Revision Of Qualification Procedures For High Voltage And .

Revision of Qualification Proceduresfor High Voltage and Extra High VoltageAC Extruded Underground Cable SystemsTutorial vor the ICC Educational Session onNovember 11 2009 inScottsdale, AZby Wim Boone2/5/20101

Table of contents IntroductionLong duration test EHV (150-500kV)Extension of prequalification test (EQ)Long duration test HV (30-150kV)Functional AnalysisConclusions2/5/20102

Introduction Innovative changes are necessary to improvethe product, to remain competitiveThere is little incentive for the manufacturerto make improvements, if the expensive longterm testing has to be repeatedCIGRE WG B1-06 was asked to providerecommendations to qualify a modification toa cable system, without making the full set oftests, which are currently specified instandardsWG B1-06 has published Technical Brochure303 in 20062/5/20103

Terms of reference WG B1-06 -----AC extruded cables 30-500 kVReview and complete qualification procedures (typetests, PQ tests)Prepare innovative solutions, without jeopardizing thesystem reliabilityEvaluate whether present long term tests can bereplaced by shorter onesExamine if a modification to a cables system can bequalified without making the full set of testsThe conclusions have been offered to IEC forfurther standardisation2/5/20104

Reference standards IEC 62067, October 2001,Power cables withextruded insulation and their accessories forrated voltages above 150 kV (Um 170kV) upto 500 kV (Um 550kV)-Test methods andrequirementsIEC 60840, April 2004,Power cables withextruded insulation and their accessories forrated voltages above 30 kV (Um 36kV) up to150 kV (Um 170 kV)-Test methods andrequirements

PQ tests Focus on PQ tests, because of costs and timePQ test recommended by CIGRE andincorporated in IEC 62067Only those manufacturers whose productshave passed the PQ tests have been allowedto participate in subsequent EHV cableprojects2/5/20106

Experience with HV cable syst. In general experience is goodA new generation HV XLPE cables “slimdesign” is developed with similartechnology and higher operatingstresses, as high as EHV XLPE cablesThe experience with slim design HVcables is still limited2/5/20107

Experience with EHV cable syst.For more details (see tutorial on serviceexperience) XLPE cable is at present preferredtransmission type cable (availability, leakage) Experience with EHV XLPE cable is stilllimited, althoughapplication of EHV XLPEcable is fast growing(see next table) 2/5/20108

Application of EHV extruded cable South4001600 Cu221997Denmark(Copenhagen:North4001600 Cu121999Germany (Berlin/ BEWAG4001600 Cu6.31998Germany(Berlin/ BEWAG4001600 Cu5.52000Japan (Tokyo)5002500 Cu39.82000UAE (Abu Dhabi)400800 Cu1.32000Spain (Madrid)4002500 Cu12.82004Denmark (Jutland)4001200 Al14.52004United kingdom (London)4002500 Cu202005The Netherlands (R’dam)4001600 Cu2.2520053801200 Cu5.22005Austria (Wienstrom)2/5/20109

Long duration test EHV cablesystems --Long duration test PQ test was introduced tocompensate for lack of experience with EHVXLPE cablesThe PQ tests checks the performance underrealistic conditions:Design conceptLong term performance (heat cycling overvoltage)Installation aspects2/5/201010

Long duration test PQ test shows in particular critical position ofthe joints; impulse test at the end of the testAlthough manufacturers are learning fromproblems in early PQ tests results , PQ test isconsidered to be necessary2/5/201011

Main items of PQ test to beconsidered for revision Range of approval in relation withcalculated nominal stressesThe duration of heating cycle voltagetestPD testsProcedure in case of component failureduring testFinal control at the end of the test2/5/201012

Range of approval New PQ test has to be performed incase of higher system voltage withhigher insulation screen stress than inthe qualified system2/5/201013

Heating cycle test The duration of the voltage application (1.7Uo) is an important factor because ofaccessory failuresAt present the duration is 180 heat cycles(8/16) up to 95 gr.C max.(with largeconductor and installed in the soil 1 cycletakes more than 1 day)The duration of the voltage application shouldremain 1 year 8760h2/5/2010

PD tests Reduction of insulation thickness may result inconsiderable higher stress at defects, voids, fissures,increasing risk of PD activityConsequently the size of defectshas to be reduced accordinglyPD tests are therefore anecessary tool as an earlywarning for degradation andsubsequent failure2/5/201015

System component failure 2/5/2010Repair/replacement of a failed accessoryduring test is allowedRepair of cable failure is not allowed, unlessfailure has been caused by external incidentor the cable has already been prequalified16

Final control test After the test has been completed an impulse testhas to be performed on the whole test loopThe whole test loop has todo with the desirability tocheck the insulatingproperties at the interfacesin the accessories and thecable.An impulse test on thecable only, as was done inthe past, is not sufficient2/5/201017

Changes in a prequalified system What changes are “substantial” in sucha way that the PQ test has to berepeated?Functional Analysis Method correlatesthe function performed by a certainitem to the test required to check thatfunction.2/5/201018

Changes in a prequalified syst.(2) Some small changes do not require therepetition of a full PQSome major changes require therepetition of the full PQ testSome changes require the performanceof a simplified long term-test, calledExtension of Prequalification test (EQ)2/5/201019

Situations of changes in aprequalified system The exchange of components (cable oraccessories), already prequalified insystems from different manufactures orfrom different plants from the samemanufacturerThe modification to cable componentsThe modification to accessorycomponents within the same family2/5/201020

