undland51.John's.NewfoundlandCanadaDecember1989 Engineering AppliedScienceMemorialUniversityof ofEngineeringFaculty oftherequirementsforthedegreeof theschoolofGraduateStudiesinpartialfu @JoseChoi.n.Eng.Athesissubmitted crl

Ai\1ESSAGE PRIORITI' LOCAL AREANE1WORKFOR SUBSTATioN PROTEcrlONANDcmITRQ1

Dy

@JoseChoi.n.Eng.

A thesissubmitted

10

theschool of Graduate Studiesin partial fulfilment of the

requirementsfor the degree of

Master

of Engineering

Fac ulty

of

Engineering

and

AppliedScience Me morial University of Newfoundland

51.John's. Newfoundland

Canada

December 198 9

.+.

^{Nalional01Canadalibrary} BlbliolhcQuenalionale cucenaoa

Canadian Thesesservce servcodes mesescaoaoenoes

The author has grantedanirrevocablenon- exclusivelicenceallowingtheNationalUbrary of Canadatoreproduce,loan,distributeor sell copies ofhis/herthesisby anymeans andIn anyformortormat,makingthis thesisavaIlable to inte rested persons.

The authorretains ownershipofthe copyright inhis/her thesis.Neuberthethesisnor substantialextractsfromitmay beprinted or ctherwise reproduced without his/her per- mission.

L'auteur a accorce unelicenceIrrevocable at non exclusivepermettant

a

1aBibl101heQue natonatedu Canadadereproduire,preter.

distribuerau vendredescopies desathese dequelque maotereatsous qoeloueforme que ce solt pour mettre des exemplalresde cette these a12.dispositiondes personnes

eteressees.

t'auteurconservelaproprfeledudroitd'autour quiprotegesathese.NiIatheseoi desexlraita substantielsdeceue-ctne dolvent euc jmprlmes ou aulrementreproduitssansson aulorisation.

ISBN 0-315-59232-X

Canada

A specializedmicrocomputernetworkIs del/eloped to meet merear-tn r e processIngrequirements 01a digijallyprotectedsubstation.Thisapplicationhas strict limingconstraints and requiresalastcommunication response.Thenetwork Is based on the principlethaidirectaccess tochannel is grantedexclusivelyto lhe ready messagewllhthecurrenthighestpriority.

The networkreqairements 01the digitallyprotected substationare delined.The data Ilow ctme substafcnresembles the messagepriorityinnature.To implementthe messagepriorityscheme,a totallydistributed networkIsemployed.

Asimulation modelis del/elopedto predict thecer tcrmance 01 Ihenetwork.

Resultsfrom the sjnurauen indicatethatthenetworkiscapableof meetingthe timing constraintsofthe real-timeapplication.

ACKNOWLEDGEMENTS

1wou ld like to thankmy supeNisor,Dr.M.A. Rahmanforhis guidance,support andpeuercethroughout our assoc iation.Hisassistancewas instrumentalin detining the researchprojectand hiscrilical review01 thetextduringpreparaHonwasanInvaluable asset.I also thankDr.D.W.Close, associate professorof Political Science forhis assistanceduring preparalion of the flnal version01Ihiswork.

Mysincerelhanks are also dueto Or.N.Ekanayake,Dr.B.Jeyasuryaand Mr.Kin Lam lor Iheir Invaluablehelp duringthisresearch.A note 01 thanks to the stall and graduat e stude nts 01 thefacully01 Engineeringand Appli edScienc efortheir contributiOnsviadiscussion01topicsrelatedto thethesis

ABSTRACT ACKNOWLEDGEMENTS CONTENTS USTOFFIGURES

Page

viN LISTOF ABBREVIATlQNS

1. INTRODUCTION

1.1 REVIEW OFCURRENTRESEARCH 1.2 RESEARCHAPPROACH 1.3 CONTENTSOFTHETHESIS

2. DlGITAl PROTECTIONANDCONTROL INPOWER SUBSTATION6 2.1 POWER SYSTEMFAULTS & PROTECTIVERELAYS 6

2.1.1 THEFUNCTION OFPROTECTIVERELAYS 8

2.1.2 TYPEOF PROTECTIVERELAYS 8

2.1.3 THESHORTCOMINGSOFCONVENTIONALRELAYS 9

2.2 THEDIGITAl RELAYS 10

2.2.1 THE CONCEPTSOF 01GITAlPROTECTiONSCHEME 10

2.2.2 ll-lE ADVANTAGESOFDIGITAl..AELWS 12

2.3 INTEGRATEDMICROCOMPUTERBASEOSUBSTATION

PROTECTIONANDCONTROL 13

2.3.1 ll-lE NEEDSFORTRANSMISSION PROTECTIONAND

CONTROL 14

2.3.1.1 NEEDFORFASTSPEEDRESPONSEAND SYSTEM

DEPENDABILITY 14

2.3.1.2 NEEDFORCENTRALIZEDCONTROL FUNCTIONS 14

2.3.1.3 LARGEDISTANCES 14

2.3.1.4 WITHSTANDINGTHEElECTROMAGNETICENVIRONMENT 15

2.3.1.5 NEEDFOREVENTRECORDING 15

2.3.1.8 NEEDFORUNATIE NDEDOPERATION 15

2.3.1.7 NEEDFORSYSTEMWIDECONTROL 16

2.3.1.8 NEEDFOR PERIODIC MODIFICATION 16

2.3.2 SUBSTATIONFUNCTIONALREQUIREMENTS 16

2.3.2. PROTECTIONFUNCTIONS 17

2.3.2.2 AUTOMATICCONTROLFUNCTIONS 17

2.3.2.3 MONITORINGFUNCTIONS 18

2.3.2.4 RECORDINGANDDISPLAYINGFUNCTIONS 18

2.3.3 SYSTEMRELIABILITY 19

2.3.4 SUMMARY 19

3. LOCALCOMPUTER NETWORKING 20

3.1 LOCAL. AREANETWORKS(LANS) 20

3.1.t TRANSMISSION MEDIA 21

3.1.2 INTERFACE 23

3.1.3 PROTOCOLCONTROl 24

3.1.4 ENDUSERS 24

3.2 TOPOLOGIES 24

3.3 L4NSPROTOCOl 2.

3.3.1 CARRIER SENSENElWORK 27

3.3.2 CSI,A A PROTOCOL 28

3.3.2.1 l·PERSISTENTCSMA 28

3.3.2.2 NON·PERSISTENTCSMA 2.

3.3.2.3 P-PERSISTENTCSMA 2.

3.3.2.• CSMAlCD 30

3.3.2.5 COlLISIONFREEPROTOCOlS 32

3.3.3 RINGNETWORKS 34

3.3.3.1 TOKEN RING 34

3' lANS STANDARDS 3.

3.5 SUMMARY 37

THEARCHITECTURE OF THE SUBATATIONPROTECTION

ANDCONTROLSYSTEM 3.

4.1 SYSTEMARCHITECTURE 40

4.1.1 DATAACQUISITIONUNITS (CAU) 42

4.1.2 MICROPROCESSORCLUSTER(Me) 42

4.1.3 DATACQMMUNICAnONSNETWORK 43

4.1.4 STATIONCOMPUTER 44

42 THEWESPACSYSTEM 44

4.2.1 THESYSTEM ARCHITECTURE 45

4.2.1.1 DATAACOUISTIONUNIT(0AlJ) 45

4.2.1.2 SERIAl DATAlINKS 4B

4.2.1 .3 PROTECTIONClUSTER(PC) 4B

4.2.1. 4 DATAHIGH'NAY 50

4.2.1 .5 STATIONCOMPUTER(SC) 50

4.2.2 SYSTEMOPERATION 51

4.2.3 SYSTEM HEARTBEAT 52

4.2.4 REOUNDACY 52

4.3 NOOR"SASCDNElWORK 53

4.3.1 ASSIGNED-SLOT-esMAlCO PROTOCOl 53

4.4 SUMMARY 5.

5. CONCEPTUAl.. DESIGNOF "THE PROPOSEDNETWORK 57

5.1 NETWORKREQUIREMENTS 57

5.'.1 VOLUMEOFDATA FLOW 58

5.1.2 RESPONSETIME 60

5.1.3 SYSTEM AVAILABILITY 61

52 THE PROPOSEDNETWORK 62

5.2.1 THE. ADVANTAGES OFTHENEWAPPROACH 65 5.2.1.1 SIMPLICITY

"

5.2.1.2 MQOUlAAlTY

"

5.2.1.3 EXPANDABIUTY

"

5.2.1.4 MESSAGEPRIORITY 67

5.2.2 PRIORITYClAS SES 67

5.3 THEMESSAGE PRIORITYCARRIERSENSEMULTIPLE

ACCESSPROTOCOL

..

