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FINAL PROJECT REPORT

MULTI-AREA REAL-TIME TRANSMISSION LINE RATING STUDY

Prepared for CIEE By: Stuart Consulting

Project Manager: Bob Stuart Author: Bob Stuart Date: October, 2007

A CIEE Report

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Acknowledgements

Theauthorswouldliketothankandexpresstheirappreciationfortheirexpertopinionsto the followingpeople:KenMartin,DmitriKosterovand JinGronquistofBPA;CarlImhoff,RossGuttromson,YuriMakarov andHenryHuang ofPNNL;Ed SchweitzerandArmandoGuzmanofSEL;PatAhrens,GeorgeNoller,BharatBhargava,ArmandoSalazar andMikeMontoya of SCE; JimMcIntosh andDaveHawkins of theCAISO;VahidMadaniofPG&E;andArunPhadkeofVirginiaTech.

DISCLAIMER

This draft final report was prepared as the result of work sponsored by the California Energy Commission. It does not necessarily represent the views of the Energy Commission, its employees or the State of California. The Energy Commission, the State of California, its employees, contractors and subcontractors make no warrant, express or implied, and assume no legal liability for the information in this report; nor does any party represent that the uses of this information will not infringe upon privately owned rights. This report has not been approved or disapproved by the California Energy Commission nor has the California Energy Commission passed upon the accuracy or adequacy of the information in this report.

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Preface

The Public Interest EnergyResearch (PIER) Program supports public interest energyresearch and development thatwill help improve the quality of life inCalifornia bybringingenvironmentallysafe,affordable,andreliableenergyservicesandproductstothemarketplace.The PIER Program, managed by the California Energy Commission (EnergyCommission) conducts public interest research, development, and demonstration(RD&D)projectstobenefittheelectricityandnaturalgasratepayersinCalifornia.ThePIERprogramstrivestoconductthemostpromisingpublicinterestenergyresearchbypartneringwithRD&Dorganizations,includingindividuals,businesses,utilities,andpublicorprivateresearchinstitutions.PIERfundingeffortsarefocusedonthefollowingRD&Dprogramareas:

Buildings End-Use Energy Efficiency Industrial/Agricultural/Water End-Use Energy Efficiency Renewable Energy Technologies Environmentally Preferred Advanced Generation Energy-Related Environmental Research Energy Systems Integration Transportation

ScopingStudyofIntelligentGridProtectionSystemsisthedraftfinalreportfortheScopingStudy of Intelligent Grid Protection Systems Project, work authorization numberBOA153P05 conducted by the PIER Program. The information from this projectcontributestoPIERsEnergyResearchandDevelopmentprogram.For more information on the PIER Program, please visit the Energy Commissionswebsiteatwww.energy.ca.gov/pierorcontacttheEnergyCommissionat(916)6545164.

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Table of Contents

Acknowledgements............................................................................................................................iiiPreface ................................................................................................................................................vTableofContents................................................................................................................................viiAbstract................................................................................................................................................ixExecutiveSummary...........................................................................................................................1Introduction.........................................................................................................................................1Purpose................................................................................................................................................2ProjectObjectives................................................................................................................................2ProjectOutcomes................................................................................................................................3Conclusions.........................................................................................................................................4Recommendations..............................................................................................................................5BenefitstoCalifornia..........................................................................................................................51.0 Introduction..........................................................................................................................62.0 ProjectApproach..................................................................................................................8

2.1. Interviews........................................................................................................................82.2. Meetings...........................................................................................................................82.3. Papers...............................................................................................................................83.1. TASK1REPORT.............................................................................................................9

3.1.1. Background................................................................................................................93.1.2. KeyFindings..............................................................................................................93.1.3. WECCTransmissionPathsandMajorRAS/SPS..................................................133.1.4. ScopeofR&DProject................................................................................................153.1.5. August14,2003DisturbanceRecommendation...................................................16

Task2Report.................................................................................................................................163.2.1Background......................................................................................................................163.2.2BasicTheoryofSynchrophasors...................................................................................173.2.3SynchrophasorStandards..............................................................................................183.2.4Areasofconcernandareasforfurtherdevelopment................................................193.2.5SynchrophasorManufacturers......................................................................................203.2.6KeyFindings....................................................................................................................22

3.3Task3Report...........................................................................................................................223.3.1Introduction.....................................................................................................................223.3.2Background......................................................................................................................23

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3.3.3SynchrophasorDataApplications................................................................................243.3.4R&DinWideAreaControl............................................................................................283.3.5InfrastructureR&DforWideAreaControl.................................................................283.3.6R&DinControlApplications........................................................................................31

3.4Task4Report...........................................................................................................................343.4.1Background......................................................................................................................343.4.2 IssuesinIntelligentGridProtection.......................................................................353.4.3PotentialDemonstrationProjects.................................................................................393.4.4Discussion........................................................................................................................413.4.5Recommendation............................................................................................................42

4.0ConclusionsandRecommendations..........................................................................................424.1Conclusions..............................................................................................................................424.2CommercializationPotential.................................................................................................444.3Recommendations...................................................................................................................454.4BenefitstoCalifornia...............................................................................................................45

5.0References......................................................................................................................................456.0Glossary.........................................................................................................................................487.0Appendices....................................................................................................................................48

3.1.6. August14,2003DisturbanceRecommendation...................................................49

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Abstract

Thispaperexploresthestateoftheartofsynchrophasor/pmutechnologyintheUnitedStates,thetransmissionconstraintsofimportedpowerintoCalifornia,thestateoftheartof RAS/SPS schemes in California and recommends appropriate projects to applysynchrophasor technology for a new or improved special protection scheme inCalifornia.

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Executive Summary

Introduction InvirtuallyallofthemajorblackoutsdatingbacktothefirstbigNewYorkblackoutin1965,protectiverelayshaveplayedamajorroleineithercontributingtothecauseoftheblackoutor failing tomitigate thespeedof theblackout. Ironically,zone3 impedancerelaysplayedamajorroleintheJuly2,1996blackoutontheWestCoast,theAugust14,2003blackoutontheEastCoastandintheoriginal1965NewYorkblackout.Inallthreeblackouts the zone 3 impedance relays which are intended only as backup to theprimaryprotective relaysoperated incorrectlyunderheavy load conditions. Unusualcircumstances in termsofweatherand configurationof thehighvoltage transmissiongrid that was not anticipated or studied by protection and operation engineers alsocontributedtotheseblackouts.Thereareacoupleofsignificanttrendsthathavebeentakingplaceoverthelastfifteento twenty years that have had an impact on the vulnerability of the high voltagetransmissiongridtowithstandmajorblackouts. AllovertheUnitedStatesand infacttheworld,utilitieshavebeenoperatingthehighvoltagetransmissiongridclosertothemarginmeaningasmallerdifferencebetweenreliableandunreliableoperation.Byandlarge they have been pressured intodoing this because of the rapid growth in largemetropolitan areas, the lack of investment in the transmission infrastructure and thereluctance of the general public to allow transmission lines to be built near theirneighborhoods. Another trend has occurred at the same time which has been theinstallationof remedialaction schemes (RAS)and specialprotection schemes (SPS) toprotect againstmultiple contingencies. While these schemes provide a safety net toprotectagainstextremeconditions,theyareprescriptivebynature.Theprotectionandoperation engineers must anticipate these conditions and set the special protectionschemes accordingly. This oftentimes means taking precipitous action and leavingtransmissioncapabilityonthetableunderlessstressedoperatingconditions.Theinstallationofglobalpositioningsatellite(gps)technologybythemilitaryinthemidto late 1980s along with the rapid development of microprocessor technology hasallowed for more intelligent protective relays and special protection schemes. Thesmartertechnologycanaccuratelymeasurethephaseangle(phasor)andvoltageandbyapplyingagpstimestamptotheflowofpowerbetweentwosubstationshavingthissmarter technology. Byapplying thisphasor technologyoverawidegeographicarea,theactualstressonthesystemcanbemeasuredveryaccurately. Thisallowsformoreadaptive and flexible protective relay schemes and special protection schemes andwouldleadtoatransmissiongridoperatedbothmorereliablyandeconomically.

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TheWesternUnitedStateshasledtheeffortininstallingandapplyingpmutechnologyforthelasttenyears. TheeffortintheWesthasbeentermedWAMSwhichstandsforWide Area Measurement System and is governed by the Western ElectricityCoordinating Council (WECC). The Eastern Interconnection started a phasorinitiativeafter theAugust14,2003blackout called theEIPPwhich stands forEasternInterconnectionPhasorProject. Recently the two initiativeshavebeenmergedunderone umbrella organization called NASPI which stands for North AmericanSynchrophasor Initiative Project. BPA, Pacific Northwest Laboratories (PNL), PG&Eand SCE have led the effort in installing synchrophasor (pmu) capability at theirfacilities. Thereareasufficientnumberofpmus installedon theCaliforniaOregonIntertie fromWashington toCalifornia to havewide area visibilitymeaning that theactual real timestateof thepowersystem isknownandapplicationprojectscouldbeutilized.FromawestwidestandpointthereisalackofvisibilityintheRockyMountainareawithinsufficientpmusinstalled.Purpose

Thepurposeofthisprojectistoperformascopingstudytoanalyzetransmissionsystemprotection issues, identifystateoftheart technicalprotectionsolutionsand theirvaluefor an intelligent system, and develop stakeholdersupported recommendations for atechnologyprogram.Project Objectives

Thespecificprojectobjectiveswereto: Evaluatesystemprotectionissues,needsandopportunitiesinconsultationwiththe

organizationsparticipatingintheTRPPolicyAdvisoryCommittee(PAC); Review the stateoftheart in intelligent system protection technologies for

addressingtheseissues,needsandopportunitieswithmanufacturersandsuppliersofpromisingsystemprotectiontechnologies;

ReviewongoingsystemprotectionR&D, field testvalidationprojectsand industrystandards activities and explore opportunities to collaborate on RD&D that issynergisticwithCaliforniassystemprotectionissues,needsandopportunities;

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Developprioritized recommendations for intelligent systemprotectionR&D, fieldtestvalidationandotherrelatedtechnologytransferactivitiesthatofferthepotentialto yield significant reliability, increased transfer capacity and other benefits forCaliforniaselectricityconsumers;and

Reviewandobtain feedbackon thisrecommendedsystemprotectionR&DagendafromtheTRPPAC,TechnicalAdvisoryCommittees,equipmentmanufacturersandotherindustryexperts.

