send a communication signal to the protection B:2 at remote end, which is measuring afault in reverse direction.en99000043_ansi.vsdStrongsourceLINE 1LINE 2A:1A:2B:1B:2A BWeaksourceFAULTCLOSEDCLOSEDCLOSEDCLOSEDANSI99000043 V1 ENFigure 197: Current distribution for a fault close to B side when all breakers are closedWhen the breaker B: 1 opens for clearing the fault, the fault current through B: 2 bay willinvert. If the communication signal has not reset at the same time as the distance protectionfunction used in the Teleprotection scheme has switched on to forward direction, we willhave an unwanted operation of breaker B:2 at B side.en99000044_ansi.vsdStrongsourceLINE 1LINE 2A:1A:2B:1B:2A BWeaksourceCLOSEDCLOSEDOPENCLOSEDFAULTANSI99000044 V1 ENFigure 198: Current distribution for a fault close to B side when breaker B: 1 hasopenedTo handle this the send signal CS from B: 2 is held back until the reverse zone IRVL hasreset and the tDelayRev time has elapsed. To achieve this reverse zone on the distanceprotection shall be connected to input IREV and the output IRVL shall be connected toinput BLKCS on the communication function block ZCPSCH. The function can beblocked by activating the input IFWD or the general BLOCK input.12.3.2.2 Weak-end infeed logicPermissive communication schemes can basically operate only when the protection in theremote terminal can detect the fault. The detection requires a sufficient minimum faultcurrent, normally >20% of In. The fault current can be too low due to an open breaker orlow short-circuit power of the source. To overcome these conditions, weak-end infeed(WEI) echo logic is used. The fault current can also be initially too low due to the fault1MRK 506 334-UUS A Section 12Scheme communication403Application manual
