Ground Time Overcurrent Protection (51G) - GE 889 Instruction Manual

CHAPTER 4: SETPOINTS
Ground Time
Overcurrent
Protection (51G)
NOTE:
NOTE
889 GENERATOR PROTECTION SYSTEM – INSTRUCTION MANUAL
The 889 is equipped with the Ground Time Overcurrent protection element. The settings of
this function are applied to the ground input current to produce Trip or Pickup flags. The
Ground TOC Pickup flag is asserted when the ground current is above the PKP value. The
Ground TOC Trip flag is asserted if the element stays picked up for the time defined by the
selected inverse curve and the magnitude of the current. The element drops from Pickup
without operation if the measured current drops below 97 to 98% of the Pickup value
before the time for operation is reached. When Definite Time is selected, the time for
Ground TOC operation is defined only by the TDM setting.
FUNCTION
Range: Disabled, Trip, Alarm, Latched Alarm, Configurable
Default: Disabled
INPUT
Range: Phasor, RMS
Default: Phasor
PICKUP
Range: 0.050 to 30.000 x CT in steps of 0.001 x CT
Default: 1.000 x CT
When Signal Input is selected as K1 ground input from 50:0.0.25 CT (B1/B5 order code), the
pickup setting must be done considering 1:1 CT ratio. The relay applies a ratio of 2000
internally to directly measure primary side ground current and apply into this function. For
example, a pickup setting 1.000 x CT translates to the pickup of the element when CT
primary current exceeds 1.000 Ampere (i.e. 0.5 mA injected into the relay from CT
secondary.)
CURVE
Range: 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 Inverse
FlexCurve A/B/C/D, I2t, I4t
Default: IEEE, Moderately Inverse
TDM
Range: 0.05 to 600.00 in steps of 0.01
Default: 1.00
RESET
Range: Instantaneous, Timed
Default: Instantaneous
DIRECTION
Range: Disabled, Forward, Reverse
Default: Disabled
BLOCK
Range: Off, Any FlexLogic operand
Default: Off
OUTPUT RELAY X
For details see Common
EVENTS
Range: Enabled, Disabled
Default: Enabled
Setpoints.
PROTECTION
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