Supervision is disabled in the following cases:
•
On pickup of the Circuit-breaker failure protection function (only in the case of an external start). This
prevents an unwanted pickup of the supervision if the external protection that starts the Circuit-breaker
failure protection function uses a lockout functionality. When the starting signal drops out, the supervi-
sion is enabled again.
•
As long as the function or the device is in test mode. This allows to check the function without the super-
vision blocking the function.
If the >Start signal is active and no release signal is present after elapse of the settable supervision time for
the starting signal, the pickup is blocked and an indication to this effect is output. The Health signal changes
to the state Warning. The blocking is reset with the dropout of the starting signal.
The binary input signals only take effect if the binary inputs are activated for at least 10 ms (SW filter, see
Figure 6-251).
[logikext-070611-02.tif, 2, en_US]
Figure 6-251
External Start of the Circuit-Breaker Failure Protection Function, Logic
Current-Flow Criterion
The current-flow criterion is the primary criterion for determining the circuit-breaker switch position. A circuit-
breaker pole is supposed to be closed, and the current-flow criterion fulfilled, as soon as one of the phase
currents exceeds the phase-current threshold value and a plausibility current exceeds the associated threshold
value at the same time. The plausibility current can be either a 2nd phase current (to compare with the phase-
current threshold value) or the zero-sequence or negative-sequence current (to compare with the sensitive
threshold value). The additional evaluation of the plausibility current increases the safety of the criterion.
In the case of ground faults, the sensitive threshold value can be dynamically applied to the phase currents as
well. The current-flow criterion is fulfilled when the currents exceed the sensitive threshold value. The phase-
current threshold value is then ineffective. The binary signal >Threshold sensitive is used for the switch-
over.
Protection and Automation Functions
6.41 Circuit-Breaker Failure Protection
SIPROTEC 5, Overcurrent Protection, Manual 839
C53000-G5040-C017-8, Edition 07.2017
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