
seconds it display resistance value in K ohms, less than 2 M ohms
for fault between limb B to Earth. If Insulation resistance is less
than 2000 K ohms, the distance to the fault can be located in the
pair as per procedure given in section 2.5.2.
Insulation Resistance is 1500 K Ohms
CAMTECH/S/PROJ/2020-21/SP1 31
Cable Fault Localization April 2020
2.5.4 To measure Foreign potential Connect pair under test to Line1
terminals In the Main Menu, using Up & Down arrow keys, Go to
Foreign Potential
Press Select, it will display
Go to Scan & press Select. After a few seconds a display
similar to that shown below:
1. Pulse Echo Reflection 2. Low Insulation Faults 3.Insulation
Resistance 4.Foreign Potential
POTENTIAL MODE Scan
CAMTECH/S/PROJ/2020-21/SP1 32
2.6 Menu Flowchart
Cable Fault Localization April 2020
2.7 Instrument charging procedure Connect external supply (15VDC)
and switch ON the
instrument. Observe for charging enabled on the screen after
few
seconds. Please do not charge the instrument more than 14
hours.
Aishwarya Technology & Telecom Model FM111 Cable Fault
Locator
3.1 Introduction Model FM 111 cable fault locator is a product of
M/s Aishwarya Technologies & Telecom Ltd., Hyderabad. It
combines both Time Domain Reflectometer (TDR, pulse reflection
testing) and intelligent bridge testing (Bridge) for measuring the
exact fault location such as the broken line, cross faults,
earthing, poor insulation and poor contact of the lead covered
cables as well as plastic cables.
Fig.15: Cable Fault Locator Model FM 111
CAMTECH/S/PROJ/2020-21/SP1 35
Features Large colour LCD Display (480 x 280 dot); humanized
operation interface; six function keys for simple operation.
Combination of pulse reflection testing (TDR) and intelligent
bridge testing (Bridge) techniques.
Manual testing function is preserved. Megameter and ohmmeter, to
test insulation resistance
and loop resistance. USB Port, to upload testing data to computer
Rechargeable lithium battery, intelligent charging
without duty. Small dimension, light weight and portable
design.
3.2 Specifications Pulse reflection testing(TDR)
Max range: 8 km Dead Zone: 0 m Testing Accuracy: 1m Pulse width: 40
ns-10 μs with automatic adjustment Automatic impedance balance
adjustment Automatic and manual gain adjustment
Intelligent bridge testing(Bridge)
Max poor insulation resistance: 100 MΩ. Testing accuracy: ±1%×cable
length The max length of testing cable: 15 Km Charging time: 3
hours Continued operating time: 8 hours Dimension: 220×160×90 (mm3)
Weight: 1Kg
CAMTECH/S/PROJ/2020-21/SP1 36
3.3 Front Panel Description
: Power Supply On/OFF switch
ADJ : Adjust testing parameters
: To move the cursor - Under Pulse Reflection testing To adjust
relevant parameters - Under Electric Bridge testing. Users can also
complete the operations with Menu prompt.
PULSE :To process Manual pulse testing - Under Pulse
Reflection testing.
CAMTECH/S/PROJ/2020-21/SP1 37
To enter the Pulse Reflection testing interface automatically -
Under Electric Bridge testing.
Users can also complete the operations with Menu prompt. AUTO : To
perform the testing automatically. TEST : To insert and connect the
testing lead lines. USB : To communicate with hot computer CHARGE :
Socket for charging the instrument
Testing line There are three clips at the end of testing lead line
-Red, Yellow & Black. Under Pulse Reflection testing - Only red
& yellow clips to be used. Under Intelligent Bridge testing -
All the three clips red, yellow & black to be used. Testing
socket
Fig.17: Testing lead line
3.4 To choose Testing Mode When the cable lines have faults, first
use testing board, megameter (or megger) or multimeter to find the
character and degree of fault, so as to choose most suitable
testing mode. When the fault resistance is smaller than several
hundred to several kilo ohms, we call it low insulation fault
otherwise it is called high resistance (or bad insulation)
fault.
