4–180 889 GENERATOR PROTECTION SYSTEM – INSTRUCTION MANUALPROTECTION CHAPTER 4: SETPOINTSFUNCTIONRange: Disabled, EnabledDefault: DisabledPOLARIZING MODERange: Voltage, Current, DualDefault: VoltageThis setting selects the polarizing mode for the directional unit.• If Voltage polarizing mode is selected, the element uses the zero-sequence voltageangle for polarization. The user can select either the zero-sequence voltage V_0,calculated from the phase voltages, or the zero-sequence voltage supplied externallyas the auxiliary voltage V_X.The calculated V_0 can be used as polarizing voltage only if the voltage transformersare connected in Wye. The auxiliary voltage can be used as the polarizing voltage ifthe auxiliary voltage is connected to a zero-sequence voltage source (such as theopen delta connected secondary of VTs).The zero-sequence (V_0) or auxiliary voltage (V_X), accordingly, must be greater than0.02 x VT to be validated for use as a polarizing signal. If the polarizing signal is invalid,neither forward nor reverse indication is given.• If Current polarizing mode is selected, the element uses the angle of the groundcurrent measured on the ground current input. The ground CT must be connectedbetween the ground and neutral point of an adequate source of ground current. Theground current must be greater than 0.05 x CT to be validated as a polarizing signal. Ifthe polarizing signal is not valid, neither forward nor reverse indication is given.For a choice of current polarizing, it is recommended that the polarizing signal beanalyzed to ensure that a known direction is maintained irrespective of the faultlocation. For example, if using an autotransformer neutral current as a polarizingsource, it should be ensured that a reversal of the ground current does not occur for ahigh-side fault. The low-side system impedance should be assumed minimal whenchecking for this condition. A similar situation arises for a wye/delta/wye transformer,where current in one transformer winding neutral may reverse when faults on bothsides of the transformer are considered.• If Dual polarizing mode is selected, the element performs both directionalcomparisons as described above. A given direction is confirmed if either voltage orcurrent comparators indicate so. If a conflicting (simultaneous forward and reverse)indication occurs, the forward direction overrides the reverse direction.POLARIZING VOLTAGERange: Calculated V0, Measured VXDefault: Calculated V0Selects 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 calculated from the phase voltages ("Calculated V_0") or suppliedexternally as an auxiliary voltage ("Measured VX")POS SEQ RESTRAINTRange: 0.000 to 0.500 in steps of 0.001Default: 0.063This setting controls the amount of the positive-sequence restraint. Set to zero toremove the restraint. Set higher if large system unbalances or poor CT performance areexpected.
