VON SST15-832 User manual

OPERATING INSTRUCTIONS
FOR
MODEL SST15-832
Arc Reflection Sectionalizing System
THE VON CORPORATION
1038 LOMB AVENUE
P.O. BOX 110096
BIRMINGHAM, AL 35211
TELEPHONE: [phone]
FAX: [phone]

VON MODEL SST15-832 ARC REFLECTION SECTIONALIZING SYSTEM Page 1
I INTRODUCTION ................................................... 2
II RECEIVINGANDCHECKINGOUT .................................... 3
III SAFETY.......................................................... 4
IV DESCRIPTIONANDSPECIFICATIONS ................................. 5
V CONTROLSANDINDICATORS ....................................... 6
VI-F SECTIONALIZINGURDLOOPSYSTEMS ............................... 8
VI-B HINTSANDTYPICALTRACES ...................................... 10
VI-E TESTINGANISOLATEDCABLE ..................................... 13
VI-G RADAROPTIONSMENU ........................................... 13
VII IN CASE OF DIFFICULTY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
VIII TEST LEADS, BATTERY MAINTENANCE, AND STORAGE . . . . . . . . . . . . . . . . 14
IX CIRCUITDIAGRAMANDPARTSLIST................................. 15
X RADARTHEORY ................................................. 16
XI THEORYOFARCREFLECTIONMETHOD ............................ 17
XII CABLEDISTANCEMEASUREMENTS................................. 18

VON MODEL SST15-832 ARC REFLECTION SECTIONALIZING SYSTEM Page 2
I INTRODUCTION
Your new Model SST15-832 Sectionalizing system was designed to aid in URD loop
sectionalizing and fault locating on primary underground cable. All components have been
built and carefully tested to give you years of trouble free service.
We, at the VON Corporation, are constantly trying to improve our equipment. We would
appreciate any comments or suggestions which you may have.
We hope you will share any techniques or applications you find especially useful with us, so
that we may share them with all VON users through application notes and instruction
manual changes.
Please keep us informed of the names of personnel to receive application notes and
instruction manual changes.
For any questions concerning this equipment or its application, write or call:
The VON Corporation SHIPPING ADDRESS
P. O. Box 110096 1038 Lomb Avenue, S.W.
Birmingham, Alabama 35211 Birmingham, Alabama 35211
Phone Number: [phone] Telefax Number: [phone]
e-mail: [email protected] Website: www.voncorp.com
It is extremely important that the operator practice using the radar in this system before
attempting to use it on an actual cable fault. Suggestions on setups to practice on are
contained later in this manual.

VON MODEL SST15-832 ARC REFLECTION SECTIONALIZING SYSTEM Page 3
II RECEIVING AND CHECKING OUT
The Model SST15-832 is packed to arrive in good condition. Unpack and check to see that
there is no physical damage or parts which have come loose during shipment. A reel of
cable at least 50 feet (15m) long is required to check out the unit. A roll of RG-58 works
very well for this purpose. Two or three reels of URD cable connected together can provide
longer lengths. If there are questions about the instructions which follow, see Section VI for
more information and sample radar screens. Ground the unit using the green ground cable
provided to the system neutral or building ground if inside. Connect the output lead of the
system to the test cable. The red lead goes to the center conductor and the green lead
goes to the neutral.
1. Turn the unit ON to view the cable with the radar. The unit will momentarily show a
screen that says “AutoAnalyze cable, wait one moment.” The unit will then show the
cable with the right marker at the end. If the end is not marked correctly, push the
"RANGE" button until the “brick” on the right side of the screen lines up with the word
RANGE, and increase the range with the ARROW keys until the typical up blip for the
far end of the test cable is observed. With a jumper, ground the clamps at the end of
the HV output lead and watch the display as the “up” blip changes to a “down” blip.
The left point where the two waveforms diverge is the end of the HV lead and the
beginning of the test cable. If the left marker does not already line up with this point,
consult with the factory.
2. Now connect the conductor at the far end of the reel of test cable to its neutral or
shield with a jumper. Observe the leftmost point at which the two traces diverge.
The up blip at the open end will have an identical down blip from the short. The
leftmost point where the two blips change direction is the end of the cable.
3. Make a gap at the far end of the test cable between the center conductor and the
cable shield to simulate a fault which can be impulsed (thumped). A distance of
.0625" (1.5mm) to .188" (5mm) will do fine for this gap. When additional cable is
available, it may be connected to the test cable at this point so the fault will not be
exactly at the end. Temporarily short the gap with a jumper and observe the radar
screen. Remove the short at the gap.
4. Push the START button. A second trace(reference) will appear and the words
“WAITING FOR THUMPER” will should appear at the top of the screen. The
voltage should rise to the set voltage and then discharge. When the gap fires,
the top trace should change. The fault will have a down blip just like when a
shorting lead was placed from the center conductor to the shield at the same
point. The bottom trace is the cable without the short created by the arc, and will
now be active. The left point where the two traces diverge is the fault. By
putting the right marker at this point the distance to the fault can be determined.
If the gap is too large at the simulated fault, the capacitor will not discharge and
the voltage will not fall. In that case, push the STOP button, reduce the gap, and
try again.

