Electrical Cable Fault Locating

WELCOMEWELCOME

CANADIAN ELECTRICITY FORUMCANADIAN ELECTRICITY FORUMELECTRIC POWER SYSTEM MAINTENANCEELECTRIC POWER SYSTEM MAINTENANCE

ELECTRICAL CABLE FAULT LOCATINGELECTRICAL CABLE FAULT LOCATING

GORD PARKER, C.E.T., Radiodetection CanadaGORD PARKER, C.E.T., Radiodetection Canada

(Details of presentation in binder)(Details of presentation in binder)

TYPES OF FAULTSTYPES OF FAULTS

bb Many types of faultsMany types of faults Short, Low, High, Infinite (open) ResistanceShort, Low, High, Infinite (open) Resistance

Low

Fault Location MethodsFault Location Methods

A-Frame

Time Domain Reflectometry

High Voltage Surge

Wheatstone Bridge

Intermittent Fault Location

Integrated Test Sets

CABLECABLEFAULTFAULT

LOCATINGLOCATINGMETHODMETHODFLOWFLOWCHARTCHART

A-FRAME BASICSA-FRAME BASICS

bb Must be earth fault. Cable must be isolated.Must be earth fault. Cable must be isolated.

bb The A-frame basically turns the locator into a veryThe A-frame basically turns the locator into a verysensitive micro-voltmeter.sensitive micro-voltmeter.

bb The flow of current through the resistance of theThe flow of current through the resistance of theearth creates a small voltage.earth creates a small voltage.

bb The polarity of the voltage gives the direction to theThe polarity of the voltage gives the direction to thefault. For this reason, transmitter now sends DCfault. For this reason, transmitter now sends DCsquare wave (shift) with AC locate tone.square wave (shift) with AC locate tone.

bb Dry topsoil, gravel, concrete and asphalt all reduceDry topsoil, gravel, concrete and asphalt all reducethe voltage that can be measured on the ground.the voltage that can be measured on the ground.

bb Good, Remote ground stake is CRITICAL !Good, Remote ground stake is CRITICAL !


bb


bb If cable under road, A-frame along the grass medianIf cable under road, A-frame along the grass medianand draw perpendicular line out from it.and draw perpendicular line out from it.

bb Scrape dry earth / rocks from under A-frame.Scrape dry earth / rocks from under A-frame.bb Bring water jug, wet down earth / concreteBring water jug, wet down earth / concretebb TDR first (coming up) to reduce walking with A-frame.TDR first (coming up) to reduce walking with A-frame.bb Trust the equipment, it is normal to lose Fwd/BkwdTrust the equipment, it is normal to lose Fwd/Bkwd

lock in the middle of long spans, if you havent walkedlock in the middle of long spans, if you havent walkedover it, keep going.over it, keep going.

bb Prelocate cable path to save time.Prelocate cable path to save time.

ADVANCED A-FRAME TECHNIQUESADVANCED A-FRAME TECHNIQUES

The TDR presents information in the form of a trace

Distance tobreak

Time Domain ReflectometryTime Domain Reflectometry How it works..How it works..

TDRs really detect ImpedanceTDRs really detect Impedance

bb When the relationship between theWhen the relationship between theinsulating materials is constant, there is noinsulating materials is constant, there is nochange in impedance and the waveform willchange in impedance and the waveform willbe constant.be constant.

.Here, the relationship has changedsignificantly with the untwisting andseparation of the pairs. The resultingwaveform shows a larger raising ofimpedance.

Here, the relationship has changedslightly with the untwisting of the pairs.The resulting waveform shows a partialopen caused by a raising of impedance.

Impedance = Series and Parallel Resistance and ComplexImpedance = Series and Parallel Resistance and ComplexInductive and Capacitive ElementsInductive and Capacitive Elements

TDRs really detect Impedance /2TDRs really detect Impedance /2

bb Small relative changes in impedance will notSmall relative changes in impedance will notshow upshow up

bb Rule of thumb is impedance change must beRule of thumb is impedance change must beunder 8x to detectunder 8x to detect

bb Often HV cables faults are 1k-100kohms and makeOften HV cables faults are 1k-100kohms and maketoo small of a reflection to be detected when HVtoo small of a reflection to be detected when HVcables characteristic impedance is ~25 ohmscables characteristic impedance is ~25 ohms

bb Concentric gives best traces, braided the worstConcentric gives best traces, braided the worstbb Heat Trace Cable very good applicationHeat Trace Cable very good application

TDR Trace SignaturesTDR Trace SignaturesWHAT THEY MEAN . . .WHAT THEY MEAN . . .

