綜合輸電線路差動保護繼電器.doc

Abstract-This paper presents a new integrated protectionscheme for transmission lines.The concept of the integratedprotection is firstly introduced,in which a centralized protectionsystem provides the protection of multiple power plant or asubstation.A total integrated protection scheme based on currentdifferential protection techniques is further described.In theproposed scheme,the specially designed protection relays areinstalled at each substation of a network and are responsible forthe protection of every line sections connected to the substationbusbar.The current differential algorithms with multiple settingsare implemented into the relay to cover all the protected linesections.The scheme is supported by advanced communicationnetwork and standard.Studies show that the new scheme not onlyoffers the new protection features for individual power line,butalso provides the characteristics of integrated protection.Studiesalso show that the new relay offers more protection functions andsignificant economic advantages over the conventional currentdifferential relays.Index Terms-Centralized Protection,Current DifferentialProtection,Integrated Protection.I.INTRODUCTIONURRENT differential protection has been playing a majorrole in power transmission line protection1.Inparticular with the development of optical communicationtechnology,the current differential relay has become the mainprotection device for transmission lines at and above EHVlevel.In recent years,there has also the fast development inboth microprocessor and transducer technologies.This hasenabled protection techniques to be considered which wereimpractical in the past.Studies have found that the faultgenerated high frequency transients can be detected andquantified and open the possibility for developing newprotection principles and techniques.Considerable effort hasnow been devoted to research on high frequency transientdetection2.A number of new techniques have beenproposed and their associated measurement and signalprocessing techniques investigated.At the same time,thedramatic growth in signal processing power of relay platforms,and the availability of suitable communications schemes,hasZ Q Bo and A Klimek are with the AREVA T&DAutomation,UK.(e-mail:).Y L Ren and J H He are with the Department of Electrical Engineering,Beijing Jiaotong University,China.978-1-4244-1762-9/08/$25.00?2008 IEEEprovided a new opportunity to improve the existing anddevelop new protection techniques based on power frequencymeasurements.Research shows that information obtained frommultiple power plants and components can be used to derivenew protection principles and schemes3-14,which couldhave significant advantages over the existing protectiontechniques based on individual plant or component.In thisrespect,it has been found that the new transient basedprotection techniques not only inherit the capability to protectindividual plant,but can also be used to produce novelschemes for the integrated protection of a power network whensupported by modern communication technology.Recently,anovel integrated protection scheme based on fault transientdetection is proposed15.In the scheme,a centralizedprotection relay is installed at a substation and interfaced toevery line,through the CTs.The fault generated transientsignals are captured by the relay,the polarities and levels ofthe signals are then compared,from which the direction of thefault can be derived.The directional decision is thenforwarded to relevant substation relays and the integratednetwork protection and automation unit,the faulted linesection can be isolated by local protection or networkprotection.This paper presents a completed integrated protectionscheme.In the scheme,an integrated current differential relay,interfaced to the CTs on all of the output lines connected to thesubstation busbar and connected to neighboring substations atthe remote ends of the lines,is responsible for the protection ofall the transmission lines associated with the substation.Thecurrent differential algorithm with multiple settings to cover allthe protected line sections is used as the main protectiontechnique and the design of the new integrated currentdifferential relay is also described in this paper.Studies showthat the new scheme is not only use friendly but also economic,at the same time provide the features of integrated protection,which could represent the direction of future development inpower system protection.II.CONCEPT OF INTEGRATED PROTECTIONWith the development of digital technology,more and moreprotection functions for an apparatus(line,transformer,generator etc.)have been implemented within one protectivedevice to achieve a certain degree of integration.For example,a numeric line protection relay may have distance or currentdifferential function as the main protection,and directional andovercurrent functions,etc.as the backup protection.Howeverin this paper the term“Integrated Protection”is used to denotethe integration of protective devices for multiple powerapparatuses within the substation into one protective relay.Fig.1 shows an example of a complete integration,in which allprotective functions in a substation are integrated into onerelay to form a centralized protection system.There are three major redundant components in the system:(1)The Interface Unit(IU)is a measurement and control unit,which interfaces to apparatus through different types oftransducer,such as conventional CTs and VTs,opticalcombined sensors and electronic combined sensors.Theanalogue and digital signals measured are converted intooptical format and sent to the central protection relay throughthe redundant optical network.The IU unit also receives andexecutes control signals from the relay through the controlcircuit.