VON MODEL SST15-832 ARC REFLECTION SECTIONALIZING SYSTEM Page 4
III SAFETY
Personnel safety is a most vital concern when sectionalizing. Only qualified electrical
personnel should operate this equipment. Always follow your company’s safety procedures.
If any recommendation in this manual conflicts with your company’s safety procedures,
contact the factory for clarification before operating the equipment.
The wearing of insulated safety gloves is strongly recommended while operating the unit
and must be worn when making or breaking connections to the faulted cable being worked
on. ALWAYS ground the faulted cable with a properly sized grounding set before touching
the cable termination and making connections to this equipment .
Always ground the cable to be connected to before connecting or disconnecting this unit.
This equipment is designed to be used on unenergized cable only. Connecting the
equipment to an energized cable causes severe equipment damage.
While using this equipment, all exposed terminations of the cable being worked on must be
roped off or otherwise protected so that the unaware can not come in contact with them.
In sectionalizing, grounding is the most important concern and safety precaution. The
heavy green ground lead must be connected to same ground system to which the cable
neutral is connected. BEFORE USE: ALWAYS check to insure that the high voltage output
is tied to the center conductor of the faulted cable and the green high voltage return is
connected to the faulted cable neutral.
THE MOST IMPORTANT SAFETY FEATURE: A full recognition on the part of the operator
of the inherent danger always present with the use of high voltages will be the most
important safety feature that can be applied in the use of this equipment. Your operating
procedures should be so designed as to minimize this danger. The operator of this
equipment should be responsible for seeing that each member of the assisting crew is
thoroughly familiar with the dangers involved.