Clips Red Yellow Black
Cable Fault Localization April 2020
The Pulse Reflection Testing is suitable for testing open circuit
(break) faults and low insulation faults. This testing is simple
and direct-viewing, requiring no co-ordination at other end. The
Bridge testing method is suitable for high resistance faults of the
order of 2 Mega ohms or slightly less. It requires a good line
(reference line) and co-ordination from other end. The test
preparatory work is also tedious. Sometimes the high resistance
faults can also be detected using Pulse Reflection Testing. Hence
Bridge Testing method should be resorted to only after confirming
that Pulse Reflection Testing cannot detect the fault. Switching
between Pulse Reflection Testing and Bridge Testing Press On/Off
key to turn on the instrument, the testing mode will be selected as
Pulse Reflection Testing by default. Press Adjust until "Press or
to enter into Bridge mode" appears in reverse colour. Press or to
enter Electric Bridge Testing. Under Electric Bridge Testing press
Pulse to switch over to Pulse Reflection Testing.
3.5 Pulse Reflection Testing
Under Pulse Reflection testing, analog signal is sent to locate the
fault in a cable which after reflection is converted to digital
pulse for distance measurement.
Preparatory steps
Before commencing the process, disconnect the faulty cable at both
ends. Make sure the cable to be tested is free from any supply
voltage.
CAMTECH/S/PROJ/2020-21/SP1 39
Cable Fault Localization April 2020
First the instrument should be used to perform Intelligent testing.
If the fault cannot be detected with the above process, then it can
be changed to Manual testing.
3.5.1 Intelligent Testing Intelligent Testing means Pulse
Reflection Testing
(Finding Open or short circuit fault) in AUTO mode. First Power On
the instrument.
Connect the cable pair under test to red and yellow test lead
lines. Press AUTO and the instrument will show the result. Note:
The default setting of wave velocity of propagation (VOP) is 200
m/µs. Before performing Intelligent testing, user shall check
whether it is required to adjust the velocity. (Refer "Adjust
Velocity" in next section).
3.5.2 Manual Testing The relevant setting and parameters to be
adjusted are displayed below the display screen. Press Adjust to
adjust the following settings and parameters:
(i) Gain Press Adjust until Gain XX shows reverse colour display.
Then press or to adjust the amplitude (adjustable 1- 99). Press
Pulse the screen will display the wave after gain adjustment.
(ii) Range During manual testing the range value shall be chosen
longer than the actual length of cable to be tested. To adjust the
range repeatedly press Range until Range XX
CAMTECH/S/PROJ/2020-21/SP1 40
Cable Fault Localization April 2020
shows reverse colour display. Then press or to adjust the
range.
(iii) VOP The wave velocity shall be calibrated according to the
cable character to improve the precision of testing result. Press
Adjust until VOP XX shows reverse colour display. Then press or to
adjust the wave velocity. Adjust Range and Velocity according to
the character and estimated length of cable. Appropriately adjust
the wave amplitude to make waveforms on the display screen to be
observed easily. Move the cursor to the inflection (point of
rising) of the reflected waveform. The fault distance will be
displayed at the bottom of display screen.
(iv) Zoom in & Zoom out Users can Zoom in or Zoom out when zoom
value is not "1". Continuously press Adjust till Zoom is selected.
The prompt box will display "press or to zoom the wave". Zoom to
the proper size and press Pulse. Users can move the cursor to fix
position. Press Pulse to return to original state.
(v) Save waveform to RAM The waveform should be saved to RAM when
comparing
the fault line and good line under manual testing. Continuously
press Adjust till Save is selected. The prompt box will display
"press or to save wave". Users can save the current waveform by
pressing or .
CAMTECH/S/PROJ/2020-21/SP1 41
Cable Fault Localization April 2020
(vi) Compare Current Wave with stored Wave in RAM Users can compare
the current waveform with the already stored waveform in RAM.
Continuously press Adjust till Both is selected. The prompt box
will display "press or to both display".
(vii) Save file Press Adjust until "press or to do file management"
appears. Now press or to enter into save file mode. One can not
only save and test the current file but check and analyze previous
wave files. Saving file to U disk: When "Current Test" is chosen,
press Auto to test the current cable. Press Adjust to save the
current file. A display showing "Press to quit file mode, press to
save current wave" will appear. Press to quit file mode or press to
save current file to U disk.
3.6 Intelligent Bridge Testing When the insulation resistance of a
faulty cable pair is very high (above several thousand ohms) and is
much larger than characteristic impedance of cable. In this case
the pulse reflection is weak hence it is not easy to detect the
fault by Pulse Reflection Testing. At this time Bridge Testing has
to be carried out. Testing principle Suppose the resistance of the
entire core is R. The resistance of core from one end (test point)
to the fault is Ra
CAMTECH/S/PROJ/2020-21/SP1 42
Cable Fault Localization April 2020
The core length is L, and The fault distance is La , then La =
(Ra/R)L The instrument adopts Intelligent Electric Bridge
technique, so the user has to connect lines, input some data such
as length and diameter of the core and the fault distance is
calculated.
