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2iec61850–thestandardisation
inmosttraditionalprotocolsforsubstationcommunications,alistofmessagestransferredbetweentwodevicesisdefined.toeachmessage,abinarywordisassigned.forexample,“opencircuitbreaker”maycorrespondtoaword“110101000…”.suchcodingisinflexiblebecauseextensionisdifficult.furthermore,itdoesnottieinwithmoderncommunicationtechniquesinwhichlow-levelbitsandbytesaretransparenttotheapplications.

sinceautomationfunctionshardlychangeinthelifetimeofasubstation,iec61850standardisesthenamesofthedataofthesefunctions,thedatamodels.forexample,theposition(on/off)ofacircuitbreakerhasanameandisfixed.theservicesfortransferringthedatafromonedevicetoanotherarealsostandardised.forexample,theserviceforsendingatripsignaltoacircuitbreakerandtheserviceforreadingfaultdatafromaprotectivedevicearedefined.iec61850furtherstatestheprotocolswhichimplementbestthesegenericdatamodelsandservices,andthesearemanufacturingmessagespecification(mms),tcp/ipandethernet–aprocesscalledmapping.theconversionfromatextmessageofanapplicationtothebit-streamonthecommunicationwire/cableispurelyapropertyofthecommunicationstack.inthisway,theapplicationsandthestackareseparated.

tobuildupansasfromdevicesofdifferentmanufacturers,thesystemintegratormusthaveinhandthecapabilityofeachdeviceinvolvedi.e.whatdataandservicesitsupports.thedevicemustthenbeboundtotheotherdevicesandtotheprimaryequipmentcommunicationwise.iec61850offersthetoolsubstationconfigurationdescriptionlanguage(scl)whichallowsthemanufacturer-independentexchangeofthenecessaryinformation,andsignificantlylightensthetaskofsystemconfiguration.separately,aprerequisitetoconfigurationanddefinedinthestandard,conformancetestingservestoindicatewhetherthedevicesareinteroperable.
3benefitsofiec61850
3.1general
usersofiec61850areelectricalutilities,consultantsandmanufacturersandtheybenefitfromthestandardinsevenareasofsubstationautomationnamely
-openenergy-marketandinternationalactivities
-specification
-design
-manufacturing
-installationandcommissioning
-operationandmaintenance
-assetmanagement

thebenefitsineachoftheseareasarediscussedbelow.
3.2openenergy-marketandinternationalactivities
owingtoderegulations,utilitiesfindithardertoforecastpowergenerationanddemand,andoftenfaceanuncertainfuture.eliminatingthestrategicunknownsinsubstationautomation,iec61850bringscertaintytothemanagementofsubstationsandthevitaldatanecessaryforthesecureoperationofthenetwork.

manyutilitiesstrivetosimplifyoperations,maintenanceandsubstationinstallation,andalsoreduceoperatingcosts.sasscompliantwithiec61850havethecharacteristicsoflowmaintenanceandlowlife-cyclecostswhichbringthelong-termfinancialadvantagesneededbytheutilitiestostaycompetitiveintheopenenergymarket.

consultantshavelongoperatedinternationallyandmanyutilitiesarenowextendingtheiractivitiesbeyondtheirownnationalbordersoroverseas.iec61850wasestablishedwiththerequirementsofsubstationsworldwideinfocus.consultantsandutilitiesadheringtoiec61850canapplytheirexpertiseonthestandardandequipmenttomostnetworksintheworldandconsequentlybroadentheirclientbase.
3.3specification
iec61850standardisesthenameofthedataofautomationfunctions.ithasalistofstandardisednamesofalltheanticipatedfunctionscalledlogicalnodes.atthespecificationstageofasubstationautomationproject,ambiguityormisinterpretationisunlikelytoarisebetweentheconsultantandthetenderers.

thestandarddefinesmean-time-to-failure,uptime,downtimeandotherreliabilityrelatedtermsandlaysdownpreciselytherequirementsforavailabilityinansas.describingalsoautomaticrecoveryandgracefuldegradation,thestandardprovidesthetendererswithaclearframeworkforsystemdesign,andtheutilities/consultantswithaplatformforfairadjudication.ethernetismoreoverflexibleandtenderershavemorefreedomtotailorthesastomeettheavailabilityrequirements.

therearenogatewaysforinter-iedcommunications.thetendererscanfocusonoptimisingthesasandmakingtheoverallsystemcost-effective.

sasscompliantwithiec61850canbescaledeasily.thetendererscanoffermoreoptionstotheendcustomersothatthesassmatchthefuturechangesinthesubstationsaswellasthepowernetwork.