Project Outcomes

TheWesternUnitedStateshasbeeninstallingpmussincetheearlytomid1990s.BPAhasacceptedtheresponsibilityofbeingtherepositoryformostifnotallofthepmudataattheirDitmercontrolcenterinVancouver,Washington.TheyhavetwoPDCs(phasordataconcentrators)attheirsitethatacceptthepmudataonarealtimebasis.Thedataisprimarily used for: a) disturbance analysis; b) generation modeling; and c) datamodeling.TheBPAreliabilitycoordinatorattheDitmercontrolcenterismonitoringthedataandgettingexperiencewith itbut theyhavenooperatoractionavailable to thembecausenoengineeringstudieshavebeendonetocorrelatetheangularrelationshipandthelevelofstressonthesystem.PacificNorthwestLaboratorieshasbeenintheforefrontofresearchtoproviderealtimedisplays and operator screens to enhance situational awareness for operators. Theyhavebeendoingadvancedresearchintosimulatingactualrealtimeoperatingscenariosat control centers to include the trending of data and a RTDM (real time displaymonitor).The IEEE (Institute of Electrical and Electronic Engineers) established the firstsynchrophasorstandard in1995named13441995. Thestandardwasupdated in2005and renamed C37.1182005. The present standard defines measurement convention,measurement quality and communication protocol and all pmus must meet theserequirements to be compliant. Communication latency, performance under dynamicconditions,aliasingand instrument transformererrorsareareas thatneed tobebetterdefinedandfurtherresearched.Thereareover14manufacturersofpmus that canbegrouped into two categories;1)manufacturers whose primary product line is disturbance recorders and monitoringequipment;and2)manufacturerswhoseprimaryproductlineisprotectiverelays.SEL

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(SchweitzerEngineeringLabs) andGE are twomain stream relaymanufacturers thathavesomewhatdifferentphilosophies.SELprovidespmuandrelayfunctionalityinonehardwarepackagewhileGEprovidesastandalonepmupackage. Bothmanufacturersmakequality equipment,however someprotection engineershave expressed concernaboutthereliabilityoftheoverallpmuandprotectiverelayinonepackage.Almostallprotectionandcontrolschemeson thegrid todayare local innature. Thismeans that the sensingand tripping takeplace inone substation typicallywith someschemes utilizing telecommunications between adjacent substations to coordinate theprotection. The primary interest in applying synchrophasors is from a wide areastandpointbecauseoftheintelligencetodetectastressedsystemthatisclosetocollapsecan only be determined from a wide area. Some potential applications that holdpromise are wide area voltage control, small signal stability control andtransient/dynamicstabilitycontrol.Special protection schemes (SPS) are the primary means of wide area control todayalthough some areused for localproblems aswell. SPS schemes todayhowever areprescriptive in that typically load flow and transient stability studies must be doneassumingworstcaseconditionstoensurethatthereisadequateprotectionduringthesetimes.A step forward inapplying specialprotection schemeswillbe todevelopmethods tocontrol transientstability thatare lessdependentonofflinestudiesandusemoreonline computation. What is proposed is to develop softcomputing techniques usingpatternrecognition,neuralnetworksandexpertsystemstodecideuponthebestcontrolaction. This type of approach for special protection schemes is unprecedented andwouldbeconsideredaproactivetypeofschemeinthatactioncouldbetakenaheadoftimetopreventoutagesfromoccurringinthefirstplace.Conclusions

Pmu/synchrophasortechnologyhasbeenavailableforthelastfifteenyearsandhasbeenusedprimarilyasasystemmonitoringandanalysistool.Thistechnologyhasprovidedinvaluable insight intofindingtherootcausesformajorsystemdisturbances includingtheAugust10,1996andAugust14,2003disturbances.Therehasbeenagrowingtrendacross theUnited States that systems are operatedmuch closer to themarginwherevoltagecollapseandtransientstabilitycouldoccur.

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California reliesheavilyon importedpower fromboth theNorthwest andSouthwestand many special protection schemes determine how much power can be importedbased on voltage and transient stability limits. More intelligent special protectionschemesthatwouldtakeactionbasedonactualrealtimeconditionswouldallowpowertobeimportednearerthemaximumlimit.Nooneacrossthecountryhasemployedanykindofpmubasedapplicationyet.NERChasbeenverysupportiveandhasencouragedtheuseofpmusinarealtimeapplicationand sooneror later itwillhappen. Theauthorsbelieve it isvery important toapplypmus in a real time application as quickly as possible to get confident with thetechnologyandtowringoutanyoftheconcernssuchastelecommunicationlatencyanddynamicresponse.BothPG&EandSCE(SouthernCaliforniaEdison)haveextensivespecialprotection/RASschemeapplicationsthatimpactbothpowerimportedintoCaliforniaaswellasinternalgeneration in California. PG&E has special protection schemes that impact theCaliforniaOregon Intertie, loadandgeneration inSanFranciscoandDiabloCanyongeneration. SCE has special protection schemes for power imported into SouthernCaliforniaandgenerationatBigCreek. Allofthesespecialprotectionschemesprotectagainstmultiple contingencies. BothPG&E and SCE alsohave installed a significantnumber of pmus on their bulk transmission system and have extensive high speedtelecommunicationinfrastructure.BothPG&EandSCEwouldbegoodcandidatesforademonstrationproject.TheauthorsfeltthatSCEhadaslightadvantageintermsoftheirsoftwareandexpertiseinpmutechnology.Recommendations

TheprojectteamrecommendsthatPIERsponsorasynchrophasordemonstrationprojectat SCEs Big Creek project to include the installation of a PDC, centralizedprogrammable logic controller (plc) and the software toprogram theplc as a specialprotectionscheme.Benefits to California

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California will benefit in the short term by increased reliability of generation at BigCreek.TotheextentthatBigCreekcanbeoperatedathigherlevelsofgeneration,morecostlygenerationcanbebackeddown,savingCalifornianstheincrementalcostbetweenBigCreekgenerationandmorecostlygeneration.In the long term the knowledge gained from the demonstration project could betransferred to more complicated special protection schemes such as the California OregonRASscheme.ThepotentialforsavingsisverylargeassumingthatmorepowercouldbeimportedintoCaliforniaatleastpartofthetime.ThecostsavingwouldbetheincrementalcostbetweenprimarilythermalgenerationinCaliforniaandveryeconomichydroelectricpowerinthePacificNorthwest.1.0 Introduction System Protection stateoftheart technology utilizes discreetmicroprocessor (digital)relays that can be programmed individually or to work in tandem to protecttransmission lines, transformer banks and generation. Some of the more advanceddigitalprotectiverelaysincorporateGPSreceivers,digitalfaultrecordercapability,andphase angle measurement (PMU) technology engineered into one relay. EHVtransmission lines have redundant primary protective relays that utilize highspeedtelecommunications at each end of the line to operate in tandem as high speeddifferential protection (directional/phase comparison, pilotwire and permissive overreaching transfer trip). Additionally therearebackuprelaysoneachtransmission linethatserveaslocalrelayfailureandremotebreakerfailureprotection.Alloftheserelaysare set based on a prescribed set of conditions assuming relatively normal system

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configuration. During abnormal system conditions, however, where voltages, phaseangles, frequency and/or fault currents vary significantly from preset conditions, theprotectiverelayscansometimesmissoperate,eitheroperatingwhentheyshouldnt(nofault, loadencroachmentorstableswingcondition)ornotopeningwhen theyshould(faultconditionsorunstableswingcondition).In virtually all of themajor blackouts in the last thirty years, protective relays haveplayed a major role in causing the blackout, exacerbating the blackout or failing tomitigatethespreadoftheblackout.Forexample,intheAugust14,2003blackoutontheEastCoastandtheJuly2andAugust101996blackoutsintheWest,zone3impedancerelaysplayed amajor contributing role aswell asmany transmission andgenerationprotectiverelays.Ineachoftheseblackouts,duetoanunusualandunanticipatedsetofcircumstances, the EHV transmission grid became configured in highly abnormaloperational states that were not anticipated or studied by protection and systemoperatingengineers.Oneotherobservedtrendthathasbeentakingplaceatanacceleratedrateoverthelastten years is the installation ofRemedialAction Schemes (RAS) or Special ProtectionSchemes(SPS).ThereareSPSinstalledintheWECCthatactasafirstlineofdefenseandas a safety net to mitigate the impact of cascading outages in WECC. The mostimportant is the California Oregon Intertie (COI) RAS/SPS, which responds to theinitiationofmultiple500kV transmission faults inCaliforniaandOregonby trippinggenerationintheNorthwest,insertingbothseriesandshuntcapacitorsinCaliforniaandOregonandultimately separating theWECC into twomajor controlled islandsunderworstcasescenariosastheultimatesafetynet.Thecomplexitycausedbyproliferationofthese schemes, particularly in the Western interconnection (WECC), could haveunintended consequences,potentially causingmajorproblems and becoming amajortrapfortransmissionoperatorsandISOs.

Thereare,however,new,potentiallymore intelligent, systemprotection technologies,utilizing phase angle (phasor) measurement and other features, which offer thepotential to create amore ductile and adaptive grid system. These new protectiontechnologiescanmoreeffectively isolate faults,helpgenerators tosustain their instepoperation,andotherwiseadaptivelyrespondtoavoidblackoutsandotherfracturedgridoperatingconditions.Forexample,althoughtheCOIRAS/SPShasoperatedsuccessfullymanytimestopreventorarrestcascadingoutages,thereisthepotentialtouseadaptivesystem protection technologies to allow the COI to operate more reliably and withgreaterpostdisturbancetransfercapacity,byadaptingtheoperationofrelaysandothersystemprotectionequipment tovaryingsystemconditionsbasedon information fromwideareaphasormeasurementtechnology.

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2.0 Project Approach

2.1. Interviews SeveralmeetingswereheldwithBPA,PNNL,SEL,CAISO,PG&EandSCE todiscusstheirapplicationsutilizing synchrophasorsand toask themwhat their concernswereandvision for the future. Asimilar listofquestionswasdeveloped forallcompaniesbutsomequestionsweretailoredtofitthecompanypersonnelbeinginterviewed.ThecompanieswerepickedbecauseoftheirleadershipandinvolvementinsynchrophasorsandimportancetotheCaliforniamarketandWECCgrid.

2.2. Meetings Theauthorsattendedseveralindustrymeetingsandseminarstolearnandinteractwithindustry experts regarding the state of the art of special protection schemes andsynchrophasorapplications.Amongthemeetingsandseminarsattendedwere:WesternProtectiveRelayConference inSpokane;Several IEEEPSRC (SystemProtectionRelayCommittee); two protection seminars at PG&E; and one synchrophasor applicationseminaratSCE.TheauthorshasseveralphonecallsandfollowupmeetingswithSCEregardingtheirBigCreekspecialprotectionschems.

2.3. Papers TheauthorsdownloadedseveralpapersfromtheIEEEdigitallibrarytoreviewwhatthestatedofsynchrophasortechnologywasaroundtheworld.Someofthosepapersarelistedinthereferencesectionofthisreport.

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3.0 Project Outcome

3.1. TASK 1 REPORT 3.1.1. Background

Therearetwomajorwideareamonitoring(measurement)systemprojectsacrosstheUnitedStates:1)WAMSWideAreaMeasurementSystemintheWECChasbeendevelopedandinuseoverthelast10years;2)EIPPEasternInterconnectionPhasorProjectthatwasinitiatedprimarilyasaresultoftheAugust14,2003blackout.ThisresearchprojectofcourseisfocusedonthebenefitsofR&DforCaliforniaUtilitycustomersand,sinceCaliforniaisoneof14statesthatcomprisetheWECC,allofourattentionisonWAMS.AftertheJuly2andAugust10,1996disturbancesintheWECCtherehasbeenagrowingconcernaboutimpactsofwideareadisturbancesandasignificantlyincreasedneedtoimplementabroaderWideAreaMeasurement(Monitoring)System.Today,WAMShasover60phaseanglemeasuringunits(PMU)installedatvarioushighvoltagesubstationslocatedthroughouttheWesterngrid.ThesePMUdevicesutilizesynchrophasortechnologytomeasurethevoltagemagnitudeandphaseangleofavoltagewaveformthatisreferencedintimebyaGPSsignal.SinceeverythingisreferencedtoacommonGPSsignalthatisveryaccurate,onecanthenmonitorveryaccuratelythephaseanglebetweensubstationlocationsregardlessofhowfaraparttheyare.Byknowingthephaseangleandvoltagemagnitude,onecancalculatetherealpower(MW)andreactivepower(Mvar)betweentwosubstationsassumingtheimpedancedata(modeldata)isknown.Thisishugebecauseifbothphaseangleandvoltagemagnitudeareknownandcontinuouslyupdated,onecanmeasuretheelectricalstressonthesystemandmakeaccuratepredictionsonhowstablethepowergridwillbe.Absolutephaseanglebetweentwomajorsubstationsdoesgivesomemeasureofhowmuchpowerisflowingbutevenmoreimportantistherateofchangeofthephaseanglebetweenthetwosubstations.Bytrendingthephaseangledifferenceonecanstartbuildingaknowledgebaseofthestressonthesystem.Alsobecausesynchrophasorscanmonitorphaseanglesaminimumof30timespersecond,onecandeterminethedynamicstressonthesystem.Itispossibletomeasurethefrequencyofoscillationonthesysteminadditiontodetermininghowwelldampedtheoscillationfrequencyis.Thisisanotherimportanttoolthatsystemoperatorsneverhadavailabletothembefore.

