rem L1.2 Z2 Z-revZ ³ ×EQUATION2314 V1 EN-US (Equation 250)Where:ZL is the protected line impedanceZ2rem is zone 2 setting at remote end of protected line.In many applications it might be necessary to consider the enlarging factor due tofault current infeed from adjacent lines in the reverse direction in order to obtaincertain sensitivity.8.9.3.5 Setting of zones for parallel line application SEMOD55087-50 v2Parallel line in service – Setting of zone 1 GUID-F10BF2FF-7B0F-40B0-877B-081E1D5B067B v1With reference to section "Parallel line applications", the zone reach can be set to85% of protected line.However, influence of mutual impedance has to be taken into account.Parallel line in service – setting of zone 2 GUID-8EAD617A-D33B-453C-83FC-21E3CFC37CB1 v1Overreaching zones (in general, zones 2 and 3) must overreach the protected circuitin all cases. The greatest reduction of a reach occurs in cases when both parallelcircuits are in service with a single phase-to-earth fault located at the end of aprotected line. The equivalent zero sequence impedance circuit for this case isequal to the one in figure 113 in section "Parallel line applications".The components of the zero sequence impedance for the overreaching zones mustbe equal to at least:R0E R0 Rm0+=EQUATION553 V1 EN-US (Equation 251)X0E X0 Xm0+=EQUATION554 V1 EN-US (Equation 252)Check the reduction of a reach for the overreaching zones due to the effect of thezero sequence mutual coupling. The reach is reduced for a factor:00 1 2 1 0mfZK Z Z R= - × + +EQUATION1426 V1 EN-US (Equation 253)Section 8 1MRK 506 369-UEN BImpedance protection308 Line distance protection REL670 2.2 IECApplication manual
