5-80 L90 Line Differential Relay GE Multilin5.5 GROUPED ELEMENTS 5 SETTINGS55.5.5 DISTANCEa) MAIN MENUPATH: SETTINGS !" GROUPED ELEMENTS ! SETTING GROUP 1(6) !" DISTANCEThree common settings (DISTANCE SOURCE, MEMORY DURATION, and FORCE SELF-POLAR) and six menus for three zone ofphase and ground distance protection are available. The DISTANCE SOURCE identifies the Signal Source for all distancefunctions. The Mho distance functions use a dynamic characteristic: the positive-sequence voltage ñ either memorized oractual ñ is used as a polarizing signal. The memory voltage is also used by the built-in directional supervising functionsapplied for both the Mho and Quad characteristics.The MEMORY DURATION setting specifies the length of time a memorized positive-sequence voltage should be used in thedistance calculations. After this interval expires, the relay checks the magnitude of the actual positive-sequence voltage. Ifit is higher than 10% of the nominal, the actual voltage is used, if lower ñ the memory voltage continues to be used.The memory is established when the positive-sequence voltage stays above 80% of its nominal value for five power systemcycles. For this reason it is important to ensure that the nominal secondary voltage of the VT is entered correctly under theSETTINGS " SYSTEM SETUP ! AC INPUTS !" VOLTAGE BANK menu.Set MEMORY DURATION long enough to ensure stability on close-in reverse three-phase faults. For this purpose, the maxi-mum fault clearing time (breaker fail time) in the substation should be considered. On the other hand, the MEMORY DURA-TION cannot be too long as the power system may experience power swing conditions rotating the voltage and currentphasors slowly while the memory voltage is static, as frozen at the beginning of the fault. Keeping the memory in effect fortoo long may eventually lead to incorrect operation of the distance functions.The distance zones can be forced to become self-polarized through the FORCE SELF-POLAR setting. Any user-selected con-dition (FlexLogicô operand) can be configured to force self-polarization. When the selected operand is asserted (logic 1),the distance functions become self-polarized regardless of other memory voltage logic conditions. When the selected oper-and is de-asserted (logic 0), the distance functions follow other conditions of the memory voltage logic as shown below.The distance zones of the L90 is are identical to that of the UR-series D60 Line Distance Relay. For additional infor-mation on the L90 distance functions, please refer to Chapter 8 of the D60 manual, available on the enerVista CDor free of charge on the GE Multilin web page.# DISTANCE#DISTANCESOURCE: SRC 1Range: SRC 1, SRC 2MESSAGE MEMORYDURATION: 10 cyclesRange: 5 to 25 cycles in steps of 1MESSAGE FORCE SELF-POLAR:OffRange: FlexLogicô operandMESSAGE # PHASE DISTANCE Z1# See page 5ñ81.MESSAGE # PHASE DISTANCE Z2# See page 5ñ81.MESSAGE # PHASE DISTANCE Z3# See page 5ñ81.MESSAGE # GROUND DISTANCE Z1# See page 5ñ90.MESSAGE # GROUND DISTANCE Z2# See page 5ñ90.MESSAGE # GROUND DISTANCE Z3# See page 5ñ90.NOTE