5.3.1 THE MPeO PROTOCOL 69

5.4 SUMMARY 73

6 PERFORMANCE ANAl VSIS 7S

6.1 CONSTRUCTIONOF THE MPCOSIMULATION MODEL 76

6.1.1 SIMULATIONCLOCK 77

6.1.2 EVENTQUEUEDISCIPLINE 78

6.2 RANI):)M NUMBERGENERATION 79

6.3 SIMULATION~OOEL 79

6.3.1 PACKETSIZE 60

6.3. 2 DATA PRIORITYLEVEL 61

6.3.3 PERFORMANCESTATISTICS 61

6.3.4 SIMULATIONRESULTS 62

6.3.5 COMPARISONTO NOOR'SASCDNETWORK 65

6.3.6 SUMMARY

"

7. CONCLUSIONS 6.

7.1 MAINCONTRIBUTIONS 89

72 SUGGESTIONS FOR FUTURERESEARCH 90

REFERENCES

"

APPENDICES .6

A.B. L1STlNGOFTHEMPeD MOOElLISTINGOf THE SMPLSIMULATIONENVIRONMENT

•

106

•

. ,

LIST OF Elot !RES

FIGURE Page

2.1 ARRANGEMENT OF A POWERSYSTEM 7

2.2 THE BASICARCHITECTURE OF A DIGITALRElA V

"

3.1 MAJORCOMPONENTSIN A LAN 21

J.2 KEY CHA'<ACTERISTICS OF LANS'STRANSMISSION

MEDIA 22

J.J lOCAL AREANE;IWORK TOPOLOOIES 25 J.4 lOCAL AREANEIWORKACCESSCONTROL

ll:CHNIQUES 2'

3.5 COMPARISIONOFTHE CHANNELlITlUZATION

(S)VS LOAD(0) FORVARIOUSCSMA PROTOCOLS JO

3.' ETHERNETOPERATION 31

3.7 THE CHANNELEFFICIENCYVS NO.OF READY

STATIONOF A ETHERNET J2

J.8 THEBIT MAP PRaTOCOl (N_8) 3J

3.9 (A) LISTEN MODE(B) TRANSMITMODE l5

3.10THEIEEE802 STANDARD 37

4.1 DATAF1..0WINSUBSTATION 40

4.2 TtIEHIERARCHICALARCHITECTUREOFTHE SPC

SVSTEM 4'

4.3 THEWESPACSYSTEMARCHITECTURE 4'

4.4 THE DATAACQUISTIONUNIT 47

4.3 THE PROTECTION CLUSTER 4'

4.' THESfATIONCOMPlITER 49

4.7 COLLISIONDETEcrIQ"lMACHANlSMFORTHE

NODESASSIGNEDTOTHESAMESLOT

ss

3.1 THE CONAGURATIONOF AD1STRlBl1I"ED LAN

FORSUBSTATIONPROTECTION ANDCONTROL 62 5.2 THE F1..0W OIARTOF11IE MPCDPRorocoL fOR

DATA (i) 72

6.1 CSMA/CDFRAMEFORMAT 81

6.2 AVERAGEDEI..AV FORVARIOUSLOAD 83 6.3 CHANNELUTILIZATIONAT DlFFERNETLOAD

FACJOR 84

6.4 AVERAGEDELAYCOMPARISONOF MPCD

PROTOCOLANDASCDPROTOCOL

ss

6.3 CHANNELUTn.IZATIONCOMPARISON OF MPCD

PROTOCOLAND ASCDPROTCCOL 87

viii

B AID AI AS(])

ADC CI

CD

CSMA CSMAlCD DAU DlOB

rrc

EPRl I 110

LANs

Mbps Me

MFCD

ms PC

sc

VLSI WESPAC

J1ST OF ABBREVIATIONS

END·m END PROPAGATIONDELAY PACKETSIZE

ANALOGTO DIGITALCONVERTER ANALOGINPUTCARD

ASSIGNEDSLOTCARRIERSENSE MULTIPLE ACCESS

WITH

COLLISION DETECTED ANALOGTODIGITAL CONVERTER CONTACTINPUTCARD CONTACTOUTPUTCARD CARRIERSENSEMULTIPLEACCESS CARRIERSENSEMULTIPLE ACCESSWITH COLLISION DETECTED

DATA ACQUISITIONUNIT DISTRIBUTEDINPUT/OUTPUTBUS ENDOFCARRIERPACKET

ELECTRIC POWERRESEARCHINSTITUTE INTERFACE

INPUT/OUTPUT LOCALAREANETWORKS MEGABITSPERSECOND MICROPROCESSOR CLUSTER

MESSAGEPRIORITYCARRIERSENSE MULTIPLE ACCESS

WITH

COLLISIONDETECTED MILLI-SECOND

PROTECTION COMPUTER STATIONCOMPUTER VERYLARGESCALE INTEGRATION WESTINGHOUSESUBSTATION PROTECTION ANDCONTROL SYSTEM

ix

CHAPTER1 INTRODUCTION

Duringthepast decade,localAreaNetworks(tANs) have developedrapidlyinto a eomoantrcrce in thefield 01computercommunications.Themejcr reasonbehind this rapid developmentis the vastimprovemenls in theVery large ScaleIntegration tVl Sljtechnology IIIAs the numbernfcomputersncreaees.networkdesignersbecomemoreandmore interestedinconnectingtr.emto forma dislributedcompuler networ!<ferapplicationslhat wereonce thoughtimpossible.By havingdillerentmachinesper/armdifferenttasks. the approach of distributedcomputing hasavariety of advantages(21.inckJding

•sharingexpensiveresources

•Improving productivity -addinglunctionalily

•exchanging data betweencomputers

However,rotunlilrecently,LANshavebeenused mainlyincmce and business environmentsfor suchapplicationas once automation.Duringthepasl few years,numerous studieshavebeen conductedusing tANsin areal-time controlenvironment.One oflhese studiesis the digitalprotectionand controlschemeat powersub-stations [3J.

11 REyiEW OFCURRENT RESEA RCH

As earlyas.978. a study of distributedcompu ter nelwol1<slorappllcatlonto the control andprotectio n01electric power substat!on was published by RummerandKezunovlc [4.51.wherethe needs andthe required lunc uons ofme dlgila lprotectionand contro l scnermhave been identified and defined. ADistributedprocessingMlc roprocessor·based Hierarchically-structured(OMH) systemwas alsopresented In thepaper.

About the sametime,a dedicateddigitalsystem,developed jointlyby KansiEleclrlc PowerCompany andMit sublshlElectricccrccreucnInJapa n 16]. used thirtee n microprocessorsto perform all Ihe control and protective functi onsat asubstation.The fundamental concept underly ingthis systemIsathreedata chann elstructuretomanageall the signalllows forcontrol and protection.Satisfactory results havebeen reportedfrom field tests.and promisingresults fromthesetwoearlystudies led10subsequentstudies.

In the early 1980's , the ElectricPower Res earch Institute(E PRI) Initiatedand sponso rednumerous resear ch anddevelopme ntpro jects inintegrated microproc essor basedpower substatio ncontroland protectio n systems[3,7·9J.Theaims01these studies were to reduce the Iile tim e costs01substationco ntroland protection functions while achievingpenc nnerc e and leaturing benefits01new digitalescrcecnee by employingrecent advancedelectronicstechnology. TheWesting hous e substatio nprotectio nandcontro l (WESPAC) systemIs the directresult ofthesestudi es 1101, The WESPACsystem,an integratedmodu larsystembuilt onthestate-ct-me-andigitalcommunica tions lechnology, providesprotecti on,control.andmonltoring at the substation.Test systemshave been operatedaltheBranchburg substationalthaPublic serviceEleclllcand GasCo.(PSE&G) 01 New Jersey sinceSeptember1984 and altha Deans 5001230 KV substation01PSE&G since early 1986111).

A study ota microcomput er network lorreal-timeprocessi~requirement s in a subslationwasdonebyNoorrn OClober1982[12}.In hisWQl1l:,Noofproposedtouse an assigr.ed-slot.csMAlC D(ASCDl nelwOrk protocollor thereal-timesubsl<n~nprotection and controlsvst em.Ananalyticmodelanda simJlationmodelwere develo ped 10predictttle performance otthi!As e D network.Bolh theWestinghouseWESPAC and Neats ASCD netwQr;l; arediscussed indetaitinet\apl:er 4

Several otherstudies[14,151have addressedlheproblems01aLANinreal-life cMlrol andprotecnon environmenl.One of the moreInterestingstudieswas done atthe Universily01 ReQina,to getherwilhthe Saskalchewan Powercerpc reuc n,lheyconducted a study on a Local AreaNelworktor anelectricpowersubstationIn seprerreer1964 1131.ThIs stud y.suppo rtedinpartbyNaturalScienceandEngineeringResearch Council01Canada, investigatedvarious LANarchi t ectures andprotocols for thesull . bllil y01anautomated prOlection andcontrolsubstat io n.Atoken passingringwasproposed10'this application.

Simulationresulsshowlhat!hepel10rmanceotthenetwork meetsthe dala comrB.lnlcat ion requirementswiltinasubstalion.These studi es were generatln scope.

,2 RESEAR CH tPPRQ ACH

The objeclive 01thisresearchIsto propose alOCalarea nelwOr1<(LAN)protocolwith cencrmerc ebestsuitedforareal ·timeenvironmentin adigital protection andcontrolpower substation .The approach take ntowardslhe develop ment 01thisresearchis10developa simulation model 'or thepropo sed protocol.Numer icalresultsIromthe simulationarethen analyzed to predictthe networ1< pertcrmance.

Prior tothe

seteencn

oftheproposed oelWOr1(.adetailedstudyofthedig/lal prolectionand controJ schemeIscarriedout todltlermlnethe substation·srequiremltn!s,A LANprOl oco l is thenproposed forsubstatio~application on the !)asis of the defined requirements.

A comparaliveSiudy 01 the network perlo rmanceisItHJnperlorrned beteeen the proposed prOlocoland the previously mentionedNoofs ASCO protocol112!10 determine whichprolocol is bettersuitedfor arP1icationtosubstationprotectionancl COnlrol.

The majorconcerns Inthe perlormance sludyare;

1) ChanneluUllzalion(throughput) 2) response time (speed requirement)

areeraret e

4)size of thenetwork 5}lypeofdal a

1 3 CONTENTSOfTHE THESIS

This study begins withabrief historyoIlhe developmenl01digitalprotectio n and centrcl of thepowerapparalus at the subs1atio n.This chapter alsointrodu ces the lundamental concepts 01 digitalprotect ionand control. A study is conducted 10 identily and ceune mesubstation functio nsandrequirements.FourmaJo~lunctions ot the networ kare discussed: protect ion,conlrol, monitoring andrecording/displa ying.

The concept01LANsisdescribedinchapte r3,whichInclud esthemotivation,the lopoiogyandthenetworkprotocol .Two majorLAN protocols are reviewed ,the CarrierSense Multiple Access(CSMA)prOlocolandlheTokenringprotocol.

