The weak-end infeed logic is used in cases where the apparent power behind the protectioncan be too low to activate the distance protection function. When activated, receivedcarrier signal together with local undervoltage criteria and no reverse zone operation givesan instantaneous three-phase trip. The received signal is also echoed back during 200 msto accelerate the sending end.On verification of a weak end infeed condition, the weak end infeed logic provides anoutput for sending the received teleprotection signal back to the remote sending end andother output(s) for tripping. For terminals equipped for single-, two-, and three-poletripping, outputs for the faulted phase(s) are provided. Undervoltage detectors are used toselect the faulted phase(s).12.2.3 Function blockANSI09000007-1-en.vsdZCRWPSCH (85)V3P*BLOCKIFWDIREVWEIBLK1WEIBLK2BLKZCBOPENCRLIRVLTRWEIECHOANSI09000007 V1 ENFigure 234: ZCRWPSCH (85) function block12.2.4 SignalsTable 337:ZCRWPSCH (85) Input signalsName Type Default DescriptionV3P GROUPSIGNAL- Three phase group signal for voltage inputsBLOCK BOOLEAN 0 Block of functionIFWD BOOLEAN 0 A signal that indicates a forward fault has been detectedand will block tripping if there was a pre-existing reversefault condition (IREV)IREV BOOLEAN 0 A signal that indicates a reverse fault has been detectedand activates current reverasl logicWEIBLK1 BOOLEAN 0 Block of WEI logicWEIBLK2 BOOLEAN 0 Block of WEI logic due to operation of other protectionsthat would effect a pilot trip or the detection of reversefaults that will be tripped by an external deviceTable continues on next page1MRK 506 335-UUS A Section 12Scheme communication503Technical manual