tenderassessmentissimplifiedbecausetherearemorecommonfeaturesamongvarioussass.allsystemsusemms,tcp/ipinthecommunicationstackandethernetasthedatatransfermedium.whiletheremaybevariations,mostethernetnetworkswillrunatthestate-of-the-artdatarateof100mbit/swithswitches.itisnolongernecessarytocomparetwounlikeprotocolssuchaslonanddnp3.0.
3.4design
inthepast,thedatamodelsinthespecificationwereoftenmadesufficientlygeneralsothatawidevarietyofmanufacturerssupportingdifferentprotocolscouldtender.thestandardiseddatamodelsofiec61850areunderstoodbyallmanufacturersandcanbestatedinthespecification.thesemodelscanbecarriedforwarddirectlyintothedesignstage,savingtimeandreducingerrors.

ifasubstationisalreadyinstalledanethernetnetwork,thisexistingstructurecanbereusedwithlittleextradesignwork.ingeneral,hardwiredesignofthesasissimplifiedbecause
-nogatewaysarerequiredamongtheieds.
-theethernetcomponentsusedareofindustrialgrade,suitableforoperationinhigh-voltagesubstationsandavailablereadilycommercially.exceptforthepossibleadditionalprecautionsagainsthighlevelsofelectromagneticinterference,littleadaptativeworkisrequired.
-fewercomponentsinthesasmeanslesstimespentonco-ordinationandfewerreviewmeetings.

thescldefinesthespecificationofprimaryandsecondaryequipmentinthebaysthroughthesystemspecificationdescription(ssd)file.basicprotectionandcontrolschemesforbayscanbecreatedastemplatesandsimplymodifiedtosuitspecificprojects.

inconventionalparallelwiring,eachpairofwirescarriesonlyonesignalandthewiresarerunfromonedevicetoanother.preparingtheschedulesforthesemulticorecables,thesupportingtrays,terminalblocksandmarshallingboxesisatime-consumingtask,letalonethenumerousdrawingsinvolved.withiec61850,thesubstationdataareserialandsentoverethernetcables.theethernetbackboneisoftenlightandeasy-to-handleopticalfibres.thisnewcommunicationplatformmeansasignificantreductioninthenumberofmulticorecablesandtheaccessoriesinmostsubstations,andhenceareductionindesignefforts.
3.5manufacturing
owingtothescl,theconfigurationtaskissimplifiedandpartlyautomatedthroughthemanufacturer-independentinformationexchange.lesstimeisneededforco-ordinationandansascanbeup-and-runningquickly.becausethechanceoferrorsintheinformationexchangeislower,lessreworkandretestareexpected.thesclunderpinsthenotionof‘right-first-time’.workingtoacommonsinglestandard,thetestpersonnelneednotlearnandtestunfamiliarprotocols,andcanexpendtheireffortsmorefruitfullyonfindingandremovingfaultsintheautomationfunctions.

inthefactory,aniec61850sascanbetestedcompletewithethernetcablingexactlylikethatonsite.anyerrorsfoundcanbefixedquicklyandeasily.testsonacompletesaswithconventionalparallelwiringcanbecarriedoutonlyonsite,wheretherectificationoferrorsmaybemoredifficultandtime-consuming.
3.6installationandcommissioning
asethernetentailsfewercablesandaccessories,installationtimeisreduced.lesscablingmeansthatthechanceofconnection/terminationerrorsislower.

over95ofthelocalareanetworksofofficesareethernet.standardtoolsforcheckingethernetsystemsarereadilyavailableandcanbeappliedinsubstationsduringcommissioning.

owingtotheuseoftcp/ip,thehumanmachineinterface(hmi)maybemovedaroundinthesubstationandpluggedintoanyethernetswitchduringcommissioningtodisplaythedataofthewholesubstation.inparticular,manytestsinvolveschecking‘cause’and‘effect’,whichtakeplaceatdifferentlocationsrespectivelyinthesubstation.thedatapanoramaatasinglelocationcanhelpspeedupsuchtests.ifwirelesslocalareanetworkisused,themobilityofthehmiwouldbefurtherenhanced.

theworkplaceoftechnicalspecialistsisoftentheoffice,wheretheyareclosetotheirowndatabasesandcanserveotherpersonnelpromptly.thespecialistscantakepartincommissioningwithoutleavingthedesksandcanreadsitedataviatheinternet,guidingandofferingadvicetositepersonnel.

havingplayedakeysupportingroleinmanyearliersuccessfuldemonstrationsoninteroperability[1],simulatorsmaybeusedwhenadeviceisunavailableduringcommissioning.thishelpsavoiddelaysonthecriticalpathandkeeptheprojectoncourse.
3.7operationandmaintenance
theadvancedprinciplesbehindiec61850willbynomeansshowthemselvesasdifficultoperationsandmanoeuvresonthehmi,becausethecommunicationtheoryinvolvedistransparenttotheusers.infact,manufacturersareprovidinginterfaceswhichmakethenavigationandmanoeuvresfriendlierthanbefore.remoteoperationsfromofficessuchasadjustingsettingsofdevices,interrogatingdevicesandretrievingdataleadundoubtedlytofewersitevisitsinthefuture.