3.1.2. Key Findings

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InourdiscussionswithBPA,PNNL,SchweitzerEngineeringLabs,SCE,PG&E,CAISOandVirginiaTechweaskedanumberofquestionsandlearnedwheretheindustryisatthepresenttime.Followingarethekeyfindings:

BPAhasinstalled24PMUsandreceivesdatafromatotalof36PMUsinto2dataconcentrators.

BPAhasassumedtheresponsibilityofthesuperdataconcentratorsitewhereamajorityofPMUdataissenttotheirdataconcentratorsandarchived.

Thisdataisprimarilyusedfor:a)Disturbanceanalysis;b)Generationmodeling;andc)Datamonitoring.

DataispresentedinthreeformstoBPAdispatchersandPacificNorthwestreliabilitycoordinators;a)streamingdatareaderrealtimeinformationingraphicalformthatiscontinuouslyupdated;b)clockdisplayphaseanglesatvariouslocationsareshowninrealtime;c)RTDMrealtimedisplaymonitor.

Thisdispatchersandreliabilitycoordinatorsaremonitoringthedataandgettingexperiencewithitbutnooperatoractionsaretakenasaresultofthemonitoringofthedata.

MostofthePacificNorthwest,CaliforniaandtheArizona/NewMexicoareashavefairlygoodPMUcoverage.TheUtah,IdahoandAlbertaareashaveverypoorcoveragebyPMUs.

BPAsdispatchersarecomparingtheresultsofthestateestimatorandPMUdataandfindingveryclosecorrelation.

BPAisinterestedinfindingadditionalapplicationsandtheWACS(WideAreaControlSystem)projectisapossibleapplicationthatcouldbeusedinthefuture.DuringtheJune14,2004Westwingdisturbance,WACSwouldhavetakenthesamecontrolactionsastheCOIRASdidalthoughitwasinmonitormodeonly.ItsnotclearwhereWACSisgoinginthefutureasCarsonTaylorhasretiredfromBPAandsomeonenewwillhavetopickupwhereheleftoff.

ArevaisinvolvedinusingPMUdataintheWECCWesternWideSystemmonitoringprojectforstateestimation.

BPAindicatedtheydontcalibratethePMUs.Theyreveryaccurateanddontappeartodriftverymuch.Potentialtransformerandcurrenttransformersareanotherstory.Typicallypotentialtransformersare1%accurateandCCVTsparticularlyatthehighervoltagesarenotveryaccurateandcandrift.Currenttransformersareprobablyalittlemoreaccurateandtendnottodriftasmuch.ItsstillnotclearhowaccuratethePMUsneedtobebecausetherearenospecific

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applicationsyet.Iftheyareusedforstateestimation,accuracywithin1to2%maybeOK,butiftheyareusedforsystemprotectionandspecialprotectionschemes,theymayneedtobemoreaccurate.Inanyevent,theaccuracyoftheinstrumenttransformersispartoftheequation.

IEEEStd.C37.1182005isthepresentstandardregardingsynchrophasors. TherearenospecificalarmsprovidedbythePMUdatabecausetherearenotyet

guidelinesontherelativephaseanglesatvariouslocationsversusstressedoperatingconditionswherenomogramlimitsmaybeofconcern.

BPAisdoingshorttermtrendingonflowsandvoltageparticularlytovalidatemodeldatawithactualdataduringdisturbances.Thedatacanbearchivedforayearormore,howeverthereisnolongtermanalysisintermsofpatternrecognitionofrelativephaseanglesduringdifferentseasonsandoperatingscenarios.

Therewasconcernexpressedaboutthereliabilityandsecurityofthetelecommunicationsystemparticularlyregardingcontrolschemes,systemprotectionorspecialprotectionschemes.ItisonethingtousePMUdataforstateestimationpurposeswhereifsomedatadropsoutforacoupleof2secondscansitisnotaproblem.Ifontheotherhandthereisevenamomentaryfailureofthetelecommunicationsystemforaspecialprotectionscheme,itcouldmeanthefailureofthespecialprotectiontoeithertaketheappropriateactionortotakeittoolate.Thatmeansthatveryreliableandredundantmicrowaveand/orfiberoptictelecommunicationsmustbeused.

ThereissomeplannedR&DintheareaofdataconcentratorswhichtakeinputsfrommultiplePMUs.DataconcentratorscoordinatetheamountofPMUdatainputintothembutdoaddsomeadditionaltimedelayintotheprocess.

SouthernCaliforniaEdisonandLADWParedoingsomeresearchanddemonstrationprojectsforPMUsandspecialprotectionschemes.BharatBhargavafromSCEhasbeenheadingupthiseffort.

AlsoEPRIhasbeeninvolvedinR&DregardingWAMSandWACS.StephenLeefromEPRIhasbeentheprojectmanagerinthisarea.

ThelongtermvisionistocontinueinstallingPMUsanddataconcentratorstoobtainbettervisibilityoftheWECCsystembutwhateveryoneislookingistoinstallanapplicationthatutilizessynchrophasortechnologytotakecontrolactiontokeepthesysteminastableandsecurestate.

PNLislookingforapplicationsofPMUtechnologytoimprovesequenceofevents,operatorsituationalawareness,andL&Pstateestimation.

PNLhasheardfromseveralprotectionengineersthroughoutthecountryaboutthereliabilityofincludingsynchrophasormeasurementandprotectiverelayinginonebox.

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PNLisconcernedabouttelecommunicationnetworkissuesandtheroleitplaysinreliablecommercialapplications.

PNLisconcernedaboutthesparsePMUdataavailablesofar. PNLhasalsobeenactivelyinvolvedintheWACSprojectthatCarsonTaylorand

DennisEricksonworkedonfromBPA.JohnHauerandSteveWidergartenhavebeenworkingonaprojecttomakethegridmorerigid(robust)andlessimmunetoundampedoscillations.

PNLhasbeencollaboratingwithTVAonasuperPDCdataconcentratortoimprovetheapplicationofPMUdata

SEL(SchweitzerEngineeringLabs)areusingsynchrophasorsimbeddedintheirrelays.TheSEL421relayhasafullsynchrophasor(GPStimestampedphaseangleandvoltage)builtintotherelay.TheSEL451relaysalsohavesynchrophasorcapability.Thereare1199SEL421/451relaysinstalledontheWesterninterconnectionand2664SEL421/451relaysinstalledontheEasterninterconnection.

TheSEL321and351relayscanberetrofittedwithfirmwaretoenablesynchrophasors.Asanindicationofthenumberofpotentialsynchrophasorsthatcouldbeutilized,thereareover10,000SEL321/351relaysinstalledinERCOTalone.

SELdoesextensivesimulationtestingintheirlaboratoriesandthePMUsmeetorexceedtheexistingIEEEstandards.OtherthanusingthesameinstrumentPTsandCTs,thesynchrophasorsareisolatedfromtheprotectiverelayfunctions.Thesameconcernwasexpressedyearsagoregardingfaultlocationinthesamepackageasprotectiverelaysandhasprovennottobeaconcern.

SELisinvolvedinadataconcentratorprojectwithSDG&EandwithTasmaniainalineimpedancemeasuringproject.

SELisverysupportiveofPMUdatabeingabletoprovideaccuratedataforstateestimationandmodelvalidation.Theydemonstratedthatonanideal14busmodel,2PMUlocationswouldbesufficientdataforastateestimatortoconverge.Infactwith30%ofavailabledatafromPMUs,therethestandarddeviationwouldbe0%andwith10%availabledatafromPMUs,therewouldbe.1%deviation.

SELrelaysarecalibratedfromthefactorytomeetexistingstandardswhichiswithin1electricaldegree.TheGPSreceiversaregenerallyaccuratewithin100nanosecondsbuttheyarespecifying500nanosecondstobeontheconservativeside.ThebasicrecommendationwouldbetotestthePMUatthesameintervalthattherelayistested.TheymeetIEEEC37.118standard.

CAISOusesRTDMdisplaysthatfeaturesynchrophasordataasafurthertoolfortheirreliabilitycoordinators

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CAISOeffectivelydiagnosedsystemoscillationsonthePacificDCIntertieinearlyFebruary2008byusinggraphicaltoolsdevelopedforRTDM.

SCEhasinstalled16PMUsthatareconnectedtoonePDC. SCEhaswrittensomeverypowerfulandusefulsoftwaretoanalyze

synchrophasordata.FromarchivedPMUdata,theycananalyzemodesofoscillation,frequencydampingandphaseangles.

SCEhasusedtheiranalysissoftwaretoanalyzearchiveddatafromtheAugust4,2000,June6,2002andJune14,2004disturbances.

TheirPDCcanhandleupto30PMUs. SCEidentifiedtheBigCreekprojectasapotentialcandidateforsynchrophasor

wideareademonstrationproject. PG&Ehasinstalled7PMUswithimmediateplanstoinstall4morePMUs.This

shouldgivethemexcellentcoverageoftheir500kVsysteminadditiontoDiabloCanyonandHelmspowerplants.

TheyareupgradingtheirArevastateestimatortoincludePMUmeasurements. PG&EwillbeupgradingtheirCOIRASschemeandcommunicationnetworkin

2008. PG&Ehasacouplecandidatesforawideareademonstrationproject:A)Diablo

CanyondoublelineoutageSPS;andB)MetcalfSPS.

3.1.3. WECC Transmission Paths and Major RAS/SPS TheWECChasover70transmissionpathsthathaveplanningandoperatingratings.Thesetransmissionpathsconsistofmultipletransmissionlinesinatransmissioncorridorthatconnectonegeographicregiontoanotherone.Stabilityandloadflowstudiesaredoneundervariousconditionsandseasonstoensurethatthetransmissionpathcanbeoperateduptoitsmaximumratingreliablyandsecurely.ManyofthetransmissionpathsinWECCarenotconstrainedandthereforedonothaveoperationaltransfercapability(OTC)ratingsappliedtothem.ThemajorpathssuchastheCaliforniaOregonIntertie(COIPath66),Path15andPath26andEastofRiver(EOR)haveasignificantimpactonthereliabilityoftheWECCgridandallhavecomplicatedoperatingproceduresandoperatingnomogramsthatmonitorsimultaneousconditionstoensureasafeandreliableoperatingpoint.ThefollowingpathshaveoperationaltransfercapabilityratingsthathavesignificantimpactimportsintoCalifornia:

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ManyoftheabovementionedpathshaveSpecialProtection/RemedialActionSchemesthatareassociatedwiththem.Withoutthesespecialprotectionschemes,allofthesemajorpathswouldbederatedbyasubstantialmargin.UnderworstcasescenariosthousandsofMWofgenerationandloadaredroppedtopreventinstabilityandvoltagecollapseundermultiplecontingencyconditions.TherearemanyotherRAS/SPSinCaliforniathatimpactinternaltransmissionpathsandlocalgeneration.Thesespecialprotectionschemeseithertripgenerationorrunbackgenerationand/ortriploadtoassurereliableoperationunderunexpectedmultiplecontingencies.Allofthesespecialprotectionschemesareeventdriven(basedonline/transformer/generatoroutages)whichthentakeprescriptiveactionsbaseduponapredefinedsetofbasecaseconditions.Theseschemesareconservativebecausetheyarebasedonthemoststressedsystemconditions.Undermostoperatingconditions,capacityisleftonthetable(unused)becauseoftheconservativeassumptionsandstrategy.Havingsaidthat,thereisnoothergoodoptiontodootherwisebasedontechnologythatwasavailableatthetime.Eventhoughmanyoftheseschemesusefaulttolerantlogic(twooutofthreevotingscheme),theystillarereactiveinthattheymustwaitforaline,transformerorgeneratortorelayandtheybasetheiroutputactionsonanalogvaluesflowingacrossthetransmissionpathsorindividualtransmissionlines.