Open circuit

Short circuit

Splice / Joint

Wet splice

High resistancesplice

Transceiver(non linear response)

Tap / Lateral

Water ingress

Split and Resplit

(telecom apps)

Cross

A 100 nanosecond pulseA 100 nanosecond pulsewaveform on a straight run ofwaveform on a straight run ofstreet lighting cable. There is astreet lighting cable. There is a

complete open circuit at 280 complete open circuit at 280meters.meters.

A 100 nanosecond pulseA 100 nanosecond pulsewaveform on a straight run ofwaveform on a straight run ofstreet lighting cable. There is astreet lighting cable. There is acomplete short circuit at 280complete short circuit at 280meters.meters.

Two 25 nanosecond waveforms,Two 25 nanosecond waveforms,taken on a low-voltage networktaken on a low-voltage networksimulation cable. One waveformsimulation cable. One waveformis of a good phase and the otheris of a good phase and the other

shows the same run of cable withshows the same run of cable witha short circuit at ~40 meters (justa short circuit at ~40 meters (justahead of the cursor). The two areahead of the cursor). The two aredisplayed together with thedisplayed together with theoverlay adjusted to zero offset.overlay adjusted to zero offset.

This is a difference waveform,This is a difference waveform,using the 1 microsecond pulse,using the 1 microsecond pulse,taken on a low-voltage networktaken on a low-voltage networksimulation cable. It shows thesimulation cable. It shows thedifference between a gooddifference between a goodphase and a partial open circuitphase and a partial open circuitat 125 meters.at 125 meters.

TDR Trace of Faulted HV CableTDR Trace of Faulted HV Cable

Analysis of HV Cable TDR TraceAnalysis of HV Cable TDR Trace

bb Perfect trace, cable features are easilyPerfect trace, cable features are easilyvisiblevisible

bb Since we know cable is open circuit atSince we know cable is open circuit atnext transformer, we know that is atnext transformer, we know that is at292m292m

bb Solid cursor is at splice at 199m (93.5Solid cursor is at splice at 199m (93.5meters back)meters back)

bb Features past open are the sameFeatures past open are the samereflections just bouncing back andreflections just bouncing back andforth (distances are all multiples)forth (distances are all multiples)

bb Sometimes the end isnt what you thinkSometimes the end isnt what you thinkit is, have helper short far endit is, have helper short far end

bb This was used with A-frame, we statedThis was used with A-frame, we statedlooking from the far end and foundlooking from the far end and foundsplice had failed.splice had failed.

Using TDR measurements..Using TDR measurements..

bb Knowing Velocity Of Propagation (VOP / PVF) of cable isKnowing Velocity Of Propagation (VOP / PVF) of cable iseasier but there are ways around that.easier but there are ways around that.

Even without VOP we can use TDRs just as well ! ! (sample or ratio methods)Even without VOP we can use TDRs just as well ! ! (sample or ratio methods)

bb Have a distance from the TDRHave a distance from the TDRbb However, cables do not run in straight linesHowever, cables do not run in straight lines

Use a cable locator and measure wheel / GPSUse a cable locator and measure wheel / GPS (even C$200 GPS are 3-5m accurate now)(even C$200 GPS are 3-5m accurate now)

Make notes while wheeling off (i.e.: 65m post)Make notes while wheeling off (i.e.: 65m post)bb Cable pairs in multicore cables are laid up in spirals insideCable pairs in multicore cables are laid up in spirals inside

the sheaththe sheath The pairs in the middle are shorter than the pairsThe pairs in the middle are shorter than the pairs

closer to the sheath (only 1-2%)closer to the sheath (only 1-2%)

2-Line Live TestingView individual waveformsCompare two live lines

Show difference between two live linesCrosstalkCleans up false reflections on streetlight and similar wire

minus

=

Wet cable, operating pair. Wet cable, non operating pair.

Fault position

Hard to interpret readingsHard to interpret readings

bb Sometime due to loose wraps on cable such asSometime due to loose wraps on cable such asstreetlights, braided and triplex cablestreetlights, braided and triplex cable

bb Multiple faults, and/or Ts and splices (sometimeMultiple faults, and/or Ts and splices (sometimeundocumented)undocumented)

bb Remove other featuresRemove other featuresbb Move towards faultsMove towards faultsbb Use filtering (60 Hz. and/or averaging)Use filtering (60 Hz. and/or averaging)bb Use 2 line mode to subtract all the noiseUse 2 line mode to subtract all the noisebb Find the end first, have helper short far endFind the end first, have helper short far end

The software allows forinformation stored in theinstrument to be uploadedto a computer. Waveforminformation can bearchived, adjusted,compared to originalbenchmark, or analyzedon your PC while your TDRgoes back into the field towork for you.