3.6.1Testing set up Intelligent Bridge Testing First confirm that
the type of fault for example core to earth resistance is low (in
thousand ohms) or bad insulation fault between same pair cable
(self-crossed) or two conductors of different pairs
(other-crossed). The testing setup for locating the distance of
fault, requires two conductors - one consisting earth fault and the
other one with good insulation with earth. One end is designated as
testing end and the other as co- ordination end. Disconnect both
the conductors at either ends from the circuit. If core to earth
resistance is low (in thousand ohms) Loop the faulty and good line
at the co-ordination end. At testing end, connect the black clip of
testing lead line to earth, the yellow clip to good line and red
clip to faulty line as shown in Fig.18
Fig.18: Localization of earth fault
CAMTECH/S/PROJ/2020-21/SP1 43
Cable Fault Localization April 2020
If there is poor insulation between conductors of same pair
(self-crossed) Loop one conductor of the faulty pair with one
conductor of good pair at the co-ordination end. Connect the same
faulty and good conductors to red and yellow clips of testing lead
line respectively at testing end. Connect second conductor of
faulty pair to black clip at testing end as shown in Fig.19.
Remaining ends are left free.
Fig.19: Localization of fault in self - crossed lines
If there is poor insulation between conductors of different pairs
(other-crossed) Here we require two good conductors besides faulty
pair. Loop the faulty core of first cable and first good line at
the co-ordination end. At testing end, connect the red clip of
testing lead line to faulty core of first cable which is looped
with first good line at co-ordination end (the first good line is
left free at testing end), yellow clip to second good line which is
left free at co-ordination end, and black clip to faulty core of
second cable which is left free at other end as shown in
Fig.20.
CAMTECH/S/PROJ/2020-21/SP1 44
Fig.20: Localization of fault in other- crossed lines
Testing procedure Check the connections and ensure that they are
correct and intact. When everything is ready Press Auto, the
instrument will give ratio of Fault resistance and Resistance of
entire cable span. Next input cable span (Length) to get fault
distance. Note: The cable length here refers to the cable length in
testing fault sector i.e. length from testing end to co- ordination
end. To input the known cable length, press Adjust the "line span =
0000m" starts blinking. Depending upon the value of known cable
length using or keys increment or decrement the digits. The
instrument will automatically calculate the fault distance during
inputting data.
3.6.2 Megameter and Ohmmeter The instrument consists Megameter and
Ohmmeter under Electric Bridge Test method to test line insulation
electric resistance and loop electric resistance.
CAMTECH/S/PROJ/2020-21/SP1 45
Cable Fault Localization April 2020
Function of Megameter To test insulation resistance of a conductor
with respect to ground, connect the black clip with ground and red
clip to the conductor under test. Press Adjust, the test result
will be shown at the top of the screen. For example if the
insulation resistance is 3.6 M it will show "red & black 3.6 M,
yellow & black ∞ no loop".
Fig.21: Testing of insulation resistance of conductor
w.r.t. ground with Megameter Function of Ohmmeter
To test Loop resistance of a cable pair, the loop the far end of
cable pair. Connect the red and yellow clips to the two conductors
at testing end. Press Auto key, the loop resistance is displayed
after a few seconds. For example, if the loop resistance is 1360 ,
then it will show " Insulation ∞ loop resistance =1360 ".
CAMTECH/S/PROJ/2020-21/SP1 46
Fig.22: Testing of loop resistance of a pair with
Ohmmeter
3.7 Charging Current battery power is displayed at the top right
corner on the screen. If battery power is inadequate, instrument
charger should be used for charging. The indication light of the
charge adapter will be red when charging, and it will turn green
after the instrument is fully charged. The charge time should not
be more than 4 hours.
3.8 Precautions Keep display screen away from direct sunlight.
The
contrast ratio of LCD will drop when temperature higher than 60°C
and it will return to normal when temperature is lower than
60°C.
Before testing it is better to measure voltage in faulty cable to
be tested, in order to avoid test errors or damage to the
instrument.
Avoid damage to LCD screen.
“ . . .. ”
, , , , "