Power system automation with SCADA System

1. POWER SYSTEMAUTOMATION
OVERVIEW
Powerprovidersconstantlydeal withdemandstoincrease productivityandreduce costs.This
translatesintothe needforadministrators,engineers,operators,planners,fieldcrews,andothersto
collectandact ondecision-makinginformation.Powersystemvendorsare followingatrendtomake
devicessmartersotheycan create and communicate thisinformation.The term“powersystem”
describesthe collectionof devicesthatmake upthe physical systemsthatgenerate,transmit,and
distribute power.The term“instrumentationandcontrol (I&C) system”referstothe collectionof
devicesthatmonitor,control,andprotectthe powersystem.Powersystemautomationrefersto
usingI&C devicestoperformautomaticdecisionmakingandcontrol of the powersystem.
PowersystemautomationreferstousingI&Cdevicestoperformautomaticdecisionmakingand
control of the powersystem.
Data Acquisition
Data acquisitionreferstoacquiring,orcollecting,data.Thisdatais collectedinthe formof
measuredanalogcurrentor voltage valuesorthe openorclosedstatusof contact points.Acquired
data can be usedlocallywithinthe devicecollectingit,senttoanotherdevice inasubstation,orsent
fromthe substationtoone or several databasesforuse byoperators, engineers,planners,and
administration.
Power SystemSupervision
Computerprocessesandpersonnel supervise,ormonitor,the conditionsandstatusof the power
systemusingthisacquireddata.Operatorsandengineersmonitorthe informationremotelyon
computerdisplaysandgraphical wall displaysorlocally,atthe device,onfront-panel displaysand
laptopcomputers.
Power SystemControl
Control referstosendingcommandmessagestoadevice tooperate the I&C andpowersystem
devices.Traditional supervisorycontrol anddataacquisition(SCADA) systemsrelyonoperatorsto
supervise the systemandinitiate commandsfromanoperatorconsole onthe mastercomputer.
Fieldpersonnel canalsocontrol devicesusingfront-panel pushbuttonsora laptopcomputer.
Power SystemAutomation
Systemautomationisthe act of automaticallycontrollingthe powersystemviaautomated
processeswithincomputersandintelligentI&Cdevices.The processesrelyondataacquisition,
powersystemsupervision,andpowersystemcontrol all workingtogetherinacoordinatedauto- 2
matic fashion.The commandsare generatedautomaticallyandthentransmittedinthe same fashion
as operatorinitiatedcommands.

2. I&C SystemIEDs
I&C devicesbuiltusingmicroprocessorsare commonly referredtoasintelligentelectronicdevices
(IEDs).Microprocessorsare single chipcomputersthatallow the devicesintowhichtheyare builtto
processdata, acceptcommands,and communicate informationlike acomputer.Automatic
processescanbe run in the IEDs, andcommunicationsare handledthroughaserial portlike the
communicationsportsona computer.IEDsare foundinthe substationandon the pole-top.
Instrument Transformers
Instrumenttransformersare usedtosense powersystemcurrentand voltage values.Theyare
physicallyconnectedtopowersystemapparatusandconvertthe actual powersystemsignals,which
include highvoltage andcurrentmagnitudes,downtolowersignal levels.
Figure 1: Instrument Transformers
Transducer
Transducersconvertthe analogoutputof an instrumenttransformerfromone magnitude to
anotheror fromone value type to another,suchas froman ac currentto dc voltage.

3. Remote Terminal Unit, RTU
As the name implies,aremote terminal device,RTU,isan IED that can be installedinaremote
location,andacts as a terminationpointforfieldcontacts.A dedicatedpairof copperconductors
are usedto sense everycontactandtransducervalue.These conductorsoriginate atthe power
systemdevice,are installedintrenchesoroverheadcable trays,andare thenterminatedonpanels
withinthe RTU. The RTU can transfercollecteddatatootherdevicesandreceive dataandcontrol
commandsfromotherdevicesthroughaserial port.User programmable RTUsare referredtoas
“smart RTUs.
Figure 3: RTU
Communications Port Switch
A communicationsswitchisadevice thatswitchesbetweenseveral serial portswhenitistoldtodo
so.The remote userinitiatescommunicationswiththe portswitchviaaconnectiontothe
substation,typicallyaleasedlineordial-uptelephone connection.Once connected,the usercan
route theircommunicationsthroughthe portswitchtoone of the connectedsubstationIEDs.The
port switchmerely“passesthrough”the IEDcommunications.
Figure 4: CommunicationSwitch