VON MODEL SST15-832 ARC REFLECTION SECTIONALIZING SYSTEM Page 5
IV DESCRIPTION AND SPECIFICATIONS
The Model SST15-832 is a self contained portable unit for determining the distance to a
fault in a URD loop by the Arc Reflection Method. The weather resistant unit is designed to
be operated in most all weather conditions from its internal 12 volt battery, an external 120-
240 volt source or an external car battery.
System Specifications
!Capacitor bank provides 832 joules at 15 kV (7.4 mfd)
!Simplified controls: Pushbuttons: "START","STOP", “RADAR/THUMP”, Knob
“VOLTAGE ADJUSTMENT”, Radar Controls; Toggle switch "ON/OFF"
!Gap and discharge are electrically operated.
!0-15 kV digital kilovoltmeter
!Discharge voltage preset to 15 kV. Unit can be discharged at other voltages using the
VOLTAGE ADJUSTMENT knob.
!Pulse interval 15 seconds
!Distance: Digitally displayed on the display. The resolution is .5% of the range
selected.
!Ranges: 0- 500, 1500, 3000, 6000, 12000, 24000 and 48000 feet (0-150, 500, 1000,
2000, 4000, 8000, 16000 meters) when using a velocity propagation factor of 50.0%.
The ranges are selected by pushing the "RANGE" button and then the “UP” or
“DOWN” arrow buttons.
!Velocity Factor: Digitally shown on the screen. The initial turn on value of 53.0% can
be increased or decreased to the desired value. The velocity factor can be set from
25.0% to 99.0%
!Screen: LCD 3.5"(8.9 cm) x 4.5" (11.4 cm) with 320 x 240 dot matrix providing both
trace and text. The display can be easily read in direct sunlight. A backlight is
provided so the screen can be viewed in total darkness.
!Memory: Fifteen memories are provided for storage of traces. Traces are stored using
the options menu.
!Environmental: Operating temperature -25°F (-31°C) to 110°F (43°C). Sealed so it
can be operated in the rain. The radar screen is backlighted so the unit can be
operated in total darkness.
!Battery: The internal battery charger has a regulated output so the unit can be left in
the charge mode without damaging the battery. The external 12 volt DC input is
protected against polarity reversal. The external 12 volt DC source is connected to the
unit in parallel with the internal battery and charges the internal battery. The unit
automatically switches from internal 12 volt DC to external 120-240 volt AC when
connected to 120-240 volts AC.
!Leads: 15 foot (4.5m) long shielded high voltage lead with male MC connector. A hot
line clamp, vise grip and elbow adapter with female MC connector are provided to
terminate the high voltage lead. Longer lengths are available by request. 15 foot
(4.6m) #2 ground cable

VON MODEL SST15-832 ARC REFLECTION SECTIONALIZING SYSTEM Page 6
V CONTROLS AND INDICATORS
ON- OFF switch operates the main power.
START pushbutton - When the "START" pushbutton is pushed the motorized discharge
switch opens, the motorized gap opens, and the high voltage supply begins charging the
internal capacitor bank to the set limit. The “START” pusbutton also toggles the TDR
between arc reflection and radar modes. In the RADAR position the sentence "WAITING
FOR THUMPER" must appear at the top, If “WAITING FOR THUMPER” does not show
push the “START” pushbutton a second time. “WAITING FOR THUMPER” indicates the
system is armed and can be triggered by a "thump" The trigger pulse from the thump starts
the ARC REFLECTION SEQUENCE. After a very short delay which is controlled by the
DELAY switch, a radar pulse is injected into the faulted cable. The resulting waveform is
automatically transferred into the bottom trace.
STOP pushbutton- Drops out the high voltage ready relay which kills the high voltage
supply, closes the motorized discharge device to discharge any internally stored charge,
and after a delay closes the impulse control gap to discharge the output cable.
RADAR/THUMP pushbutton- Alternates mode of operation between “Radar” or Arc
Reflection for pre-location and “Thump” for pinpointing. When in “Thump” mode, the TDR
screen will go blank, to indicate this..
VOLTAGE ADJUSTMENT knob - adjusts the discharge voltage from a low value to the
maximum voltage of 15kV.
GAIN button - Provides manual vertical gain adjustment from 0 to 20 dB by using the up
and down arrow keys
OPTIONS pushbutton - Pressing the OPTION key presents a menu of available options
such as delay and left starts. This button is not normally used during operation.
RANGE pushbutton- allows the operator to use the arrow buttons to change the range. The
width of the transmitted pulse is adjusted automatically when the range is changed. When
the power is turned on, the unit will automatically attempt to find the end of the cable and
select the appropriate range. If the software is unable to identify the end of the cable, the
default (normally 1500 foot/500m) range is automatically selected. The current range is
displayed in the bottom right hand corner of the screen.
ARROW / pushbuttons- Changes the function where the “brick” or onscreen is
located.
RIGHT MARKER pushbutton - Allows the operator to use the arrow buttons to move the
right vertical line. The vertical line on the right of the display that sets the end point for all
measurements.
LEFT MARKER pushbutton - Allows the operator to use the arrow buttons to move the left
vertical line. The vertical line on the left of the display sets the beginning point for all
measurements. When the radar is turned on the left marker is put at the saved end of the

