7.1.3.2 Meshed network with parallel line M12915-34 v6In case of parallel lines, the influence of the induced current from the parallel line to theprotected line has to be considered. One example is given in figure 38 where the two lines areconnected to the same busbars. In this case the influence of the induced fault current from thefaulty line (line 1) to the healthy line (line 2) is considered together with the two through faultcurrents IfA and IfB mentioned previously. The maximal influence from the parallel line for theIED in figure 38 will be with a fault at the C point with the C breaker open.A fault in C has to be applied, and then the maximum current seen from the IED (IM ) on thehealthy line (this applies for single-phase-to-earth and two-phase-to-earth faults) iscalculated.IEC09000025-1-en.vsd~ ~ZA ZBZL1A BI MFaultIEDZL2MCLine 1Line 2IEC09000025 V1 EN-USFigure 38: Two parallel lines. Influence from parallel line to the through fault current: IMThe minimum theoretical current setting for the overcurrent protection function (Imin) will be:Imin MAX IfA IfB IM, ,( )³EQUATION82 V1 EN-US (Equation 20)Where IfA and IfB have been described in the previous paragraph. Considering the safetymargins mentioned previously, the minimum setting (Is) for the instantaneous phaseovercurrent protection 3-phase output is then:Is ³1.3·IminEQUATION83 V2 EN-US (Equation 21)The protection function can be used for the specific application only if this setting value isequal or less than the maximum phase fault current that the IED has to clear.The IED setting valueIP>> is given in percentage of the primary base current value,IBase. Thevalue forIP>> is given from this formula:100IsIP IBase>>= ×EQUATION1147 V3 EN-US (Equation 22)Section 7 1MRK 504 158-UEN ACurrent protection88Application manual
