Fault Location on Land and Submarine Links (AC & DC)

06/03/2018
Auteurs : Robert Donaghy
OAI : oai:www.see.asso.fr:1301:2018-1:22502
DOI :
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Fault Location on Land and Submarine Links (AC & DC)

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JICABLE HVDC'17 KEYWORDS : Fault Location, Submarine Cable, Underground Cable. DOSSIER 2 114 ZREE N°1/2018 Fault Location on Land and Submarine Links (AC & DC) Robert Donaghy; ESB International (Ireland) robert.donaghy@esbi.ie Introduction In 2014, CIGRE SC B1 established WG B1.52 to develop a Technical Brochure on “Fault Location on Land and Submarine Links (AC & DC)”. The terms of reference for the working group are as follows: s 4OCOVERFAULTLOCATIONONTHEFOLLOWINGINSTALLEDCABLETYPES -6(6%(6!#$#LANDANDSUBMARINECABLESYSTEMS SINGLECORE 
COREANDPIPETYPECABLES s &OCUSONMAININSULATIONSHEATHFAULTS s 0ROVIDEOVERVIEWOFEXISTINGFAULTLOCATIONTECHNIQUESAND UNDERLYINGPRINCIPLES s &ORLANDANDSUBMARINECABLESYSTEMS PROVIDEGUIDANCE AND STRATEGIES FOR EFFECTIVE FAULT LOCATION FOR A VARIETY OF INSTALLATIONTYPESINCLUDINGBUTNOTLIMITEDTO
$IRECTBURIEDCABLESYSTEMS
$UCTEDLANDCABLESYSTEMS
#ABLESBETWEEN')3BAYS - Cables installed in horizontal directional drills and tunnels - Cables at large burial depths
#ABLESYSTEMSWITHDIFFERENTBONDINGTYPES
6ERYLONGCABLES s %XAMINE THE DIFFERENT METHODS OF PRE
LOCATION AND PINPOINTINGFROMANACCURACYANDSUITABILITYVIEWPOINT s 0REPARE A mOWCHART TO ASSIST IN SELECTING APPROPRIATE METHODSACCORDINGTOFAULTTYPEANDCABLETYPE s $ESIGN FACTORS CABLE DESIGN AND INSTALLATION METHOD AFFECTINGFAULTLOCATIONCAPABILITY s3AFETYCONSIDERATIONS s -ARINE VESSEL AND SUPPORT REQUIREMENTS FOR lNDING submarine cable faults s#OLLECTCASESTUDIESOFFAULTLOCATIONEXPERIENCES s4RAININGREQUIREMENTSFORFAULTLOCATIONPERSONNEL s !SSESS APPLICABILITY OF ON
LINE METHODS TO SUPPORT FAULT location s 2EVIEW NEW AND INNOVATIVE FAULT LOCATION TECHNIQUES  future developments The brochure should not cover: s,EAKLOCATIONINmUIDlLLEDCABLES s'ASLEAKLOCATIONONGASCOMPRESSIONCABLES s$IAGNOSTICTESTING s$EFECTSINCATHODICPROTECTIONSYSTEMS &ORLEAKLOCATIONINmUIDlLLEDCABLES REFERTO#)'2%4" BY#)'2%7ORKING'ROUP";= Fault location steps Fault types Open Circuit Fault !LSOKNOWNASASERIESFAULTORCONDUCTORCONTINUITYFAULT the current path is broken resulting in the current being COMPLETELYORPARTLYHINDERED4HEYAREGENERALLYUNCOMMON in submarine cables and land cables. Some open circuit faults HAVEBEENREPORTEDINSUBMARINECABLESCUTBYANCHORSAND UNDERGROUNDCABLESINEARTHQUAKESWHEREJOINTSCONNECTORS are pulled apart. The increasing number of land and submarine cable assets globally has created a focus on cable fault location capabilities. All faults in cable systems are different and cable fault location depends to a great extent on applying the appropriate technique or combination of techniques. The methods for locating power cable faults require competent engineers and service providers. Guidance is therefore required for engineers on the correct application of the various techniques available. This paper outlines the work that is being undertaken by CIGRE Working Group B1.52 on the topic of Fault Location on Land and Submarine Links (AC & DC). ABSTRACT Figure 1: Fault Location Steps. REE N°1/2018 Z 115 Fault Location on Land and Submarine Links (AC & DC) Shunt Fault Also known as insulation fault or short circuit fault, two or more main conductors come