Chapter4 deals with the architecturalstructure 01the substation protectionand control system.Athreelevelhierarchical structure isused to illustratethe digitalprotection andcontrolsystem.Thefunctions ofeocnelementin thehierarchy are reviewed.Inaddition.

thearcratec nnarstructure01the WESPACsystemaswellasthe Nocrs ASCD protocolare alsodiscussed In detail.

Inchapter5, the proposedprotocol,messagepriorilyCSMAlCD (MPCD).is presented.Adetaileddescription of the MPCDproll'lr.~!ISoutlined.TheMPCDptctccclis basedon the principlethat accessrightto thec~ ,annel(network)is exclusivelygrantedto ready messages01the currenthighestprioritylavel.An analysisIs performed10classllythe subsraucndataIntolhreepriority classes, lauRdata,protectiondata and systemeeta. The advantages 01theMPCDprotocolare alsoreviewedInthischapter.

Chapter6 IsdevotedtothE simulationmodeling 01 Ule MPCD pretecet.A perlormanceanatysis Isperformed10 examinethe numericatresultsobtainedIrom the enmnattco.Thethroughput·detaycharacteristic ofthe MPCD protocolIs derived.These resultsare also compared with theNoo(s ASCDresults.

FInally.on thebasis 01thisstudy,conclusionsand suggestionslor tunberresearch arepresenteein chapler7.

CHAPTER2

DIGITAL PROTECTIONANO CONTROLINPOWER SUBSTATIONS

Theidea touse digitalcomputerslorreal-lime

acouceuooe

suchas pretecton and controlor powersystem equipmentwas firststartedIn thelate 1960·s.Althatime,several studieswere done to examinethe leasibility01usIngamini-computer as a dedicateddigital protectiverelay to detect and locate faultsin power systems.Since then,(here has been considerableinleresland researchconducledin this area.

The development0110''1 cost,001 powerful microcomputersprovided anlmpcr tant element needed lorthe cost-effectiveimplemenlallon01 computerprotection andcontrol of powersystems.Anumber01ercteeeoalgorithms have been proposed and developed [17·22]. The latesltrendIslaInterconnect these newlydeslgnedproteclive relays and control cevcee10formadatacommunications network(local areanetwork) within thepower substation13-14].

Inthischapter,medevelopmenl 01digilalprcteeucn andcontrolschemeIs doscribed.The advantagesof the digitalrelayaarealsodiscussed.

21pOWERSYSTEM FAULT S&PROTECTtVERElAYS

Modern electric powersystems are dependable,andready 10deliverenergy10the customer wilhoutarr{interruption.Protective relays play anIrrpo rtanl role in assuring\his continuousservice. Occasionally,power systemsdoeaperlencefaultsandabnormal

operatitIQcondili o ns.These are idenlifiedbythe proteclive relays. Once a faun.is del ected,!herela)'$ lnitiale correctiv eac:lion tolTlinmizeanyserviceint:erruption.

ApowersyStem can beconsidered as achainconsisting01generalors. power lranstormers,swilchyard,transmission~,dslribJtioncirt:uits,andutilizationapparatus {seeligtJ"e 2.11.

Power Tra~ission ^Power Distribut ion

8uPf~to~r~:rfB _tcw-vcuace

High-Vollage Distribution

Switchgear Sw~chgear Circuit

F9Jre 2.1Arrangemernorapowersssem

There arearumtler01cau ses forlhe failure

or

breakdown01these components.

Faults01shortcircuits can occur betweenUdvldualphasewires or coilsand ber....eena phasewreorcoi togroun:l as a resul01breakdownoftheinsulatiOn protecti"lg them.The resultingelectricarcwhidlCOlilainsconsiderable powercancausesevere damageinavery shorttime. Theselaulls orshortcircuits are caused mainty~i!t'JsulatiOnfailure.butmay esc inducedbysuchthingsas"ollaoe surges.overtoadll'lrj withsubk.~uentovemell!ing01 the equipment and abrasiondLie10 expansion and contraction.Transmission line racttscanbe caused by some ractcrssuchaswind,leeandsleet,fargebirdsbridging the insulators, lightn ing,swinging tree limbs,andcrane booms,etc. Otherabnormal ccon cn swhich impaira component'stuncuenIn thepower systemareoverheallng ofbearings. over or underspeed.and reversephasesequerce. etc.

2 1 1 THEFI!Ne TION OF PROTECT IYEBEley s

Relaysareplacedin the powersystem to ensureuninterrupted servicetothe customers.They do soby avoidingequipmentdamage or bylimiling it to thesingle unitIhat maybeIntrouble.Therelayslocatethefaultandtripthecircuitbreakerswhichwill breakoil anylin~.sto thedelectlveapparatus, thereby isolatingif,

TheprotectiverelaysobtainthenecessaryInformationtolocateafaultin theIorm01 currentsand vonagestrcm Instrument nanstcnn er (transducersorInterfaces)whchare locatedon eceeucpartsof thepower systembeing protected. Thispiece otInformallonis then relayedtothecircuitbreakersinthe form01 a trippingpulse (slgnat).Finally,theclrcult breakersIsolate the defectiveapparaiusbyinteffiJptingthe row ofcurrent fromall sources.

21 2n-pEsOFPROTECTIYEREI AyS

Protectiverelaysbasically consistofan operatingunit andaset01ccrnects.The operalingunitlakeson thentermaucnfrom theInstrument lranslormersfrltheformof currents andvoftages,performsa comparisoooperation10determineif thereIsa fauft,and convertstheresultinto amotion01 contactsaccordingly. Whenthey close, the contacts eitheractuatea warningsignal or completethetr~circuit01acircuil breaker,which III nrrn comptetes theisolationofthetault y elementby interruptingtheflow01current intothat element

ConvenHonally,thereare two majortypes ofrelaysavailable, electromechanical relaysandsolidstaterelays.Theelectromecharicalrelaysarethe older of thetwotypes,but arestill widely used in theindustry.The solidstate relays werenrst lntrcducedInthe 1950's. However,theywere not widely accepteduntjlhe late 1560's.

Solidstate relaysreael consklerably fasWthaneecirorreebanlca treiays.Thesolid slatecircu~saredesigned10providevariousture ens suchasleveldetectio n,phase angle measurement, arrcecaucn,pulsing,squaring,timing andothers.These analog andpartly dgrtalclrcuhsreactnstantanecusly to the inputs0'current andvoRage so asto supplythe properoutputsfor thltrequiredcberectedsucs.

213THESHORTCOMINGSOFCONVENTION AlBE'AXs

Despitegenerallyperformingadequately,there arelewdetlciencies and problems associatedw~hthe conventionalelectromechanicalandsoUdstate relays,Thelollowinglists lhesa liemshortcomings oftheserelays:

Sjleolseoljrn:II YQe'

socethe ccnvenuonalrelay hardwa reisInprotracteddlesta te unlita faullis detected, Iheymay 'ail withoutwaffling. Most utilities haveconducted periodic rremeoerceprogramsIn whichtherelaysaretested.Theseprogram5arecosily,andmaystill lail10 catch manyprob lems untilalterthetanrre.Futhermore,suchperiod ichuman tamperingmaycauseadditionaldamagesand problems.

TheCOSI of convenllonalralayscontinued 10rcreeseduringthelast twenly years,while thecost of digrtat devicesandmicrocomputershas beendec reasing duringthe sameperiod.Thus economicsmakethedevelopment01dgilal relays evenmoreattractive.

~e...:

All ccnveracnatrelays are01 eededicatedtype.Diflerentprotectionfunctions requirediNerent typesotrelays.

2 2 THEDIGITAlBElAy S

Therehasbeenaconsiderable amountofIntereslIndigita l prol ection 01 POWllf apparatu s since the late1960·s.In1969.dedicateddigital relaysus ingnW1Ico~erswerl proposed byG. D. ROCkeleUer(24].who

eenree

^andexaminedprolect io nbyusi ng

a

mcxiJlarapproachfora_types01statiOne~ n1.Hisproposatisoftenrel e ITecl10aslhe lound ation olthaconcePt01dig ital relayi ng.

Digital relaysaf:!desirablesincethey pennll continuousmonftori ngandsell·

checking. They alsohave theabilitytoconsolidatethe Iogicallunctlo ns01many dovicesInto one processor unit, therelo reavoidi ngduplicatio ninsituationswheremany sepa rate pieces ofequlpmenluseIdenticalInput sor perform similar functions.Th eselead10the possibilityollheintegral ed automatedsubstatiOn.

Therapiddevelopment01micrOCOfT1lUte rshas broughl abo Ulnovel ~iOw-cost possb Trties lorthedevelopmenl01digil a lrelayS.TI"o(,high capability01pres el1!t available mic rocom pul ers are suchthatall lhe digit al rela ying functio ns performedbythe minicomputersoltha late1960's cannowbedonebythesernictoCQnllUte rs.Asaresult.

many res earchworkshavebeencordJetedonlhe specifichardwareandsoltware lechniques for microcompulerbasedrelaYS(3-1<lJ.

2 21THE CONCEPTS OfplGITAIPsmECTIQNSCHE ME

The basic archllectureo!adigita l relayisouJUn&dIn ligul e2.2.Theblocksincludea data acquisitionunit(OAUj,ananalog10digijalccreener(ADCl.a microcompulerand an InpulloutpUl subsyslem.

10

To Sysl&m Trip Signal

MIcr o compu t er I/O

FromSystem

Figure2.2Thllbasicarchitectu re01adigitalrela y

The DAUreceivesanal og sign alsthat represent powe rsyslem currentsand voltages; thesesign als are cc nvenectrue digita lform (bi ts)by theADC. Thedigi tal inlormalionis then passed on 101Mmicrocomput er wh ereanapp roprlale relayprog ram (p r o l eC1ionalgorithm) isexecute dbased on lheinpuldig italdata todelermine11\9 sy s tem ccncaen.Thedecisionsof lhe relay are conveyedto the systemthroughthe input/o utp ul su bsystem.