VON MODEL SST15-832 ARC REFLECTION SECTIONALIZING SYSTEM Page 7
test lead position. This setting is changed via the options menu.
VELOCITY pushbutton - Allows the operator to use the arrow pushbuttons to adjust the
velocity factor. Adjust velocity factor as needed to match the faulted cable. When the unit
is initially turned on, the radar is automatically set to the default VF of 53% (Correct for most
primary cable)
TRACE pushbutton- Allows the operator to use the arrow pushbuttons to move the bottom
waveform up and down.
CONTRAST knob- This control adjusts the LCD background intensity and allows the
operator to optimize the contrast of the display for the particular viewing conditions such as
direct sun or shade. The backlight is always on.
LCD DISPLAY - All information is displayed on this screen. The number in the bottom left
corner is the distance between the two markers. The number in the bottom center is the
velocity factor. The number in the bottom right corner is the current range. When a single
trace is shown (active radar mode), it is “active” and shows what the unit is currently
connected to. When two traces are shown (arc reflection mode), the bottom trace is an
active trace and the top trace is the “captured” trace from the arc.
The FUSE is next to the on off switch. This 12V control fuse is rated 10 amps slow blow
and disconnects the internal battery from the control circuit and motors. The fuses are
intended to limit and damage due to a component failure or short to the case. Remove the
fuses and unplug the unit when taking the unit out of it’s case for maintenance.
VI-A BASIC OPERATION
Practice in a test situation with the radar before field use is very important. Be sure that you
know how to locate the end of the units test lead with the radar before connecting to a
faulted cable. Sample traces in various situations are provided in later sections.
1. Remove all the green ground cable and uncoil it. Route the cable without loops to the
system neutral and tightly fasten its clamp to the ground grid where the faulted cable
neutral is connected. Connect the output lead of the system to the faulted cable or
loop. The output lead can be terminated with a hot line clamp, vise grip, or feed
through adapter since MC connectors are provided. Be sure the ground return clamp
(normally painted green) fastened to the shield of the coaxial HV output cable is
connected to the neutral of the faulted cable as close to the cable end as possible.
This connection should be closer to the faulted cable than the green safety ground.
Connect the center conductor of the HV output lead (normally marked with red) to the
center conductor of the faulted cable.
2. The unit can be operated from its internal battery, an external battery, or 120-240 volts
AC. To operate from an external battery plug in the battery leads to the DC power
input connector and then connect to an external battery. To operate from 120-240
volts AC connect to a 120-240 volt source.

VON MODEL SST15-832 ARC REFLECTION SECTIONALIZING SYSTEM Page 8
3. Turn the unit ON.
4. Identify the far end of the cable under test. When the unit is turned on, it will
automatically attempt to mark the far end of the cable. Always look at the trace to see
if you agree with the software. If the Autorange software fails the unit will go to the
default range (normally the 1500 feet/500 meters). Increase the range until the
upward blip typical of the open end is seen on the display. The relative size of the blip
depends on the length of the cable and how much pulse energy is absorbed by the
cable. To increase the range: first push the Range button, then press the up Arrow
button. If the you pass the range that puts the cable end closest to the right side of
the display, push the “DOWN” arrow button until the desired range is selected. As the
ranges get longer the amplification normally needs to be increased with the GAIN
button.
If a downward deflection is seen instead of an upward deflection, either the end of the
cable is shorted or there is a grounded fault in the cable.
To verify that a given upward blip is the cable end, alternately ground and open the far
end while observing the display. The end blip will be downward when the end is
grounded and upward when it is open.
Normally the far end has a distinctive up blip and is the highest up indication on the
waveform. If the cable has a fault with low resistance (less than 200 ohms at 10 volts)
a down blip will appear at the fault. The far end of the cable will not show past such a
low resistance fault.
5. The maximum voltage can be adjusted using the VOLTAGE ADJUSTMENT knob. It
is recommended that except on 5kV and below cable, the VOLTAGE ADJUSTMENT
be kept at or near maximum, as the transformers in the loop dissipate much of the
energy. With the entire section on the display, push the START button until the
sentence “WAITING FOR THUMPER” appears on the top of the display and the
thumper will start charging up to the selected voltage. When the gap fires, the ARC
REFLECTION SEQUENCE should begin in the radar and a new trace made during
the arc will appear at the bottom.
6. On loops with transformers connected the sound inside the unit is the same for a good
cable and a faulted cable. If the radar pulse that was sent out by the trigger circuit
arrived a the fault while it was arcing over to ground the top memory will contain the
trace of the cable showing a low impedance down blip at the fault. If both displays are
the same then there is no apparent fault. Two approaches are available if the radar
does not still indicate the fault.
7. After pulsing the cable, the bottom trace will be identical to the top trace until the
location of the fault. At that point the bottom trace will diverge and change shape from
the top reference trace. The first left hand point at which the two traces diverge is the
fault. (After the divergence the two cable waveforms do not match up) Units with
Autolocate software will attempt to automatically mark this point. If autolocate fails
you can manually determine the distance to the fault by setting the left and right hand
markers. The left marker is normally preset for the end of the test lead and the

