Section 1UnrestrainedLimitSection 2 Section 3RestrainOperateunconditionally5432100 1 2 3 4 5IdMinEndSection1EndSection2Restrain current[ in pu of IBase]Operate current[ in pu of IBase]SlopeSection2SlopeSection3en05000300.vsdOperateconditionallyIdMinHighACBIEC05000300 V1 EN-USFigure 33: Overestimated charging currentIf a high resistive fault is considered, the voltage in the fault location will not bemuch reduced. Consequently, the value of the pre-fault “false” differential currentwill be a good estimation of the actual charging current.Subtracting the pre-fault charging current from the differential current under faultconditions will make it possible to set Idmin mainly without considering thecharging current in order to achieve maximum sensitivity. The stability at externalfaults will not be affected.6.1.2.4 Time synchronization M12022-66 v3Time synchronization of sampled current values is a crucial matter in numericalline differential protections. The synchronization is made with the so called echomethod, which can be complemented with IRIG-B time synchronization. Inapplications with symmetrical communication delay, that is, send and receive timesare equal, the echo method is sufficient. When used in networks with asymmetricaltransmission times, the optional IRIG–B time synchronization is required.6.1.2.5 Communication channels for line differential protection M12022-69 v7The line differential protection function uses 64 kbit/s communication channels toexchange telegrams between the line differential protection IEDs. These telegramsSection 6 1MRK 505 393-UEN BDifferential protection82 Line differential protection RED650 2.2 IECApplication manual