into contact with each other or with earth. Intermittent shunt faults are nonlinear voltage dependent faults with high resistance until the insulation BREAKSDOWN$URINGARCING THEYARELOWRESISTANCE )N 8,0% LAND CABLES FAULTS ARE OFTEN HIGH RESISTANCE OR intermittent. In submarine cables, the arc often penetrates ALLWATERTIGHTLAYERSRESULTINGINSEAWATERINGRESS RESULTINGIN low fault resistance, making the fault a persistent shunt fault. Sheath Fault )N CABLE OVERSHEATH  METALLIC SHEATH DAMAGE USUALLY opens a current path from the metallic sheath to earth due to water ingress. It often causes metallic sheath corrosion, leading to further damage in the metallic sheath or even- TUALLYINTHEMAININSULATION3HEATHFAULTSCANBELOWORHIGH resistance. Cable fault location techniques Prelocation 0RELOCATIONINVOLVESTESTINGTHECIRCUITFROMTHECABLETER- minations to estimate distance to the fault. It can determine the fault position to within a few percent of the cable length. /NVERYLONGCABLES THEMARGINOFERRORCANBESIGNIlCANT Sometimes the fault has to be conditioned to make it detec- table e.g. burned to a low resistance fault. 4HEMAINPRELOCATIONTECHNIQUESCONSIDEREDARE s4IME$OMAIN2EmECTOMETRY4$2 s"URN$OWN4ECHNIQUES s!RC2EmECTION-ETHODS!2-3)--)- s$ECAY-ETHODAND$IFFERENTIAL$ECAY-ETHOD s )MPULSE #URRENT -ETHOD INCLUDING #OMPARISON AND Differential Modes) s&REQUENCY$OMAIN2EmECTOMETRY s"RIDGE-ETHODS Pinpointing 0INPOINTINGISATESTTOCONlRMTHEEXACTPOSITIONOFTHE CABLEFAULTFOLLOWINGPRELOCATION)TISCARRIEDOUTDIRECTLYOVER the cable. 4HEMAINPINPOINTINGTECHNIQUESCONSIDEREDARE s!COUSTIC-ETHOD s3TEP6OLTAGE-ETHOD s-AGNETIC&IELD-ETHODS
)MPULSEMAGNETOMETRYPRIMARYFAULTS
$#MAGNETOMETRYSHEATHFAULTS
!UDIOFREQUENCYMETHODS s3ECTIONALISING-ETHODS 'UIDELINES AND EXAMPLES OF THE APPLICATION OF THESE PRELOCATIONANDPINPOINTINGTECHNIQUESAREPROVIDEDINTHE technical brochure. Design factors affecting fault location &AULTLOCATIONCAPABILITYISNOTALWAYSAPRIMARYCONCERN INSYSTEMDESIGN3OMEEFFECTIVEACTIONSCANBETAKENATTHE DESIGN AND PROJECT IMPLEMENTATION STAGE TO ENHANCE FAULT LOCATIONCAPABILITYINCLUDING s %NSURETHATAGOODSETOFASLAIDRECORDSANDCABLESYSTEM INFORMATIONISCOMPILED4HISINFORMATIONMUSTBEPROPERLY STOREDANDREADILYAVAILABLETOFAULTLOCATIONPERSONNEL s 5SELINKBOXESATJOINTSANDTERMINATIONSTOENABLETHECIR- cuit to be split into sections to narrow down the fault and to give additional access points to conductor or screen. Ensure LINKBOXESAREREADILYACCESSIBLE s !VOID USING CABLES WITHOUT AN OUTER SEMICONDUCTING OR GRAPHITE SHEATH AS DETECTING AND LOCATING FAULTS REQUIRES CURRENTmOWFROMTHEMETALLICSCREENORSHEATHTHROUGHTHE fault to earth. s )N THE CASE OF HYBRID CIRCUITS PROVIDE A MEANS OF disconnecting cable from the overhead line. s 3OMEINSTALLATIONTYPESPOSEPARTICULARCHALLENGESFORFAULT location: - Cables terminated into GIS at both ends - Cables in ducts - Cables in tunnels Figure 2: Open Circuit Fault. Figure 3: Shunt Fault. Figure 4: Sheath Fault. JICABLE HVDC'17 DOSSIER 2 116 ZREE N°1/2018 Emergency planning !TTENTION GIVEN TO EMERGENCY PLANNING ASPECTS OF FAULT LOCATIONWILLENABLEAMOREEFlCIENTFAULTLOCATIONCAMPAIGNTO BEUNDERTAKEN PARTICULARLYINTHECASEOFOFFSHORESUBMARINE CABLE FAULTS 4HE BROCHURE IDENTIlES THE KEY ELEMENTS OF EMERGENCY PLANNING WHICH OPERATORS SHOULD CONSIDER IN ADVANCEOFANYFAULTOCCURRING s#ABLE3YSTEM2ECORDS s0ERMITS s0REPARATORYWORKS s-ARINELOGISTICS s #OOPERATIONARRANGEMENTSIFTHEREAREDIFFERENT43/SINVOLVED s !SPECTSOF2EPAIR0REPAREDNESS0LANSRELEVANTTOFAULTLOCATION s&AULT,OCATION-ANUAL