VON MODEL SST15-832 ARC REFLECTION SECTIONALIZING SYSTEM Page 9
beginning of the faulted cable. This eliminates the need to subtract the apparent lead
length from the distance shown. The right marker is normally adjusted to the location
of the fault to give the distance to the fault from the hook up location. Distance
measurements are displayed in the lower left portion of the display which represent
the distance between the left marker and the right marker.
8. Push the STOP button to discharge the cable and the internal capacitor.
9. Use the distance indicated to determine which section the fault is in.
VI-F SECTIONALIZING URD LOOP SYSTEMS
The arc reflection system is a method for determining the faulted cable section in a loop
without using fuses and subjecting the system to excessive fault currents or opening each
transformer cabinet to inspect fault indicators. By connecting the SST15-832 at the open
cutout or at a center transformer cabinet the operator can determine the distance to the
cable fault using the radar. Then the faulted cable section can be disconnected and all
customers can be returned to service. When all customers are returned to service the
SST15-832 can then be connected to the faulted cable and the distance to the fault
determined using traditional methods.
Some customers have expressed concerns that putting an arc reflection pulse on the
source side or transformers feeding customers would send damaging pulses into the
customers system. Only a small percent of the energy can go through the transformer.
Since the SST15-832 is rated 60 watts and typically the customers connected are
attempting to pull many thousands of watts there is no way that damaging pulses can get
into the customers system.
Currently the most popular approach to sectionalizing using an arc reflection system is to
open a transformer halfway between the pole and the open point. The arc reflection system
is then connected to both pieces of the circuit one at a time to determine where the fault is
located. If both traces are identical on a run then it does not have a fault and can be
refused. The arc reflection system will not locate internal transformer failures so if the fuse
blows each transformer in that section should be inspected for failure. The arc reflection
system should be connected to the second section and impulsed using the “START” button.
The low voltage radar pulses alone can be used to verify that the faulted cable has been
disconnected from the system so that power can be restored to the customers.

VON MODEL SST15-832 ARC REFLECTION SECTIONALIZING SYSTEM Page 10
VI-B HINTS AND TYPICAL TRACES
1. The radar must show the faulted cable ends before any attempt is made push
the START button which automatically puts out a high voltage pulse.
2. Remember that the magnitude of down blip at the fault can not be greater than the
magnitude of the up blip due to an open circuit at the same point.
3. If different types of cable are spliced together, the trace itself can go up or down after
the discontinuity at the splice.
4. The first step in sectionalizing using radar is to find both ends of the cables. This is
done by touching each end to ground and finding the left most point where the trace
changes direction.
5. Notice that locating the beginning of the cable by shorting it to ground requires the
most skill. Everything past the fault changes.
6. Notice that a short at the end of the cable is easy to find and locate.
7. Remember that the first major divergence between the reference trace and the
active trace is what you are looking for. The down blip at the fault may not be
down on the screen but only below the reference trace. In some faults at the
divergent point the captured trace is a straight line while the reference trace goes
up. This is most likely to happen on very short cable where the cable trace is
very wavy.
8. When the cable trace looks similar to the trace of the end of the test lead alone
then the faulted cable is very short (most likely burned in two pieces) Very short
runs have a large number of ups and downs in the waveform.