utilitieswillseeanimprovementinthegeneralperformanceofthesasbecause
-thedataflowexperiencesnodelayduetogateways.
-incontrasttopolling,ethernetmulticastingallowsmessagestobesentsimultaneouslyandhencefaster.
-thereisnobottleneckfoundinmaster-slavecommunication.
-100mbit/sisthestate-of-the-artdatarateofethernetinsubstationcommunicationandcanhardlybeachievedbyotherprotocols.
-prioritytaggingofethernetenablesimportantmessagestobesentfaster.

theavailabilityofthesasisexpectedtobehigherbecause
-distributedintelligenceisadvocatediniec61850.certainfunctionssuchasinterlocking,canbeimplementedwithoutacentralco-ordinatingdevice.peer-to-peercommunicationmeansthatafunctionstillrunsnormallyevenafteroneormoredeviceshavefailed.
-ethernetswitchesentailnocollisionsandthereforethedatathroughputishigher.
-eventsarereportedassoonastheyoccur,incontrasttomaster-slavewhosepollingintervalmaybesolargethatthetransmissionofmessagestakeslonger.

withonlyafewprotocolstohandle,maintenancebecomeseasierfortheutilities.trainingeffortisreducedbecausethestaffneednotlearnmanyprotocols.theknowledgeaboutthesasresidesintheentirestaffinsteadofclustersofspecialists,eachspecialisedononeofthemanyprotocolsused.globallyoperatingorganisationswouldappreciateequallythisbenefit.

newiedscanbeaddedwiththeminimaloperationalimpactonexistingieds.thismeansshorterdowntimeofthesaswhenthesubstationisextendedorwhenoldequipmentisreplacedwithnewequipment.

theusualpracticeinutilitiesisthatonlyauthorisedpersonnelhasaccesstothedatarelatedtooperationsandmaintenance.suchsecuritymeasurescanbebuiltinusingexistingmethodsininformationtechnology.furthermore,tcp/ipformstheinformationhighwaylinkingtheofficesandsubstations.personnelinofficesandonsitescanexchangeinformationmoresmoothlyandefficientlythroughouttheenterprise.
3.8assetmanagement
iec61850relievessomeoftheburdensinassetmanagementwhichinvolvesevaluatingthepresentequipmentandestablishingreplacement/purchaseplansforthefuture.thestandardadoptsafixedsetofmainstreamcommunicationprotocols.oneisthereforenolongertroubledbythequestion‘whichhorsetobet?’andisnotstrainedbytheburdensometechnology-watch.inparticular,thedatamodelsarelonglastingandethernetishighlyforwardandbackwardcompatible,inadditiontopossessingafavourablecost-to-performanceratio.anyupgradeorreplacementofansaswillclearlyincurasmallerfinancialoutlaythanbefore.

iec61850definessystemlife-cycle,whichcoversthemanagementofproductversionsandthesupportafterproductdiscontinuation.utilitiescancontinuetorunanequipment-replacementschedulewithoutspeculatingonthefutureoftheproducts.

theinteroperabilityofiedsnowadvocatedbyiec61850isexpectedtolastformanyproductgenerations.conformancetestingformsalong-termreferencebasisfortheconfirmationofinteroperabilityofieds.thedocumentationofthetestscarriedoutandproductversionnumbershelptheutilitiesinkeepingtrackoftheinteroperabilitycharacteristicsofeachied,whichareimportantformanagingequipmentinthelongterm.

theextensionofthedatamodelsofiec61850tomonitoringsubstationequipmentistakingplace,helpingutilitiesinmovingawayfromthetime-basedmaintenancetothemoreefficientcondition-basedmaintenance.
4migrationtowardsiec61850
4.1newsubstations
itisenvisagedthatfromnowon,mostnewsubstationswillbefittedentirelywithiec61850equipmentandthereisnomigrationissue.in2004,compliantproductsjustbegintobeavailableandtheproductrangeisnotyetcomplete.somenewsubstationsmayrequireamixtureofiec61850equipmentandnon-iec61850equipment,andhenceamigrationpathtoenabletheformerequipmenttobeexpandedandthelatterequipmenttobephasedout.asystemsuitableforthismigrationgenerallycomprisesastationunittowhichdevicesrunningotherprotocolsanddevicesrunningoniec61850areconnected.theprotocolconversionsarecarriedoutconvenientlyinthisunit.seefigure2.thisunitalsoservesastheinterfacebetweenthesubstationandthecontrolcentrerunningontheiec60870-5-101protocol.shouldtheiec60870-5-104protocolbeused,thecommunicationcanbemadeviatherouterontothestationbus.