(2)The Optical communication network interfaces notonly to critical equipment IU and the central protection relay,but also to a number of other equipment,such ascommunication gateway,Human machine interface and GPSclock,etc.The use of standard communication protocol for thenetwork will enable IEDs from different manufacturers to beeasily interfaced to the system.(3)The Central protectionrelay unit receives measurements from all locations in thesubstation through the network and information from otherrelated substations through the communication gateway.Therelay then performs all calculation to determine whether thereis a fault within the substation or on its associated line section.The relay will issue a trip command to open the associatedcircuit breaker through the control unit if a fault is detected.Fig.1.Diagram of a Centralized Integrated Protection System.III.INTEGRATED PROTECTION SCHEMEBased on the latest developments in non conventionalinstrument transformer and communication technology20-28,a total integrated protection scheme is proposed usingcurrent differential protection techniques.A typical powernetwork as shown in Fig.2 is used to demonstrate the proposedprotection scheme.As shown an integrated current differentialrelay(ICD)is installed at each substation busbar andinterfaced to the busbar VT and the CTs on each of linesconnected to the busbar.The current differential algorithmwith multiple settings for each associated line is incorporatedinto the relay to be responsible for the protection of all the linesections associated with the busbar.When a fault occurs on thesystem,for example,at F1 on line section Line1 as shown inFig.2,the relays ICD1 and ICD2 will detect the fault and sendthe measurement to its associated remote relays.Comparisonsbetween the measurements obtained from locations ICD1 andICD2,the current differential algorithms within both relayswill detect an internal fault on the line section and trip thefaulted line section instantly.The relays ICD3 and ICD4 willalso communicate with the ICD2 to determine whether thefault is within their associated line sections.Fig.2.Integrated Network Protection Scheme.IV.RELAY SYSTEM DESIGNFig.3 shows the block diagram of the proposed integratedprotection system with ICD relay units respectively andcommunication unit.As can be seen from the figures,the relayunit basically consists of four blocks,and can implement dataexchange to different relays via the Ring Ethernet.A.ICD RelayThe relay unit consists of a communication interface unit,line selection,multi-channel current differential(MCD)unitand a trip decision-making unit.Unlike conventional approach,the differential algorithmswithin ICD relay are responsible for performing differentialcalculations between all remote ends for all its associated linesections.The line selection unit selects the line in turn andpasses the currents to the MCD unit.The MCD unit alsoreceives currents from the remote ends of the ICD relaysthrough communication gateway via the Ethernet.The MCDthen conducts the differential calculation for each protectedline and takes the corresponding setting from the settingdatabase.The trip decision unit will send the trip commend tothe CB associated with the faulted line section through theEthernet.The communication gateway is responsible for sending andreceiving current signals from all remote ICDs on itsassociated line sections.Fig.3.Integrated Current Differential Relay System.B.Substation Communication NetworkIn the proposed protection scheme,the substationmeasurements,control information from typical conventionalsubstation equipments and other remote integrated protectionrelays etc.,are interfaced with the central protection relaysthrough the Ethernet as shown in Fig.3.The interface unit(IU)and a communication network are introduced in details asfollow.Interface Unit;An interface unit is used with the digitalinterface and provides the interface from the electronic currentand voltage transformers to the secondary equipment likeprotection in a distributed protection system or to the Ethernetin a centralized protection system.In the integrated current differential system,the interfaceunit may be synchronized by receiving an external signal likeGPS signal and it creates a time-coherent set of samples withthree phase voltages,three phase currents and neutral voltageand current.Under the viewpoint of IEC 61850 data format,the interface unit implements the logical nodes representingthe current and voltage transformers in the data format.Thesecondary converter is typically part of the instrumenttransformer while the interface unit may be located in thecontrol cubical.The link between the secondary converter andthe interface unit is proprietary and can be analog or digital.The secondary converter can directly have an output accordingto IEC 61850-9-X.However,considerations for centralizedsystems like the requirements of synchronized sampling andthe existence of a synchronization network make the use of aninterface unit suitable in a first step.Communication Network;The optical communicationnetwork interfaces not only to critical IUs and the relays,butalso to a number of other equipments,such as communicationgateway,Human machine interface,etc.The network offers the many advantages:(i)High speeddata exchangeEthernet links operating at 100 Mbit/sexchange polled data and commands between devices at a farfaster rate than traditional serial/fieldbus protocols.Clients(mater stations)can perform supervisory control withnegligible delay.