GE Multilin L90 Line Current Differential System 5-1975 SETTINGS 5.6 GROUPED ELEMENTS5– If “Dual” polarizing is selected, the element performs both directional comparisons as described above. A givendirection is confirmed if either voltage or current comparators indicate so. If a conflicting (simultaneous forwardand reverse) indication occurs, the forward direction overrides the reverse direction.• NEUTRAL DIR OC1 POL VOLT: Selects the polarizing voltage used by the directional unit when "Voltage" or "Dual"polarizing mode is set. The polarizing voltage can be programmed to be either the zero-sequence voltage calculatedfrom the phase voltages ("Calculated V0") or supplied externally as an auxiliary voltage ("Measured VX").• NEUTRAL DIR OC1 OP CURR: This setting indicates whether the 3I_0 current calculated from the phase currents, orthe ground current shall be used by this protection. This setting acts as a switch between the neutral and groundmodes of operation (67N and 67G). If set to “Calculated 3I0” the element uses the phase currents and applies the pos-itive-sequence restraint; if set to “Measured IG” the element uses ground current supplied to the ground CT of the CTbank configured as NEUTRAL DIR OC1 SOURCE. If this setting is “Measured IG”, then the NEUTRAL DIR OC1 POLARIZINGsetting must be “Voltage”, as it is not possible to use the ground current as an operating and polarizing signal simulta-neously. IG current has to be above 0.05 ps to be used as operate quantity.• NEUTRAL DIR OC1 POS-SEQ RESTRAINT: This setting controls the amount of the positive-sequence restraint. Setto 0.063 for backward compatibility with firmware revision 3.40 and older. Set to zero to remove the restraint. Sethigher if large system unbalances or poor CT performance are expected.• NEUTRAL DIR OC1 OFFSET: This setting specifies the offset impedance used by this protection. The primary appli-cation for the offset impedance is to guarantee correct identification of fault direction on series compensated lines. Inregular applications, the offset impedance ensures proper operation even if the zero-sequence voltage at the relayingpoint is very small. If this is the intent, the offset impedance shall not be larger than the zero-sequence impedance ofthe protected circuit. Practically, it shall be several times smaller. The offset impedance shall be entered in secondaryohms.See chapter 8 for additional details and chapter 9 for information on how to calculate this setting• NEUTRAL DIR OC1 FWD ECA: This setting defines the characteristic angle (ECA) for the forward direction in the"Voltage" polarizing mode. The "Current" polarizing mode uses a fixed ECA of 0°. The ECA in the reverse direction isthe angle set for the forward direction shifted by 180°.• NEUTRAL DIR OC1 FWD LIMIT ANGLE: This setting defines a symmetrical (in both directions from the ECA) limitangle for the forward direction.• NEUTRAL DIR OC1 FWD PICKUP: This setting defines the pickup level for the overcurrent unit of the element in theforward direction. When selecting this setting it must be kept in mind that the design uses a ‘positive-sequencerestraint’ technique for the “Calculated 3I0” mode of operation.• NEUTRAL DIR OC1 REV LIMIT ANGLE: This setting defines a symmetrical (in both directions from the ECA) limitangle for the reverse direction.• NEUTRAL DIR OC1 REV PICKUP: This setting defines the pickup level for the overcurrent unit of the element in thereverse direction. When selecting this setting it must be kept in mind that the design uses a positive-sequence restrainttechnique for the “Calculated 3I0” mode of operation.