Path Name Path # Max. Rating Op. Proc. Sys. Prot.

COI Path 66 4800 MW N-S Nomogram RAS/SPS

PDCI Path 65 3100 MW N-S Nomogram RAS/SPS

IPP DC P1th 27 1900 MW E-W RAS/SPS

Midway Los Banos Path 15 5400 MW S-N Nomogram RAS/SPS

SCIT N/A 18,860 Nomogram

Midway - Vincent Path 26 3700 MW N-S RAS/SPS

NJD Path 73 7800 MW Nomogram

East of River Path 49 7550 MW E-W

West of River Path 46 10,000 MW

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3.1.4. Scope of R&D Project Thescopeofthisprojectistoidentifythoseapplicationswhereanadaptivespecialprotectionschemecanbeusedtotakecontrolactionsthatwillmaintainsystemstabilitywithoutsacrificingequipmentortrippingtoomuchloadorgeneration.Thereareothercontrolactionsthatcouldbetakensuchasrunningbackgeneration,controllingSVCsandinsertingseries/shuntcapacitorsthatareaseffective,andlessdraconianthandroppinglargeamountsofloadandgeneration.Synchrophasorsaretheperfectvehicleforaccomplishingthisbecausetheyaremonitoringthetwoquantities(phaseangleandvoltage)thathavethebiggestimpactonthetransmissiongrid.Andtheycantakecontrolactionsbeforethereisaneventandsoaremoreproactiveandprecisethanexistingspecialprotectionschemes.Regardlessofsystemconditionsandeventsbasedconditionsincludingbothscheduledandforcedoutages,thesynchrophasorsaremonitoringtheprecisehealthofthetransmissiongridinrealtimeandinfractionsofasecond.Therearestillanumberofissuesthatneedtobeaddressedandironedoutbeforethistechnologycanbeputintoservice.ThefollowingaresomeoftheissuesthatanR&Dprojectcansortout;

Reliabilityoftelecommunicationsnetwork. Latencyoftelecommunicationequipment. AccuracyofPMUs. PerformanceofPMUsunderfaultandstressedconditions. AccuracyneededforCCVTsandCTs. Identifyingwhentotakeaction(basedonstabilitystudies?). Identifyingwhatactiontotakeandhowmuch. MaintenanceintervalsofPMUsandassociatedequipment

Thesearesomeoftheissuesthatneedtobeaddressedbuttheupsidetosynchrophasortechnologyishugewhiletheriskscanbeidentifiedandmanaged.

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3.1.5. August 14, 2003 Disturbance Recommendation OneofthekeyAugust14,2003recommendationswastoEvaluateandImplementDefenseinDepthSystemMonitoring,Control,andProtectionMeasurestoSlowDownandMitigatetheSeverityofCascadesThefollowingkeyobservationcameoutoftheAugust14,2003recommendation:Anoveralldefenseindepthphilosophyandintegratedstrategyisneededtoprotecttodaysbulkpowersystemfromcascadingblackouts.Suchasystemwouldhavetointegrateexistingsystemmonitoring,control,andprotectionsystemswithnewmeasurement,analysis,andprotectioncapabilitiesintotheoveralldefenseindepthstrategy.Allsystemelementshavetobecoordinated.Theessenceofthisrecommendationistoensurethatallrealtimemonitoring,controlandprotectionoftransmissionandgenerationelementsbecoordinated.Whilesynchrophasorsareplayingalargerpartinthemonitoringofthepowersystem,thereareapplicationsinprotectiverelayingandspecialprotectionschemeswheresynchrophasortechnologycouldandshouldbeused.Itistheintentofthispapertochampionsynchrophasortechnologyforspecialprotectionschemes,butthereisavastareaofresearchthatneedstoinvestigateanintegratedapproachtomonitoring,controlandprotectionthatutilizessynchrophasortechnology.SeeAppendixAfordetailedrecommendationfromtheAugust14,2003disturbancereport.

Task 2 Report 3.2.1 Background Theindustryfirststarteddevelopingsynchrophasortechnologyaround1988.ArunPhadkewasapioneerinthiseffortin1988atVirginiaTechwheresomeofthefirstprototypephaseanglemeasuringunitsthatweresynchronizedtoaninternaltimeclockwerebuilt.TheinstallationofGlobalPositioningSatellites(GPS)allowedthemeasurementofphaseanglestobesynchronizedtoaveryaccuratetimeclock.Macrodynestartedbuildingsomeofthefirstcommercialpmu/synchrophasorsinthelate1980s.TheWECC(primarilyBPA)startedinstallingpmusintheearly90sandwasthebasisforWAMS.Alotofthatdatawasveryinstrumentalinanalyzingthe1996systemdisturbancesintheWest.EIPP(EasternInterconnectionPhasorProjectwasformedaftertheAugust14,2003blackout.EIPPandWAMSwerecombinedintoNASPIjustrecentlytohaveaconsistentfocusonthesynchrophasortechnology.

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3.2.2 Basic Theory of Synchrophasors

Thetheorybehindsynchrophasors,orsynchronizedphasormeasurements,istoprovideaphasorrepresentationofapowersystemvoltageorcurrenttoanabsolutetimereference.Whenthisisdone,thevoltageorcurrentwaveformcanbedefinedasacomplexphasorwithaphaseangle(ascomparedtoatimereference)andmagnitude.Aninternalhighaccuracyclockwhichissynchronizedtocoordinateduniversaltime(UTC)viaaGlobalPositioningSatelliteSystem(GPS)providesthetimetagorabsolutetimereference.Asseeninfigure1thenthevoltagewaveformcanbedefinedasaphasorwithaphaseangleandmagnitude.Thephaseangleismeasuredbycomparingthepeakofthesinusoidalwaveformtothetimetag.Figure1ashowsthepeakofthewaveformcorrespondingtothetimetagsotherelativephaseangleis0degrees.Infigure1bthepeakofthewaveformcomparedtothetimetagis90degree.Ifforinstancethevoltagewaveformsrepresentedinfigure1aand1bwereatdifferentsubstationsitwouldindicatetheamountofrealpowerthatcouldbetransferredbetweenthesubstations.Withoutasynchronizedtimestandardtherelativephaseangledifferencebetweenthetwosubstationswouldntmeananything.

Byinstallingsynchrophasorsataselectnumberofimportantsubstations,thepowersystemengineercanimmediatelyknowtheamountofrealandreactivepowerflowing

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betweenthesubstations.ThedifferenceinphaseanglecausesrealpowerasmeasuredinMWtoflowandthedifferenceinvoltagemagnitudecausesreactivepowerasmeasuredinMvartoflow.KnowingenoughofthesteadystaterealandreactiveflowsalongwithvoltageandphaseanglecansubstantiallyaidstateestimationprogramswhichisthebasisforalladvancedpowerflowandcontingencyanalysisprogramsinEMS(energymanagementsystem)centers.Knowingtherateofchangeofangleandvoltagewilldeterminewhetherthepowersystemisnearinginstabilityandwhetherthesystemwillrecoverfromanoutageofamajortransmissionlineorgenerator.Sothistechnologycanbeusedeitherasatooltoestimatethestateofthesystemorastooltotakeremedialactioninthecaseofanoutage.3.2.3 Synchrophasor Standards

TheIEEE(InstituteofElectricalandElectronicengineers)definesmanystandardsthroughouttheindustry.Theydefinedstandard13441995whichwasapprovedin1995tosetstandardsforsynchrophasormeasurementsandcommunicationprotocol.Theyrecentlyupdatedthestandardin2005underanewstandardC37.1182005.Thisnewstandarddefinesmeasurementconvention,measurementaccuracyandcommunicationprotocol.InorderforPMUstobecompliantwiththestandard,theymustmeetthesynchrophasoraccuracystandard,conformtomeasurementconventionandconformtocommunicationprotocolforreportingmeasurements.ThenewstandardspecifiesthatPMUsmustbelessthan1%errorconsideringtheaggregateoftiming,magnitudeandangleerror.Forinstanceiftherewerenotimingormagnitudeerrors,themaximumallowangleerrorwouldbe.573degrees.Theconventionformeasuringphaseangleisdepictedinfigure1above.Alsotomeetthestandard,aPMUmustprovideasamplingrateof10reportsperseconduptohalfthenominalfrequencywhichinthiscountryis30reportsorsamplespersecond.PMUsmustalsoprovideestimatesoffrequencyandrateofchangeoffrequencyaspartofthePMUoutputdatastream.Eventhoughthereisnostandardonhowthisistobecalculated,thePMUshouldbeabletodothisveryaccurately.ThestandarddefineshowcommunicationishandledbetweenasynchrophasordeviceandaPhasorDataConcentrator(PDC).APhasorDataConcentratorarchivesandpresentsdatatovariousapplications.ThisprotocolcanbeusedtodefineexchangeinformationbetweenPDCs.Tobecompliantwiththestandard,PMUsmustmeettheminimumrequirementsbutthereisnothingtopreventthemanufacturerfromaddingadditionalfeaturessuchas

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noisesuppression,filteringandbetteraccuracy.DatafromPMUsmadebydifferentmanufacturersshouldbecompatible.3.2.4 Areas of concern and areas for further development

Communicationlatency,performanceunderdynamicconditions,aliasingandinstrumenttransformererrorsareareasthatneedtobetterdefinedandbetterunderstoodwhenapplyingsynchrophasorbasedprotectionschemes.Dependingontheapplication,communicationlatencymayormaynotbeamajorconcern.Ifsynchrophasorsarebeingusedtoenhancestateestimatorsortoprovidealarmordatatrendingtotheoperators,thenthedelayincommunicationsignalsisnotabigconcern.IfontheotherhandsynchrophasorsarebeingusedinSpecialProtectionSchemes,outofstepschemesorforapplicationswheredynamic/transientinstabilityisinvolved,thencommunicationdelaysareamajorconcern.Communicationdelayscanbecategorizedintothefollowingareas:

Fixedtimedelayinstrumentationtransformers,analoganddigitalfiltering,signalprocessing,dataconcentrators,etc.

Propagationdelaytheinherenttimedelayoflinkandphysicaldistancewhichthedatahastotravel.

TransmissiondelayAmountofdatatotransmitandthedatarate.Thetimedelaycouldaddanywherefrom100to300microsecondsbasedonthecommunicationmediumandphysicaldistancethatthedatahastotravel.SynchrophasorstandardC37.1182005intentionallydoesnotaddresstheperformanceofPMUdevicesduringtransientconditions.Thenextupdateofthestandardwilladdressthisbutfornowitissomethingthattheindividualmanufacturersmustdecideontheyaddressit.Highspeedprotectionschemesthatprotectagainstinstabilitywouldhavetoaddressthisonanadhocbasisfornow.C37.1182005addressesinterferingfrequenciesandphasoraliasingbriefly.ItaddressestheNyquisttheoremwhichstatesthatinordertoproperlydetectanddisplayadesiredfrequencythesamplingfrequencymustbeatleasttwicethedesiredfrequency.Soifa

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frequencyof15Hzwastobemonitoredthesamplingfrequencywouldhavetoatleast30Hz.TheWECChasstandardizedonasamplingfrequencyof30timesasecondsodetectingfrequenciesbelow15Hzshouldnotbeaproblem.SincetheoscillationfrequenciesintheWestvaryfrom.25to.7Hz,thisisnotamajorissue.Thestandardalsoaddressesinterferingfrequenciesbysuggestingthatappropriateantialiasingfilteringbeusedtoaddresstheconflictingfrequencies.CurrentandpotentialtransformersintroducesomeerrorsintoSynchrophasormeasurement.Themoreheavilyloadedacurrenttransformeris,themoreerrorcurrentintermsofexcitationcurrentthatisproduced.Asmostmoderncurrenttransformersaredesignedtoproduceaccuratesecondarycurrentsduringfaults,thereisagreaterpercentageoferrorcurrentproducedduringlightloadconditions.Generallyameasurementerrorgreaterthan.3%wouldnotbeexpected.Agreaterconcernintermsofperformanceispotentialtransformers.AttheEHV(extrahighvoltage)levels,potentialtransformersaremostlycouplingcapacitortransformersandcanproduceerrorsof1%orhigher.Duringtransientconditions,potentialtransformersarealsopronetoproblemsandthisshouldbetakenintoaccountifSynchrophasorapplicationsarebeingusedfortransientstabilityapplications.3.2.5 Synchrophasor Manufacturers