Evaluation of changes in a prequalified system.Cableand/oraccessoryAlready qualified onanother cable systemwithin the sam e or higherinsulation screen stressAlready qualified onanother cable system witha low er insulation screenstress (calculated) or notqualifiedcablenon electrical Type Test electricalandnon(TT) Extension of electricalTT qualification test (EQ)Prequalification Test (PQ)JointEQTT PQMetalEQenclosedTerminationTT PQOutdoorEQTerminationTT PQ2/5/201021

Tests because of modifications to a cable in a prequalified EHV cable sulation2/5/2010Copper to Aluminium Larger cross-sectionTT and PQTTChange of base resin Changeincrosslinkingpackage(peroxide/antioxidant) Nature of polymer (XLPE, LDPE, HDPE, EPR) Higher conductor stress, no increase ofinsulation screen stress Increase of insulation screen stress New extrusion line or transfer of extrusionline with earlier experience in-house New extrusion line, or transfer of extrusionline without earlier experienceTTTT TT and PQTTTT and PQTTTT and PQ22

Tests because of modifications to an accessory within the samefamily in a prequalified EHV cable systemComponentType of modificationProposedtestJoint Higher calculated electrical stress designand construction Compound of main insulation body Changing nature of polymer, (EPR,Silicone .) Material of semi-con electrodes Fixation of cable ends on either side ofthe jointEQPQEQEQEQ

Principles of the Extension of PQtest (EQ) 60 thermal cycles witout voltage20 cycles with 2Uo PD hot impulse testThe 60 daily cycles 20 cycles are intendedto allow relaxation of mechanical stressestrapped in the cable during manufacture,resulting in retraction of the XLPE insulationThe retraction of the cable insulation withinan accessory can initiate PD activity2/5/201024

Retraction of XLPE insulation and PE oversheath.35.0Retraction ofoversheath30.0Retraction ofinsulationRetraction (mm)25.020.015.010.0Evolution ofthe retraction5.00.001020304050607080-5.0Num be r of he at cycle sIn addition the heat cycles are producing a radial expansion and retraction of the cable insulationand of the accessory components that can also influence the interfacial pressure in accessories.2/5/201025

Recommendations to IEC 62067 --New cable systems:Maintain 1 year PQ testAllow in case of an accessory failure thecontinuation and completion of the PQ testfor the undisturbed componentPerform PD tests during PQ testPerform impulse test at the end of the test onthe complete test loopMaintain unchanged present range of TT andPQ approval2/5/201026

Recommendations to IEC 62067Exchange of a prequalified component:- Introduce a simplified long term test of60 20 cycles in case of exchange ofprequalified components with othercomponents or in case of lesssignificant modifications of cable oraccessory 2/5/201027

Long duration test HV cablesystems Traditionally EHV cables are operating athigher stresses than HV cablesDue to good experience with EHV cables, HVcables are being produced with reducedinsulation thickness (slim design)Higher stresses at main insulation and atinterfaces between cables and accessories2/5/201028

Increase of Electric stress withsystem voltage100Working stress (kV/mm)Impulse stresses10AC stresses1101001000Voltage level (kV)2/5/201029

Arguments pro Long term test High electric stresses increase failure riskShrinkage is only stabilized after 80 cyclesNew accessorydesigns are comingFailures in highstress cables2/5/201030

Arguments against long term test Many manufacturers have good experience sofarReluctance of some utilities, to test entiresyst. if they buytheir HV cablesand accessoriesseparatelyLongterm test iscostly2/5/201031

Range of PQ test For prefabricated joints , mainly impulsestresses at the cable interface are criticalFor taped or field-molded joints also AC andimpulse stresses at the conductor are criticalTherefore the PQ test is recommended forcable systems with conductor stresses higherthan 8kV/mm and insulation screen stressesabove 4 kV/mm2/5/201032

Recommendations to IEC 60840Intoduce the following PQ test: Voltage, 1.7 Uo 180 heating cycles, to max. 95 degr C Cooling to ambient PD tests Impulse test on the complete loop Examination of the test loop2/5/201033

Exchanges and modifications The procedure and the sequence of EQtests are the same as for the EHV cablesystems2/5/201034

Functional Analysis International standards are necessary forboth manufacturers and customersAn advantage of International standards isthe world wide acceptance of the testevidenceA disadvantage of international standards isthe limited incentive of manufacturers tomake incremental improvements, as thisrequires a complete repetition of the typetesting2/5/201035

Functional Analysis (2) According to IEC 62067 the PQ testneed to be repeated in case of“substantial” changesThere is no agreed method to decidewhat is substantial

Functional Analysis (3) -In the Functional Analysis method a processis developed, where the significance of achange can be evaluated and the need forfurther testing agreed:PQ testEQ testType testOther test2/5/201037

Functional Analysis Method Consider the functions performed byeach part of a cable or accessoryconstruction and indicate how eachfunction is testedConsider a number of possible changesthat can be made and indicate whatadditional testing might be required2/5/201038

Functional Analysis Tables Table for cablecomponentsTable for JointcomponentsTable for Terminationcomponents2/5/201039

Functional Analysis TableStructure of the table with 5 columns: Component Function Specification/threat Test to ckeck the functionality Comments2/5/201040

Cable components ConductorInner semiconducting screenInsulationOuter semiconducting screenLongitudinal water tight layerMetal screenOversheath2/5/201041

Functions/properties Electrical conductivity (conductor, screen)Dielectric properties (insulation, oversheath)Mechanical propertiesThermal-mechanical propertiesChemical propertiesInterfaces with other componentsWatertightnessOverall properties2/5/201042