5-60L90 Line Differential RelayGE Power Management5.5 GROUPED ELEMENTS 5 SETTINGS55.5.7 DISTANCEPATH: SETTINGS ÖØ GROUPED ELEMENTS Ö SETTING GROUP 1(8) ÖØ DISTANCETwo common settings (DISTANCE SOURCE and MEMORY DURATION) and two menus for one zone of phase and ground dis-tance protection are available. The DISTANCE SOURCE identifies the Signal Source for all distance functions.The MHO distance functions use a dynamic characteristic: the positive-sequence voltage – either memorized or actual – isused as a polarizing signal. The memory voltage is also used by the built-in directional supervising functions applied forboth 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 – 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 sys-tem cycles. For this reason it is important to ensure that the nominal secondary voltage of the VT is entered correctly underthe SETTINGS Ø SYSTEM SETUP Ö AC INPUTS ÖØ 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 cause maloperation of the distance functions.Figure 5–21: MEMORY VOLTAGE LOGIC DISTANCEDISTANCESOURCE: SRC 1Range: SRC 1, SRC 2,..., SRC 6MESSAGE MEMORYDURATION: 10 cyclesRange: 5 to 25 cyclesMESSAGE PHASE DISTANCE Z2MESSAGE GROUND DISTANCE Z2827842A2.CDRDISTANCE SOURCE:MEMORY DURATION:Use V_1Use V_1 memANDANDANDORS QRSETTINGSETTINGIA IA < 0.05 puIB IB < 0.05 puIC IC < 0.05 puV_1 V_1 > 0.8 puV_1 < 0.1 pu5 cyRUNUPDATE MEMORY00t RST