3AFETY PROCEDURES AND RISK ANALYSES TO BE PERFORMED prior to fault location
3TEPSTOFOLLOWFORFAULTLOCATIONmOWCHART - Chronological overview of tests and measurements to be performed in different scenarios
4ESTING AND MEASURING EQUIPMENT NEEDED FOR FAULT location which is adapted to the characteristics of the cable connection 0OLITICALANDLEGALASPECTSCANHAVETHEPOTENTIALTOINTERFERE with fault location activities, but it is vital for successful fault LOCATIONTHATTHATFAULTLOCATIONISCARRIEDOUTMETHODICALLYIN an evidence-based and forensic manner. Innovation and future developments The brochure describes some of the innovative methods WHICHARECURRENTLYEMERGINGANDBEINGDEVELOPEDWITHINTHE INDUSTRY4HESEMETHODSARECOVEREDUNDERTHREECATEGORIES 1. Fibre Optic Fault Location Methods - Distributed Temperature Sensing (DTS) - Distributed Acoustic Sensing (DAS) - Distributed Vibration Sensing (DVS) - Brillouin Strain Measurements 2. Electrical/ Conventional Fault Location Methods
0ARTIAL$ISCHARGE-EASUREMENTS - Advances in conventional fault location Methods - Online Fault Location Methods 3. Submarine Pinpointing Techniques Using ROVs
6ISUAL TONETRACING STEPVOLTAGEMETHOD USEOFHYDROPHONES
3UBMERSIBLEHABITATTECHNIQUE
-ULTIBEAMEQUIPMENT Fibre optic cables enable a wider range of fault pinpointing methods to be applied including Distributed Temperature Sensing, Distributed Vibration Sensing and Distributed Acoustic Sensing through the application of Raman and Brillouin SPECTROSCOPY)N2AMANSPECTROSCOPY THESCATTEREDMAGNITUDE IS TEMPERATURE DEPENDENT )N "RILLOUIN SPECTROSCOPY THE Brillouin shift is temperature and strain sensitive. 4HElBREOPTICCABLECANBEINSTALLEDEXTERNALLY DIRECTLY attached to the cable, or contained in a separate duct. For best FAULTLOCATIONRESULTS THElBREOPTICCABLESHOULDBEINSTALLED ASCLOSEASPOSSIBLETOPOWERCABLECORE!NEXAMPLEOFAN INTEGRATEDlBREOPTICCABLEISSHOWNIN&IGURE 3OMEFAILURESOFSUBMARINECABLESWITHEMBEDDEDlBRE optic cables have been reported, so particular attention should BEPAIDTOTHEINTEGRITYOFTHEOVERALLCABLEDESIGNINSUCHCASES Distributed Temperature Sensing (DTS) 7ITH$43 THElBREACTSASALINEARSENSORTODETECTHOT SPOTSALONGTHECABLEWITHHIGHACCURACYOVERLONGDISTANCE 4HEACCURACYOF$43ISINDEPENDENTOFTHELAYINGDEPTH ITIS insensitive to electromagnetic interference and can be used from the shore. Distributed Acoustic Sensing (DAS) Thumping high resistive faults with surge generator creates vibration at the fault. Localised vibrations are captured on the DAS interrogator (onshore) and compared with the initial surge vibration detected at the fault location. $!3 CAN BE UNDERTAKEN BY LAYING A TEMPORARY EXTERNAL lBREOPTICCABLEADJACENTTOCABLENEARTHEFAULT3INGLEMODE lBREISGENERALLYPREFERREDFOR$!3APPLICATIONS Distributed Vibration Sensing (DVS) 7ITH $63 THE SINGLE MODE lBRE OPTIC CABLE ACTS AS VIBRATION SENSOR ! DISTURBANCE ON THE lBRE GENERATES A Figure 5: 3-core cable with integrated fibre optic. Figure 6: Distributed Temperature Sensing. REE N°1/2018 Z 117 Fault Location on Land and Submarine Links (AC & DC) MICROSCOPIC ELONGATION OR COMPRESSION OF THE lBRE WHICH causes a change in the phase relation. If there is no integrated FO element, DVS can be UNDERTAKENBYLAYINGEXTERNALlBREADJACENTTOTHECABLE Safety considerations 4HE HIGHEST PRIORITY SHOULD BE SET FOR THE SAFETY OF THE FAULT lNDING PERSONNEL &AULT LOCATION SHOULD BE PERFORMED ACCORDINGTOTHERELEVANTNATIONAL INTERNATIONALANDCOMPANY SAFETYREGULATIONS0ERSONNELPERFORMINGFAULTLOCATIONSHALLHAVE APPROPRIATETRAININGANDAUTHORISATIONTOCARRYOUTTHEWORKS "EFORETHEEXECUTIONOFCABLEFAULTLOCATION ITISRECOMMENDED that a risk assessment is carried out and method statements for THEFAULTLOCATIONTECHNIQUESAREPREPARED3OMEPARTICULARRISKS APPLYINFAULTLOCATION FOREXAMPLE 0ARTICULAR2ISKSIN&AULT,OCATION s-AXIMUMALLOWEDTESTPARAMETERSANDTESTVOLTAGES s3TOREDENERGYINLONGANDEXTRA
