The minimum primary setting (Is) for the instantaneous phase overcurrentprotection is then:min1.3sI I³ ×EQUATION79 V3 EN-US (Equation 15)The protection function can be used for the specific application only if this settingvalue is equal to or less than the maximum fault current that the IED has to clear, IFin Figure 41.IEC09000024-1-en.vsd~ ~ZA ZBZ LA BIEDI FFaultIEC09000024 V1 EN-USFigure 41: Fault current: IF100IsIP IBase>>= ×EQUATION1147 V3 EN-US (Equation 16)7.1.3.2 Meshed network with parallel line M12915-34 v7In case of parallel lines, the influence of the induced current from the parallel lineto the protected line has to be considered. One example is given in Figure 42,where the two lines are connected to the same busbars. In this case the influence ofthe induced fault current from the faulty line (line 1) to the healthy line (line 2) isconsidered together with the two through fault currents IfA and IfB mentionedpreviously. The maximal influence from the parallel line for the IED in Figure 42will 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 the healthy line (this applies for single-phase-to-earth and two-phase-to-earth faults) is calculated.Section 7 1MRK 504 169-UEN ACurrent protection104 Transformer protection RET650 2.2 IECApplication manual
