L1L2A1A2B1B2IEC9900043-2.vsdIEC99000043 V3 EN-USFigure 124: Current distribution for a fault close to B side when all breakers areclosedL1L2A1A2B1B2IEC99000044-2.vsdIEC99000044 V3 EN-USFigure 125: Current distribution for a fault close to B side when breaker at B1 isopenedWhen the breaker on the parallel line operates, the fault current on the healthy lineis reversed. The IED at B2 recognizes the fault in forward direction from reversedirection before breaker operates. As IED at B2 already received permissive signalfrom A2 and IED at B2 is now detecting the fault as forward fault, it willimmediately trip breaker at B2. To ensure that tripping at B2 should not occur, thepermissive overreaching function at B2 needs to be blocked by IRVL till thereceived permissive signal from A2 is reset.The IED at A2, where the forward direction element was initially activated, mustreset before the send signal is initiated from B2. The delayed reset of output signalIRVL also ensures the send signal from IED B2 is held back till the forwarddirection element is reset in IED A2.13.5.2.2 Weak-end infeed logic M15285-6 v5Figure 126 shows a typical system condition that can result in a missing operation.Note that there is no fault current from node B. This causes that the IED at Bcannot detect the fault and trip the breaker in B. To cope with this situation, aselectable weak-end infeed logic is provided for the permissive overreachingscheme.Section 13 1MRK 505 393-UEN BScheme communication292 Line differential protection RED650 2.2 IECApplication manual