ThefollowingcompaniesmanufacturePMUs:

Ametek Metatech USI NextPhase ZIV RFL GE ABB Siemens Schweitzer Arbiter Hathaway/Qualitrol Macrodyne

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Hitachi

ThePMUmanufacturerscanbeputintotwogroups:Thosewhoseprimarybusinessareprotectiverelaysandthosewhoseprimarybusinessisdigitalfaultrecorders,metersandmonitoringequipment.Fromatechnologystandpointitdoesntmakeanydifferencebutitisinterestingtoseethedifferentapproaches.TheprimaryrelaymanufacturerssuchasGE,ABB,Schweitzer,SiemensandHitachiallmakePMUssomeasstandaloneunitsandsomethatareintegratedintotherelaypackageitself.ForinstanceSchweitzerEngineeringLabsphilosophyistoprovidePMUcapabilityintegratedintoalloftheirmodernrelays.TheSEL421and451relaysareprimarylineandbusprotectiverelaysthathavePMUcapabilityintegratedintotherelaypackage.SELofferscustomersfirmwareupgradepackagesfortheSEL311,321and351relaysthatprovidefullPMUfunctionality.Mr.SchweitzersvisionistoprovidePMUcapabilityinalloftheirrelaysatnoextracostsothattheendusecustomerwillbeabletoutilizesynchrophasorsforanyapplicationincludingstateestimation,realtimemeteringandspecialprotectionapplications.ManyprotectionengineershaveexpressedconcernaboutincludingPMUsaspartoftheprimaryrelaypackage.TheirconcernisthatthePMUdesignwillcompromisetheperformanceoftherelay.Thereisnotechnicalreason,however,whythereshouldbeanylossofaccuracyorqualityintherelayasthePMUandrelayaretwoseparatepackages.SELhasbeenverysuccessfulinthepastintermsofpackagingfaultlocationfunctionalitywithprimaryrelayfunctionsandthereiseveryreasontobelievehecandothesamethingwithPMUtechnologybasedontheirtrackrecordofthoroughlytestingtheirproduct.PresentlySELhas15,000relaysinstalledwithPMUcapabilityacrossthecountrywithapotentialfor80,000relayswithPMUcapabilityifthealloftheolder300seriesrelayswereupgradedbythecustomers.GEisanothermajorrelaymanufacturerthatoffersfullrelayandPMUfunctionalityintheproductlineofMultilinrelays.GEprovidesstandalonecapabilityintheirN60aspartoftheUR(universalrelayfamily).ItfullymeetstheC37.1182005standardandprovidesabroadrangeofcapabilityinadditiontherequiredfeaturesoftheSynchrophasorstandard.PG&EhasplanstoutilizetheN60relayaspartoftheupgradetothePacificIntertieRAS/SPS.Arbiter,MehtaTech,MacrodyneandQualitrolarePMUmanufacturerswhoseprimaryfocusisondigitalfaultrecorders,monitorsandPMUs.Someofthemmaymakeancillaryrelaysandassociatedequipmentbuttheyarenotviewedprimarilyasrelaymanufacturers.

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3.2.6 Key Findings

Ofthemajorrelaymanufacturers,Schweitzer,ABB,SiemensandGEmanufacturePMU/sychrophasorproducts.

Arbiter,MacrodyneandHathawaymanufacturePMUsaspartoftheirproductline.

SchweitzerhasadoptedthephilosophyofprovidingPMUtechnologyintegratedintohislatestdigitalrelayssuchasSEL421and451.Yearsearlierheprovidedthesamefunctionalitywithfaultrecordersthatwerewellreceivedbytheindustry.

ProtectionengineersareskepticalaboutusingthePMUfunctionalitywhenincorporatedintothesamerelaybox.

ExistingIEEEstandardC37.118doesnotaddressthedynamicperformanceofpmus.

InordertoutilizePMUsoverawidearea,communicationlatencyisamajorissue.Thetimedelaytocommunicatephaseanglefromdifferentlocationscannotbegreaterthanthetimeittakesforinstabilitytooccur.

AllRASandSPSschemestodayareprescriptive.Inotherwordsforagivensetofconditions,theSPSwilltakespecificactionregardlessofhowstressedthesystemis.MoresophisticatedRAS/SPSschemesincorporatetablesthatmonitoractualsystemconditionsandtakeactionaccordingtothetable.

AmajornextsteptotakewouldbetoapplycomputerlogicbasedonsignalsfromPMUstotakeactiontoavoidareliabilityproblem.

Therearedataerrorandaliasingissueswithexistingpmus.Notallpmusperformthesame.

Instrumenttransformeraccuracyimpactstheaccuracyofthesynchrophasor. C37.118doesdefinetheperformanceofpmusduringoffnominalfrequencies. C37.118allowsfordifferentsamplingrates.IntheWECC,thesamplingratehas

beenstandardizedat30samplespersecond.

3.3 Task 3 Report 3.3.1 Introduction

ThissectiondescribesvariousresearchanddevelopmentactivitiesintherealmofIntelligentGridProtectionSystems.Atthispointintimewhenvarioustechnologiesare

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beingintroducedintothegrid,thereisnocleardefinitionofeitherIntelligentGridorIntelligentGridProtectionSystem.ItisgenerallyunderstoodthatSpecialProtectionSchemes(SPS)orRemedialActionSchemes(RAS)thathavebeeninstalledinvarioussystemsaroundtheworldareIntelligentGridProtectionSystemsbecausetheysurpassthefunctionalityofthemorecommonProtectionSystemswhoseonlypurposeistoprotectcertainspecificpiecesofequipmentfromharm.SPS/RASusuallyhasacoupleoffeaturesthatdistinguishesitfromsimpleprotectionschemes:(1)itusuallywillhavemorethanoneinputoroneoutputsignaloftenfromortomorethanonelocation(substation),and(2)itusuallywillhavealogicthatwillbemorecomplexthanusedforsimpleprotectionschemes.BecauseofthesefeaturestheboundarybetweenprotectionandcontrolisnowquitefuzzyandthereisnoclearlinebetweenSPSandwideareacontrol(WAC).AspointedoutintheTask2Reportamajorevolutioninthegridtodayistheavailabilityofrealtimedataacrossthegridatmuchfasterratesthataretimesynchronized.AlthoughuniqueSPShasbeenimplementedforsometimeutilizingspecificrealtimedatapointsandspecificlogic,theprospectofuniversalavailabilityofsynchrophasordataacrosstheinterconnectionhasbroughtaboutaqualitativechangeinthepotentialforintelligentgridprotectionandcontrol.InthisTask3Report,wetrytosummarizeallthevariousR&Dactivitiesthatintendtoutilizesuchsynchrophasordatafortheoperationandcontrolofthegrid.

3.3.2 Background

Almostalltheprotectionandcontrolsystemsonthegridandthesenumberinthetensofthousandsalmostallarelocal,i.e.theinputvariablesandtheoutputvariablesofeachprotectionorcontrolschemearelimitedtowithinonesubstation.Allcommonformsofprotectionfallintothiscategoryandallcontrolssuchasgovernors,voltageregulators,powersystemstabilizers,transformertaps,reactorbankswitching,variousFACTSdevices,etc.areinthiscategoryaswell.Onlythefollowingexistingcontrolscanbeconsideredtobewidearea:SpecialProtectionSchemes(SPS)Thisisaclassofprotection/controlthathasbeenusedaroundtheworldtoalleviateparticularlimitationsinthegrid.(TheacceptedgenericnameforthisclassisSpecialProtectionSchemes(SPS)butbecausetheyhavebeenutilizedmoreextensivelyintheAmericanWestthananywhereelse,thelocalnameRemedialActionSchemes(RAS)isstillcommonlyused.)

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AutomaticGenerationControl(AGC)Thesecondaryportionofthiscontrolutilizesallgeneratoroutputsandalltielinepowerflowsforthecontrolareaasinputstocontrolthegovernorsettingsatthegeneratorssothatgenerationandloadarealwaysinbalance.Theprimaryportionisthelocalgovernorcontrol.(NomenclatureisagainaproblemforthiscontrolfunctionasithasbeencalledLoadFrequencyControl(LFC),LoadFollowing,andmorerecentlyLoad/GenerationBalancing.)SecondaryVoltageControlThisisasecondaryvoltagecontrolschemetocontrolthevoltagesinalocalregionandissuperposedontheusuallocalvoltagecontrollerslikevoltageregulators,transformertapsandshuntreactorswitchings.Ithas,sofar,onlybeenusedinEurope(France,Belgium,Italy).Thefirstoneisknownasprotectionbecausetheactiontakenisfastofteninmillisecondswhichisintheprotectiontimescale.Moreover,itusesrealtimeinputdatathatisupdatedatfast(protectiontype)timerates.Alsotheoutputsignaloftenistheopeningorclosingofbreakerswhichiswhatprotectionsystemsnormallydo.Finally,theSPSistriggeredonlywhensomethinghappens,likeaprotectionsystem,andisdormantotherwise.TheothertwoarecalledcontrolbecausetheyworkcontinuallytoadjustoutputsandtheyworkatslowspeedsutilizingrealtimedataatSCADAspeeds.Whatisbeinganticipatednowisfastprotectionandcontrolofmanydifferenttypes,i.e.controllersthatwouldoperateatfastspeedsutilizingsynchrophasordata.WedescribesomeoftheR&Dthatisbeingconductedtodevelopvariousapplicationsutilizingsynchrophasordata.3.3.3 Synchrophasor Data Applications Obviously,amajorapplicationofthesynchrophasordataisthevariouspossibleengineeringanalysesthatcanbeconductedwiththisdata,nottheleastofwhichisthepostmortemanalysisofsmallandlargedisturbances.Thepostmortemanalysisofthe2003Northeastblackoutwouldhavebeenaloteasierifmoresynchrophasordatawereavailableandthelittlethatwereavailableturnedouttobeinvaluable.However,thefocusofthisreportistheoperationandcontrolofthegridinrealtime,soonlythoseapplicationspertainingtooperationandcontrolarementionedhere.Theseapplicationscanbebroadlycategorizedintothreetypes:MonitoringapplicationsTheoperativephrasetodayisthesituationalawarenessofpowersystemoperators.AllthealarmsanddisplaysinthecontrolcenteraredrivenbySCADAdatawhichisupdatedrelativelyslowlyeveryfewsecondsandthedataisnotsynchronized.The

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synchrophasordatacanthenbeutilizedtobetterthesedisplaysandalarmsinmanydifferentways.ThemostobviousmonitoringthatsynchrophasordatacanprovidenotavailabletodayontheSCADAisthatofphaseangledifferencesacrosskeytransmissionlinesorcorridors.ThisisalreadyavailableinmanycontrolcentersalthoughthedisplaysareoftennotyetintegratedwiththeSCADAdisplays.Obviously,manytypesofdisplaysandalarmscanbegeneratedfromthesephaseangledifferences.Anextensionofthisistoobtainphaseangledifferencesbetweennodesthatareindifferentcontrolcenterjurisdictions.Theproblemhereisnotoneofsynchronizationasallsynchrophasordataeverywherearesynchronizedtoauniversalclock,butoneofdatatransferbetweenonejurisdictiontoanother.UsuallycontrolcentersexchangedataataveryslowrateslowerthantheSCADAsamplingratesandareuselessforthispurpose.However,boththeWesternandEasternInterconnectionshavesetupdatatransfermechanismsbetweenthesynchrophasordataconcentratorsandthesedoprovidedatatofarflungcontrolcentersinnearrealtime.Asecondapplicationhasbeenthedetectionandidentificationofslowoscillations.TheSCADAdatasamplingistooslowtodetectsuchoscillationsbutsynchrophasordataisfastenoughforthispurpose.Moreover,aPronyanalysisofthisdatacanactuallycalculatethefrequencyanddampingofsuchoscillations.Ifanoscillationofknownmodeisdetectedandidentifiedandithaslowdamping,operatorinitiatedcontrolactionscanbeusedtodampouttheoscillations.ThistypeofsituationalawarenesstoolsarealreadybeingusedatSouthernCaliforniaEdisonandBonnevillePowerAdministrationusingtheWAMS.IntheEasternInterconnectionPSERChasaresearchprojecttodevelopsimilartoolsforEntergyandTVAalthoughtheproblemofoscillationsintheEasternInterconnectionisrelativelynew.Athirdapplicationforthismonitoringdataisvisualization(whichhasbecomealmostsynonymouswithsituationalawareness).Thephaseangledifferencescandrivedisplaysthatinsomeinstancescanprovidemoreanddifferentinformationthanpowerflows.Butmorethanthat,thefastsamplingofotheranalogdataalsoprovidestheprecisesequenceofevents(breakeroperations),informationonfaults,andothertransientconditionsofthegrid.Moreover,thesecanbeobtainednotjustfromthecontrolcentersownjurisdictionbutfromacrosstheinterconnectionifnecessary.SuchvisualizationresearchworkhasbeensupportedbyPSERCandbyUSDOEthroughtheCERTSprogram.

