GE Multilin D30 Line Distance Protection System 5-1115 SETTINGS 5.6 GROUPED ELEMENTS55.6.4 DISTANCEa) MAIN MENUPATH: SETTINGS GROUPED ELEMENTS SETTING GROUP 1(6) DISTANCEFour common settings are available for distance protection. The DISTANCE SOURCE identifies the signal source for all dis-tance functions. The mho distance functions use a dynamic characteristic: the positive-sequence voltage – either memo-rized or actual – is used as a polarizing signal. The memory voltage is also used by the built-in directional supervisingfunctions applied 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 – 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 (FlexLogic™ 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 can be forced to become memory-polarized through the FORCE MEM-POLAR setting. Any user-selectedcondition (any FlexLogic™ operand) can be configured to force memory polarization. When the selected operand isasserted (logic 1), the distance functions become memory-polarized regardless of the positive-sequence voltage magni-tude at this time. When the selected operand is de-asserted (logic 0), the distance functions follow other conditions of thememory voltage logic. DISTANCEDISTANCESOURCE: SRC 1Range: SRC 1, SRC 2MESSAGE MEMORYDURATION: 10 cyclesRange: 5 to 25 cycles in steps of 1MESSAGE FORCE SELF-POLAR:OffRange: FlexLogic™ operandMESSAGE FORCE MEM-POLAR:OffRange: FlexLogic™ operandMESSAGE PHASE DISTANCE Z1 See page 5–112.MESSAGE PHASE DISTANCE Z2 See page 5–112.MESSAGE PHASE DISTANCE Z3 See page 5–112.MESSAGE GROUND DISTANCE Z1 See page 5–120.MESSAGE GROUND DISTANCE Z2 See page 5–120.MESSAGE GROUND DISTANCE Z3 See page 5–120.
