3
965AMS
Fault Locating Overview
Presented by
Gary Morris
Outline
• Fault Locating
– RFL
– TDR
Fault Locating
• When to Use TDR and RFL
• Opens and TDR for Capacitive Faults
• RFL and TDR for Resistive Faults
When to Use TDR or RFL
• You should know what fault or condition you have
before trying to isolate with the RFL or TDR.
TDR
RFL
Load Coil
Yes
No
Tip/Ring Open
Yes
No
Water
Yes
No
Bridge Tap
Yes
No
High Res Opens
Yes
No
= or < 500 Ohms
Yes
Tip Ground
No
Yes
Ring Ground
No
Yes
Battery Crosses
No
Yes
Short
TDR
• Press the TDR
key
• Choose Setup to enter cable information.
• When finished choose a test and press OK
TDR Trace Examples - Open
• Here is a pair the is open at 1780 feet.
TDR Tip Open
• Here is a pair the has an open tip open at
780 feet.
TDR Series Resistance
• Here is a pair the has a high resistance
open at 950 feet.
TDR Short
• Here is a pair the has an short at 1000 feet.
TDR Water
• Approximately 100 Feet of water.
Expert Pair Test
RFL Fault Locating Tips
1.
RFL test is used for faults under 20 mΩ.
2.
Always draw a diagram of the fault for better analysis.
3.
There three factors that is always involved in RFL (Resistance Fault Locating) - Gauge, Length and
Temperature of the cable. Any two of the three must be known for RFL to work. The best option is to know the
Gauge and Length of the section under test and the test set will compute the cable temperature. This is done
during RFL Setup.
4.
A pair may have some light faults in it but it can be used as a ‘Good Pair’ as long as the light fault is at least 200
times better than the magnitude of the fault in the faulted pair. Ex: If the fault on a pair is 1 kilo-ohms, a pair
with a 200 kilo-ohm fault can be used as a good pair. Of course, the higher the magnitude, the better.
5.
For best RFL accuracy , make a long cable section shorter by going to the middle of the section and open the
pair to cut it in half. Check for the fault in one direction and then the other and then isolate the clean side.
Repeat the process until the cable section becomes short enough where the following becomes practical:
a)
the length of a short section can easily be measured physically with a roller tape. If gauge and section
length are known, the test set will compute cable temperature.
b)
With a short cable section, the use of a reel of jumper wire as a “Good Pair” placed above ground is now
possible, instead of digging into the cable for a good one. Saves time. With a separate good pair and
knowing the gauge and length of the section is the best and most accurate RFL option.
6.
In a ‘Single Pair Hookup’, the best good conductor to use is the mate of the faulted one and the next best is any
good conductor from any of the adjacent pairs in the same group. Ex: If a pair has TIP(A) is faulted and
RING(B) is good, RING(B) is then the best good conductor to use to shoot the fault on TIP(A).
7.
If DTF (Distance-To-Fault) and DTS (Distance-To-Strap) are equal, the fault is either at the strap or beyond.
RFL TIPS
The use of a
“Separate Good Pair”
is always the most accurate way to
locate any type of a resistance fault.
Resistance Faults
GROUND : A fault between ‘Tip [A]’ and ‘Ground’, ‘Ring [B]’ and ‘Ground’ or both conductors and ‘Ground’.
Resistance Faults Cont..
SHORT : A fault between ‘Tip [A]’ and ‘Ring [B]’ conductors.
Resistance Faults Cont..
Battery CROSS : A fault between a working pair and a non-working pair (pair under test).
Pair # 1 - Working pair
Pair # 1 - Working pair
-48 VDC
Solid
-48 VDC
Cross Fault
Water
-46 VDC
-7 VDC
Pair # 2 - Non-working
(Pair under test)
Resistive Cross fault
RFL Hookup Examples
“Separate Good Pair”
It can be any pair of any gauge, longer or shorter than the faulted one,
it doesn’t matter.
For short cable section lengths (1000 feet or less), the good pair can be a
reel of a CO jumper wire or a telephone jacketed wire placed above ground.
Reel of CO jumper wire
End-2
or
Good Pair
telephone jacketed wire
End-1
Good Pair
Strap
Faulted Pair
Ground
Near-End
Shield/Ground
Fault
Far-End
“Separate Good Pair”
It can be any pair of any gauge, longer or shorter than the faulted one,
it doesn’t matter.
For long cable section lengths (several thousand feet), the good pair can come
from another cable adjacent to the cable with the faulted pair.
End-2
Good Pair
Good Pair
End-1
Strap
Fault
Common
Faulted Pair
Faulted Pair
Short
Near-End
Far-End
How To Extend The “Far-End Strap” If Necessary
Reel of CO jumper wire or
telephone jacketed wire or
any two wires, same length
(any gauge)
Good Pair [ from a distant cable ]
Strap
extension
End-1
Far-End Strap
Faulted Pair
Near-End
Short
Common
Far-End
End-2
RFL Single Section Setup
T-G
R-G
Short
Tip Cross
Ring Cross
Wet Pulp
Choose fault type.
Choose single pair or
separate pair.
Select single or multiple
section.
Choose the gauge.
Length or temperature
must be “unknown.”
RFL Multiple Section Setup
T-G
R-G
Short
Tip Cross
Ring Cross
Wet Pulp
Choose fault type.
Choose single pair or
separate pair.
Select single or multiple
section.
Choose the gauge.
Length or temperature
must be “unknown” on last
section.
Estimating Cable Temperature
Aerial Cable:
1. If cable is not in direct sunlight. Add 20oF to the air temperature.
2. If cable is in direct sunlight. Add 40oF to the air temperature.
Buried Cable:
1. Use temperature of tap water (city water). Let water flow out of a water
faucet for several minutes and then measure the temperature.
2. In cold climates, use soil temperature at cable depth.
RFL Cont..
Press setup to
change section
1 from 24 awg
to 26 awg.
3640.8 ft
234.8 ft
3406 ft
Distance To Strap (DTS)
Distance To Fault (DTF)
Strap To Fault (STF)
= 4000 feet
= 2500 feet
= 1500 feet
The bridge tap does not affect this reading.
1000 ft
3000 ft
500 ft
400 ft
Distance To Strap (DTS)
Distance To Fault (DTF)
Strap To Fault (STF)
= 4000 feet
= 1000 feet
= 3000 feet
Fault
measures
here!
1000 ft
3000 ft
500 ft
400 ft
Distance To Strap (DTS)
Distance To Fault (DTF)
Strap To Fault (STF)
= 3900 feet
= 400 feet
= 3500 feet
Fault
measures
here!
1000 ft
3000 ft
500 ft
400 ft
Questions ?
• Live Demo
• 1-800-426-8688 Option 3