LONGCABLES s2ETURNVOLTAGEIN$#CABLESYSTEMS s)NDUCEDANDIMPRESSEDVOLTAGES s)MPULSEVOLTAGES s4OUCHANDSTEPVOLTAGES s2E
ENERGIZINGTHECABLE Training considerations 4RAINING REQUIREMENTS FOR WORKING IN THE HIGH VOLTAGE environment are registered in international standards national REGULATIONSFORELECTRICALOPERATIONSANDCOMPANYSTANDARDS )TMAYALSOOCCURTHATFAULTLOCATIONMUSTBEPERFORMEDON INDUSTRIALPLANTSOROTHERSPECIlCAREASEACHWITHTHEIROWN SPECIlC TRAINING AND CERTIlCATES REQUIREMENTS DEPENDING ON THE CIRCUMSTANCES 3OME EXAMPLES OF GENERAL TRAINING REQUIREMENTSARELISTEDBELOW s'ENERALTRAINING
%LECTRICALSAFETYTRAINING
"ASICSAFETYTRAINING - Working at height - First aid training - Fire awareness training
/FFSHORETRAININGREQUIREMENTSWHERENECESSARY s3PECIlCTRAINING
3AFETYRULES
5NDERSTANDINGFAULTTYPESANDFAULTBEHAVIOUR - Connection methods - Understanding the various pre-location and pinpointing methods
%QUIPMENTSPECIlCTRAINING Accuracy and suitability of prelocation methods 4HESUITABILITYOFTHEPRELOCATIONANDPINPOINTINGMETHODS ARE DESCRIBED IN 4ABLES  AND  RESPECTIVELY 4HE COLOUR CODESINDICATESTHESUITABILITY Fault Type Method Low Resistance High Resistance Open Circuit Intermittent Sheath Fault TDR Land & Submarine 1-3 % accuracy Fingerprint reference helpful Limitations for X bonded & screen interrupted systems Fault Burning Required Land & Submarine 1-3 % accuracy Fingerprint reference helpful limitations for X bonded & screen interrup- ted systems Fault Burning Required Arc Reflection Methods No need as TDR will work Land & Submarine 1-3 % accuracy Length limited limitations for submarine cables (water ingress). Limitations for X bonded & screen interrupted systems No need as TDR will work Land & Submarine 1-3 % accuracy Length limited limitations for submarine cables (water ingress). Limitations for X bonded & screen interrupted systems Decay No need as TDR will work Cable cannot be charged to a DC voltage due to low resistance fault. No need as TDR will work Land & Submarine 1-10 % accuracy Propagation velocity unknown, no reference points available. Limitations for X bonded & screen interrupted systems Differential No need as TDR will work Land & Submarine 1-3 % accuracy Access to ref. conductor required No need as TDR will work Land & Submarine 1-3 % accuracy Access to ref. conductor required JICABLE HVDC'17 DOSSIER 2 118 ZREE N°1/2018 Impulse Current No need if TDR works Land & Submarine 5-10 % accuracy Limited by breakdown voltage & distance to fault. Limitations for X bonded & screen interrupted systems No need as TDR will work Land & Submarine 5-10 % accuracy Limited by breakdown voltage & distance to fault. Limitations for X bonded & screen interrupted systems Bridge Methods Land & Submarine ~ 1 % accuracy Need 1 healthy return conductor Land & Submarine ~ 1 % accuracy Up to few MW fault resistance, Need 1 healthy return conductor Land ~ 1 % accuracy Need 1 healthy return conductor Voltage Drop Land & Submarine ~ 1 % accuracy