4. Meter
A meterisan IED that isused to create accurate measurementsof powersystemcurrent,voltage,
and powervalues.Meteringvaluessuchasdemandandpeakare savedwithinthe metertocreate
historical informationaboutthe activityof the powersystem.
Figure 5: Meter.
Digital Fault Recorder
A digital faultrecorder(DFR),isanIED that recordsinformationaboutpowersystemdisturbances.It
iscapable of storingdatain a digital formatwhentriggeredbyconditionsdetectedonthe power
system.Harmonics,frequency,andvoltage are examplesof datacapturedby DFRs.
Figure 6: Digital FaultRecorder

5. Load Tap Changer (LTC)
Load tap changersare devicesusedtochange the tap positionontransformers.These deviceswork
automaticallyorcan be controlledviaanotherlocal IEDor from a remote operatororprocess.
Recloser Controller
Reclosercontrollersremotelycontrol the operationof automatedreclosersandswitches.These
devicesmonitorandstore powersystemconditionsanddeterminewhentoperformcontrol actions.
Theyalsoaccept commandsfroma remote operatororprocess.
Figure 7: SEL-351R RecloserControl
Time Synchronization Source
A time synchronizationsource isanIED that createsa time-of-dayvalue whichisthenbroadcastto
the IEDs in orderto setall theirclocksto the same time.
Figure 8: Time SynchronizationSource

6. Protocol Gateway
IEDs communicate overserial connectionsbyspeakingaparticularlanguage orprotocol.A protocol
gatewayconvertscommunicationsfromone protocol toanother.Thistaskis oftenperformedby
software ona personal computer.
Human Machine Interface (HMI).
The front panel displayandpushbuttonsora personal computeract as interfacestosystemdata
and controlsforpersonnel inthe substation.
Figure 9: Protocol Gatewayor HMI
Programmable Logic Controller (PLC)
As the name implies,aprogrammable logiccontroller(PLC),isanIEDthat can be programmedto
performlogical control.Aswiththe RTU, a dedicatedpairof copperconductorsfor eachcontact and
transducervalue are terminatedonpanelswithinthe PLC.Personnel familiarwiththe PLC
developmentenvironmentcanprogramPLCs to create informationfromsensordataandperform
automation.The PLCcan transfercollecteddatatootherdevicesandreceive dataandcontrol
commandsfromotherdevicesthroughaserial port.

7. Figure 10: Programmable LogicControllerRightCabinet,PCandAccessoriesLeftCabinet
Protective Relay
A protective relayisanIED designedtosense powersystemdisturbancesandautomaticallyperform
control actionson the I&C systemandthe powersystemtoprotect personnel andequipment.The
relayhas local terminationsothatthe copperconductorsfor eachcontact do not have to be routed
to a central terminationpanel associatedwithRTUsandPLCs.Transducersare not necessarysince
the relayacceptssignalsdirectlyfromthe instrumenttransformers.Protective relayscreate
meteringinformation,collectsystemstatusinformation,andstore historical recordsof power
systemoperation
Figure 11: SEL-351 Relay
Communications Processor
A communicationsprocessorisasubstationcontrollerthatincorporatesthe functionsof manyother
I&C devicesintoone IED.Ithas many communicationsportstosupportmultiple simultaneous
communicationslinks.The communicationsprocessorperformsdataacquisitionandcontrol of the
othersubstationIEDsand alsoconcentratesthe datait acquiresfortransmission toone ormany
mastersinside andoutside the substation.The communicationsprocessorincorporatesfeaturesof
manyof the otherIEDs includinganRTU, a communicationsportswitch,aprotocol gateway,atime