11

The heart01thedigitalrelay systemis therelay program.Various algorithms have beenproposedandimplemented lorall types of protectionover the years (17J. Promising resultshave beenobtainedrromIhesestudies The followinglists some01the relay algor~hmsbasedontheprotectionapparatus:

Transmissionline(25,261:

-FoorierAlgordhm

•CorrelationTechnique

•Kalman Filtering Approach Translormerj17.22.26J:

•Fourier Algordhm

•A&ClangularTranslonnApproach -WaIsh Algor~ hm -HaarFUnc1ion Approach

•Fln~eImpulse ResponseApproach

•leastSquareCurve Filling Algorithm

???THEADVANTAGESOFDIGITAlBElAYS

The main reasonsfor thodevelopmentordigital relays aretheireconomy.ro l iabll~y, flexibility,andimprovedperformanceovertheconventionalretese. Some 01Ihe salient advantages otdigital relays are:

1)Fasterbreakertripplngtime;This givessecurity againstundesiredoperalionscomparable to conventional relays.

2)Morereliable : Sincethe hardwareofthe digdal relayisintrequeotuse,thlsincreasesthe conlidencelevelintheserviceabilityof the retay.Also.

n e

dlgi1a1 relaycanbedesignedto mcracr itselfand alertoperatorsin theeventof equiprnenllallure.

12

3)Mor e economical: Costs 01microcompute rsaredecreasingrapidly while theirpow er is increasin g

4)Moreflexible:Most 01 thehardware is

me

eeme for alltypesof digitalrelays,only their scnwaresaredifferentThiscreaes a greatdeal oflIexibi:ity lor therelay.

5)Auto matiOn:Thereis the possibilityof integrali ng the digitalrelays intoa computer nelwor1';to term anautomated(unmanood)prctedjonandcontrol substation.

23 INTE GRATE D MIC BOCOMPII T ERBAS EDSUBSTATION pSOTECT!ON AND CONTROlSYSTE M

Compute r apptications In prot ection and co ntrolof powersyste ms havebeen anectec bythe ceveccmemsin digitalrelaysandmicrocomputersystems.A number0' projectsrelated to substation controlanddigitalpretecucnhavebeenrepo rtedby um y compan iesandresearch organizationsthroughoutthe world sincethe late1970's.Themajor objectiveof Ihese studiesis to develop a digital protectio n andcontrolsubstation co ncept using the latesttechnology.The newapproachenables processInformationtromthe digital rel::lys01thopowersystemconvertedtodigital fo rm andmu~lplexedontoa single trunk or highwayleadingtothe controlarea, where stationcompu ters record data, controlprocess cperauons.andprovide cara recordslor ope ra tors.This provide sthepotential lormore sophisticatedcapabilijies atlower instalialiOncost.

The concepts bohind thedevelopmentof the microcompu ternelWol1l tome etthe objective01theprocessingrequirements ot atransmissio n level substation are describe din lhis sec tion.A numrollunctions and requi rementsermenetwol1l.are speclged.These 'unctions have formeduebasis lor the fateranal ysis01 thenetwork.

13

231THENEEDS fORTRANSMISSIONpROTE CTIONANDCONTROl

BelOTedes cribingthe functional requhe muets lor Ihe substallon protection and control system,itis necessary to definethe need lorlhe system.

23'1 NEED fOR EASTRESPONSEAND SYSTEMDEPENDABil ITy

The mostlI11porlanttacror in lheprotectionaod controlscheme is the dependability of the system fora wide range 01power systemenects. Rapidresponse to events by subtle cntererces Inmeasured signalsis requiredformany of the functions.scptaencetee relayingand control are required10maintain overallreliability01the power syste m.

2 312 NEEDfOflCENTRAl iZEDCONTAOt fUNCTIONS.

To achieve thediscrimination which is essentiallor effacttveprotection arc!

corurot.a variety of sophisticatedsensing lunctlons IT'IJst respond ina co-ordlnatedway.

This Implies that auinformation from lhe swilchyard must be collectedat a cemrallocatlcn, the cont rolcente r.

?313tARGE DISTANCES

The physical size ofa typicalFlItraHig~Voltage (EHIJ)stationisperhapsits most striKing reeure. Theconcern is that,he utilitymustrun many wires hundredsoreven thousand s 01 teet between swilchyardap para tus andthe conlrolcenter torsignat transmission andlor powerequipmentcontrol. Whalisneeded10 solve theproblem is an inlegrat ionof fu nctionsso toatthe equipment requires a minimum of interconnections,and theretcre.eborterwkes.

14

23'4 WITHSTANDI NGTHEEL ECTROM A G NfTl CENYIRON Mf:NT

The powerapparatus produces an environment 01 severetransien t Electromagne t icfnterterence(EMI) whichthreatensanylow level signal electronic system (suchas digil aldevices) Inslalledinlh e substatlon,

23J5NEEDfOR EyENTRECORplNG

Theoperalionof controlorprotPClionelementstee a direct effecton the securily of the transmissionnetwor\(.Therefore,re coldlng equipmentmusl manilor me btlhavior andoperationat thesecrilical devices.This reCOrdinggearmust beautomaticto capture me responseofimportant eventssuchas faults,powerswings,and switching.This inlormation is tmpcrtentfor lateranalysis which rescstofu rther adaptationsofoperating

cracucea ooccrurcrsvstem

2 316 NEED FDAUN ATIENDE DOPERATION

The remotenessof somesubstations,the cost ofhavinganoperatoron sne,and the need forthespeed o! automaticcontrolacucns haveled to me desire lorunmanned SUbstations. For eachsubstation. alletnlrol activities must be performed eithe r automalically,orat the command01a remeresserem operatorvia the Supervl'..oryControl AndData Acquisition(SCAOA)system(27}.Itwould be alsodesirableto havesomesort of sell-diagnosisorInternalandexternalmoniloringso thatsystemmaintenance personnel arealertedwhensomethingdoes 00 wrong.

15

23 17 NEE D fa R SYSTEMWIDECONTRO!

Comprehensivecentralizedmonitoringandcontrol 01the system Is essentialto modernpowersyslem.DatafromaroundIhe stationarecolleaedlor detailed analysis and modeling. Theresultslead10rec:onllgurationor readjustment commandswhichImprove the securilyofthe system. System·wide control functions must be supportedby interlace equipmentwhich suppliesdigesteddata 10the controlcenteratthesubstation.

2:' 1 e NEED fORPERIOPICMODifiCATION

IIisuncommon 10designaOO builda malortransmesc nsubstation fromscratch to itsultimate configuration.Ontheconlrary,it typicallybeginsas a nodelor onlya fewlines, andevolves Instepsover aperiod of years lnloa major junctionwith rr..:.ny lines and transformerslinkIng diflerentlevelscute grid.Eachexpansionrequires~ddillQn alcontrol andprotectionequipment. Therefore, It

is

dealrable10have asystemIhat is flexit.1:l enough tofacilitate suchchangeswitha mJnimJm of ellort and expense.

232 SIlBSTNION FUNCTIQN A!REQUIREMENT S

A functionlist was compiledIn the ERPl'sprotec ts17·9)to deline Ihelunctlons Ihatmustbe supportedbythe substationprotection and controlsystem. These functionslall underlourgeneral categories:

16

2 3 21PRffiECTlQN FUNCTIONS

These functions Initialehigh speedl~plngof clrctJilbreakers al eachterminal when alault is detected anywherealongthe protected zone01the correSpOndingcomponent.

Theyare -unefaullprotection -Iranslcrmertautprotectlon -bueren crcrectcn

<shumreactor protectlon

•breakerlai lurepr olection -translertripping

Uneprntectlc n consists of pilot and non-pilotprctecte nwith delayed remote backup protection.TransformertriplogicIncludescver-excueucn,differ entialovercurrent, and lime cvercurrentcrcrecucn. Transformerrestrainlogic IncludesmagnetislngInrush currenlcrcrecncn.

2322AUTO MATICCONT ROl fllNCTIONS

Automatic controlfunctio nsare' -Jocatccorro!01voltage and VARflow -Ioac:lshending

-autorn.l licreciosing

-synchronlsm checking ard synct,ronizer closing -automateswilching sequences

17

2323 MONIT ORING FUNCTIONS

The monitoringlunctionsinclude supervision andperiodic tesUng01 theinl egrity of systemcorrponents.Themonitoringfunctionsare:

.pilotand l ransler l ripc ha nne l mo n ~olf ng

•loadmon~oringandoutof stepprotection

•monitorinGandcontrol01breakersandswitches -diUlerentialmeasurement check -e ene tcereroverloadand tappositionmonitoring

• selfchecking

2;' 2 4 RECORDING AND DISPI AYINGFUNCTiONS

Thiscategorygroupsauthefunctlcna whichpertaintome interfacesbetweenme prctecucnand controlsystemandthe externalworld-SCADAmasters,localandremote operatorsaswell as Ihein/ormationdisplayedto them.Thesefunctionsare:

• localman-machinesubsystem

• remoteSCADAinterlace -alarming -cetalogging .revenuemetering

•recordingand IndicaUon01sequence 01events -oscillography

-uneraueicceucn esumancn

18

?3 3 SYSTEMBf!IABlllTV

A weiprOlectedsubstallon needs an extremelyhighdegree ofreUabllltylorthe 8ntl,echain01proteClioll,includi ng the networkRnk. Unlike

many

computer network systems.thesystemdownt imetruSIbelow.1Msubslalion protection arw:S control system mustensure praclicaRyInslantaneousrecovery fromfaults weto elementfailure.TherefOf8.

reciJndancy ofeach protectiveIUnc:lions isrequiredbythesystem10obtain ahigh degree ofre~ability.

The

ccrcect

of protectiverelays has beenoutlinedincluding theshortcomingsof the ccnventlcnalreta ys.

Thedevelopmentof digifairelays usil'lQ'microco~ulerswas presentedandlheir advantageswere described.In addition.theconceptoldigitalprotectionschemehas also been described.