Need 1 healthy return conductor Land & Submarine ~ 1 % accuracy Up to few MW fault resistance, Need 1 healthy return conductor Land ~ 1 % accuracy Need 1 healthy return conductor Fibre Optic Methods Land & Submarine 1-3 % accuracy Vibration from fault spot or magnetic force along route needed Land & Submarine 1-3 % accuracy DAS & DTS Land & Submarine 1-3 % accuracy Already OTDR will work Land & Submarine 1-3 % accuracy Sound/heat needed at fault Land & Submarine 1-3 % accuracy Vibration from fault spot needed Table 1: Accuracy and Suitability of Prelocation Methods. applicable not applicable POSSIBLY Fault Type Method Low Resistance High Resistance Open Circuit Intermittent Sheath Fault Acoustic Land & Submarine Limited application. A solid short circuit will not create noise. Can be used for submarine faults with water ingress Land & Submarine 1-3 m accuracy Not for cables in ducts Land & Submarine 1-3 % accuracy Earthing of disconnected sections needed Cables in ducts Land & Submarine 1-3 m accuracy Not for cables in ducts Step Voltage Land 1-3 m accuracy Fault needs soil contact Not for cables in ducts Land 1-3 m accuracy Fault needs soil contact Not for cables in ducts Land 1-3 m accuracy Fault needs soil contact Not for cables in ducts Land 1-3 m accuracy Fault needs soil contact Not for cables in ducts Land 0.1 m accuracy Fault needs soil contact Not for cables in ducts Galvanic contact of neutral conductor to grounding systems Audio Frequency Land & Submarine Land: 1-3 % accuracy Submarine: 10m - several hundred meters accuracy Land & Submarine Land: 1-3 % accuracy Submarine: 10m - several hundred meters accuracy Land Audio frequency measurement with capacitive probes Step voltage usually preferred Fibre Optic Methods Land & Submarine 1-3 % accuracy Vibration from fault spot or magnetic force along cable route needed Land & Submarine 3-5m accuracy Up to few M ohms fault resistance, Need at least one healthy return conductor 3-5m accuracy 3-5m accuracy Sound or heat production in fault spot needed Land 1-3 % accuracy Vibration from fault spot needed Table 2 – Accuracy and Suitability of Pinpointing Methods applicable not applicable POSSIBLY REE N°1/2018 Z 119 Fault Location on Land and Submarine Links (AC & DC) CONCLUSIONS This paper has outlined the work that is being undertaken BY#)'2%7ORKING'ROUP"ONTHETOPICOF&AULT,OCATION ON,ANDAND3UBMARINE,INKS!#$# 4HEREAREMANY WELL ESTABLISHED TECHNIQUES AVAILABLE FOR FAULT LOCATION IN CABLESPARTICULARLYFORBURIEDUNDERGROUNDCABLES'UIDANCE IS PROVIDED ON THE APPLICATION OF DIFFERENT TECHNIQUES IN VARIOUSSCENARIOS.EWANDINNOVATIVETECHNIQUESAREALSO being developed which increase the toolkit for fault location. -ANYOFTHESETECHNIQUESUSElBREOPTICCABLESINTEGRATED ORINCLOSEPROXIMITYTOTHEPOWERCABLE!PPROPRIATESAFETY measures should be put in place for fault location activities and fault location personnel must be competent and ADEQUATELYTRAINEDFORTHEWORKBEINGUNDERTAKEN The technical brochure for Working Group B1.52 will be published in 2018. Acknowledgments The contribution of the members of CIGRE Working Group "ISHEREBYACKNOWLEDGED References [1] CIGRE B1.37, Technical Brochure 652 “Guide for the Operation of SCFF Cable Systems” Glossary DAS: Distributed Acoustic Sensing DTS: Distributed Temperature Sensing DVS: Distributed Vibrations Sensing FO: Fibre Optic GIS: Gas Insulated Switchgear ROV: 2EMOTELY/PERATED6EHICLE TDR: 4IME$OMAIN2EmECTOMETRY