4.3.3.2 Function blockGUID-A04FED1B-8424-4A84-A327-262E4CC5628F V2 ENFigure 223: Function block4.3.3.3 FunctionalityThe stabilized restricted low-impedance earth-fault protection LREFPNDF for a two-winding transformer is based on the numerically stabilized differential currentprinciple. No external stabilizing resistor or non-linear resistor are required.The fundamental components of the currents are used for calculating the residualcurrent of the phase currents, the neutral current, differential currents andstabilizing currents. The operating characteristics are according to the definite time.LREFPNDF contains a blocking functionality. The neutral current secondharmonic is used for blocking during the transformer inrush situation. It is alsopossible to block function outputs, timers or the function itself, if desired.4.3.3.4 Operation principleThe function can be enabled and disabled with the Operation setting. Thecorresponding parameter values are "On" and "Off".The operation of the stabilized restricted low-impedance earth-fault protection canbe described using a module diagram. All the modules in the diagram are explainedin the next sections.GUID-079EB39A-B62C-47DF-9B53-9432AB24A9CE V2 ENFigure 224: Functional module diagram1YHT530004D05 D Section 4Protection functions615 series 423Technical Manual
