CHAPTER 5: SETTINGS GROUPED ELEMENTSL90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL 5-2915into account when using the negative-sequence directional overcurrent element to directionalize other protectionelements. The negative-sequence current must be greater than the PRODUCT SETUP DISPLAY PROPERTIES CURRENTCUT-OFF LEVEL setting value.SettingsNEG SEQ DIR OC1 OFFSET — Specifies the offset impedance used by this protection. The primary application for the offsetimpedance is to guarantee correct identification of fault direction on series compensated lines (see the Application ofSettings chapter for information on how to calculate this setting). In regular applications, the offset impedance ensuresproper operation even if the negative-sequence voltage at the relaying point is very small. If this is the intent, the offsetimpedance shall not be larger than the negative-sequence impedance of the protected circuit. Practically, it is severaltimes smaller. Enter the offset impedance in secondary ohms.NEG SEQ DIR OC1 TYPE — Selects the operating mode for the overcurrent unit of the element. The choices are “NegSequence” and “Zero Sequence.” In some applications it is advantageous to use a directional negative-sequenceovercurrent function instead of a directional zero-sequence overcurrent function as inter-circuit mutual effects areminimized.NEG SEQ DIR OC1 POS-SEQ RESTRAINT — Controls the positive-sequence restraint. Set it to 0.063 (in “Zero Sequence” mode)or 0.125 (in “Neg Sequence” mode) for backward compatibility with revisions 3.40 and earlier. Set it to zero to remove therestraint. Set it higher if large system unbalances or poor CT performance are expected.NEG SEQ DIR OC1 FWD ECA — Select the element characteristic angle (ECA) for the forward direction. The elementcharacteristic angle in the reverse direction is the angle set for the forward direction shifted by 180°.NEG SEQ DIR OC1 FWD LIMIT ANGLE — Defines a symmetrical limit angle (in both directions from the ECA) for the forwarddirection.NEG SEQ DIR OC1 FWD PICKUP — Defines the pickup level for the overcurrent unit in the forward direction. This pickupthreshold applies to zero-sequence or negative-sequence current based on the NEG SEQ DIR OC1 TYPE setting. Whenspecifying this setting, keep in mind that the design uses a positive-sequence restraint technique.NEG SEQ DIR OC1 REV LIMIT ANGLE — Defines a symmetrical limit angle (in both directions from the ECA) for the reversedirection.NEG SEQ DIR OC1 REV PICKUP — Defines the pickup level for the overcurrent unit in the reverse direction. This pickupthreshold applies to zero-sequence or negative-sequence current based on the NEG SEQ DIR OC1 TYPE setting. Whenselecting this setting, keep in mind that the design uses a positive-sequence restraint technique.
