Parameter Range
Earth inverse time
over-current
Time multiplier setting (TMS) 0.01 to 100.0 1.0
Threshold 1.0 to 1.3 1.1
k (only used if custom curve is selected) 0.001 s to 2 min 0.14 s
c (only used if custom curve is selected) 0 s to 1 min 0 s
alpha (α, or a) (only used if custom curve is
selected)
0.001 to 1 0.02
Enable Not enabled, Enabled Enabled
Latch Not enabled, Enabled Enabled
Alarm action Trip breaker
More information
See Source AC protections, Inverse time over-current (ANSI 51N) in this chapter for the calculation method, the
standard curves, and information about the definite time characteristic.
3.6.3 Neutral inverse time over-current (ANSI 51N)
Protection
IEC symbol (IEC60617) ANSI (IEEE C37.2) IEC 61850 Operate time
Neutral inverse time over-current 51N -
This is the inverse time over-current alarm for the neutral current
measurement.
The alarm response is based on the unfiltered (except for anti-aliasing)
neutral current, as measured by the 4th current measurement.
The alarm response time depends on an approximated integral of the
current measurement over time. The integral is only updated when the
measurement is above the activation threshold.
Note: The diagram on the right is a simplified representation of this alarm.
The diagram does not show the integral over time.
Wiring
You must wire the 4th current measurement on ACM3.1 (terminals 15,16) to measure the neutral current.
More information
See Wiring examples for controller functions, AC measurement wiring, System AC configuration in the Installation
instructions for an example of how to wire the neutral current measurement.
INFO
The Earth inverse time over-current and Neutral inverse time over-current alarms each require the 4th current
measurement. You therefore cannot have both of these protections at the same time.
DESIGNER'S HANDBOOK 4189340911K UK Page 86 of 521
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