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889 GENERATOR PROTECTION SYSTEM – INSTRUCTION MANUAL
PROTECTION
CHAPTER 4: SETPOINTS
Sensitive Ground Time
Overcurrent
Protection (51SG)
The 889 is equipped with the Sensitive Ground Time Overcurrent protection element. The
settings of this function are applied to the Sensitive Ground input current to produce Trip or
Pickup flags. The Sensitive Ground TOC Pickup flag is asserted when the Sensitive Ground
current is above the PKP value. The Sensitive 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 97-98% of the Pickup value before the time for operation is
reached. When Definite Time is selected, the time for Sensitive Ground TOC operation is
defined only by the TDM setting.
Path
:
Setpoints > Protection > Group 1(6) > Current > Sensitive Ground TOC 1(X)
FUNCTION
Range: Disabled, Trip, Alarm, Latched Alarm, Configurable
Default: Disabled
INPUT
Range: Phasor, RMS
Default: Phasor
This selection defines the method of processing of the current signal. It can be Root
Mean Square (RMS) or Fundamental Phasor Magnitude.
PICKUP
The 50:0.025 Ground input (K1-Ig) range is as follows:
Range: 0.50 to 15.00 A in steps of 0.01 A
Default: 10.00 A
In the case of 50:0.025 Ground input (K1-Ig as current input), the pickup level is specified
as Ampere in primary. For example, with a PKP setting of 10.00 A, when ground current
(primary) is 10.00A, the K1-Ig will measure 10.000 A, and this function should pick up.
CURVE
Range: IEEE Extremely/Very/Moderately Inverse,
ANSI Extremely/Very/Normally/Moderately Inverse,
IEC A/B/C and Short Inverse,
IAC Extremely/Very/Inverse/Short Inverse,
I2t, I4t, FlexCurve A/B/C/D, Definite time
Default: IEEE Mod Inverse
This setting sets the shape of the selected over-current inverse curve. If none of the
standard curve shapes is appropriate, a FlexCurve can be created. Refer to the User
curve and the FlexCurve setup for more details on their configurations and usage.
TDM
Range: 0.05 to 600.00 in steps of 0.01
Default: 1.00
This setting provides the selection for the Time Dial Multiplier by which the times from
the inverse curve are modified. For example if an ANSI Extremely Inverse curve is
selected with TDM = 2, and the fault current is 5 times bigger than the PKP level, the
operation of the element will occur but not before 2.59s of time has elapsed from pickup.
RESET
Range: Instantaneous, Timed
Default: Instantaneous
The selection of an Instantaneous or a Timed reset time is provided by this setting. If
Instantaneous reset is selected, the Sensitive Ground TOC element will reset
instantaneously providing the current drops below 97-98% of the Sensitive Ground TOC
PKP level, before the time for operation is reached.
