CHAPTER 4: SETPOINTS PROTECTION889 GENERATOR PROTECTION SYSTEM – INSTRUCTION MANUAL 4–189The 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 polarizingcurrent measured on the ground current input K1-CT (if available). The polarizingcurrent must be greater than 0.05 x CT to be validated as a polarizing signal. If thepolarizing 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.• 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")FORWARD ECARange: –90° to 90° in steps of 1°Default: 75°This setting defines the element characteristic angle (ECA) for the forward direction in"Voltage" polarizing mode. "Current" polarizing mode uses a fixed ECA of 0°. The ECA inthe reverse direction is the angle set for the forward direction shifted by 180°.FORWARD LIMIT ANGLERange: 40° to 90° in steps of 1°Default: 90°This setting defines a symmetrical (in both directions from the ECA) limit angle for theforward direction.FORWARD PICKUPRange: 0.050 to 30.000 x CT in steps of 0.001 x CTDefault: 0.050 x CTThis setting defines the Pickup level for the overcurrent unit of the element in theforward direction.NOTENOTE:When Signal Input is selected as K1 ground input from 50:0.0.25 CT (B1/B5 order code), thepickup setting must be done considering 1:1 CT ratio. The relay applies a ratio of 2000internally to directly measure primary side ground current and apply into this function. Forexample, a pickup setting 1.000 x CT translates to the pickup of the element when CTprimary current exceeds 1.000 Ampere (i.e. 0.5 mA injected into the relay from CTsecondary.)