8. synchronizationsource,andalimitedPLCfunctionality.The communicationsprocessorhaslocally
terminatedI/Oandcan performdial-outtoalertpersonnel orprocesseswhenastatuschanges.
Figure 12: SEL-2030 CommunicationsProcessor
POWER SYSTEM COMMUNICATIONS
Communications Protocols
The IEEE definescommunicationsprotocol as:aformal setof conventionsgoverningthe formatand
relative timingof message exchange betweentwocommunicationsterminals.A strictprocedure
requiredtoinitiate andmaintaincommunication.Thisregulatesthe orderandarrangementof
information,transferspeedorbaudrate and errorchecking.Ingeneral,powersystem
communicationnetworkssupportfourbasicoperations:establishcommunications,terminate
communications,writedata,andreaddata. The write data functioncanbe usedtotell an IED to
performa control action,change settings,orsenddata to the requestingdevice.Errorcheckingis
done byeach device todetermine if the message datawascorruptedduringtransmission.The type
of protocol,message format,andtransferspeedare parametersthatare configuredduring
installation.Communicationsschemesare polled,scheduledorunsolicited.Ina polledsituation,one
IED acts as the hostand initiatesalmostall dataexchange.The otherIEDacts as a slave anddoes9
onlywhatit istold.The slave rarelyinitiatesdataexchange,itsimplyreactstorequestsfordatafrom
the host.The exceptionisanunsolicitedmessage fromaslave whichsendsdatatothe host without
the host requestingit.Often,thisisaresultof an unexpectedchange.
Popular Protocols
ASCII - Protocol thatis easilyconvertedtohuman-readable charactersandnumbers.Thisprotocol is
simple butgenerallyslow.
Modbus® - A popularprotocol withindustrial usersthathasalsobecome somewhatpopularin
substations.DesignedtoemulatePLCstransferringregisterdatato one another.
Modbus® Plus - A mediumspeednetworkbuiltwithproprietarynetworkinterfacesusingan
extensionof Modbusprotocol.

9. DNP 3.0 - An everincreasinglypopularSCADA protocol,governedbyastandardscommittee and
usersgroup,that was designedtooptimize efficiencythroughreportbyexception,remotemodem
connections,andmultidropcapabilities.PredominantlypopularinNorthAmerica.
UCA/MMS - UtilityCommunicationsArchitecture,currentlybeingdesignedbyNorthAmerican
utilities,vendors,andconsultantstosatisfymostrequirementsinsubstationfeederequipmentand
eventuallyall powersystemequipment.
Proprietary - Protocolscreatedbythe product vendorstocommunicate withtheirdevices.These
are generallyunique foreachvendorandare not inter-operable.Some vendorsdesigntheirown
protocol because existingprotocolslacknecessaryrobustnessandefficiency.
Interleaved - Interleaveddatastreamsisasimple waythatmultiple communicationsmessagescan
occur on a single communicationsconnection.Dataacquisition,control,configuration,andtime-
synchronizationcommunications canoccur at the same time.
Communications Media
Many differenttypesof communicationsmediacanbe usedto conduct the data betweenIEDsina
powersystem.Theyinclude coppercommunicationscables,powerline carrier(PLC),landline
telephone,fiber, andwireless.WirelessincludesFMandmicrowave radioas well ascellular
telephoneandsatellite communications.
Direct copper- A coppercommunicationcable dedicatedtopowersystemcommunications
betweentwodevices.
Land line telephone- Conventional dial-uporleasedlinesdedicatedtopowersystem
communications.Powerline carrier(PLC) - A methodof passingdataon the powerline conductorat
highfrequency.
Fiber- Fiberapplicationscommunicate datainthe formof lightconductedoverasingle direct
connectionormultiple directconnectionsbundledtogether.

