Negative Sequence Time Overcurrent Protection - GE 845 Instruction Manual

CHAPTER 4: SETPOINTS
Negative Sequence
Time Overcurrent
Protection
845 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
The 845 relay is equipped with the Negative Sequence Time Overcurrent protection
element. The Negative Sequence Time Overcurrent element may be used to determine
and clear unbalance in the system. The input for computing negative-sequence current is
the fundamental phasor value. The 845 computes the negative sequence current
magnitude |I_2| using the following formula:
|I_2|=1/3*|Ia+Ib*(1∠240º)+Ic*(1∠120º)|
The settings of this function are applied to the calculated negative sequence current to
produce Trip or Pickup flags. The Negative Sequence TOC Pickup flag is asserted when the
negative sequence current is above the PKP value. The Negative Sequence 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 Negative Sequence TOC operation
is defined only by the TDM setting.
Path:
Setpoints > Protection > Group 1(6) > Current > Negative Sequence TOC
FUNCTION
Range: Disabled, Trip, Alarm, Latched Alarm, Configurable
Default: Disabled
PICKUP
Range: 0.050 to 30.000 x CT in steps of 0.001 x CT
Default: 1.000 x CT
CURVE
Range: IEEE Extremely/Very/Moderately Inverse
ANSI Extremely/Very/Normally/Moderately Inverse
IEC Curve A/B/C and Short Inverse
IAC Extremely/Very/Inverse/Short Inverse
FlexCurve A, FlexCurve B, FlexCurve C, FlexCurve D
I2t, I4t, Definite time
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
PROTECTION
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