CHAPTER 5: SETTINGS GROUPED ELEMENTSL90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL 5-2375The ground mho distance function uses a dynamic 100% memory-polarized mho characteristic with additional reactance,directional, current, and phase selection supervising characteristics. The ground quadrilateral distance function iscomposed of a reactance characteristic, right and left blinders, and 100% memory-polarized directional, overcurrent, andphase selection supervising characteristics.When set to non-directional, the mho function becomes an offset mho with the reverse reach controlled independentlyfrom the forward reach, and all the directional characteristics removed. When set to non-directional, the quadrilateralfunction applies a reactance line in the reverse direction instead of the directional comparators.The reactance supervision for the mho function uses the zero-sequence current for polarization. The reactance line of thequadrilateral function uses either zero-sequence or negative-sequence current as a polarizing quantity. The selection iscontrolled by a user setting and depends on the degree of non-homogeneity of the zero-sequence and negative-sequenceequivalent networks.The directional supervision uses memory voltage as polarizing quantity and both zero- and negative-sequence currents asoperating quantities.The phase selection supervision restrains the ground elements during double-line-to-ground faults as they, by theprinciples of distance relaying, can be inaccurate in such conditions. Ground distance zones 1 and higher apply additionalzero-sequence directional supervision.Each ground distance zone is configured individually through its own setting menu. All of the settings can be modifiedindependently for each of the zones except:• The SIGNAL SOURCE setting (common for both phase and ground elements for all zones as entered under the SETTINGS GROUPED ELEMENTS SETTING GROUP 1(6) DISTANCE menu)• The MEMORY DURATION setting (common for both phase and ground elements for all zones as entered under theSETTINGS GROUPED ELEMENTS SETTING GROUP 1(6) DISTANCE menu)The common distance settings noted at the start of this section must be properly chosen for correct operation of theground distance elements.Although all ground distance zones can be used as either instantaneous elements (pickup [PKP] and dropout [DPO]FlexLogic signals) or time-delayed elements (operate [OP ] FlexLogic signals), only zone 1 is intended for the instantaneousunder-reaching tripping mode.GND DIST Z1 DIR — All ground distance zones are reversible. The forward direction is defined by the GND DIST Z1 RCA settingand the reverse direction is shifted by 180° from that angle. The non-directional zone spans between the forward reachimpedance defined by the GND DIST Z1 REACH and GND DIST Z1 RCA settings, and the reverse reach impedance defined bythe GND DIST Z1 REV REACH and GND DIST Z1 REV REACH RCA settings.GND DIST Z1 SHAPE — This setting selects the shape of the ground distance characteristic between the mho andquadrilateral characteristics. The selection is available on a per-zone basis.The figures show the directional and non-directional quadrilateral ground distance characteristics. The directional andnon-directional mho ground distance characteristics are the same as those shown for the phase distance element in theprevious section. GND DIST Z1 BLK:OffRange: FlexLogic operand GND DIST Z1TARGET: Self-ResetRange: Self-Rest, Latched, Disabled GND DIST Z1EVENTS: DisabledRange: Disabled, EnabledEnsure that the PHASE VT SECONDARY VOLTAGE (see the SETTINGS SYSTEM SETUP AC INPUTS VOLTAGE BANKmenu) is set correctly to prevent improper operation of associated memory action.