10. Figure 13: Fiber-OpticTransceivers
Wireless - Where available,cellulartelephone canbe usedasa dial-upconnection.Radios
supportingFMandmicrowave are installedasadedicatedconnectionforpowersystem
communications.
Communications Connections
Directconnectand multidropare the twotypesof communicationsconnectionsavailabletocreate
networks.Ina directconnection,there are onlytwodevicesconnectedtoeachother.The network
media,orconductor,usedfor passingdatacan be metallic,wirelessorfiber.Eachinterface consists
of a separate transmitandreceive connectionateachdevice.Since there are onlytwodevices,each
of themcan constantlycontrol the connectiononwhichtheyare transmittingandbothcan know
implicitlytowhichotherdevice theyare connected. Havingseveralindividual directconnectionsto
manyIEDs wouldalloweachof themto communicate simultaneously.A systemof manydirect
connectionsoriginatingfromone deviceiscalledastar networktopology.Figure 14illustratesthe
star topology.Manystar networkscan be connectedtogether.Anyprotocol,includingthose
designedformultidropapplications,canbe usedfordirectconnectionsina star topology.Virtually
all microprocessor-basedrelays,LTCs,andmetershave asimple EIA-232serial port connectionto
supportdirectconnections.Fiber,wireless,andPLCcan be usedina directconnectionaswell.Star
networkdesignssupportawide range of IED capabilities.Simple,slow communicatingdevicescan
coexistwithmore complex,fastcommunicatingrelays.Devicesfromdifferentmanufacturerswith
differentprotocolscancoexistinthe same starnetworkbecause eachhasa dedicateddirect
connection.Mostethernetsystemstodayare developedasstarnetworkswiththe centerof the star
beinga hub,switch,orrouter.

11. Figure 14: Star Topology
In a multidropnetworktopology,several devicescanbe physicallyconnectedinabusor ring
network.Figure 15 illustratesdevicesconnectedinabustopology,andFigure 16 illustratesrelays
connectedina ringtopology.A multidropconnectionrequiresthatonlyone device communicate at
a time.Devicesona multidropnetworkmustspeakthe same protocol,withthe same baudrate,and
the same physical networkconnection.A broadcastmultidropisacommonnetworkthatdiffers
slightlyinfunctionandpurpose.Onesidedconversationsare sentfromthe hostto multiplereceiving
devicesthatdonot respond.Inter-range instrumentationgroup(IRIG) time-synchronization
messagesare oftensenttoIEDs inthisfashion.IEDsoftenneedcommunicationsconnectionsforthis
broadcast,separate froma data acquisitionandcontrol connection.
Figure 15: BusTopology

12. Figure 16: RingTopology
It isimportantto keepinmindthatif the control overwhichIED has permissiontocommunicate
shouldfail,none of the multidroppeddevicescancommunicate.Thiscanbe causedbyIED
communicationshardware failure,IEDcommunicationssoftware failure,orcorruptionof the
network.Therefore,acommunicationsproblemmayappeartobe inone IED thatis actuallyin
anotherIED
AUTOMATED METER READING (AMR)
Automatedmeterreadingisacommunicationsservice thatpermitsthe transferof datafromutility
meterstoa utilitycompany’smeteringcollectionsystem.Assuch,AMRautomatesthe previously
manual processof readingmeters.Also,itallowsthe collectionof muchmore anddifferenttypesof
informationtobenefitthe utilityandcustomeralike.
AMR Benefits to Utility
Utilitiesthatuse AMRbenefitinseveral ways.First,AMRreducesthe laborcostsof individually
readingeach meter.Italso improvesthe safetyof personnelwhopreviouslyhadtoenterhighriskor
difficulttoaccessareason a regularbasis.Otherbenefitsincludereducedfieldvisits,fasterbill
processing,andeliminationof special readsandestimatedbills.Customerservice isalsoimproved
by: • The abilitytoanswerbillingquestionsquicklyandaccuratelybycheckingcurrentandhistorical

