3Fault Locating When to Use TDR and RFL Opens and TDR for Capacitive FaultsRFL and TDR for Resistive Faults
4When to Use TDR or RFLYou should know what fault or condition you have before trying to isolate with the RFL or TDR.TDRRFLLoad CoilYesNoTip/Ring OpenWaterBridge TapHigh Res OpensShort= or < 500 OhmsTip GroundRing GroundBattery Crosses
5TDR Press the TDR key Choose Setup to enter cable information. When finished choose a test and press OK
6TDR Trace Examples - Open Here is a pair the is open at 1780 feet.
7TDR Tip OpenHere is a pair the has an open tip open at 780 feet.
8TDR Series ResistanceHere is a pair the has a high resistance open at 950 feet.
9TDR ShortHere is a pair the has an short at 1000 feet.
12RFL Fault Locating Tips RFL test is used for faults under 20 mΩ.Always draw a diagram of the fault for better analysis.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.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.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: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.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.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).If DTF (Distance-To-Fault) and DTS (Distance-To-Strap) are equal, the fault is either at the strap or beyond.
13RFL TIPS The use of a “Separate Good Pair” is always the most accurate way tolocate any type of a resistance fault.
14Resistance FaultsGROUND : A fault between ‘Tip [A]’ and ‘Ground’, ‘Ring [B]’ and ‘Ground’ or both conductors and ‘Ground’.
15Resistance Faults Cont.. SHORT : A fault between ‘Tip [A]’ and ‘Ring [B]’ conductors.
16Resistance Faults Cont.. Battery CROSS : A fault between a working pair and a non-working pair (pair under test).Water-48 VDC-7 VDCResistive Cross faultPair # 1 - Working pairPair # 1 - Working pairPair # 2 - Non-working(Pair under test)-48 VDC-46 VDCSolid Cross Fault
17RFL Hookup Examples Resistance Fault Locate 4-10 Press: to choose the type of hookup (single pair) or (separate good pair).Note: Defaults to the last setup.Explain: The clip and strap hookups. The user now hooks up the test setat the near end, and the strap at the far end.Press: to setup for Single Pair Hookup.1015 Simulator: Turn Switch #3 ON;Hookup test set clips to terminal#1; Hookup Strap at terminal #5.Tip of pair 2 is GoodRing of pair 2 is faulted 10K Ohms Ground.Press: to use the setup and measure.Go to the next slide.
18telephone jacketed wire “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 areel of a CO jumper wire or a telephone jacketed wire placed above ground.Reel of CO jumper wireortelephone jacketed wireEnd-2Good PairGood PairEnd-1Faulted PairStrapGround FaultNear-EndShield/GroundFar-End
19from another cable adjacent to the cable with the faulted pair. “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 comefrom another cable adjacent to the cable with the faulted pair.End-2Good PairGood PairEnd-1StrapFaultCommonFaulted PairFaulted PairShortNear-EndFar-End
20How 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 extensionEnd-1End-2Far-End StrapCommonFaulted PairShortNear-EndFar-End
21RFL Single Section Setup Choose fault type.Choose single pair or separate pair.Select single or multiple section.Choose the gauge.Length or temperature must be “unknown.”T-GR-GShortTip CrossRing CrossWet Pulp
22RFL Multiple Section Setup 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.T-GR-GShortTip CrossRing CrossWet Pulp
23Estimating 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.
24RFL Cont..Press setup to change section 1 from 24 awg to 26 awg.ft234.8 ft3406 ft
25Distance To Strap (DTS) = 4000 feet Distance To Fault (DTF) = 2500 feetStrap To Fault (STF) = 1500 feetThe bridge tap does not affect this reading.1000 ft3000 ft500 ft400 ft
26Distance To Strap (DTS) = 4000 feet Distance To Fault (DTF) = 1000 feetStrap To Fault (STF) = 3000 feetFault measures here!1000 ft3000 ft500 ft400 ft
27Distance To Strap (DTS) = 3900 feet Distance To Fault (DTF) = 400 feet Strap To Fault (STF) = 3500 feetFault measures here!1000 ft3000 ft500 ft400 ft