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EMSapplications

TheexchangeofSCADAdataoverICCPlinksbetweencontrolcentershasmadeitpossibleforthesystemoperatorsinoneregiontomonitorhappeningsintheirneighborssystems.Thisprovidesgoodinformationaboutthepresentconditionsoftheinterconnectioninnearrealtimetotheoperators.However,thisdoesnotinitselfallowtheoperatortoassesstheabilityofthegridtowithstandthenextcontingency.Todothistheoperatorneedsthelocalcontrolcentertohaveastateestimatorthathasitsreachbeyonditsownboundaries.ThetraditionalstateestimatorinacontrolcenterlimiteditsmodeltoitsownjurisdictionalboundarybecausetheSCADAdatawereavailableonlyfromthosesubstationswithinitsownboundary.Therestoftheinterconnectionwasrepresentedasanexternalmodelwhichwasagoodrepresentationofthestaticnetworkbutwashighlyerroneousbecauseoftheabsenceofrealtimedatafromthisexternalsystem.Theseerrorsinthestateestimatoraffectedtheresultsofthecontingencyanalysisespeciallyifthecontingencywastohappenoutsidethelocaljurisdictionorevenneartheboundary.Thisproblemwasparticularlyhighlightedinthe2003Northeastblackoutasmostoftheoperatorsintheoutagedsystemwerenotawarethatthenextcontingencyseveraljurisdictionsawaywouldblackoutsuchavastarea.InterconnectionwidemonitoringandEMSfunctions(contingencyanalysis)havebeenrecommendedbyaDOE/FERCreportfromlastyear,andvariousR&Dandimplementationeffortsareunderway.Intheimplementationarena,mosteffortsareusingtheSCADAdatathatarebeingexchangedbetweenneighborstowidenthereachofeachstateestimator.IntheEasternInterconnectionthereareeffortsbetweentheISOsintheNortheast(NEISO,NYISO,PJM),betweenPJMandAEP,betweenEntergyandTVA,andmanyothers.ProbablythemostambitiousistheeffortintheWesternInterconnectionwhereonestateestimatormodeltorepresentthewholeinterconnectionisbeingdeveloped(knownastheWesternorWECCmodel).Theuseofsynchrophasordatainthesestateestimatorsishelpfulintwoways.First,thedatafromthesynchrophasorsinsteadystateisusuallymoreaccuratethushelpingstateestimatoraccuracy;unfortunatelythenumberofsynchrophasormeasurementsinNorthAmericaisstillsominisculecomparedtothesystemmodelsthattheimpactonaccuracyisnegligible.Second,thisdataissynchronizedunliketherestoftheexchangedSCADA

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datawhichhassignificantandunknowntimeskewsandthishelpsthestateestimatoraccuracyaswell.Thereare,ofcourse,majorissueswiththesevariousimplementations.TheseexchangesofdataareusuallybetweentheReliabilityCoordinatorandmanyoftheReliabilityCoordinatorsgettheirSCADAdatathroughdatalinksfromtheirlowerlevelBalancingAuthorities.Thusthetimeskewsbetweenthesedatasetscanbesignificanttothesolutionofthestateestimator,whoseaccuracy,ofcourse,affectsthecontingencyanalysisresults.R&Disbeingconductedontheseissuesundervariousdifferenttopicalnamesdistributedstateestimator,hierarchicalstateestimator,externalmodel,wideareamodel,etc.butthemainissueishowtoprovideastateestimateofthewholeinterconnectionsuchthatcontrolcenterscanhaveaccesstoarealtimemodelofalargeenoughsystemthatwillgiveaccuratepredictionsofitsabilitytowithstandcontingenciesanywhereontheinterconnection.SuchresearchisbeingconductedatseveraluniversitiesundersponsorshipofNSF,DOEandPSERC.Inaddition,theEMSvendorsaretiedtomanyoftheseR&DprojectsastheyareallupgradingtheirstateestimatorstoincorporateexchangedSCADAdataandsynchrophasordata.ControlapplicationsTheseapplicationsarequalitativelydifferentthanthemonitoringandEMSapplicationsbecauseboththosetypesoftoolsareadvisorytothehumanoperatorwhereascontrolimpliesactualchangemadeautomaticallytothesystem.Thusthedemandsforaccuracyandcorrectnessarefarhigherasnonoperationorfalseoperationscouldhavedrasticconsequences.ObservationofthevariousSPSimplementedaroundtheworldmakesitclearthatadhocwideareacontrolapplicationsarenotonlyfeasiblebutalsoverybeneficial.WesaythattheseareadhocbecauseeachSPSimplementationisuniqueinitsdesign,implementationandtheproblemitaddresses.Asaresult,eachimplementationisalsoexpensiveandbecauseitsolvesaparticularsystemproblem,theSPSusuallybecomesobsoleteinafewyearsasthesystemchangesandtheproblemdisappears.AnexamplemaybeanSPStohandlearegionalvoltageproblemwhichdisappearswhennewgenerationsourcesbecomelocallyavailable.ThusR&Dinthisareafollowstwodifferentbutparalleltracks:oneistheneedfortheupgradingofthepowersysteminfrastructurecomputers,communicationsandcontrolsthatwillmakeiteasierandmoreflexibletodevelop,designandimplementwideareacontrols;theotheristheneedtodevelopcontrolapplicationsforspecific

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phenomenathatlimittheoperationofthegrid.Inthefollowingsection,thesetwotracksareexploredinmoredetail.3.3.4 R&D in Wide Area Control Therearesignificanteconomicincentivestoincreasethetransmissionlimitsofexistingsystems.Infact,themajorconstraintsofthederegulatedpowermarketsarethetransmissionsystemlimits.Todaygenerationcompaniessellpowertodistributioncompanies(ordirectlytolargecustomers)throughbilateralagreementsorauctionmarkets.Thesetransactionshavetoflowoverthetransmissionsystemandifthetransmissioncapacitywashigherthanallpossiblepowerflowssuchtransactionsmayproduce,thenthemarketwouldbeideal.This,however,isnotthecasebecausethetransmissionsystemwasbuiltwhenthepowercompanieswereverticallyintegratedandtheyweresizedfortheexpectedpowerflowsresultingfromplannedoperationofthegenerators.Thetransmissionsystemwasnotdesignedtoaccommodateallbuysellagreementsbetweengeneratorsandconsumers.Thusallpowertransactionsmustbecheckedbeforehandtoensurethattheflowsarewithinlimits.Astheremaybehundredsofsimultaneoustransactionsbetweengeneratorsandconsumers,andbecausetheeffectsofthesetransactionsontheflowsarenotlinear,allsimultaneoustransactionsmustbestudiedtogethertocheckwhethertransmissionlimitsareviolated.Ifcongestionisexpected,allthetransactionscannotbeallowedanddifferentISO/RTOhaveworkedoutproceduresabouthowandwhichtransactionswillhavetobecutback.Theprocedureshavetobefairtoallpartiesandagreeduponbeforehand.ThereliabilityoftheregionrestswiththeReliabilityCoordinatorwhohasthefinalsayoncongestionmanagement.Sothetransmissionlimitsaretheconstraintsthatalsolimitthepowermarkets.Forsystemsthatarethermallylimited,theonlywaytoraiselimitsistobuildmoretransmission.Forthosesystemsthatarestabilitylimited,bettercontrolscouldincreasethestabilitylimit.Thusourinterestinthispaperisonbettercontrolofstability.3.3.5 Infrastructure R&D for Wide Area Control

Essentially,therearethreeclassesoftechnologiesthatarerelevant: Faster,cheapercomputers,

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Broadband,cheapcommunications,and Betterpowerelectroniccontrols(alsoknownasFACTSflexibleAC

transmissionsystemswhichcoversthisclassoftechnologyspecificallydevelopedtocontroltheACpowersystem).

SomeofthesetechnologiesarealreadyinuseinthepowersystemsasmentionedinSection2.Whatweareproposinghereisthedevelopmentofnewcontrolsutilizingacombinationofthesetechnologies.Thesecontrolswillbesignificantlydifferentinconceptthantheexistingones,andwillbefastandsystemwidetodramaticallyincreasestabilitylimits.ComputersComputers(ormicroprocessors)areembeddedineverythingmeters,protectiverelays,dataconcentrators,communicationswitches.Theyareprogrammable,thatis,thefunctionsofthegadgetinwhichtheyareembeddedcanbechangedbysoftware.Thuscontrolsthatutilizethesecomponentscanbeadapted,throughchangedsettings(simple)orchangedlogic(moredifficult),providingflexibilityinthedesignofthissoftware.Workstationcomputersarealsomuchfasterandcheaper.Thusverylargeamountsofcalculationscanbedoneveryquickly.Suchanalysiscanthenbepartofthecontrolbringingevenmoreintelligenceintothecontrolloop.Forexample,ifacontrolisdevisedtoshedloadtoavoidinstability,anoptimalpowerflowcoulddeterminewhichloadsaretobeswitchedoff.CommunicationsElectricpowercompanieshavealwayshadtheirowncommunicationsystems.Thishasmainlybeenmicrowavechannelsthatconnecteverysubstationandgeneratingstation.Theuseofopticalfiberisnowincreasingatatremendousrate.Atfirst,theopticalfiberhasbeenusedwithinsubstationsandgeneratingstations,especiallythenewerinstallations,buttheolderonesarebeingrapidlyretrofitted.Thisisbeingdonetogathermorerealtimedataatfasterratesatthesubstationssothatfastappearingemergencyconditionslikerightafteralightningstrikecanbebetterprotectedagainst.Thedatacanalsobecapturedbuthastobestoredlocallytobelatertransmittedovercommunicationnetworks.

