The heavy load transfer that is common in many transmission networks may in some casesbe in opposite to the wanted fault resistance coverage. Therefore, the function has a builtin algorithm for load encroachment, which gives the possibility to enlarge the resistivesetting of both the Phase selection with load encroachment and the measuring zoneswithout interfering with the load.A current-based phase selection is also included. The measuring elements continuouslymeasure three phase currents and the residual current and, compare them with the setvalues.The extensive output signals from FDPSPDIS (21) give also important information aboutfaulty phase(s), which can be used for fault analysis.8.11.3 Setting guidelinesThe following setting guideline consider normal overhead lines applications where φloopand φline is greater than 60°.8.11.3.1 Load encroachment characteristicsThe phase selector must at least cover the overreaching zone 2 in order to achieve correctphase selection for utilizing single-phase autoreclosing for faults on the entire line. It is notnecessary to cover all distance protection zones. A safety margin of at least 10% isrecommended. In order to get operation from distance zones , the phase selection outputsPHSELZ or DLECND must be connected to input PHSEL on ZMQPDIS (21), distancemeasuring block.For normal overhead lines, the angle for the loop impedance φ for phase-to-ground faultis defined according to equation 96.LLX1arctan R1+j = +XNRNEQUATION2115 V1 EN (Equation 281)In some applications, for instance cable lines, the angle of the loop might be less than 60°.In these applications, the settings of fault resistance coverage in forward and reversedirection, RFltFwdPG and RFltRevPG for phase-to-ground faults and RFltRevPP andRFltRevPP for phase-to-phase faults have to be increased to avoid that FDPSPDIS (21)characteristic shall cut off some part of the zone characteristic. The necessary increasedsetting of the fault resistance coverage can be derived from trigonometric evaluation of thebasic characteristic for respectively fault type.Section 8 1MRK 506 369-UUS -Impedance protection348 Line distance protection REL670 2.2 ANSIApplication manual
