CHAPTER 4: SETPOINTS PROTECTION889 GENERATOR PROTECTION SYSTEM – INSTRUCTION MANUAL 4–183Ground TimeOvercurrentProtection (51G)The 889 is equipped with the Ground Time Overcurrent protection element. The settings ofthis function are applied to the ground input current to produce Trip or Pickup flags. TheGround TOC Pickup flag is asserted when the ground current is above the PKP value. TheGround TOC Trip flag is asserted if the element stays picked up for the time defined by theselected inverse curve and the magnitude of the current. The element drops from Pickupwithout operation if the measured current drops below 97 to 98% of the Pickup valuebefore the time for operation is reached. When Definite Time is selected, the time forGround TOC operation is defined only by the TDM setting.FUNCTIONRange: Disabled, Trip, Alarm, Latched Alarm, ConfigurableDefault: DisabledINPUTRange: Phasor, RMSDefault: PhasorPICKUPRange: 0.050 to 30.000 x CT in steps of 0.001 x CTDefault: 1.000 x CTNOTENOTE: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.)CURVERange: IEEE Extremely/Very/Moderately Inverse,ANSI Extremely/Very/Normally/Moderately Inverse,Definite time IEC A/B/C and Short Inverse,IAC Extremely/Very/Inverse/Short InverseFlexCurve A/B/C/D, I2t, I4tDefault: IEEE, Moderately InverseTDMRange: 0.05 to 600.00 in steps of 0.01Default: 1.00RESETRange: Instantaneous, TimedDefault: InstantaneousDIRECTIONRange: Disabled, Forward, ReverseDefault: DisabledBLOCKRange: Off, Any FlexLogic operandDefault: OffOUTPUT RELAY XFor details see Common Setpoints.EVENTSRange: Enabled, DisabledDefault: Enabled