13. usage while the customerisonthe phone;• Specializedbillingandinformationservices,suchas
summarybillingtoconsolidatebillingformulti-siteoperationsandbestrate analysistohelp
customerschoose the optimal rate planfortheirneeds;•Improvedbill accuracydue to a decrease
inestimatedbills;and• The abilitytoletcustomersselectbillingdates,and/ortoreceive summary
bills.The more detailed,customer-specificusage dataavailable throughAMRmakesiteasierfor
utilitiestodevelopnewproductsandservices.Thisdataisalsokeytodevelopingtargetedmarketing
strategiesforattractingandkeepingcustomers.The loweroperatingcostsandincreasedspecific
data made possible byAMRmay helpsmoothautility’stransitionfromregulatedtoderegulated
markets.Loweredcostscan increase the resourcesavailableforproductdevelopmentandother
needs.More,andfurtherdetailed,dataprovidesbetterinsightintoanincreasinglycomplexpower
market,as well asan opportunitytodifferentiate service viaoptionssuchason-line dailyusage
information,outage status,andcustomeroutage notification.
AMR Benefits to Customer
• Flexiblerate programsdesignedtoreduce energycosts.
• Energyusage informationtohelpmanage energycostsandbetterallocate usage.
• Reducedoutage time andfeweroutages.
• Consolidatedbillingservicesandflexible billingdates.
AMR Technology
The basic systemconsistsof a "thermostat-like"panelwhichallowsconsumerstouse electricity
more efficientlybyprogrammingappliances,suchasthe Heating,VentilationandAirConditioning
(HVAC) system,andhotwaterheater.Deviceswithinthe home will communicate withone another
overexistingelectrical wiringusingpowerline carrier(PLC) technology.Whenconnectedtoa
wirelessnetwork,AMRsystemsbecomealow-cost,two-waycommunicationsinterfacebetween
customersandtheirutilitycompanies.Some systemsallowcustomerstocontrol andmaintain
desiredtemperature levelsintheirhomesatthe lowestcost;monitorelectricityusage;receive daily
updatesoncommunityinformation;paybillselectronically;andultimatelyintegrate andcontrol
lightingandhome securitysystems.
AMR Communications Technologies
AMR technologydecisionsare dominatedbythe choice of a communicationsscheme.Costispartof
the communicationsscheme choice.The followingare the choices:Powerlinecarrier(PLC)
technologyusesthe powerlinesasmediaforsendingandreceivinglow-bandwidthdataatverylow
speed.Thisoptiontendstobe costeffective formetersservedbyasingle substation.Inthe US,this
technologyhasbeenwidelyadoptedbyrural cooperatives.Telephone-basedtechnologyuses
telephonelines(eitherdedicatedorsharedwithvoice communications)tosendandreceive meter
data. Withdial outboundsystems,the utilitymustknow the customer’sphone numbertogetthe
data, whichcan cause administrativeproblems.Thisfactor,alongwiththe relativelyhighprices
chargedby phone companiesforthistype of service,hasmade thisoptionlessattractive.Withdial-
inboundsystems,bycontrast,metersare equippedwithanautomateddialerthatcancall the utility
at pre-assignedtimes,whenanalarmconditionisdetected,orwhensignaledbythe utility.
Telephone-basedsystemstendtobe costeffective forselectedmetersthatare sparselyspread
throughouta service territory,andare typicallyusedforlarge commercial andindustrial customers.