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Opticalfiberhasalsobeenstrungalongtransmissiontowers.Powercompaniesmainlydidthistobecomecommunicationsprovidersbecauseoftheprojectionsofeverincreasingdemandforbandwidth.Althoughthisventureintonewbusinesshasnotpannedoutbecauseoftheglutofunusedbandwidth,abroadbandnetworkisnoweasilyavailabletothepowercompanies.Ifthisnetworkbandwidthisbroadenough,thenallthedatabeingcollectedatthesubstationscanbetransmittedinrealtimetootherlocationslikethecontrolcenter.Infact,anetworkcanbeenvisionedsuchthattherealtimedatawouldbeavailabletodifferentcomputersdependingontheirfunction.Thisopensupthepossibilityofdecentralizingthecontrolcentersothatfunctionscanbeputindifferentplacesdependingonwhereitisneeded.Withanetworklikethis,thestarkdifferentiationtodaybetweencentralizedcontrolandlocalcontrolwouldgoawayandcontrollerscouldusethemostappropriatedataneededforcontrol.AcommunicationnetworkthatcanmeetthevariedneedsfortheoperationofthepowersystemwouldbemuchmorecomplexthanthesimplestarnetworkusedtodayforthecontrolcentertopollsubstationRTUs.Moreover,thecontrolfunctionswillnotbeallconcentratedatacentralcomputerinthecontrolcenterbutwouldbedistributedovernumerouscomputerswhethertheyareinsubstations,generatingstationsorengineeringoffices.Suchdistributedcomputercommunicationisbeingdevelopedtodayforvariousapplications.Insuchacommunicationsnetworksomeofthefunctions(measurementsorcalculations)willbepublishersofdatawhileotherswhowillusethisdata(applications,controls)willbesubscribers.Thenetworkwillbecontrolledbyothercomputersthatwillbequalityofservice(QoS)managers.Suchmiddlewarearebeingdevelopedforotherapplicationsandwillhavetobedevelopedforthearchitectureappropriateforthepowergrid.Itshouldbementionedthat,giventheconcernforthesecurityofsuchcriticalinfrastructuresasthepowergrid,suchcomputercommunicationsystemsforthepowergridmustbesecurefromexternalintrusionsandhastobebuiltintotheQoS.FACTSFACTSdevicesavailabletodaywerediscussedinSection2.Althoughtheyaredifferentindetailbymodelandmanufacturer,buttheyfallintothreeclasses:

DCtransmissioncontrols, SVC(staticvarcontroller),and PFC(powerflowcontroller).

Inaddition,specialcontrollerscanbebuiltforspecificpurposesusingthesameprinciples.Onemajoradvantagetothesecontrollersistheirspeedwithcontrolactionstakingplaceinmillisecondswhichisinthesametimeframeasprotectionactions.

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3.3.6 R&D in Control Applications Theproposedcontrolconceptsdescribedhereareallwideareacontrols.Althoughlocalcontrolscontinuetobeimprovedusingnewertechnologies,theconceptualfunctionalityoftheselocalcontrolswillremainthesame.Thewideareacontrolspresentedherewilloftentakecareofthelocalcontrollersbutthemainobjectiveistoimprovetheoverallstabilityofthepowersystem.Theconceptsarepresentedintheorderofincreasingcomplexity,alsoimplyingthattheonespresentedfirstwouldbeeasiertoimplement.FrequencyControlAsnotedbefore,frequencyiscontrolledbybalancingloadwithgeneration.TheprimarygovernorcontrolatthegeneratorsislocalwhilethesecondaryAGCcontrolthatadjuststhegovernorsetpointsisareawide.Theprimarycontroliscontinuouswhereasthesecondarycontrolisdiscreteusuallyusing24secondsampling.Giventhatallgeneratorsinaregionarenolongerownedbythesameorganization,thisareawideAGCcontrolwillbecomemoredecentralized.TheFederalEnergyRegulatoryCommission(FERC)ancillaryserviceregulationsdoallowthirdpartyAGCbutanewcommunicationcomputationcontrolschemeneedstobedeveloped.Asthiscontrolisquiteslow(24secondsampling),feasibilityofcontrolisnotaproblem.Themorecomplexcommunicationschemerequiredisalsonotaproblem;althoughameshedcommunicationnetworkisrequiredratherthanthepresentstarnetwork,thebandwidthrequirementremainsmodest.However,suchanetworkintroducesothermodesoffailureslikesignaldelaysandthecontrolhavetoberobustenoughtohandlethem.RegionalVoltageControlVoltagecontrolinNorthAmericahasalwaysbeenlocal,althoughEuropeistryingsomeregionalcontrolschemes.FERCrecognizesvoltageVARcontrolasanancillaryservice.Controlschemesforsuchregionalcontrolneedtobedevelopedbuttheschemeshavetobesuchastoensurethatsuchservicecanbequantifiedandpaidforasanancillaryservice.Thistypeofcontrol,likefrequencycontrol,isrelativelyslowandsothefeasibilityofthecontrolandcommunicationisnotanissue.Themainhurdlehasbeentheselectionofinputandoutputvariablesofthecontrollerthatcanhandleallthevariedoperatingconditionsthatthepowersystemendures.Thusthischallengeisaclassicaloneofdevelopingapracticalrobustcontroller.

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SmallsignalstabilitycontrolSmallsignalinstabilityoccurswhenasystemperturbation,evenasmallone,excitesanaturaloscillatorymodeofthepowersystem.Theseoscillationsareslow,usuallyunder1Hz.Themainmethodusedtodaytoguardagainstsmallsignalinstabilityistheofflinetuningofpowersystemstabilizers(PSS).ThesePSSarelocalcontrollersonthegenerators.Thuslocalcontrollersareusedtomitigatesystemoscillationmodes,aprocedurethatisrecognizedtohavesignificantdisadvantages.Newcontrollersneedtobedevelopedthatcanusesystemwideinputs(notnecessarilymoreinputspercontrollerbutinputsignalsfromfurtheraway).Suchremotesignalinputswillobviouslyrequirecommunicationchannelswhichcouldbededicatedorcoulduseamoreflexiblecommunicationmeshnetwork.AnothercontrolconceptistoadaptivelychangethePSSsetpointsaccordingtothepowersystemoperatingconditions.ThiswouldbeanalogoustotheAGCcontrolbyintroducingasecondarycontrolschemethatwouldperiodicallyadjustthesetpointsofthelocalPSScontrollersasthesystemchanges.ThechallengehereisthatthecalculationofPSSsetpointsrequireslargeanalyticalcalculations,whicharetodaydoneofflinebutwillhavetobedoneonlineinthiscase.Thespeedofcalculationisnotamajorconcernaschangingthesetpointscanbedonequiteinfrequently,probablyminutes.VoltagestabilitycontrolVoltageinstabilityoccurswhenachangeinthepowersystemcausesanoperatingconditionthatisdeficientinreactivepowersupport.Guardingagainstsuchinstabilityrequirestheanticipationofsuchcontingenciesthatcancausevoltageinstabilityandtakingpreventiveaction.Newpreventivecontrolschemesareneededthatcanalsoincludespecialprotectionschemesthatcouldisolatethoseareaswithvardeficiencies.Thisisnotastabilitycontrolinthetraditionalsensethatrespondstoadisturbance.Thisisanactionplantoensurethatthesystemoperatingconditiondoesnotstrayintoanareawhereaperturbationcancausevoltageinstability.Thecontrolofthetransientconditionafteradisturbanceoccursishandledinthenextsection.TransientstabilitycontrolThedevelopmentofsuchacontrolschemeisbyfarthemostdifficultbecauseadisturbancethatcancauseinstabilitycanonlybecontrolledifasignificantamountof

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computation(analysis)andcommunicationcanbeaccomplishedveryrapidly.Thisconceptisapproachedinthreeincreasinglydifficultlevels:

thefirstistouseofflinestudiestomanuallyadjustprotectiveschemeswhichwouldoperateonlyifthedisturbanceoccurs;

thesecondistoautomaticallyadjusttheseprotectiveschemeswithonlinecalculations;

thethirdandfinalwouldbetodirectlyoperatethecontrolactionsafterthedisturbanceoccurs.

SoftwiredremedialactionschemesAstepadvanceinthisdirectionwillbetogeneralizeremedialactionschemes(RAS),alsoknownasspecialprotectionschemes,tocontroltransientstability.TheseRAStodayaredevelopedfromtheresultsofvoluminousofflinestudiesandareimplementedwithahardwiredcommunicationsystem.Thus,thesystemvaluesandstatusesmonitoredandthebreakerscontrolledcannotbemodified.Whatisproposedhereisthedevelopmentofageneralizedcommunicationsystemthatcanenabletheimplementationofnewremedialactionschemesbysoftwaremodification.Althoughacomprehensivecommunicationschemewillberequiredinthistypeofcontrol,thecomputationrequirementswillbemodestasthecontrolschemesarelargelydefinedoffline.OnlinesettingofremedialactionschemesAstepforwardwillbetodevelopmethodstocontroltransientstabilitybutwithlessdependenceonofflinestudiesandmoreuseofonlinecomputation.Themainideahereistousemorerealtimedatatodeterminewhatcontrolisneeded.Whatisproposedhereisthedevelopmentofsoftcomputingtechniquesusingpatternrecognition,neuralnetworks,expertsystems,etc.toprocesstherealtimedatatodecidethebestcontrolaction.Ofcourse,muchofflinetrainingofthesoftwaremaystillberequiredofflinebuttheexpectationisthatthecontrolactionwouldbemuchmoreefficientthanthosepurelydecidedoffline.RealtimecontroloftransientstabilityTheobjectivehereistodevelopaglobalcontrolfortransientstability(withnoofflineassists).Forthistobefeasible,thecomputationneededtodeterminethedisturbancescenarioandthencomputingthenecessarycontrolsforstabilization,hastobeinthesametimeframeastodaysprotectionschemes(milliseconds).Whetherthisisindeedpossiblewithtodaystechnologyisnotknown.However,thegoalherewouldbeto

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determinewhatkindofcommunicationcomputationstructurewillbeneededtomakethisfeasible.

3.4 Task 4 Report 3.4.1 Background

Allthreeinvestorownedutilities,PG&E,SCEandSDG&EuseRAS/SPSschemestomitigateoverload,voltageandstabilityproblems.PG&EandSCEutilizespecialprotectionschemestomitigatereliabilityviolationsastheresultofmultiplecontingencieswhenitisimpracticalandveryexpensivetobuildtransmissionand/orgenerationprojects.Insomecasesthespecialprotectionschemesbuytimebeforeatransmissionorgenerationprojectcangetinstalled.OnvirtuallyallofthemajortransmissionpathsimportingpowerintoCaliforniasuchasPath66(CaliforniaOregonIntertie)orfacilitatinginterareatransfersbetweenNorthernandSouthernCalifornia(Path26andPath15)specialprotectionschemesareusedtoprotectagainstunlikelycontingenciesthatcouldresultinasystemwideblackout.Thesespecialprotectionschemesusearangeofcontrolactionstomitigatetheimpactofthecontingenciesbutunderworstcasescenariostheyalldropsomecombinationoffirmloadandgenerationtopreventinstabilityandtomaintainareasonableload/resourcebalance.Theinherentproblemwithalloftheseschemesisthattheyaredesignedtobeprescriptiveinthatworstcasescenariosmustbeassumedtopreventcatastrophicresultsunderheavilyloadedconditions.Thismeansthattherearearangeofconditionswheremoreloadandgenerationistrippedthannecessarytopreventthecatastrophicoutagesfromoccurringunderverystressedconditions.Underavastmajorityofconditionswhereloadsarelighter,theremedialactionsareeitherunnecessaryorfarlessloadandgenerationwouldneedtobetripped.Converselytheremaybetimeswhenmorecapabilityisavailablethananticipatedbecausethesystemislessstressed.Conventionalspecialprotectionschemesdonothavetheintelligencetodetectthis,butsynchrophasorbasedspecialprotectionschemeswillhavetheintelligencetodeterminethereismorecapabilityinthesystemandtakeadvantageofthis.ItshouldbenotedthatTotalTransferCapability(TTC)cantbeexceededbutadditionalcapabilityundernomogramoperationcouldbeutilized.Giventhetechnologyoftenyearsagotherewasnochoicebuttodesigntheseprescriptivetypesofschemes.TodaySynchrophasor(pmu)technologymakesitpossibletodesignschemesthattakeappropriateremedialactionbasedonactualsystemconditions.WhilesomeatPG&EandSCEhaveplanstoutilizethisnewSynchrophasor

