IEC05000435-2-en.vsdxIED IEDProtected zone in instantaneous functionIEC05000435 V2 EN-USFigure 31: Line tap with a small power transformer, the currents of which arenot measured, and consequently contribute to a (false) differentialcurrent6.1.2.3 Charging current compensation M12022-58 v6There are capacitances between the line phase conductors and between phaseconductors and earth. These capacitances give rise to line charging currents whichare seen by the differential protection as “false” differential currents, as shown infigure 32.IED CommunicationIc1 Ic2Idiff, false = Ic1 + Ic2IEC05000436-2-en.vsdxIEDIEC05000436 V2 EN-USFigure 32: Charging currentsThe magnitude of the charging current is dependent of the line capacitance and thesystem voltage. For earth cables and long overhead lines, the magnitude can besuch that it affects the possibility to achieve the wanted sensitivity of thedifferential protection. To overcome this, a charging current compensation isavailable in line differential protection. When enabled, this algorithm will measurethe fundamental frequency differential current under steady state undisturbedconditions and then subtract it, making the resulting differential current zero (orSection 6 1MRK 505 393-UEN BDifferential protection80 Line differential protection RED650 2.2 IECApplication manual