VON MODEL SST15-832 ARC REFLECTION SECTIONALIZING SYSTEM Page 11
Figure 1
Figure 2
Figure 3
Figure 1 shows a typical cable trace for
an isolated run. The cable is
approximately 589 feet long. Notice
how the right marker is at the point
where the upward movement of the
trace begins.
Figure 2 shows a typical faulted trace.
Notice that the right marker has moved
to the beginning of the downward
movement of the lower trace. The
distance now shows being
approximately 355 feet from the hook
up point to the fault.
Figure 3 shows another typical faulted
trace. This time the fault is at
approximately 387ft.

VON MODEL SST15-832 ARC REFLECTION SECTIONALIZING SYSTEM Page 12
Figure 4
Figure 5
Figure 6
Figure 4 shows a typical sectionalizing
trace. The up blips before the end of the
cable are made by transformers.
Splices along the cable route make the
same signature but smaller.
Figure 5 shows a faulted trace. Notice
that the fault is close to the far end of
the cable. Instead of measuring from
the current end to the fault, it may be
easier to measure from the far end.
The distance from the far end can be
determined by subtracting the distance
to the fault (948 ft) from the previously
determined length of the cable (1022 ft).
This gives you an approximate distance
of 74 feet from the far end of the cable.
Figure 6 shows another faulted trace
for the cable. The fault is at
approximately 364 feet.

VON MODEL SST15-832 ARC REFLECTION SECTIONALIZING SYSTEM Page 13
VI-E TESTING AN ISOLATED CABLE
NOTE: This will not work on a loop with transformers connected. The transformer will act as
a connection to ground and discharge the capacitor energy.
NOTE: This will not work on EZRS15-1264 without a voltage adjust knob.
The voltage may be adjusted using the VOLTAGE ADJUSTMENT knob. Push the START
button. If the cable is good, the voltage will not drop significantly when the gap closes and
connects the internal capacitor bank to the external cable. A small voltage drop is expected
on good cables proportional to the length of the cable due to charging current of the cable.
Push the STOP button to discharge the internal capacitor and the external cable.
VI-G RADAR OPTIONS MENU
The options menu allows you to change the default settings and access advanced features.
This menu is not normally used in day to day operation of the equipment. The available
options are different depending on the firmware revision. Please follow the onscreen
instructions for your specific firmware revision. Please contact the factory before attempting
to modify parameters in the options menu.
VII IN CASE OF DIFFICULTY
Opening the unit should only be done by trained, and qualified individuals under consultation
with the factory.
To Open Unit remove the hex head screws from around the edge of the unit. There are ten
(10) screws total around the edge. This is most easily done with a 5/16" nut driver. Take
care to save the screws, lock washers and flat washers. The unit pulls straight up and out of
the case. About half way up you must pause, and disconnect the external 12V DC and 120-
240V AC connections. Set the unit on a clean, dry surface. If troubleshooting calls for
operation of the equipment outside the case, then the surface the unit is sitting on must be
insulating to 20kV.
IN CASE OF LOW BATTERY
In case of low or dead battery, connect the unit to 120-240V AC or and external 12V DC
source. Cables have been provided for this purpose. If the battery is low, then the unit
should begin to work immediately. If the battery has gone completely dead, then it may be
required to charge the unit for several minutes before it will come on to operate.
NOTE: The sealed lead acid battery used cannot survive discharging below approximately
10.5V. There is circuitry inside the unit that will try to prevent this situation. If this still
happens, the unit will only operate from external power and the battery needs to be replaced
as soon as possible.
More To Be Added Later