PC TDR Software

HV SURGE GENERATOR (THUMPER)HV SURGE GENERATOR (THUMPER)

l Origins in the 1940sl Used to just thump and walk and listenabove ground for the whumph (sometimes atink).l New technology includes listening aids andvisual (CRT/LCD) prelocation.l Complete HV cable fault location systeml All types of fault found: high resistance, lowresistance, flashing and intermittentl Diagnosis, fault prelocation, fault pinpointing

Why Thump ?Why Thump ?

bb Unless shorted or burned open, a typical fault on aUnless shorted or burned open, a typical fault on ahigh voltage cable does not present enough of anhigh voltage cable does not present enough of animpedance change for a TDR to detect itimpedance change for a TDR to detect it

bb If there is a path to ground - A-frame is possibleIf there is a path to ground - A-frame is possible

bb With a dielectric breakdown, it looks and isWith a dielectric breakdown, it looks and isperfect at low voltages, we need to make it flashperfect at low voltages, we need to make it flash

Why Not Thump ?Why Not Thump ?

bb Some faults require higher then rated voltage to show upSome faults require higher then rated voltage to show upfaults on demand (not waiting for right combination offaults on demand (not waiting for right combination ofcircumstances)circumstances)

bb Subjecting the cable under test to repeated stresses of highSubjecting the cable under test to repeated stresses of highvoltage reduces its life expectancyvoltage reduces its life expectancy

bb Statistics prove older cables that get thumped fail muchStatistics prove older cables that get thumped fail muchfaster then non-thumped cablesfaster then non-thumped cables

bb Do what you can with low (

Typical Thumper Use

FLASHING ORINTERMITTENTFAULT

HIGHRESISTANCEFAULT

PRE-LOCATEFAULT

PINPOINTFAULT

Stage 2 Thumper setto dc mode

Stage 1Fault Diagnosis

withSurge Generator

Stage 2Prelocator

Stage 3Fine

Locator

FIXFAULT

Stage 2Thumper set to surge

mode

Typical Portable Thumper SystemTypical Portable Thumper System

Surge GeneratorSurge Generator

bb Voltage ranges: 8kV, 16kV, 32kVVoltage ranges: 8kV, 16kV, 32kVbb Make sure rated power is available in allMake sure rated power is available in all

voltage ranges (function of voltage andvoltage ranges (function of voltage andcapacitance) Add more capacitance atcapacitance) Add more capacitance atlower voltages.lower voltages.

bb Often includes D.C. mode for fault diagnosisOften includes D.C. mode for fault diagnosisand prelocation of flashing faultsand prelocation of flashing faults

bb Self dischargeSelf dischargebb SAFETY INTERLOCKS !!SAFETY INTERLOCKS !!SAFETY INTERLOCKS !!SAFETY INTERLOCKS !!

Thumper System ComponentsThumper System Components

Three on board TDR technologies:-1. TDR for evaluation prior to applying HV2. I.C.E. Impulse Current Equipment

Monitors Thump Current, sees reflections3. S.I.M. Secondary Impulse Method

Uses HV Thump to cause low impedance ARCThen uses LV TDR to bounce pulse off of faultIsolates TDR from HV via HV blocking filter


PrelocatorPrelocator

Impulse Current (w/ ionization delay)Impulse Current (w/ ionization delay)

S.I.M. Plot (before/after breakdown)S.I.M. Plot (before/after breakdown)


ll Better Ears for the technician Better Ears for the technicianll Seismophone (mechanical microphone) based Seismophone (mechanical microphone) basedll Walk down the cable path and listen for the Walk down the cable path and listen for the

whumph undergroundwhumph undergroundll Also monitor the electromagnetic pulse from theAlso monitor the electromagnetic pulse from the

current flow (no current flow past fault, hence nocurrent flow (no current flow past fault, hence noEM pulse)EM pulse)

Fine LocatorFine Locator


Splitter BoxSplitter Box For combining two test leads onto single inputFor combining two test leads onto single input Near end comparison method for complexNear end comparison method for complex

networksnetworksTest CablesTest Cables

Two x 25m test leadsTwo x 25m test leads Supplied on transportable drumsSupplied on transportable drums Connector park incorporated into drumConnector park incorporated into drum

Thumping NotesThumping Notes

bb If the breakdown voltage of the cable isIf the breakdown voltage of the cable isabove the rating of your Thumper, it isabove the rating of your Thumper, it iscommon to burn down the fault, creatingcommon to burn down the fault, creatingmore damage at the fault so that it will failmore damage at the fault so that it will failat a lower voltageat a lower voltage