Thedesign goals01thesubstatio nprotedlo nandcontrol systemnevebeen eSlabJished.AIlJrrberollunctlons have been delined and theirrequiementsarespecilied.

reese

luooionsform thebasIsforlaler design consideratio n.Thedotail design01the

required networ1(isdescribedInchaPler5.

19

CHAPTER 3

LOCALCOMPUTERNElWORKING

The ideactlccatcomputernetwor1<ing was nrstintroducedin the 1960's asan allempl to findnewfechnologies lor telephony128,29).Theinitial developmei1ls faHed due\0highcostandunreliability01contemporaryeteclronics.Duringth91970's.lhe thought 01local computernetworking was pickedupagain 10linkminicomputers 10gelherbya rcrreer01researchlaboratories suchas Xerox'sPalo Aha Research cereer(PARe)andIhe University01Hawaii.

By memid19 70's,severalnetwo!k ercnneciureshavebeenproposedwhich include the U.S.Department ofDetense's ARPA network (30,311.Ihe University01 Hawaii's Aloha nelWork[32,33]. Mitre'sMITRIX 1341.BellTelephoneLaboratory' s Spidar (34), IheUniversity of California,Irvine's DistributedComputingSystem(DeS) 135Jand Xerox'sElhernet [361.Thelrends01thisrapiddevelopment01local computingnetworlling continuedand developed Intotoday's localArea Networi<(tAN) technology.

This chapterintroduces the LANtechnology.llchal'acterizestheLANs by their topologiesand transmissio nmedia .Various medium access controlprotocols including CSMAfCDand tokenringaredesc ribed.

31I aeAIAREANETWORKSIt ANSI

localarea ne twork is disUngulShedby the area II encompasses; ilIs geogr aphically limitedwithin a distance01alewtens01kilometers.They dillerfrom large

20

computer networks In severalways. ThemaindiHerenceisthailarge networks are often economicallyandlegally restrictedto use the publictelephone network,regardless of~s lechillealsuitability.Onthe contrary,most LANs areprivatelyowned and operated.They canusa t>ighbandwidthcable swhichleads10numerousadvantages such as highdatarate (O.1·100 MbHsrs, Mbps) andlowerrorrate( 10·a to10 .11).

ALANusually contelnslourmajorcomponents (see figure3.1),whichserveto transportdata between endusers.

TRANStvfISSICN MEDIA

INTERFACE

LAN A'OfCXXX.

USERWORK STATION

Figure 3.1.Majorcomponenl!:in a LAN

311TBANSMISSIQti.MEQlA

LANs'stransmiSsionmediacanlake severaldifferent physical forms, twisledpair wire,coaxial cable anifiber optic.Figure3.2 summarizekeycharacteristics 01these medla.

Two majorrectorsareusuallyconsideredwhen choosing a lransmissionmedium:the sceeo requirementandthe distance01the transmission.

21

Transmission DalaRate Bandwidth Repeater

Medium Soacino

Twisted Pair oM,.. 250 KHz 2·10km

Coa_ial Cable 500 Mbps 350KHz 1·10 km

FiberOptic

'0,..

^{2GHz 10-100km}

(a) Pcm-tc-pclntconfiguration

Transmission Signalling Maximum Max.Aango@ Practical Media Techniques DataRate Max.DataRate No. of

(Mbps) (km) Devices

Twisted Pair Digital

t-a

F•• 10'5

CoaxialCable Digital 10 F•• 100's

50 0

CoaxialCable Digital SO

,

10'$

(75 0 )

Analog with 20 10's 1000' s

FDM

Single SO

,

10'5

Channel Analog

FiberOptic Analog 10

,

10'5

(b) Multipointconfiguration Figure 3.2.Key cnaractersncsof LANs'snansmsslonmedia

Twisted pairwiringis one ollhe mostcommonccmmmkeucnstransmissionmedia.

Duato~slow bandwidth,twistedpair wiling is used mainlylorlOwspeedtransmission.Data rates01up\0 a few Mbpscanbeachieved.One majordisadvantage01thetwis~edpairwire isits susceptibilityto interference and noise,includingcross-talk fromadjacentwires.

Theseeftectscanbeminimizedwith proper shielding. Becauseof itsrelatively lowCOSI, the twisledpairwireisthe mostcost eflectivechoicelor low trafllc requirements.

CoaxialcableIs the mostcommontyusedLAN's transmissionmedium.II possesses high capacity,agoodnoise immunity and a low errorrete. 11 provides a higherpanormance.

22

cansuppor1 a larger numberof devices,and canspangreaterdistances thanthetwiSl ed pair wire

Twotransmission techniques,baseba ndand broadband,can be employed ona ccada lcable.The main ditlerence isthat basebanduses digitalsignallingand supportsa singledatachannels, whereas broadband uses analog signafling inRFrange and supports multiple simultaneousdatachannel. In addition,baseband transmlsso nis bi-directional while broadbandis unl·directio nal.Add itional inlormation on LAN basebandand broadbandtransmissions cenbe foundinreference (37].

The transmission mediumwiththe greateSl bandw"ldlh andnoiseimmunity Isfiber optic.It has ahigher potenUalcapacitythancoaxialcable, anda number 01advantagesover bolh coanarcables andtwisted pairwire, includinglight weight,small diameter, low noise susceptibility,and practicallyno emissions.However,It has not been widely usedInthe past due to highcost, dillicuttyotfnstauaucnand othertechnical limitation s138).Fro m a technicalpoint of view, poinHo·point top ologies like the ringare feasible.Multlpo inl topologies likethebueareewith laps ateachnode arenot practical. With recentrapid developmentinliber optictechnology,the high cost for theliberoptlcintertecehasfallen into a level that makesthis mediumcompelltlve (51].ItIslikelythaifiberoptics becomethe preferredtransmission mediumlor LANs in thelutu re.

312INTER FACE

The inlerface between thetransmission pathand protocollogic cantakeseveral forms. It maybea singlecable television (C AlV) tap,infra-reddiodes for infra-r ed path, microwaveantennas,or complex Iaser·emiling semiconductorslorfiber optics .Some LANs

2 3

provideregenerative repeatersatlhei'l(erlaca,otherusetheiI1e11aceasbutlm lordata llowanG'orsirrllleconnections.

31=3pROTOCOl CONTRO l

The protocol control logic componentcontrols the LANand provides lortheend osereaccessontortenetwork.Details01the LAN protocolsare disoJssedinsee cn3.3.

314 END USERS

Endusers irdudeany dala communicaliondevicesthatcouldcomrTklnlcate over lhetransmissionmedium,they can be:

.ccmccers -terminals

•peripheraldevices

•sensors(te~raIUre,bJrnidity,securityalarmsensors,etc.) -telephones

3?TOp OLOGIES

LANs areoitencharacterizedin terms 01 their topologies,threeotIhit most commontopologiesare shownin ligure3.3.

24

The buslopologyischaracterized by theuse 01amu~ip leaccess.broadcasting mesum.Becausealldevicessharea commoncommunicaliorlSmedium, only onedevice can transmh at anyinstan!.A stationwishing10lransm~waitslor its turnandlhensends dataout ontothe busnetwor!tintheform of a packet,whichcontainsbolhme sourceand cesunancnaddresses as wellas the data. Each statenrnon ~orsthe transmisslcnmedium

Figure3.3.local areanetworfc lopologies

Theringtopology consists01a closedloop, wijheachnodeanacneo to a repealing element Datacirculate aroundthe ring on aseries 01poin(-\t,JOintdatalinks between repeaters. like thebus lopology, Ittransmitsa packetcontainrngsourceand destilalion addresses and cata.Aslhepackelclrcutates,the desllnallon r..xle copieslhedata Intoa

25

local buNer.Thepacket continuestocirculate untilItreturnstoIhe source node,providing alorm 01acknowledgement.

In the startopology,acentralswitchingelement Is usedtolinkall the devicesInthe netwo/1(.A eteucnwishing to transmitdatasercs arequesttothe cerural switchlor a connectionto a destinationetaucn.andthecentralelementuses circuitswilchlngto establish a dedicatedpath between thetwo statcns.once the circuitis setup,dataareexchanged betweenthe two stationsas if theywere connectedbya dedicaledpclnt-Io-pnlntIlnk.

33!ANS PRQTOCOI

The most commonaccess protocols lor LANs are categorizedin figure 3.4in according10theirsignallingtechniques. Twoofee mostpopular access protocols. carrier sense multiple access (CSMA) and tokenring are discussed here.

Figure3.4.Local area netwo/1(accesscontroltechniques

26

;1;11CARRfER SENSENETWOAK

IncarriersensenetworltS,a station astens tolhe transmissionbetcresending a p.:ICket.It canthenbase~sactionon wl\etherthechannelIsbusyornot.ProlooOlSinwhich staucesliste.'lora carrier (I.e.atransmission)andadacoording!yarer.anedcarrier sense prolocols.

Allorthecarrie'senseprutocetsdiscussed beloware based onme lollowlng assumplions(39j:

1lAJlpackelsare oiconstal'lllonglh

2)Thereareno encrs.ekeepC

n e se

causedbycollisions 3)Therais no captureelled

4)Thetaoccmdelayaltera coaisionisuniformlydislIbutedandIslarge corr.paredtothe packetlransmissionlime

S)PacketgeneraliOnanempls(newonesplIsretranstrisslons) iorm a PoIsson processwith mean Gpacketsperpackettime

6) A

staten

maynoltransmil andreceivesilTlJllaneoosly 7)EaChsretcncansensethetransmissionsof aDetherslatlons

8)Thepropagation delayIssmallcofTllared 10the packetlransmissionlime,andIdonlical lor all statcre

9)Sansing the state01thechannelcanbe done Instantaneously

27

:,32CSMA PROTOCOl

3321 ].p ERSISTENT CSMA

The1·perslstentC$MAprotocolisthe simplest carriersenseprotocol. Inthis protocol,aseuenwithreadydatasensesthechameland proceedsas lollows.