VON MODEL SST15-832 ARC REFLECTION SECTIONALIZING SYSTEM Page 14
VIII TEST LEADS, BATTERY MAINTENANCE, AND STORAGE
The high voltage test lead is provided with a male MC connector. This allows the lead to be
terminated with a hot line clamp, vise grip, or elbow adapter. Push the male connector into
the female to release the locking connection. Be careful to insure the sliding ring of the male
probe stays movable. Any substance which causes the ring to not move will prevent the
female connector from being removed from the male. The high voltage lead is available
with RG-8U polyethylene cable or EPR x-ray cable.
The ground lead must always connected to the neutral bus! Be sure to pull all the cable out
of the storage area and lay on the ground such that there are no loops.
The internal sealed lead acid battery should be kept charged to at least 11.5 volts during
storage since it can be severely damaged if stored below 10.5 volts. The internal battery
charger regulates the voltage at approximately 13.6 to 13.8 volts so the unit should be left
connected to 120-240 volts AC to store between uses. To check battery voltage at any time
use battery check switch. The battery can also be charged by connecting the DC input to the
unit to a van or truck battery or to an external battery charger.
The battery will eventually wear out. Projected life is 2 to 5 years. Indications of a worn out
battery are that the unit will only run a short time on battery power. Contact the factory for
details on replacing a dead battery
Keep the outer case clean and store in a dry location to prevent corrosion of the internal
connections. Tighten any parts or connections that loosen in use.
The unit should be stored plugged into a 120-240 volt supply or external 12V Supply such as
a vehicle power source.

VON MODEL SST15-832 ARC REFLECTION SECTIONALIZING SYSTEM Page 15
IX CIRCUIT DIAGRAM AND PARTS LIST
To Be Added Later

VON MODEL SST15-832 ARC REFLECTION SECTIONALIZING SYSTEM Page 16
X RADAR THEORY
Cable radar has been available for over thirty five years. Cable radar is also called the
Pulse-Reflection Method, the Pulse-Echo Method, and Time-Domain Reflectometry.
Because it works well only on shorts (less than 150 ohms at 10 volts) and opens, it has
mainly been used in the telephone industry on communication cable. Radar can be
successfully used to locate faults on electric power cable faults by permanently lowering the
fault resistance by burning or temporarily lowering the fault resistance using the arc reflection
method.
Short duration pulses are transmitted along a cable by a radar. When these pulses reach a
discontinuity such as a splice or fault in the cable, a reflection occurs peculiar to the type of
discontinuity. By observing these reflections on a CRT or scope and knowing the
propagation velocity or the speed at which the pulse travels on the cable, the distance to the
discontinuity can be determined. The cable radar is essentially a pulse generator and a
cathode-ray oscilloscope. Special circuitry is normally provided with the oscilloscope for
determining the distance and for changing the pulse length for different distance ranges.
Pulses are generated and put on a cable that must have consistent distributed capacitance.
A reflection will result when a discontinuity or significant change of impedance occurs. An
upward reflection or blip would indicate a higher-impedance discontinuity such as the cable
ends, or a place where the cable neutral is missing. A downward reflection or blip will result
from a lower-impedance discontinuity such a cable fault. The reflection is upwards when the
impedance of the discontinuity is above the characteristic impedance of the cable. The
reflection is downwards when the impedance of the discontinuity is below the characteristic
impedance of the cable.
The characteristic impedance of a transmission line is important since it affects what types of
discontinuities will show up on the radar. However it cannot be measured directly with an
impedance bridge for a finite length of line. It can be calculated from the distributed-circuit
co-efficients of the line at any frequency using the following basic equation.
The equation contains the parameters of resistance, conductance, inductance, and
capacitance and is also related to frequency. As the frequency is increased above 1
megahertz, the above equation will reduce to a simplified equation based on the distributed
inductance and capacitance; and this simplified equation is shown as follows.
In the case of primary underground cable which acts as a coaxial line we have the published

