covers the overreaching zone, used at the remote line IED for the telecommunicationpurposes.Consider the possible enlarging factor that might exist due to fault infeed from adjacentlines. The equation can be used to calculate the reach in reverse direction when the zoneis used for blocking scheme, weak-end infeed, and so on.Zrev 1.2 × (Z2rem - ZL)>_GUID-ABFB1C53-F12A-45D5-90CC-907C9FA0EFC3 V1 EN (Equation 381)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 protected line.In many applications it might be necessary to consider the enlarging factor due to the faultcurrent infeed from adjacent lines in the reverse direction in order to obtain certainsensitivity.8.13.4.5 Series compensated and adjacent linesSetting of zone 1A voltage reversal can cause an artificial internal fault (voltage zero) on faulty line as wellas on the adjacent lines. This artificial fault always have a resistive component, this ishowever small and can mostly not be used to prevent tripping of a healthy adjacent line.An independent tripping zone 1 facing a bus which can be exposed to voltage reversalhave to be set with reduced reach with respect to this false fault. When the fault can moveand pass the bus, the zone 1 in this station must be blocked. Protection further out in thenet must be set with respect to this apparent fault as the protection at the bus.Different settings of the reach for the zone (ZMFCPDIS, 21) characteristic in forward andreverse direction makes it possible to optimize the settings in order to maximizedependability and security for independent zone1.Due to the sub-harmonic oscillation swinging caused by the series capacitor at faultconditions the reach of the under-reaching zone 1 must be further reduced. Zone 1 can onlybe set with a percentage reach to the artificial fault according to the curve in 1031MRK 506 369-UUS - Section 8Impedance protectionLine distance protection REL670 2.2 ANSI 423Application manual
