When a signal picks-up or drops out there is a decision time to be added. Thisdecision time is highly dependent on the interface between communication andprotection used. In many cases an external interface (teleprotection equipment) isused. This equipment makes a decision and gives a binary signal to the protectiondevice. In case of analog teleprotection equipment typical decision time is in therange 10 – 30 ms. For digital teleprotection equipment this time is in the range 2 –10 ms.If the teleprotection equipment is integrated in the protection IED the decision timecan be slightly reduced.The principle time sequence of signaling at current reversal is shown.ProtectionFunctionProtectionFunctionTele-ProtectionEquipmentTele-ProtectionEquipmentTele-communicationSystemCS from theprotectionfunction, operateand reset timeCS initiation tothecommunicationsystem, operateand reset timeCS propagation,propagationCR selection anddecision, operateand reset timeCR to theprotectionfunction, operateand reset timeTimeFaultoccursProtectionpick-up CS initiationCR toteleprot.eq.CR toprot.func Fault currentreversalSendingprotectionresetCS tocommunicationdropCRreceptiondropCR toprot.funcdropMinimum setting of tDelay IEC05000536-2-en.vsdIEC05000536 V2 EN-USFigure 377: Time sequence of signaling at current reversal16.7.3.2 Weak-end infeed M13933-12 v6The weak-end infeed can be set by setting the parameter WEI to Off, Echo or Echo& Trip. Operating zero sequence voltage when parameter WEI is set to Echo &Trip is set with 3U0>.The zero sequence voltage for a fault at the remote line end and appropriate faultresistance is calculated.To avoid unwanted trip from the weak-end infeed logic (if spurious signals shouldoccur), set the operate value of the broken delta voltage level detector (3U0) higherthan the maximum false network frequency residual voltage that can occur duringnormal service conditions. The recommended minimum setting is two times thefalse zero-sequence voltage during normal service conditions.Section 16 1MRK 506 369-UEN BScheme communication726 Line distance protection REL670 2.2 IECApplication manual