14. Wirelessradio-frequency(RF) AMRtechnologiesrelyonthe use of a transmitteronthe meterto
communicate withareceiverthatcan be handheld,locatedinavehicle,orinstalledatafixed
location.Wirelessapproachestendtobe more costeffective formeterswithinaclustered
geographicarea.Mobile radiosystemsthatuse handheldorvan-basedreceiverscannotprovide
two-wayreal-time communications,andare bestsuitedas replacementsformanual meterreading,
especiallywhere the costof manual readingishigh.Fixed-networkwirelesssystems,bycontrast,can
supporta wide varietyof applications,includingmetering,real-time pricing,energymanagement,
and outage or theftdetection.Of course,there will be anadditional costforthese extended
features.
Impact of AMR on Field Personnel Within the Utility
The affectof AMR on fieldpersonnelinthe course of normal activitieswouldbe minimal.The field
personnel mayhave tobe trainedtoinstall,maintain,andbe aware of how the equipment
functions.ThisAMRequipmentwill varydependingonwhattype of systemthe utilityprocures.The
equipmentinvolvedwillrange fromthe metersthemselvestothe masterdevicesrequiredinthe
fixed-networkwirelesssystems.Dependingonthe type of system, theymaygetinvolvedin
installationof spreadspectrumradiosandother communicationsequipment.Fieldpersonnel will
have to recognize if AMRequipmentwasinstalledata customerfacilitysince incorrectdisconnects
while doingservice workcanresultinissueswiththe customersphone service.Utilitieswillbe
responsible forprovidingthe requiredtrainingandworkprocedure guidelinesapplicable tothe
productsand installation
POWER SYSTEM AUTOMATION
Power SystemIntegration
Powersystemintegrationisthe actof communicatingdatato,from, or among IEDs inthe I&C
systemandremote users.Substationintegrationreferstocombiningdatafromthe IED’s local to a
substationsothat there isa single pointof contactinthe substationforall of the I&C data. 14
Poletopdevicesoftencommunicate tothe substationvia wirelessorfiberconnections.Remote and
local substationandfeedercontrol ispassedthroughthe substationcontrolleractingasa single
pointof contact. Some systemsbypassthe substationcontrollerbyusingdirectconnectionstothe
poletopdevices,suchasRTUs, protective relays,andcontrollers.
Power System Automation
Powersystemautomationisthe actof automaticallycontrollingthe powersystemviaI&Cdevices.
SubstationautomationreferstousingIEDdata, control and automationcapabilitieswithinthe
substation,andcontrol commandsfromremote userstocontrol powersystemdevices.Since true
substationautomationreliesonsubstationintegration,the termsare oftenusedinterchangeably.
Powersystemautomationincludesprocessesassociatedwithgenerationanddeliveryof power.A
subsetof these processesdeal withdeliveryof powerattransmissionanddistributionlevels,which
ispowerdeliveryautomation.Together,monitoringandcontrol of powerdeliverysystemsinthe
substationand onthe poletopreduce the occurrence of outagesandshortenthe durationof
outagesthat dooccur. The IEDs,communicationsprotocols,andcommunicationsmethods
describedinprevioussections,worktogetherasa systemto performpowersystemautomation.

15. Figure 17: PowerSystemAutomationandSupervision
Power Delivery Automation
Thougheach utilityisunique,mostconsiderpowerdeliveryautomationof transmissionand
distributionsubstationsandfeederstoinclude:
• SupervisoryControl andDataAcquisition(SCADA) - operatorsupervisionandcontrol
• DistributionAutomation - faultlocation,auto-isolation,auto-sectionalizing,andautorestoration
• SubstationAutomation - breakerfailure,reclosing,batterymonitoring,deadsubstationtransfer,
and substationloadtransfer
• EnergyManagementSystem,(EMS) - loadflow,VARandvoltage monitoringandcontrol,
generationcontrol,transformerandfeederloadbalancing
• Faultanalysisanddevice maintenance
Systemswithoutautomatedcontrol still have the advantagesof remote monitoringandoperator
control of powersystemdevicesincluding:
• Remote monitoringandcontrol of circuitbreakersandautomatedswitches•Remote monitoring
of non-automatedswitchesandfuses
• Remote monitoringandcontrol of capacitor banks
• Remote monitoringandvoltage control
• Remote powerqualitymonitoringandcontrol