1)IIthe channelIssensed busy,the stationwaeeand continuallysenses thechannetuntilIt becomesIdle.

2)WhentheereucnsensesanIdlechannel,~transmits thedata.IIacollisionIsdetected, thestationwa~sa randomamounlof limeand repeatsthealgorithm

The protocolIscanedI·persistent, because thestallon transmitswithaprobability 011wheneverit fltldslhe chaMelldle.

Thepropagat!ooldelay(t)has animpol1antelledonthe eenermaoce 01this protocol.ThereIsasmaI chancethat;"slaneraS!a.lion(AIb&gtns sending, anotherstation (8) wilbecomereadytosendandsense the channel.\IA'ssignalhasnotyet reached B, thelatterwigsenseanIdle Chamelandwillalso beginsending,resulti'lginacoliSkm.

EvenifthepropagationdelayIszero,collisionwm SillOCOJr•Aand B become ready In themiddle01a thirdstation's(C) transimlssiOn,bolhwillwail unlil lhe Iransmission ends and thenbothwill beginIransmittingsimuftaneously,cOI~ls lonthuslakes place.

28

33? 2NON_PERSISTENT CSMA

The non-persistent CSMAprotocolis anIl1l'rovedt-parslstera CSMA protocol.

In thtsprctcccl,a slation sensesthe channelbefore sending.lithe chan""l.•

-ensee

idle, thestationsendsthedata. However,ifa lral'\Smisslonis alreadyin progress,the stationdoes ret continuallysenseIhe channel lor the purpose 01seizingit immedialelyupondetecting theend 01crevcuetransmission.Instead,Itwaitsarandom periodoftime and then repeats thealgorithm.This algorilhmgives a benerchannelulilizatlonand longerdelaysthanthe 1·

pllrsislefltCSMA.

3323 P-PEBSI$TENTCSMA

Unliketheprevioustwoprotocols, P·perslstentCSMA appliesonlyto the slotted channel. Inasloll ed channel,timeIsdivided Into discrete Intervals, each Interval correspondiflQto onepacket. Aready statlcnsenses thechannel andoperatesas follows. 1) lithe channelisIdle,it transmits wilh a probability01P.With a probability01

a ..

1·P, it defersuntil the nell5101.If that slotisIdle, Iteilher transmllsor delersagain,withthe probabilitiesP and a,respectively.This processIsrepealed untileithertbepacket bee been lransmittedOfanotherstationhasbe~ntransmitting.Inthe lattercase,it acts as Nthere has beena collision(ie.it wails a randomamount of lime and startsagain).

2) If the stallon iniUallysensesthe channelbusy, Itwaitsuntll the nell slot andappliesthe abovealgorilhm.

The performances01thesethree CSMA prolocols,as wellas someother well known protocols,are plotted as thechannelutiDzaliQn (S) versus load(G) curveInIigure3.5(39].

Theload Gis defined as the meanarrivalpacket (aPoissonprocess)perpackell ime.

29

Figure3.5.Compar1slon of the channelutilization (S)VS load (0)lor various protocols1391

33 2 4 CSMAWITH COll iSIO N DETECTION tCSMA/COI

CSMAlCDIs themost commonlyused mediumaccesscontrol protocollor bus topologies.In this prciccct,anstationscontinueto listento thecablewhiletransmilllog.If a collisionIsdetected,theyImmediatelyterrrsnetetransmittingthe packetandtransmita brief jamming signal10ensurethat allstations knowthere hasbeen a colllsion. Aller Iransminlng the jammingsignal,eachstationwens arandom amounl01lime, andrepeats the algorUhm.

Thisstrategy greatly reducesthe errcorrtolUme wasted ondalacollision

Ethernet,theoriginalbasebandversion 01CSMAlCD, wasproposedbythe XEROX In 1976136J.Each ememers stationmcnncrsthecable(ether)duringUsownIransmisslon, terminatestransmission immediatelyifa collisionisdetected. The operationof the

3 0

ememetis illustratedinligure3.6.At lime

to,

a station has (ust finishedtransmitting its packet.Any other stationhavingareadypacketmaynowattemptto send.Iftwoormore stationsdecidE! to transmitslmuhanecusfy,therewlll bea collision.Eachwill detectthe COllision.abort itstransmission,wait arandomamountof time, and try again,assumingthat no otherstationhasstartedtransmittingIn the meantime.

Contentio n

~o ~ ' ~

B DD DB ODDTIB D B

--

Contention Interval

Tim9---+-

Figure3.6.Ethernetoperation

....

Idle

IItIstheelld-to-erd propagationdelay, itwlll take a maximumlimeotee10detect acollision. Thecontention intervalis tberercreequivalent to2t.This isthe worst case time tora station 10realizetMI a collisionisdetectedaltera packetis senl.

It isimportantto realizethatcollisiondelection is ananalogprocess.The station's interlacehardware mustlisten to mecablewhile itis Iransminlng. II whatII readsback Is dillerenttram whatit Is putting out,itknows a

ccuecn

Isoccurring.

In!igure 3.7,the channelefficiency01anethemetisplotted againstthenumberof readystalionlort'"51Uanda dalatale0110MbpS(391.

3 I

1~ 12 ,,'~

^{1; 8}

Numbetof Illlionl 'Wlutd

Figure 3.7.The channeleffldencyvsno.ofllIadyslatlon ofaelhemet(391

3325CO!!15 1ON-EBEEpBorOCQt5

AlthoughcoDisionsdonol OCQlr on the ethemet oncea slatlonhas seiZed the Channel,theycanSlilOCQJrdutingthecontertion period.Thesecollisionsdoadversely allea the network performance,especiallywhen thecableislongand thepackets are small.

Some protocolsdoresolvethecontentiontorthechannelwithoutany collisions.

These collision-freeprolOCOIsallrequIresomekind01reservallonscheme10 determine whichstaten will gel access10Ihechannelnexl. Areservancoperiodandsome prioritylunctionsareusuailly Invovled wijhtnese protocols.

32

Bil map protocolIsone suchcoDision.freeprotocol. Inthis protocol,each reservationperiod consetsofexacdyNslots.Ifstation 0 hasapackel tosend,Itransmitsa IoOic hiohckJMolhe nrstslot(0). Noother stationIsallowedtotransmitllJringtlisslot.

Reganless01whatstaten0does, station 1 gels lhechancetotransmit a "1" duringslol l when):hasapackettosend.Ingeneral, stal il)n

I

mayanrourcethelactthalIhasapacket IOsendby lnsertlngaM1Mlnta1he slot ~Aher aBNSlOts havepassedby,eactlstal lonnas a complete knOwledgeregardi ngwhichstalionswish10 transmit.Attha tpont,theybegin transmittinginnumerical o((ter(seeflQure 3.8).Since everystal ionagrees onwhichSlal ion goesnext,there wiDneverbeany collisions.Alterthe last readyslalio nhasIransmiUedIts pacl<.et,anotherNb~reservation periodbegan.NolethatIf aslalio n becomesready

PJ$I

after its biteicthaspassed,itmustremaIn

ssent

until everyonehashad hissay andIhebRmap

«eservaucn slot) comesaround aoaln.

Figure3.8.The bitmapprol ocol(N_ a)

Themaindrawb ackal lhisprotocolis thatunderlowloadcondilion,a state nmust alwayswaitlorthe currentscan 10be IWshedeeicreitmay transmit,therebycreatingalotof overheadforIhetransmission. The Iradeoff IsbetweenIhe overheadreservatio n period andIhl$ collisionlime. Onespeclalcharacl erlstic 01thisprotocolistheasymmetrywlth respectto stationnumber;highnumberedslalionsgetbeuerservices thanlowI"llmbered Thischaracterisllc canallowpriority functions tobe~emeflledonttlenetwortl.

33

;} 3 3 RING NETWORKS

A carriersensenetworil is basically a passive,electricallyconnectedcableonto whichall stationstap,whereasa ring nelmrK15actuallya series0' pclnt-io-polntcables betweenconsecunvestations.Also,the

oterteces

usedon ring netwcrxs areactiverather thanpassive.

A majorIssuein the designandanalysis01ring networksIsthephyskal lengthata b~.IItheelatarete 01the ringisAbits, abitis emittedevery11R~,wilha signalpropagation speedofXmeters~,eachb~occupiesXlRmeterson thering.

Anumberof differentalgorithmshave been proposed forromrollingaccessto the ring.In thenextsection,tokenring, themostcommon ring prolocol,Isdiscussed.

3331mKENBING

ThetokenringprotocolIsbasedon the use01aspecialbit pallern, cal1.ldthe loken, thatcirculatesaroundtherina[28].

When all stationsareidle, the token islabeled as a 'tree"token(lorexample.

111111111.A stationwishing totransmitweaeunlil~detectsthe tokenpassingby.thenauers lhe ::>ilpaltern otme token from"free" to-"busy"token(11111110j. lmmediately aller the thetoken hasbeentransformed,the station making the transformationispermittedto begin transmilling.

34

Each arrivingb~'rom the netwo rk muslbe stcredIn aIocaJbuffH,and thena new bll Isgenera.l ed.There fo re,one bll delayisinlXJse dIneach ringInterfa ce.Iftherearemany etencnsonthe ring , the lolaleffectof these1b~delayshas an l,.,portantImpactonthe perlOfmance olthering ,Anoth erImplicaikm olthe lokenring designIslhattheringitseU mUSIhavea somceotdelaytocontainacomplete token tocirculat ewhenallstationsare idle

RingInterfacesopera teintwomodes:listenandtransmit(seeligur e3.9).Inthe usienmod e,theinpu tsaresimply copied10the outputwith a1bitdelay.Intransmitmode, whichIsentc-eeonly after th e lol<enhas been seized,theInterlac e breakstheccenecuen betweeninputandoutput,enterillgits owndataonlOthe ring.Tobeabletoswhchtrcm nstenmodetotransmitmodeIn1bittime,theinlerfaceusuallyne eds10buffer oneor more pack etsKsellrathermanhaving to lelch the m lrom thestallonIn ashortperiod01tim e.