VON MODEL SST15-832 ARC REFLECTION SECTIONALIZING SYSTEM Page 17
equation:
K = dielectric constant based on the insulation material
r1= inside radius of insulation
r2= outside radius of the insulation
Thus the characteristic impedance of the cable varies with the diameter of the cable,
thickness of the insulation and the type of insulation. A few common values of Z0are 20
ohms for 35kv 1000MCM polyethylene cable, 42 ohms for 35kv 1/0 polyethylene cable, and
74 ohm for RG59U polyethylene cable.
Any change in Z0along the length of the cable to the fault will cause reflections. The size of
the blip will be based on the reflection coefficient whose maximum value is 1 or -1. The
equation for the reflection coefficient p is:
At the far end terminals with the following impedances:
Z = 0 (short circuit) p = - 1
Z>> Z0p = 1
Z = Z0p = 0
Z = 1/2 Z0p = -.33
Thus when the fault impedance exactly equals the cable impedance it will not show up on
the screen. Fortunately this almost never occurs in the field.
Distance is figured by a radar using the time delay which is based on how fast the radar
pulse travels along the cable. The distance to the fault is related to the time the pulse takes
to get to the fault and return. The accuracy of the speed of the pulse in the cable (called the
velocity of propagation) determines how accurately the distance to the fault can be
calculated.
XI THEORY OF ARC REFLECTION METHOD
The arc reflection method utilizes the low resistance path to ground (less than 50 ohms)
created at the cable fault by an arc. The arc is provided by a capacitor discharge fault
locator (thumper) to temporarily display the fault on a standard radar. Using the low
resistance of an arc overcomes the main limitation in the past of radars which alone could
not see the high resistance faults most common in underground primary power cable. The
arc reflection method does not overcome the limitations of radar itself. The operator must
become proficient in the use of the radar especially in recognizing faults near the ends of the
cable. On cable with missing neutral, a cable radar may not even show the far end of the

VON MODEL SST15-832 ARC REFLECTION SECTIONALIZING SYSTEM Page 18
cable. Because of the time it takes for a reflection on the radar to recover to the zero level,
the operator must be skilled when locating faults near discontinuities in the cable such as
splices or the cable terminals. The radar is connected to the faulted cable through a
coupler(filter) and displays the low resistance at the fault as a down blip during the time of
the arc. The coupling system performs three functions.
1. Induce the high frequency radar signal onto the faulted cable through high voltage
isolation required to protect the radar.
2. Provide a wave trap so the radar does not see the low impedance of the impulse fault
locator with each discharge.
3. Lengthen the impulse with a large air coil inductor so that it provides current to the arc
at the fault for a longer time so the fault position can show up on the radar. The
inductor keeps the current flowing into the low resistance arc until the charge in the
capacitor bank is dissipated. Increasing the size of the capacitor bank in the impulse
fault locator lengthens the pulse and thus the time of the arc at the fault.
When the radar signal is induced on the cable, all discontinuities in the cable such as
splices, change in cable insulation, change in neutral construction, connected transformers,
and ends show up on the radar screen.
This system:
1. Reduces the number of thumps required to pinpoint a cable fault.
2. Uses standard radar so operator training is simplified.
3. Shows cable ends and splices so that an approximate location can be determined
looking at the screen.
4. Provides the conductor distance to the fault. Only the conductor distance is displayed.
Actual ground distances are subject to variations caused by the cable route and the
cable depth. The accuracy of any distance determined by the radar is dependent on
the correct velocity of propagation and the operator's skill.
XII CABLE DISTANCE MEASUREMENTS
The distance provided by a radar is conductor distance not ground distance. Accuracies of
2% of cable length are possible but not often achieved. Information is provided in this section
on how to get the most accuracy using the radar. For maximum accuracy use the two
terminal method where the fault distance is determined from both ends of the cable. The
fault will be between both marks made using these distances.
All distances provided by a radar are determined using time measurements based on the
speed at which the pulses move up and down the cable. The pulse speed is based on
characteristics of the cable such as conductor size, shielding type, insulation thickness,
eccentricity, and insulation material. The speed changes as the cable insulation ages. If the
neutral shield is solid, the dielectric constant of the insulation is the determining factor in the
velocity of propagation. For maximum accuracy, the speed (or time) must be determined
from a known length of cable with identical characteristics to the cable being worked upon.
This speed is entered into each radar in several forms. The speed is normally compared to
the velocity of an ideal conductor in free air of 983 feet/microsecond.
To determine the true velocity of propagation or velocity of propagation factor of a cable the
following procedure is recommended.