WHEATSTONE (RESISTANCE) BRIDGEWHEATSTONE (RESISTANCE) BRIDGE

ll Finds faults up to 200 M.OhmsFinds faults up to 200 M.Ohms

ll Locates faults between conductorsLocates faults between conductorsor between conductors and sheath,or between conductors and sheath,neutral or earthneutral or earth

ll High sensitivityHigh sensitivity

ll Compliment to TDR for highCompliment to TDR for highresistance faultsresistance faults


bb Two sections of the faultyTwo sections of the faultyconductor, one on each side of theconductor, one on each side of thefault, together with a goodfault, together with a goodconductor if necessary, compriseconductor if necessary, comprisethe two external arms of thethe two external arms of thebridge. The other two arms of thebridge. The other two arms of thebridge are contained within thebridge are contained within theinstrument.instrument.

bb High resistance faults inHigh resistance faults indielectrics such as rubber anddielectrics such as rubber andpolyethylene can be located withpolyethylene can be located withan accuracy well within 0.5% ofan accuracy well within 0.5% ofthe loop length and typically 0.1%,the loop length and typically 0.1%,although this may be limited by thealthough this may be limited by thenon-uniformity of the conductor.non-uniformity of the conductor.

bb Very simple deviceVery simple devicebb Typically no processors,Typically no processors,

just amplifiers, resistorsjust amplifiers, resistorsand meterand meter

bb Use: null out meter onUse: null out meter oncable, add externalcable, add externalbattery to create faultbattery to create faultcurrent and adjust 0-1000current and adjust 0-1000count resistor to re-zerocount resistor to re-zerometer, read % of distance.meter, read % of distance.


Intermittent Fault Detection mode is designed to find series resistanceproblems and intermittent, noisy static "no trouble found" typeproblems. Also good for unintentional disruptions and service theft.

Running continually, the IFD mode captures any changein the impedance, whether an open or a short.

Make sure the TDR is on line power when possible

INTERMITTENT FAULT DETECTIONINTERMITTENT FAULT DETECTION

VIXXON S3000 SPVIXXON S3000 SPA more sophisticated systemA more sophisticated system

LVFAULT

DIAGNOSIS

S300 SP(DAU)

FIXFAULT

Intermittentfault

X300DATA

RETRIEVALSOFTWARE

Locate

Fault

S300 SP (DAU)with

S300 SUB SP

FaulttriggersDAU

Persistentfault

COMBINED TEST SETSCOMBINED TEST SETS

bb TDRTDRbb Resistance Fault LocatorResistance Fault Locatorbb Multi MeterMulti Meterbb Insulation Resistance MeterInsulation Resistance Meterbb Pair Balance and Noise MeasurementPair Balance and Noise Measurement

bb Convenient and cheaper than several test unitsConvenient and cheaper than several test unitsbb Simplifies technicians job, especially when climbing orSimplifies technicians job, especially when climbing or

working in confined spaces (vaults)working in confined spaces (vaults)bb Training & familiarity on one unitTraining & familiarity on one unit

bb Sometimes have lower specs than individual unitsSometimes have lower specs than individual units

Feature several fault detection methods:Feature several fault detection methods:

DUCT NOTESDUCT NOTES

bb The A-frame fault location may not be where theThe A-frame fault location may not be where thecable damage is due to the current migratingcable damage is due to the current migratingalong the inside of the duct.along the inside of the duct.

bb Empty ducts can be located with sondes / OmniEmpty ducts can be located with sondes / Omni

TrainingTraining

bb Even the wizziest equipment will give poorEven the wizziest equipment will give poorresults of users can not use it effectively.results of users can not use it effectively.

bb Insist on complete initial and future training.Insist on complete initial and future training.bb Reasonably local support will make lifeReasonably local support will make life

easier.easier.

Radiodetection, BicoTest,Radiodetection, BicoTest,Riser-Bond InstrumentsRiser-Bond Instruments

Contact:Contact: Gord Parker, C.E.T.Gord Parker, C.E.T.Telephone:Telephone: (1) (403) 281-1808(1) (403) 281-1808Facsimile:Facsimile: (1) (403) 281-1828(1) (403) 281-1828Toronto:Toronto: 800-665-7953 / 905-660-9995800-665-7953 / 905-660-9995E-mail:E-mail: [email protected]@rdcorp.comWebsite:Website: http://www.radiodetection.cahttp://www.radiodetection.ca Website: Website: http://www.riserbond.comhttp://www.riserbond.comWebsite:Website: http://www.bicotest.comhttp://www.bicotest.com

Electrical Cable Fault Locating

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