CHAPTER 5: SETTINGS GROUPED ELEMENTSD60 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL 5-1975The following common settings are available for distance protection.The DISTANCE SOURCE identifies the signal source for all distance functions. The mho distance functions use a dynamiccharacteristic; the positive-sequence voltage—either memorized or actual—is used as a polarizing signal. The memoryvoltage is also used by the built-in directional supervising functions applied for both the mho and quad characteristics.The MEMORY DURATION setting specifies the length of time that a memorized positive-sequence voltage is 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, and 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 powersystem cycles. For this reason, it is important to ensure that the nominal secondary voltage of the VT is entered correctlyunder the SETTINGS 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, consider themaximum fault clearing time (breaker fail time) in the substation. On the other hand, the MEMORY DURATION cannot be toolong as the power system can experience power swing conditions rotating the voltage and current phasors slowly whilethe memory voltage is static, as frozen at the beginning of the fault. Keeping the memory in effect for too long caneventually 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-selectedcondition (any 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 theselected operand is de-asserted (logic 0), the distance functions follow other conditions of the memory voltage logic asshown in the following logic diagram.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 is asserted(logic 1), the distance functions become memory-polarized regardless of the positive-sequence voltage magnitude at thistime. When the selected operand is de-asserted (logic 0), the distance functions follow other conditions of the memoryvoltage logic.Never let the FORCE SELF-POLAR and FORCE MEM-POLAR settings to be asserted simultaneously. If this happens, the logicgives higher priority to forcing self-polarization as indicated in the logic diagram. This is consistent with the overallphilosophy of distance memory polarization.FAST DISTANCE enables the fast distance algorithm in phase and ground zone 1 and zone 2. Disable fast distance fordistance protection applications on a series compensated line.PH DIST PH SELECT SUPV enables phase selection supervision on phase distance zone 1 to zone 3. FAST DISTANCE:EnabledRange: Disabled, Enabled PH DIST PH SELECTSUPV: EnabledRange: Disabled, Enabled PHASE DISTANCE Z1See page 5-198 PHASE DISTANCE Z5 GROUND DISTANCE Z1See page 5-208 GROUND DISTANCE Z5The memory polarization cannot be applied permanently but for a limited time only. The self-polarization can beapplied permanently and therefore takes higher priority.