1 Bit Ring

~~

etaucn^To staten^From

I.)

To From

station station

~)

Flgure 3.9.(a)ListenMod e (b)Transm~mode

35

Asbi1sthathave propagatedaroundlheringcomoback,tReyareremoV9d!romItIP.

ringbythesender.Thesendingalalioncanell hersave Ihem, 1O

comw e

with1MorigiN!

dala10mC)I"iorring reIabiIity,or dscardItem.ThenthesencI&rwIIJegenerale the-'r&e' token k)signalthat themgisnowkrie.

WhentrafficIs

1IItt,

IhelokenwinspendmostoflhelkneIdlydrcuIalingaroun dthe ring.Occasionally,astationwillconvertit10abus~token.fGlOwedbyapack elandthena newtoken. However .when Ihe lrafflcishea'o')',SOlhallherelsaqueuealea chslalion.as soonas astationfinishesits Iranr.rnlss ionandregenerat esthefre etoI<en, thene~stancn downstreamwilseeanclremovelheloken. Inthis manner.lhepermission10 send rotetee smoottllyaround thering,Inaround-robin fashio n.

;):4'AN STANQARDS

Thekeytothedeve lopmer101theLANsmartcelIstileavalabiityofalowcost intetlace.TlisreQuiremer1asweDast he ~dyoftheLANsp rolocols.dida\eSaVery l.argeScaleIrtegr ali on(VlS1)soUiOn.Howeve r,lrtegraledClrc:ult(leimanufacturo rsare reluclanttocommit the necessaryresourcesunless !hereisahighvolImemarket.ALAN sla~rdwouktensu rethatvolumeandilllbstalsoenable equip mer1of avariet y 01 manufaCiurers10intercommunicate. Thisistheralion alebehindIhlllEE E802standard whichwasdevelope dbytheIEEEcomm ~teeon LANs In19831401.The IEEE 802 standard is Intheterm ofathre e-layer co m municaUo nsar chitectufe(s e ellgure 3.10).

Theselhreelayers,knownasIogcallink control,mediumaccess conlrol and physica l,are eqllivalentto lhe functionality oll ila lowes! twolayers(dalalink andphysical)olllle InternationalOrganizalionlor standard lzalion(ISO)relere nee modelwhiCh d~elopedb~

theCCITT139~

36

ME DIUM ICCESSCCNTfU

PHYSICAl

Figu re3.10The IEEE e02standard

The logicallinkcontrol (LLC)layer provideslor theexchangeofdal abetween servceaccesspclnts(SAPs),whicharemuk,plexed overa singlephysicalccnnectontothe LAN.TheLLCprovid esIOfboth accnnecuosess.datagram-likeservice,anda connection- crleotedvlrtual-circua-Hkeservlce.

AIthe mediumaccesscontrol layer,therearethreestandards:CSMAlCD,token bus andtokenring,DetailsontheIEEE standardscanbefoundInreference[40].

The basicprinc iplealthaLANtec hnobgy has beenIntrOOuted.Twomajor LANs, the CSMAandringnetworksha ve beenreveweo.VariousLANsInchJdlngetnemetand token ring, aredscussedinthis chapter.

37

Allthe CSMAnatworlls(includingelhemel)aresimple andeasy10expandsince allstercoe are passively tapped toacommonchannel.Onthe otherhand ,therir~,lelWOrks providea collisionlreetransmission.Majordrawbacksonthe ringnelwori<InckJdeItslackof expandabllityand lowreliabll~y112].It cnestaten

tans,

the wholenetworkwil lalso 00 down whereasthe CSMAna!wOrkwUlcontinuetooperals evenwhen soma of theslallons tail.

The concept01priority junction was alsointroduced(section3.3.2.5).The priority functionisthemajor concernInthis studyfor theIX'lwersubstallonprotect ionandcontrol,

3 8

CHAPT ER'

THESYSTEMARCH I11'CT U REOFTHESU BSTATIONPR011'CTI O N ANDCONTROL SYST EM

Thaappllcalionorm1crcproce sSOI'S makes itpossibletoccnslderadistributed processing method10 addrt s.sthe problem01substationprot ection and contrcr.The advanta ges01local arean~shave alreadybeendiscussed Inth elastchapter.

Usi'lgthe rrcdularapproach,thelot alproces singrequirements01!heprOl&c:lion and controlS)'51emaredividedirdosub-tasks andaIocaled 10 0Mormoremicroprocessors.

Thesenicft:lI:I'OCessoBarelri:ed togethertofotma disll t lUledprocessing ne1WOrkwith abeatareanetwolk protocoLThedist ibJled processi ngschemealsOprOlMes a lIexble andexpandablesystemconfiguration.

Theconc eptandthestruc ture ofthedistributedsystemarchileclureare discus s edInthischapte r.Thefunctions ofeach elementInthe $ystemare also review ed. Asmenllonedearlier inchapter 1, numerousresearchworkshave been reportedin1his area!3·14).Twoolthesestud ies,lheWestinghou se's WESPACsys1em 110,11)and Noo r'sASCDproloco l(12) areused as a guideline10 stud1 the the functionality ofthesyste merchitect ure.

39

41SYSTEMABCHITECTlIBE

Todete rminethe afchllectufes ofthesubstationprotectionand controlsystem.

~Is urst necessarytoecnsderthecriteria ollhesystem. SpecniCally, the cnerts which anect thesystemarchitec1ure are;

- volumeofdatafklw -res ponse time -syslemaveilabUity

Thedata lklw 01a substalionIs summartzedlnfigure4.1.A large amo unt01 dataisInijlal edinlheswilChyarclwhere meassremeredevk:estakeInstantaneousvalues 01 currentsandvoltages.These analog eeumustbedigitizedandtransmittedIromthe switchyardtothe controlcenter whereprocessing cantakeplace.The amountof data trans lerIntothe controlcenter islarge whilethenumberof conllo] signalssentbacll 10 thesw~chyardiscomparatively low. Thereisalsosomedata1I0wfromthe remote central complllerwhichmonitorsand controlsthe cperatlcnsofsubstationandissues ccnnct messagebacktothe controlcenter.

Figure4,1.Data llow insutsiato n(S)

40

Thecharmeristlcs01 suchdisi ri b ullon 01dala 110w implyahlerarc hleal archilectureas showninfigure4.2.Beginn ing at thelowes!leveltheeleme~sk1 lhe hiera rchyare:

•dat aacquisitio n unils (OAUl

-micrcprccesscrcester

.dat acommunlcallonsnelwor1l

-slalloncompu ler

OATACCt.lMUNCATIONSNETWORK

Figure 4.2.Thehiera rchical arc hitecture01the$PC sysllm

41

Thelol\owlngdescribesthefunctionofeachelement

..1 1nATA AC Ql,nSm ONurn slQAtu

Thedataacqu~ionunitIstheIntetlacabetween the POWtN' apparatusandthe crcreeucn and control!;ystem.OAUsare instafleclIl'voughoultheswilch~ ardlorthe dlgitalprotectio nandcontroleeneme.IttakesInstantaneoussa"llles01AC voltag e and curre nt signals from potentlaltr anslormers

(pn

andcurrerllranslonners

(en.

alongw~h the statusof contactInputs such as thebre aker state Indicator.The analog sampleIs digitizedandsenttothe ne.1 level of thehierarchy,the microprocessorc1uster,lor processingthe prolection andcontrol functions.

Inaddition,DAUs arealsoconnected10 controlcircuitsoflhe poworapparatus lor 1rf'4:)lementingcontroldecisionsorreques ts. .iatadatIMghefleYelsofthe hierarc hy.

..1? PJICSOp S <X;ES SQ RCII ISTfA(MC )

TogetherwiththedalacommunicationnelWor\(,themiCtoproceSSOl'" cluster mak esup them1croco~l ernetworkresponsibloforprolection,conlrol,recording and monitoringfunctions 11'1 real·l1me. The clusterconsists 01 a number01 microprocessors (ormicrocomputers),memory,and interlacestolhe DAUs.

High· speed protecllverelayingaou contro l programsthatresidein the microprocessor,eveuetesequences ofincominginstanlaneoussampleslromthe DAU

42

to locale power system faults,mof'litorand controlstalusof circuit breakers,switches and olherapparatus.

In general,the microprocessorclusterperforms thelollowinglunctions:

-loltatessamplingrequestsor controloutputto the DAU.

-receivesinstantaneoussamplesIromthe CAU.

- executes protectio nprograms 10 locate tault, and Informsthe respect1ve control cevces to tripthe correspondingcirculibreakersand alarmthestalloncomputerwhena taun Is detected.

•monitors and ccntrcrs slatus ofbreakersand switches andtransmits them to the stationcompuler.

•records instantaneousvaluesofvo~agesandcurrentsduringa faultand transmitsthem to the stationccrrexnerfor oscillography.

-receives reqllOsts for bothmanualand automatic controloperationsfromstation computer or other microprocessors In the cluster,and transmitsthem to the appropriate DAUs.

413 DATACOMMtJNICATIONSNETWOBK

The datacommunicationsnetworkisa multi-dropbuslocalarea networkwhich inlerconnect s anthe microprocessorsandthe statio ncomputer.It providesdatafransler betweenand withinthemic roprocessor clusterand the stationcomputer. The protocol. topologyandthetransmission media 01 thenetworltare selectedbased on the localarea networktechnology discussedearlierinchapter3.

4 3

414 STAT IONCOMpUTER

The stationccrrcuter provides a centraldatabas e controlpointlorthe entlre subslatlon. It collectsand stores systemInformation Ircm ihe microprocessorcluster, vialhe datacomrtwnlcatcnsnefwcrk.

The station computerconsists of a cluster of microprocessors mat provide control fu nctions such as mainla lnlngthe central evetendata base and interlacing10 thecursloe world,likeIhe externalcontroldevicesand the SCADA system.

