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CHAPTER 6: SETPOINTS
Negative sequence timed overcurrent protection (51_2)
350 FEEDER PROTECTION SYSTEM – INSTRUCTION MANUAL
The 3 Series relay has one Negative Sequence Overcurrent element per setpoint group.
The negative sequence overcurrent protection responds to negative sequence |I
where it is calculated as .
The negative sequence overcurrent elements are uniquely suited to detect phase-phase
faults and are not sensitive to balanced loads. While negative sequence elements do not
respond to a balanced load, they do detect the negative sequence current present in an
unbalanced load. For this reason, select an element pickup setting above the maximum
expected I
current due to load unbalance.
2
The Negative Sequence TOC1(2) Trip (Alarm) Pickup flag is asserted when the negative
sequence current is above the PKP value. The Negative Sequence TOC1(2) Trip (Alarm)
operate 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 97-99% 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. The selection of Definite Time has a base
time delay of 0.1s, multiplied by the selected TD multiplier. For example, the operating time
for TOC set to Definite Time and a TDM set to 5 will result in 5*0.1 = 0.5s.
PATH:
SETPOINTS > S3 PROTECTION > SETPOINT GROUP 1(2) > NEG SEQ TOC1(2)
NEG SEQ TOC FUNC
Range: Disabled, Latched Alarm, Alarm, Trip
Default: Disabled
For details see
Common
NEG SEQ TOC PKP
Range: 0.05 to 20.00 x CT in steps of 0.01 x CT
Default: 1.00 x CT
This setting defines the negative sequence TOC pickup level associated with the ratings
of the CTs selected under NEG SEQ CT INPUT.
NEG SEQ TOC CURVE
Range: - ANSI Extremely/Very/Moderately/Normally Inverse- Definite Time- IEC Curve A/
B/C and Short Inverse- IAC Extremely/Very/Inverse/Short, User Curve, FlexCurve™ A/B
Default: Ext Inverse
This setting defines the shape of the selected overcurrent inverse curve.
NEG SEQ TOC TDM
Range: 0.05 to 50.00 in steps of 0.01
Default: 1.00
This setting provides a selection for Time Dial Multiplier, which modifies the time
response of the selected curve. For example if an ANSI Extremely Inverse curve is
selected with TDM = 2, and the fault current was 5 times bigger than the PKP level, the
operation of the element will not occur before the elapse of 2.59 seconds from pickup.
setpoints.
S3 PROTECTION
|current,
2
6–61
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