Method of Measurement, Current-Flow Criterion
The current-flow criterion works with 2 different methods of measurement.
•
Measurement of the fundamental component:
This method of measurement processes the sampled current values and filters out the fundamental
component numerically. A direct-current component is thus eliminated. The RMS value of the funda-
mental component is compared with the set threshold.
•
Evaluation of the unfiltered measurand:
If the current exceeds the threshold value set by the current amount ≥ 2 ⋅√2 ⋅ threshold value, the stage
uses additional unfiltered measurands. Thus, very short operate times are possible.
NOTE
If using the current-flow criterion in addition to the light, prevent a potential overfunction caused by the
suddenly occurring light signal.
If you use the current-flow criterion, arcs are typically detected in 4 ms!
Self Monitoring
The Arc protection function uses a self-monitoring circuit. This circuit monitors the optical arc sensors and the
fiber-optic cables. The arc-protection module uses the fiber-optic cable to send a cyclic test signal (light) to the
arc sensors. If the channel is operating properly, the test signal is sent back to the arc protection module. If the
test signal is not returned to the arc protection module, the indication
channel # Sensor failure
is
generated.
If the self-monitoring function detects a fault, the indication
Health
is set to
Alarm
and the stage/function is
blocked.
Application and Setting Notes – General Settings
Go to General under the function Arc protection and set the following parameters. The setting values apply
to all stages.
Parameter: Threshold I>
•
Default setting (_:2311:3) Threshold I> = 2.000 A
Use the parameter Threshold I> to define the trigger threshold of the phase currents. The Threshold I>
is relevant for the current-flow criterion of the arc protection function.
Set the Threshold I> of the function Arc protection in such a manner that the RMS value of the inrush
current does not exceed the Threshold I> when activating the local circuit breaker.
For more information about how to calculate the setting value, refer to 6.3.4.2 Application and Setting Notes
Parameter: Threshold 3I0>
•
Default setting (_:2311:4) Threshold 3I0> = 1.000 A
Use the parameter Threshold 3I0> to determine the tripping threshold for the zero-sequence current. The
Threshold 3I0> is relevant for the current-flow criterion of the Arc protection function.
Set the Threshold 3I0> of the function Arc protection in such a manner that the RMS value of the inrush
current does not exceed the Threshold 3I0> when activating the local circuit breaker.
For more information about how to calculate the setting value, refer to 6.5.4.2 Application and Setting Notes
NOTE
If you set the parameter CT connection = 3-phase, 2 primary CT for the 3-phase current meas-
uring point, the parameter Threshold 3I0> has no effect.
6.10.4
Protection and Automation Functions
6.10 Arc Protection
SIPROTEC 5, Overcurrent Protection, Manual 503
C53000-G5040-C017-8, Edition 07.2017
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