13.5.2 FunctionalityM13928-3 v8The Current reversal and weak-end infeed logic for residual overcurrent protection(ECRWPSCH) is a supplement to Scheme communication logic for residualovercurrent protection ECPSCH.To achieve fast fault clearing for all earth faults on the line, the directional earthfault protection function can be supported with logic that uses tele-protectionchannels.This is why the IEDs have available additions to the scheme communication logic.M13928-6 v2If parallel lines are connected to common busbars at both terminals, overreachingpermissive communication schemes can trip unselectively due to fault currentreversal. This unwanted tripping affects the healthy line when a fault is cleared onthe other line. This lack of security can result in a total loss of interconnectionbetween the two buses. To avoid this type of disturbance, a fault current reversallogic (transient blocking logic) can be used.M13928-8 v5Permissive communication schemes for residual overcurrent protection canbasically operate only when the protection in the remote IED can detect the fault.The detection requires a sufficient minimum residual fault current, out from thisIED. The fault current can be too low due to an opened breaker or high-positiveand/or zero-sequence source impedance behind this IED. To overcome theseconditions, weak-end infeed (WEI) echo logic is used. The weak-end infeed echo islimited to 200 ms to avoid channel lockup.13.5.3 Function block M13930-3 v6ECRWPSCHU3P*BLOCKIRVBLKIRVWEIBLK1WEIBLK2VTSZCBOPENCRLIRVLTRWEIECHOIEC06000289-3-en.vsdIEC06000289 V3 EN-USFigure 210: ECRWPSCH function blockSection 13 1MRK 505 394-UEN AScheme communication424 Line differential protection RED650 2.2 IECTechnical manual