42 WE WESpACSYSTEM

The WESPACsystemisthe direct result of a series 01projects whichwere supported byth e ElectricPower Research Instllute{EPRI) and developed bV WestinghouseEleclrlcCorporation for an Integra l&d prot ective andcontrol system ina transmiss ion levelsubstation.The objectiveof these studieswas 10 employrecent electronics techno logy toreducethe fllelime costsof subslatlon prol ecllon and control functionswhile achievingperlormance and lealurebenelits01

new

digital approach.

The WESPACsystem provides prote ction,·.:onlrol. and monitoring et the substatio n . WESPAC, aninlegrate d,modu la rsystem,ulil!zescluslers01 multiple microprocessors, mulliplexed digitalccmrrerucetens, and fiber optic dala transmission media In the place 01 the convenllonalcomple ment01discrele relays, instruments, andcont ro ls with theassociatedinterconnectingwiring.

44

Asmentionedinchapter1,anumberat testtrials have beensetup by the Public ServiceElectricandGas Co. (PSEBoG) of NewJersy.Thesetestshave demonstratedme abilily of the WESPACsystem tow~hstendthe hostHeenvironmental lnlhJences01the sunsratcnwhileperlorming its tasks.Res:..ltsofthese'ieldtestswere equalto orbetter thanthe convenlional system.

The WESPACsystemprovidessome01thl!protection,control andmonijoring lunctionsthathavebeendelinedincheerer2.A briefreview01the functionaldetajaof WESPACsystemprovidesthe basislorde~JgnenvlronmenlsInthe proposedresearch atthismeals.

4 2tTHESYSTEM ARCHIT ECTURE

The WESPACsystem employsathree-level hierarchyshown In figure4.3[1OJ.

Theelementsof this three-levelhierarchicalstructureare:

- cea acqulsltan units (DAUjwithserialdatalinks -proteClion clusl er( PC)

-serer

II1Jltidrop dala highway -station computer

.1.2.11 D ATA AC OUISITION UNITID AV I

ThoblockdiagramofthoDAUisshown In Ilguro 4.4. Each DAUcontains:

.ccrrsronc euc ns ccmrcner -high-speedanalog Inputinterlace -sams Input interface

- optional eiecrtceuc optical(ElO)ccrwerter

4S

..

~

f ;.

~ ~

~ ~

3

i

CONTROL CENTRE

DAU·DATAACOUISlTJONUNli 00· ElECTRICAUOPTICAllNTERFACE PC·PROTECTIONClUSTER SC·SUBSTATIONCOMPUTER

~ ^I

^DAU

^I

^SWlTCHYAAD

POWER APPARATUS ANDCONTROLCIRCUITS

wm>

=>lECOONS TO SUBSTATION EOOIPMENT

DATA ACQUISITION

CARDS TERMINATION CAf<lS

Figure4.4.The DataAcquistion Unit

The communication conlroller receives and transmitsdataover the serial data linkand controls thetrow ofdata on the parallelWestinghouse distributed inputfoulpUl bus(0100).WhenasychronizaUon messageisreceivedfrom the protection custer, the controller initiates thesamplingand holding01the processlor analoginputs,gathers statusinputs, convertsthe analoginputsInto digital form,andsends allthe information in sequential messageform uptothe correspondil"gprotectioncluster viathe serial dalalink.

ThreeIf0cardsare attached 10theD10 B.Thehigh speedanaloginput(AI) card has sample andholdcircuit thatcansarrplea group01sixACInputssimuhaneously evE!1Y1.04rns. in synchronismwith all otherAI cardsinalilhe OAUs of lhesystem.II

47

alsoprovides anti·aliasingmees. andanAIDconverter withdynamic range (16bits) and a conversion lime 0160 I.ISperpoint.The contact input(el)

cardcertcrms

1so1al1on, level shilling and dlgilalcontactdebounce logicfunctions. II can recognIze status changes In 1ms.whnerel9CIing conlactbouncelor up to 32msafter theclosure.The contactoutput (CO)cardprovides output relaydriving with ahigh degree01SllClJrity. H energizes control circuitsusingSeR'sorrelaycontacts.

4 2 1 2SEAIA!pATA LINKS

The serialdatalink provides thecommunicatio nsbetweenDAUs andme protectionclusters. The lransmission mediumiseitherco-3)fialcable (forCAUslocatedin Ihe control room)or liberoptic cable(whenIheOAUs are locatedin the switchyard).

Modems at eitherend 01dalalink modulateanddemodu latethesignalusing frequencyshift keying(FSK)with 3MHz carrier.Datarateis1Mbps.The link network protocolis a subsetof IBMsynchronizeddata linkcontrol(SOLC) ••ISO standard3309 When fiberoptic mediumisused,erececai-io-ccncatand optical.to-electricalconverters me provided

The protectio nclusterconsists of clustersof Intel 8086 family 0116 bits microprocessor,memory, and communicationscontrollersas showninligure 4.5.These elements are connectedto a common parallel data bus,the

'''0'

Munlbus. Nonvolatile erasableprogrammable read-only memory(EPROM) holds protection andcontrol programsloreach processor,whilerando m access memory (RAM) oneachcard holds dynamicdata.Much of the RAM Is shared overthecommon bus.An additional

48

nonvolalilememorycardholds seningsandrelateddatawhich maybealtered Inservice, yel must be retainedwhen thePCIs deenerglzed.Communclationscontrollerscarry onthe data transfer betweenlhePC andthe associatedDAUsollerlneserialdata links, or among thestation computerand otherpeseverthe multi-drophighway.

DATA HIGHWAY

SERIAL SERIAL

LINK lINK

Figure4.5.'rrecrctecucnceeter

Figure4.6.Thestationcomputet

49

4214 DATA HIGHWAY

The eete highway, amujtl-dropbusnetwol1l.,provides communlcatlons between Iheprotectionclustersandstatlon computer.n ccnststs cra co-axlalceble modemaleach drop.In normalcperaucn,thestalion computerperiodically polls each protection cluster over the data highway.The highway also actsas a comm.micalion mediumbetween protection clusters in backuprelaying situations.Eleclr ically.the equipmentis the same as Ihal used lor Iheserial datalinks.Sinceboth source and destination are necessary10be specified inamutll-drop nelwork, asubset ofthe highleveldata link control(HOLC) - ISO standard3309 Is usedasmelink network protocol.

4215 SIATlO NCOMpl!TFB(SC)

The staticncomputer,lil<e theprotectioncluster,consists 01a cluster0116bil microprocessors(see figure 4.6).Itmaintains thecentrat systemdatabase and prcvldes Interlacesto state noperatorsthroughme man machine interlace(MMI)and 10 system operator and protectionengineerthrough the SCAOAsystem.

At the SC, the MMIconslsls a19 Inch colorgraphicCRT.an inputkeyboard with specialpurposeandalphanumerickeys,and a printer.The operalo rcan use the keyboard and CRTto displayalarmorsequenceoreventslisting,10acknowledge alarmsto ccnnctcircuitbreakers and switches.toview OSCillographicneces. 10check the status 01 WESPACsystemequipment.\0change setting,and other functions.

Stationccmaeterprogramsandhardwaremenacesalsomake substation data

50

available10the ul ilily',energy management system and to remote protectionor mainlenanceengineeringlocations.

4??SY STEM OPfRATION

Synchronizationoflhe samplinghstanlindiUerenlCAU's isa cmital reQUirement01the WESPAC system.ThisIsachievedby Irackingline frequencyand dividing each cycleinto 16 Intervals.Atthe beginning 01eachsynchronizedsampling rorerver.eachprOlectlOnclust er sends a message to lis DAUsthrough the corresponding serialcata links. TheCAUsimmedialel ysample and hold analog values. The lnstantanecussamplevalues 01each AC signal andstatus input are dig~ iled,lorm'lted,and sent10lheprctec:lion clusters.

The comm..rnicationconlrollersalthe cksstersdeposillhesedatainpredefined shared-memorybullers.When an data have arrived, the prctectlcnprograms commenceprocessinglhe newInformal ion. The OUlputsproducedbythe proled ion programs are conlrolsignals which are sentto the CAUs 10initialebreaker operal:ons,pluseventmessafles.osc~lographicdala collectedduring laulcona.ions, and generalupdate olthtldatabase,all 01 which are sent10 lheslallon compuIer lor storage ordisplay.

The staten computerreceives and storesatllhis information andIn turn sendsit, eilhar automaticallyor onrequest,10rerrcte operators. It alsodisplaysinfo rmation Ioca~yand allows thelocaloperator10 inili ale manualoperalions.

5I

42 3 SYST EM HEARTBE AT

A central 960Hz sampllngclock, connected 10 allof theprotection clusters.

provides COoOrdinatingpulseswhich are communicatedover the datalink to every OAU.

Redundant clod<s andclock-pulsesignallingpalhs areprovided.EachAC signaland states point in thestacnis sampled atthesameinstant.Thesamplinglmerva\151.04 ms whichcorresponds to eKactly1 sample per960Hz powercycle.

The centralClOck canejthercperate ata flxed frequency,or cantracsthe station- service power frequency(whenavailable) to malntalnexactly16samplesper cycle regardlessat frequency9KcursiOns.Thereisno requirement to maintainanyparticular phase relalionsh ipbetween the samplingprocess and Ihe sampledAC waveform.No zero-crossing cetectcnisperform ed. Eachctuster alsohas an internat timing reference sc thattiming-crockfaiture will not disableanyrelaying or crilicaloonlrol nmcncn.The data highwayoperates at a much slowerdatarate. There are two categories 01Interchanges, occurring wkh intervals ot 0.1secand1sec.

424 RfDUNDACY

The WESPACsystemulillzes a cross-linking 01OAUs,thispermitsthe sharing of OAUdala amongPC's lor severer ecoes. Inaddition,each PC intha WESPACsystem can executeits relaying taskswithout the data highway connected oroperaucnal.

protectionlormultiplezones isrotdependenton a single hardoNa reelement

52