The unwanted operations that might occur can be explained by looking into Figure 195and Figure 196. Initially the protection A2 at A side will detect a fault in forward directionand send a communication signal to the protection B2 at remote end, which is measuringa fault in reverse direction.en99000043_ansi.vsdStrongsourceLINE 1LINE 2A:1A:2B:1B:2A BWeaksourceFAULTCLOSEDCLOSEDCLOSEDCLOSEDANSI99000043 V1 ENFigure 195: 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 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 B2 at B side.en99000044_ansi.vsdStrongsourceLINE 1LINE 2A:1A:2B:1B:2A BWeaksourceCLOSEDCLOSEDOPENCLOSEDFAULTANSI99000044 V1 ENFigure 196: Current distribution for a fault close to B side when breaker B1 hasopenedTo handle this the send signal CS from B2 is held back until the reverse zone IRVL hasreset and the tDelayRev time has elapsed. To achieve this the reverse zone on the distanceprotection shall be connected to input IRV and the output IRVL shall be connected to inputBLKCS on the communication function block ZCPSCH.The function can be blocked by activating the input IRVBLK or the general BLOCKinput.12.2.2.2 Weak-end infeed logicPermissive communication schemes can basically operate only when the protection in theremote IED can detect the fault. The detection requires a sufficient minimum fault current,normally >20% of In. The fault current can be too low due to an open breaker or low short-Section 12 1MRK 506 334-UUS AScheme communication400Application manual
