The requirement that the zone 2 shall not reach more than 80% of the shortestadjacent line at remote end is highlighted in the example below.If a fault occurs at point F, see figure 218, the IED at point A senses the impedance:Z VI Z I II Z I I II R Z II ZAFAAACA CACFA C BAF ACCAC= = + + ⋅ + + + ⋅ = + + ⋅1 FFC BAFI II R+ + + ⋅1EQUATION302 V5 EN-US (Equation 379)A BZ<CICZAC ZCBZ CFIA+ I CIEC09000256-2-en.vsdFI A I BIEC09000256 V2 EN-USFigure 218: Setting of overreaching zone8.13.4.4 Setting of reverse zone GUID-C08EC148-B90C-4A20-8993-707E63545946 v2The reverse zone (zone RV) is applicable for purposes of scheme communicationlogic, current reversal logic, weak-end infeed logic, and so on. The same applies tothe back-up protection of the bus bar or power transformers. It is necessary tosecure, that it always covers the overreaching zone, used at the remote line IED forthe telecommunication purposes.Consider the possible enlarging factor that might exist due to fault infeed fromadjacent lines. The equation can be used to calculate the reach in reverse directionwhen the zone is used for blocking scheme, weak-end infeed, and so on.Zrev 1.2 × (Z2rem - ZL)>_GUID-ABFB1C53-F12A-45D5-90CC-907C9FA0EFC3 V1 EN-US (Equation 380)Where:ZL is the protected line impedance.Z2rem is the zone 2 setting (zone used in the POTT scheme) at the remote end of the protectedline.In many applications it might be necessary to consider the enlarging factor due tothe fault current infeed from adjacent lines in the reverse direction in order toobtain certain sensitivity.Section 8 1MRK 506 369-UEN BImpedance protection394 Line distance protection REL670 2.2 IECApplication manual
