on a received signal for a fast trip, so its dependability is lower than that of ablocking scheme.12.1.6.1 Blocking scheme M13893-6 v7The principle of operation for a blocking scheme is that an overreaching zone isallowed to trip instantaneously after the settable co-ordination time tCoord haselapsed, when no signal is received from the remote IED.The received signal, which shall be connected to CR, is used to block the zone tobe accelerated to clear the fault instantaneously (after time tCoord). The forwardoverreaching zone to be accelerated is connected to the input CACC, seefigure 217.In case of external faults, the blocking signal (CR) must be received before thesettable timer tCoord elapses to prevent a false trip, see figure 217.The function can be totally blocked by activating the input BLOCK. Tripping canbe blocked by activating the input BLKTR. Signal send can be blocked byactivating the input BLKCS.CACCCRtCoordTRIPAND ten05000512.vsdIEC05000512 V1 EN-USFigure 217: Basic logic for trip signal in blocking schemeChannels for communication in each direction must be available.12.1.6.2 Delta blocking scheme GUID-22E3BFAC-82E9-4434-B761-AD63BCFC68D5 v2In order to avoid delays due to carrier coordination times, the initiation of sendingof blocking signal to remote end is done by a fault inception detection elementbased on delta quantities of currents and voltages. The delta based fault detection isvery fast and if the channel is fast there is no need for delaying the operation of theremote distance element. The received blocking signal arrives well before thedistance element has started. If the fault is in forward direction the sending isimmediately stopped by a forward directed distance, directional current ordirectional earth fault element.The fault inception detection element detects instantaneous changes in any phasecurrents or zero sequence current in combination with a change in thecorresponding phase voltage or zero sequence voltage. The criterion for the faultinception detection is if the change of any phase voltage and current exceeds thesettings DeltaU and DeltaI respectively, or if the change of zero sequence voltageand zero sequence current exceeds the settings Delta3U0,Delta3I0 respectively.The schemeType is selected as DeltaBlocking.Section 12 1MRK 506 382-UEN AScheme communication436 Line distance protection REL650 2.2 IECTechnical manual