(ii)Peer-to-peer communicationsince allIntelligent Electronic Devices(IEDs)within the substation cancommunicate with each other,without extensive hardwiring inequipment bays,mater-slave is consigned to history.Thereduction in copper interwiring alone will generate largereductions in scheme engineering fixed costs.Directcommunication peer-to-peer can filter out commands which donot need to be passed to an upstream control system,reducingits processing overhead.(iii)True InteroperabilityThe self-descriptive nature of IEC 61850-compatible IEDs means thatsystem integration and commissioning is easier.(iv)UniformityOne protocol is all that is needed in thesubstation,Message and control commands are interleaved ona single network.Multiple clients can be integrated,allowingauthorized operators and engineers to interrogate and controlthe substation IEDs.The network comprises an optical fiberring with comprehensive monitoring functions;the failures ofcomponents can be detected within a few milliseconds andindicated to the operator within a fraction of a second.If adevice fails,the normal communication among the otherdevices can be restored in a few milliseconds after the networkhas been reconfigured.The measurement and control unit,relay,Ethernet and other IEDs are self-adaptive redundant toimprove system real-time ability and data transmissionreliability.Running on special monitoring protocols,the relaycan further check the condition of the network regularly andprovide time synchronization in the network with 1 ms.Anoptical Ethernet module with an integrated switch is present ineach IED.The unit is immune to electromagnetic interferencebecause of fully fibre-optical design.The use of standardcommunication protocol for the network will enable IEDsfrom different manufacturers to be easily interfaced to thesystem.V.SIMULATION STUDIESA typical 500kV transmission line system as shown in Fig.2is used for the simulation studies.The length of thetransmission line is 200km for Line1 and Line2 and 50km forLine3.The parameters of transmission line are:Positivesequence impedance:R1=0.0294 / kmX1=0.278/kmY1=4.139S/kmZero Sequence impedance:Ro=0.2052/kmXo=0.6519/kmY0=2.848S/kmThe current differential criterion used in the here is:| IM+IN|IS| IM+IN|k(|IM一IN|)Where IM and INthe currents at the two ends of theprotected zone; Is is starting current;|IM+IN| is theoperating quantity; |IN一IM| is the restraining quantity; andk is the percentage bias ratioFig.4.Single phase diagram of ICD relay CTS logic.To demonstrate the advantage of the integrated protection,a specially designed CT supervision logic is incorporated intothe ICD relay as shown in Fig.4.As shown,the CTS L1,CTSL2 and CTS L3 are standard CT supervision logic1for Line1,2 and 3 respectively.The basic principle of the logic is thatfor any phase of the CT on one of the lines has a problem,forexample the broken of the secondary connection,instead ofblocking the protection,the relay will use the phase currentson the other two lines to perform the current differentialcalculation.Fig.5 shows a phase A-earth fault occurs at the middle ofLine 1,while the phase A of the Line 1 CT secondary isbroken.The local currents,remote currents,operatingquantities and restraining quantities of each line are shown inthe figure.In this fault condition,a CTS L1 signal will begenerated,instead of block line current differential protectionas conventional distributed protection,the ICD relay CTSlogic as shown in Fig.4 will automatically switch two line2 andline3 inputs,and as a result,the relay is able to generatecorrectly responses as shown in Fig.5.The operating quantityof faulted line1 is significantly higher than the restrainingquantity after fault inception,while for line2 and line3,therelay restrains from operation.VI.CONCLUSIONA new integrated relay and integrated protection scheme forthe transmission lines are described in the paper.The relay andscheme,which are responsible for the protection of every linesections connected to the substation busbar,are able to offer anumber of significant advantages over the conventionalapproaches,such as use friendly and cost effective.Backed upby the continue developments in microelectronics,communication and non conventional transducers,it isexpected that more and more research and development will bemoved towards the area of integrated protection.(5a)Responses of on Line 1(5b)Responses of Line 2(5c)Responses of Line 3Fig.5.Typical responses to a phase A-earth fault at the middle of line 1.VII.REFERENCES1AREVA T&D Automation,“Network 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