16. System Automation Features
IEDs describedinthe overvieware usedtoperformpowersystemintegrationand automation.Most
designsrequire thatone IEDact as the substationcontrollerandperformdataacquisitionand
control of the otherIEDs. The substationcontrollerisoftencalledupontosupportsystem
automationtasksas well.The communicationsindustryusesthe termclient/serverfora device that
acts as a master,or client,retrievingdatafromsome devicesandthenactsas a slave,orserver,
sendingthisdatato otherdevices.The client/servercollectsandforwardsdatadynamically.A data
concentratorcreatesa substationdatabase bycollectingandconcentratingdynamicdatafrom
several devices.Inthisfashion,essentialsubsetsof datafromeach IED are forwardedtoa master
throughone data transfer.The data concentratordatabase isusedto pass data betweenIEDsthat
are notdirectlyconnected.
A substationarchive client/servercollectsandarchivesdatafromseveral devices.The archive data
isretrievedwhenitisconvenientforthe usertodo so.
The age of the IEDs nowinsubstationsvarieswidely.Manyof these IEDsare still useful butlackthe
mostrecentprotocols.A communicationsprocessorthatcancommunicate witheachIED viaa
unique baudrate and protocol extendsthe time thateachIEDis useful.Usingacommunications
processorforsubstationintegrationalsoeasilyaccommodatesfuture IEDs.Itisrare for all existing
IEDs to be discardedduringa substationintegrationupgrade project.
Power System Automation Benefits to Utility
The benefitsof monitoring,remote control,andautomationof powerdeliveryinclude improved
employeeandpublicsafety,anddefermentof the costof purchasingnew equipment.Also,reduced
O&M costsare realizedthroughimproveduse of existingfacilitiesandoptimizedperformance of the
powersystemthroughreducedlossesassociatedwithoutagesandimprovedvolt- 16age profile.
Collectionof informationcanresultinbetterplanningandsystemdesign,andincreasedcustomer
satisfactionwillresultfromimprovedresponsiveness,service reliability,andpowerquality
AUTOMATION SYSTEM AND EQUIPMENT OPERATION EXAMPLES
Distribution Automation System Example
Distributionautomationsystemseasilydemonstrate the valueinautomatingcontrol of the power
system.Figure 18 showsa twoline radial distributionnetworkwiththree manuallyoperated
switchesforline segregationandloadtransfer.GivenapermanentfaultonLine 1,the relayingfor
Switch1 (SW1) tripsand all loadon Lines1 and 2 isinterrupted.Torestore loadtoLine 2, operators
mustmanuallyopenSW2 andthenclose SW5. In thisexample,we assumeittakesanoperatorone-
half hourto reach and operate eachmanual switchsequentially.Thus,Line 2loadisrestoredone
hour afterthe permanentfaultisclearedbySW1

17. Figure 18: SystemSingle-Line –Manual IsolationSwitches
Let usnextlookat replacingthe manual switcheswithautomaticallycontrolledfaultinterrupting
devices(i.e.,electronicreclosers,breakers,etc.).Further,letusassume thatthe protectionsupplied
for all of the breakersandautomaticswitchesislinkedtogetherviaacommunicationslink.Figure 19
showsthe same distributionnetworkasabove,withautomaticallycontrolledswitchesandthe
associatedovercurrentprotectionandcontrol scheme. The communicationslinkdramatically
advancesthe automationandcontrol possibilities.Forthe purpose of thisexample,we assume that
each protective relayshowninFigure19 communicateswiththe adjacentrelaysthathave control
functions.Thiscapabilityallowsfastautomaticrestorationandavoidsdispatchinganoperatorto
restore load.Most importantly,itsavesapproximatelyone hourinrestoringservice tothe Line 2
load..
Figure 19: SystemSingle-Line –AutomaticIsolationSwitches

18. Equipment Interface Example
Most of the IEDs inthe I&Csystemhave at leastone simple EIA-232serial portto support
communicationstoanotherIEDor PC. Some IEDs supportdata acquisitionandcontrol
communications,aswell asconfigurationcommunications,throughasingle connection.ManyIEDs
require separate linksforeachcommunicationprocess;therefore,twocommunicationslinksare
necessary.Some productssupportmanytypesof communicationsmessagesthroughone
interleavedcommunicationsconnection.
Figure 20: IED Communications
Many IEDs require avendor-suppliedproprietaryPCsoftware applicationforconfiguration,while
otherssimplyneedaterminal emulationdevice and communicate viahuman-readable ASCIIstrings.
The followingexample demonstratesthe proceduresnecessarytoconnectanSEL-351 relayto a PC
to performa simple ASCIIdialogue..
Connecting an SEL-351 to a PC
1) Make sure you have the properequipment.
DesktopPCor Laptopcomputer
SEL-351 Directional OvercurrentRelay,ReclosingRelay,FaultLocator
Cables:SEL-C234A or SEL-2800M & SEL-2800F Transceivers&Fiber-Opticcables
2) Turn onyour computerandrelay.
3) Start a HyperTerminal session.
Clickon START, go to PROGRAMS → ACCESSORIES→ HYPERTERMINAL
Double clickonthe Hypertrm.exe
Type in a name of the sessionyouwanttocreate (e.g.,sel351),thenpressenter.
4) Selecta communications(COM) portonthe PC.

