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Functions
2.22 Circuit Breaker Failure Protection
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
398
Figure 2-185 Current flow monitoring with plausibility currents 3· I
0
and 3· I
2
1) only available/visible if
139
is set to
enabled w/ 3I0>
Monitoring the circuit breaker auxiliary contacts
It is the central function control of the device that informs the breaker failure protection on the position of the
circuit breaker (refer also to Section 2.25.1). The evaluation of the breaker auxiliary contacts is carried out in
the breaker failure protection function only if no current is flowing above the value set for current flow monitor-
ing. Once the current flow criterion has picked up during the trip signal from the feeder protection, the circuit
breaker is assumed to be open as soon as the current disappears, even if the associated auxiliary contacts do
not (yet) indicate that the circuit breaker has opened (Figure 2-186). This gives preference to the more reliable
current criterion and avoids overfunctioning due to a defect e.g. in the auxiliary contact mechanics. This block
applies to each individual phase and for 3-pole tripping.
It is possible to disable the auxiliary contact criterion. If you set the parameter switch
Chk BRK CONTACT
(Figure 2-188 top) to
NO
, the circuit breaker failure protection can only be started when current flow is detected.
The position of the auxiliary contacts is then not evaluated even if the auxiliary contacts are connected to the
device.