Jointless-track-circuit-length

JointlesstrackcircuitlengthN.NedelchevI1Abstract:Amathematicalmodelofajointlesstrackcircuit(JTC)ispresented,whichallowstheshuntsensitivityofeithercompensatedanduncompensatedJTCstobedetermined.ResultsareshownforthevalueanddistributionoftheshuntsensitivityobtainedbythemodelatdifferentvaluesoftheJTCparameters.Thepointoftheworstshuntsensitivityhasbeendefined.Acriterionisintroducedfortheadmissibilityofthetrackcircuitlength.Basedonthiscriterion,themaximumlengthoftheJTCisfound.II1IntroductionPhysicalinsulatingtrackcircuitjointshaveprovedtobeanobstacleforhigh-speedmovement,aswellasamajorreasonformanyfailures.Toovercomethesedis-advantages,jointlesstrackcircuits(JTCs)wereintro-duced.Atfirst,shortJTCswereusedasoverlaytrackcircuitsforlevelcrossingcontrol[I,21.LaterJTCswereappliedtoautoblockandcabsignallingsystems.Nowalmostallmajorsuppliersofsignallingequip-mentsproposetheirownjointlesstrackcircuits[3].OneofthemainproblemswithJTCsisthetrackcir-cuitlength.Toincreasethelength,centralfeedingandreceiversattheends[l,41areused,andperiodicalreg-ulationofthetrackimpedanceisbyaddingofcapaci-torsconnectedbetweentherails[2,5-81.Toprovethenecessityoftheseapproaches,aswellastoappreciatetheireffectonthetrackcircuitlength,themaximumtrackcircuitlengthhasbeenfound.Thisproblemhasbeensolvedexperimentallybylaboratorycircuitmodelsconstructedusingdiscretecomponents[S-lo].Asthelaboratorymodelssimulateonlysomeoftheraillineparameters,theobtainedresultsareapproximate.Differenttypesofsimulatorhavealsobeenused[8,9,111:theyareconvenientforstudyingtheraillineasamulticonductortransmissionsystem,butdemonstrateworseapplicabilitywhenthetrackcir-cuitistreatedasalineconditionsensor.Therehavebeenstudies[2,121employingthetwo-portnetworkmodellingapproachtostudyJTCs,buttheyarenotcompleteanddonotprovideexplicitandapplicableresults.Itistheobjectiveofthispapertopresentanimprovedtwo-portmodelofaJTC,andapplyittoanalysetheshuntsensitivityanddeterminethemaxi-mumlengthofthemostfrequentlyusedJTCs.OIEE,1999IEEProceedingsonlineno.19990213Paperfirstreceived23rdJanuaryandinrevisedform6thJuly1998TheauthorwaswiththeTechnicalUniversityofSofia,andisnowwiththeHigherMilitarySchoolofTransport‘TodorKableshkov’158,GeoMilevBlvd.1574Sofia,Bulgaria2MathematicalmodelofJTCMostoftheJTCscanberepresentedbyFig.1whereZinpfandZinP,,aretheinputimpedancesoftheequipmentinthetransmittingandreceivingends,respectively.Thedistinctionbetweenthedifferentkindsoftrackcircuitisintheelectricseparationjoints(ESJ)schemeandinhowtheraillinepartsareincludedintheESJs.Forthisstudy,theESJlschemeisassumedtorepresenttheportionofthetracklinelocatedtotheleftofthepointwherethepowersupplyequipmentisconnected.ThetwotracksarecloselytiedatthedistanceIleftofthatpoint,andacapacitorCJisconnectedacrossthetracktocompensatefortheinductivecomponentofthelineinputimpedance.Actually,bothCJandtheshort-circuitjunctionaremorecomplexcircuitswhich,forthesignalfrequency,representequivalentcapacityandzeroresistance,respectively.ESJ2isassumedtobethesameasESJ,andislocatedsymmetricallytotherightofthereceivingend.ThemodeldescribedisdirectlyapplicabletotheFrenchJTCUM71[5,81andBritishTI21[4,91fornon-electrifiedsections.ItcanbeadaptedtootherJTCswithminorchanges,withtheexceptionoftrackcircuitswheretheshort-circuitbondbetweentherailsisS-shaped[l].railline-ESJ2rL‘iJ2inp.rFig.1JoindesstrackcircuitmodelToevaluatetheshuntsensitivityofthetrackcircuits,thekSllcriterion[12,131isused;thisisdefinedasaratioofthecurrentsinthereceiverbeforeandaftershuntingforcriticalmodecharacteristics.Sincethesourcevoltageisthesame,kshisexpressedasaratiooftherespectivetransferimpedances:ksh=IZt.,.shl/(wztT.nl)(1)whereZtT.n=L4nz2np.T+Bnf(cnZznp+Dn)Z&t(2)Ztr.sh=AshZznpT+Bsh-k(CshZznp.~+Dsh)Zinp.t(3)Thetrackcircuittransferimpedanceisaratioofthesourcevoltageandthecurrentattheendoftherailwaytherailwaytwo-portnetworkcoefficientsInthecasesofafreetrackcircuit(e.g.normalmodeofoperation)andanoccupiedtrackcircuit(e.g.shuntmodeofoperation).AccordingtoFig.1,thecoefficientsaredeterminedasfollows:tWO-pOrtnetwork.A,,B,,,c,,D,,Ash,Bsh,.csh,D,,hare69IEEProc.-Electr.PowerAppl.,Vol.146,No.1,January1999Authorizedlicenseduselimitedto:NORTHERNJIAOTONGUNIVERSITY.DownloadedonJanuary18,2010at05:51fromIEEEXplore.Restrictionsapply.Zoandyarethecharacteristicimpedanceandpropaga-tionconstantofthetrackcircuitinnormalmode,respectively.Z,istheinputresonatedimpedanceoftheESJwithaminimumvalueoftheballastresistance(rho,-~~~l~,~,,~).zistheself-impedanceper1kmtracklength.isthetrainshuntresistance.xisthetrainshuntposition.ZJooistheinputimpedanceoftheESJwithYhcc!=W.Nisacoefficient,takingintoaccountthevar-iationofthesourcevoltage,acontingencyfactorandthereturnfactorofthereceiver;itsvalueisusually15.-Thetrackcircuitdetectsatrainispresentwhenksh21(14)Thesatisfactionofeqn.14foraphysicaltrackcircuitisanecessarybutnotsufficientconditiontocheckthetrackoccupancy:theoccupancyinthejointzonealsohastobetested.TheshuntsensitivityanditsdistributionintheESJ,zonearetestedusingeqn.14.Theshuntmodecoeffi-cientsare(15)whereZimisthein