has been activated (even if only for a short time), it prevents sending of acommunication signal and tripping through the scheme communication logic aftera settable time tPickUpRev. The prevention will last for tPickUpRev + 10 ms +tDelayRev after the IREV reset. This makes it possible for the receive signal toreset before the carrier-aided trip signal is activated due to the current reversal bythe forward directed zone. The logic diagram for current reversal is shown inFigure 201.t10 msttPickUpRevttPickUpRevBLOCKIRVBLKIRVCurrRev = OnttDelayRev IRVLIEC05000122-4-en.vsdANDIEC05000122 V4 EN-USFigure 201: Simplified logic diagram for current reversalBy connecting the output signal IRVL to input BLKCS in the ZCPSCH function,the sending of the signal CS from the overreaching zone connected to CSOR inZCPSCH will be blocked. By connecting IRVL to input BLKTR in the ZCPSCHfunction, the TRIP output from the ZCPSCH function will be blocked.The function has an internal 10 ms drop-off timer which secure that the currentreversal logic will be activated for short input signals even if the pick-up timer isset to zero.13.2.6.2 Weak-end infeed logic M16679-8 v11The weak-end infeed logic (WEI) function sends back (echoes) the received signalunder the condition that no fault has been detected on the weak-end by differentfault detection elements (distance protection in forward or reverse direction).The WEI function returns the received signal, shown in Figure 202, when:• The setting parameter WEI is set to either Echo or Echo & Trip.• No active signal present on the input BLOCK.• The functional input CRL is active for a time longer than the tPickUpWeisetting. This input is usually connected to the CRL output on the schemecommunication logic ZCPSCH.• The WEI function is not blocked by the active signal connected to theWEIBLK1 functional input or to the VTSZ functional input. The later isusually configured to the VTSZ functional output of the fuse-failure function.• No active signal has been present for at least 200 ms on the WEIBLK2functional input. An OR combination of all fault detection functions (notundervoltage) as present within the IED is usually used for this purpose.• The weak-end infeed logic also echoes the received permissive signal whenlocal breaker opens, CBOPEN prior to faults appeared at the end of line.Section 13 1MRK 505 394-UEN AScheme communication412 Line differential protection RED650 2.2 IECTechnical manual
