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 TAn 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