19. In selectingaCOMportyou needtoknow a little aboutthe computeryouare goingtouse.
• Howmany COMports doesithave available?
• Whichonesare youable to use?
Connectyourcable to one of the available COMports.
From yourworksessionselectthe COMport youconnectedtoin the back of your PC (e.g.,Connect
using:Directto COM1). SelectO.K.andthen,fromthe communicationpropertiessettingsscreen,
selectO.K..
There is an experimentyoucandoif you are usingfiber-opticcable with2800 modems,tosee if
you’ve selectedthe correctCOMport thatyou connectedyourcable to.
• Unplugthe cable from the receive (R) fromthe 2800M modem.
• Fromthe keyboard,pressenterafewtimeswhile watchingthe receiveline.
• There shouldbe aninfraredlightthatyousee whenenterispressed.Thislightisinthe visible
spectrumandis not dangerous.
Troubleshooting:
If there is noinfraredlight,thenyoumighthave selectedthe wrongCOMport or your cable is not
properlysecure.Make sure yourcable issecurelyfastened,thengotoFILE → PROPERTIESand make
sure you have selectedthe rightCOMport.19
***Note: If you do change yourwork sessionpropertiesyoumustdisconnect,thenreconnect.This
isdone by simplyclickingonthe iconof the telephonewiththe receiveroff,thenclickingonthe
telephoneiconwiththe receiverbackon.
5) SetUp CommunicationsProperties.
Once you’ve selectedthe rightcommunicationsport,youcan thensetup the communications
propertiesforthatport.Go to FILE → PROPERTIES→ CONFIGURE.
Connectthe cable to one of the EIA-232 ports, whichare clearlymarkedonback of the relay.
The COM port propertiesneedtomatchthose of the relaycommunicationsportsettings.You can
use the front panel controlsonthe relayto view the portcommunicationssettingsonthe LCDHMI.
Pressthe Setbutton,thenthe downarrow (toput the cursor on port),thenpressthe selectbutton.
Thisbringsyou to selectSetorShow,selectShow andpressthe selectbuttonsince all youwantto
do issee the settings.
AfterselectingShow,therewillbe amessage thatscrollsacrossthe screen.Justletitscroll across;
youwill thensee the PROTOsetting.Make sure thisissetto SEL.
Use the downarrow on the frontpanel toscroll downto the SPEED setting.Thissettingisthe speed
or bitsper secondat whichthe relayandthe PC communicate.The SPEEDsettingonthe relayand
the BITS PER SECONDsettingonyour hypertermworksession needtobe the same to establish
communication.If theyare different,justclickonthe BITSPER SECONDbox in hypertermandselect
the value of the SPEED settinginthe relay.

20. Nextuse the downarrowto scroll downagain onthe relay.Thisbringsyouto the BITS setting;inthe
same fashionasabove make sure thismatchesthe DATA BITS settingonyourhypertermwork
session.
Next,use the downarrowagain to scroll downto the PARITYsetting.Make sure thismatchesthe
PARITYsettinginyourhyperterm worksession.
Scroll downto the STOP settingonthe relay;make sure thismatchesthe STOP BITS settinginyour
hypertermworksession.
Set the FLOW CONTROLsettinginthe hypertermworksessiontoNone.
ClickOK.
You shouldnowbe able to pressthe enterkeyandhave equal (=) signsappearon the screen.Table
1 describesthe ASCIIcommandsavailable.