SettPickUpWEI to10 ms, a short delay is recommended to avoid that spurious carrier receivedsignals will activate WEI and cause unwanted carrier send (ECHO) signals.Set the voltage criterionUPP< andUPN< for the weak-end trip to 70% of the system basevoltageUBase. The setting should be below the minimum operate voltage of the system butabove the voltage that occurs for fault on the protected line. The phase-to-phase elementsmust be verified to not operate for phase to earth faults.When single phase tripping is required a detailed study of the voltages atphase-to-phase respectively phase-to-earth faults, at different fault locations,is normally required.13.3 Current reversal and weak-end infeed logic for phasesegregated communication ZC1WPSCH SEMOD155635-1 v213.3.1 IdentificationSEMOD156467-2 v2Function description IEC 61850identificationIEC 60617identificationANSI/IEEE C37.2device numberCurrent reversal and weak-endinfeed logic for phase segregatedcommunicationZC1WPSCH - 8513.3.2 Application SEMOD156558-1 v1SEMOD156537-5 v4Current reversal logicIf parallel lines are connected to common buses at both terminals, overreaching permissivecommunication schemes can trip unselectable due to current reversal. The unwanted trippingaffects the healthy line when a fault is cleared on the other line. This lack of security results in atotal loss of interconnection between the two buses.To avoid this kind of disturbances, fault current reversal logic (transient blocking logic) can beused.The unwanted operations that might occur can be explained by looking into Figure 133 andFigure 134. Assume that the fault has been taken place close to breaker B1. At first, theprotection A2 at A side will detect a fault in forward direction and send a communicationsignal to the protection B2 at remote end, which is measuring a fault in reverse direction.L1L2A1A2B1B2IEC14000002-1-en.vsdIEC14000002 V1 EN-USFigure 133: Current distribution for a fault close to B side when all breakers are closedWhen the breaker B1 opens for clearing the fault, the fault current through B2 bay will invert. Ifthe communication signal has not reset at the same time as the distance protection functionSection 13 1MRK 505 363-UEN AScheme communication260Application manual