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technology,itisstillaleapoffaithtodosowhentherearenoprovenschemesinserviceintheUnitedStatesusingthistechnologyinapracticalapplicationsuchasaspecialprotectionscheme.3.4.2 Issues in Intelligent Grid Protection

InthisTask4ReportwerecommendanR&Dplan.TheplanstartsoutwithgeneralR&DissueswhichwillrequirelongertermR&DtoproperlydevelopthiswholeareaofIntelligentGridProtection.ItalsolooksatpossibledemonstrationprojectsandrecommendsaparticularoneinCalifornia.OnecanessentiallythinkofthefirstSPS/RASschemesasthestartofIntelligentGridProtection.Althoughtheearliestsuchimplementationswerequitesimple,conceptuallytheyweredifferentfromthetraditionalprotectionofindividualpiecesofequipment.Inadditiontoisolatingtheshortcircuitlocally,othercontrolactionswereneededtoprotectasmuchofthegridoperationaspossible.TheseSPS/RASschemeshavebecomemoresophisticatedovertimeandcanuseavarietyofinputsfromseveralsubstationsandcansendcontroloutputstoseveralcontrolequipmentinmorethanonesubstation.ItisfairtostatethatallthehardwaretechnologiesneededforIntelligentGridProtectionarealreadyhere.Theseincludevarioussensorsandmeasurementtechnologies,thelatestbeingthesynchrophasorsorPMUsthatarenothingbutthemeasurementsofacvaluesathighratesofsamplingthataretimestampedwiththeabsolutetimestandard.Theyalsoincludehighspeedcommunicationsthatareneededtomovemeasurementandcontrolsignals.Finally,theyincludefastcircuitbreakersandothercontrollers(mainlyFACTSdevices).Thus,astandarddesignprocessforsuchintelligentprotectionschemeshasdevelopedthatgoessomethinglikeasfollows:

Haveagoodidea Testonsimulations Designtheprototype: Measurementsneeded Pointtopointcommunicationsneeded Controlsneeded Installandtestonrealtimedata

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ClosetheloopEachSPS/RASschemeisauniqueimplementation,separatelydesigned,testedandimplemented.Asistrueforanyuniquesystem,implementationsofSPS/RASsystemsareexpensive.Inadditiontheyarenoteasilymodifiedasmodificationshavetofollowthesamedesignprocessastheoriginaldesign.ThisissignificantbecausethelifetimeofaSPS/RASschememaybelimitedbythefactthatthepowersystemisbeingcontinuouslyupgradedwithnewtransmission,generationandotherprotectionandcontrol.Certaininfrastructuralimprovementinthepowersystemcouldmakethisdesignprocesssimplerandhence,overthelongrunwhensuchintelligentsystemsproliferate,thecostofimplementationwouldbemuchless.Suchinfrastructureimprovementconsistsofhardware,softwareandmethodsasfollows:Communicationsinfrastructure

Networked,highbandwidth Userfriendlyapplicationslevelmiddleware Detection/identificationalgorithmdevelopment

Controllerdesignprocess Determiningbestinputs,outputs Developingoutputcalculations

Offlinetestingmethods Nonlinear,digitalsimulations

Obviously,theavailabilityofnetworked,highbandwidthcommunicationswilleliminatetheneedforleasingpointtopointcommunicationlinksforeachSPS/RASscheme.Althoughtheinitialcostofsuchacommunicationnetworkishigh,itcanbeamortizedovermany,manyapplications.Thiscanbelookeduponasthesuccessortothemicrowavenetworkinstalledbythepowercompaniesinthe60s.Inanycase,fiberopticcablesexistalongmanytransmissioncorridorsandcanformthebackboneofsuchanetwork.ThebiggerexpenseistheapplicationslevelmiddlewareneededtorunsuchanetworkinaflexiblewaythatwillmaketheimplementationofSPS/RASschemesverysimple.Thetriggeringmechanismsfortheseintelligentschemesareimportantandnewmethodsneedtobedeveloped.Ofcourse,shortcircuitsareeasilydetected(becauseof

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thehighcurrents)andhavebeenusedroutinelytotriggerrelaysbutforthenewintelligentschemesothertriggeringmechanismsmaybemoreimportant,e.g.phaseangledifferenceorvoltagemagnitude.Thusdetectionofvarioustriggeringconditionsandtheidentificationofwhichconditionisdetectedrequiremethodologicaldevelopment.AmajordrawbacktothedesignofanySPS/RASschemeisthatthereisnostandarddesignprocess.Eachphenomenonthatrequiressomespecialprotectionactionisconsideredaspecialproblemthatrequiresanengineeredsolution.Itishopedthatforcertainclassesofphenomena,saylowfrequencyoscillationsorvoltagedips,somebestpracticesforadesignprocesswillemerge.Suchadesignprocessmayconsistofdeterminingwhichinputvariablesand/oroutputcontrolvariablesworkthebestundermostcircumstances.Also,bestalgorithmstocalculatetheoutputvariablesneedtobedeveloped.Amajorstepindesigningsuchintelligentschemesisthesimulationstep.Infact,simulationisthemaintoolthatdeterminestheeffectivenessofanyschemebeforeitcanbetriedoutontherealsystem,whichisalwaysariskystep.Theproblemisthatsuchsimulationtoolsarenotreadilyavailable.Thebesttoolavailabletodayasproductiongradesoftwareisthetransientstabilityprogram,whichhastwomajordrawbacks.Oneisthatitisdifficulttomodelalltheexistingprotectiverelayswhichisveryimportanttodobecausetheintelligentsystemsoperateinthesametimeframe.Theotheristheabsenceofthemodelofthesubstationstructuretransientstabilityandpowerflowprogramsusethenodebranchmodelandnotthebusbreakermodelofthesubstationwhichisusuallyimportantinrepresentingprotectionschemes.Thusbetterandmoreappropriatetoolsareurgentlyneededfortheencouragementofsuchintelligentprotection.InthefollowingsectionswediscussseveraloftheseinfrastructuralissuesthatrequiresignificantR&Dbeforeintelligentgridprotectionbecomescommonplace.MeasurementdataissuesatthesubstationEveryhighvoltagesubstationtodayhasaverylargenumberofinstrumentsthatmeasureandgatherdata.Theyaremicroprocessorbasedandareusedforprotection,faultdetection,recordingsequenceofeventsandamyriadofotherpurposesandaregenericallyknownasIEDs.Unfortunately,theyallmeasureatdifferentsamplerates,atdifferentaccuracies,andstorethedataatdifferentratesindifferentstoragedevices.AfewaretimestampedbyusingaGPSconnectionandmostarenot.Someofthisdatais

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availableovercommunicationchannelstoremotelocationsandsomearenot.Althoughtherearenowcommunicationstandards,therearenooverallstandardsforsampling,accuracy,storage,etc.R&Disneededtodeterminehowbesttoconsolidatethisdatasothatitcanbeflexiblyaccessedbyvariousapplicationsincludingintelligentgridprotection.DataissuesattheregionalandinterconnectionlevelThegridspansmanyjurisdictions.Forexample,intheWesternInterconnectiontherearethreeReliabilityCoordinatorsthatlookafterthreeregionsoftheinterconnectionandundertheseReliabilityCoordinatorsareabout40BalancingAuthorities,eachgatheringdatafromtheirsubstationsintotheircontrolcenters.ThusdataisbeingmovedfromthesubstationstotheBalancingAuthoritiesanduptotheReliabilityCoordinators.However,thisdataistheSCADAdatawhichiscollectedatarelativelyslowsamplingrateaboutseveralsecondsandarenottimestamped.Whatwillbeneededforintelligentprotectionisdatacollectedatmuchfastersamplingratesatthesubstationsandthenmovedatmuchfasterrates,withsmalllatencies,acrosstheinterconnection.TheneedforhighspeednetworkedcommunicationbetweensubstationsisobviousbuttheactualdesignofsuchacommunicationsystembotharchitectureandmiddlewarerequiresmuchR&D.DesignprocessfortheIntelligentGridProtectionSystemAsintelligentgridprotectionreferstoalargeclassofprotectionsystems,itisunlikelythatasingledesignprocesswillemergethatwillbeabletoproducesuchaspecialprotectionschemeforanyparticularproblem.However,somebestpracticeswillprobablyariseforparticularclassesofphenomena.Forexample,lowfrequencyoscillationsareaproblematicphenomenoninthewesterninterconnection.However,detectionandidentification(offrequencymodeanditsdamping)inrealtimehasnotbeenparticularlyeasyeventhoughitisrelativelyeasytodosousingpostdisturbancestoreddatainanofflinecalculation.Butvariationsoftheofflineanalysistoolshavebeentriedwithreasonablesuccess.MuchR&Disneededtocontinuedevelopingsuchbestpracticealgorithmsforvariousphenomenathatcanbecontrolledbyintelligentprotectionschemes. Input/outputsignalpathissues

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Unliketraditionalprotectionschemeswhichuselocalinputsandlocaloutputs,i.e.theinputsignalandthecontrolsignalarewithinthesamesubstation,intelligentgridprotectionimpliesinputsignalsandoutputsignalsthatmaytravellongdistancesfromandtomanysubstations.Sincethesearenecessarilydigitalsignalstravelingovercommunicationchannels,theirsamplingrateandlatencyimpacttheeffectivenessofthecontrolaction.Thusthedesignprocessfortheschememustalsotakeintoaccountthesamplingrateandpossiblelatencies,bothofwhichcanhaveuncertainties(i.e.theyarenotfixedandareaffectedbyotherdataflowonthosechannels).R&Disneededtohandlesuchdataflowissuesaspartofthedesignprocess.SimulationtestingNoneoftheproductiongradesimulationpackagesusedtodaytosimulatethegridtransientstabilityandpowerflowprogramsisquiteadequateforsimulatingtheseintelligentprotectionschemes.Amajordrawbackinthesesimulationsisthatthemodelingofthegridismuchsimplified:(1)thebalancedphasesinglelinemodeldoesnotpickuptheimbalancesthatmayaffectprotectionschemes,and(2)thenodebranchmodelmissesthedetailedsubstationconfigurationthatalwaysaffectsprotection.Althoughmostofthenonlinearitiesarewellmodeledinthepresentsimulations,discretecontrolsaredifficulttomodel,butanyprotectionschemeusingdatafromremotelocationsmustbeabletorepresentsampled(ratherthancontinuous)dataandpossiblelatencies.R&D(especiallyD)isneededindevelopingsuchsimulationtoolssothatthetestingofintelligentprotectiveschemesbecomesmorereliable.

3.4.3 Potential Demonstration Projects TheprojectteamhashadextensivediscussionwithbothPG&EandSCEregardingthescoping of a potential project demonstrating Synchrophasor/pmu technology. PG&EhasinstalledseveralnewspecialprotectionschemessuchastheSanFrancisco,MetcalfandDiabloCanyonSPSinthelastseveralyearstoprotectagainstunlikelycontingenciesthatwouldhaveseriousconsequencesshouldtheyoccur.Alloftheseschemesinvolvelocalareagenerationthatisdispatchedeconomicallyandthatalsohasanimpactonthelocalareareliability.ForinstancePG&EsSanFranciscoRASprotectsagainstlossofanentiresubstationwithmultiple buses and two different voltage levels which goes beyond NERC level D*planning.TheSanFranciscoRASusesGEsuniversalrelayatmultiplesubstationstododistributed processing and also communicate with centrally located fault tolerant

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programmablelogiccontrollers. EventhoughSFRASisaverysophisticatedandstateof the art scheme it still is somewhat prescriptive in that remedial actions are takenassuming heavily loaded conditions. Both the Metcalf and Diablo Canyon specialprotection schemesprotect againstmultiple contingencieswhere there is a surplusofgeneration thateither causeemergencyoverloadsand stabilityproblems. TheDiabloCanyon special protection scheme was installed recently and incorporates pmutechnology in thedetectionof thecontingenciesbut itstill takesprescriptiveaction inthataDiabloCanyonunitmustbetrippedunderawiderangeofcondit