The fault inception detection element detects instantaneous changes in any phase currentsor zero sequence current in combination with a change in the corresponding phase voltageor zero sequence voltage. The criterion for the fault inception detection is if the change ofany phase voltage and current exceeds the settings DeltaV and DeltaI respectively, or ifthe change of zero sequence voltage and zero sequence current exceeds the settingsDelta3V0,Delta3I0 respectively. The schemeType is selected as DeltaBlocking.If the fault inception function has detected a system fault, a block signal CS will be issuedand sent to remote end in order to block the overreaching zones. Different criteria has tobe fulfilled for sending the CS signal:1. The breaker has to be in closed position, that is, the input signal CBOPEN isdeactivated.2. A fault inception should have been detected while the carrier send signal is notblocked, that is, the input signal BLKCS is not activated.If it is later detected that it is an internal fault that made the function issue the CS signal,the function will assert CHSTOP output and stop the channel send CS output.Channels for communication in each direction must be available.12.1.6.3 Permissive underreaching schemeIn a permissive underreaching scheme, a forward directed underreach measuring element(normally zone1) sends a permissive signal CS to the remote end if a fault is detected. Thereceived signal CR is used to allow an overreaching zone to trip after the tCoord timer haselapsed. The tCoord in permissive underreaching schemes is normally set to zero. Thepickup of the forward directed under reaching distance element is connected to the CSURinput.The logic for trip signal in permissive scheme is shown in figure 231.PLTR-CRDCR TRIPANDen05000513_ansi.vsd0-tCoord0ANSI05000513 V1 ENFigure 231: Logic for trip signal in permissive schemeThe permissive underreaching scheme has the same blocking possibilities as mentionedfor blocking scheme.1MRK 506 335-UUS A Section 12Scheme communication499Technical manual
