2.13 Circuit Breaker Failure Protection
179
7SD610 Manual
C53000-G1176-C145-4
Figure 2-63 Current flow monitoring with plausibility currents 3·I
0
and 3·I
2
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 2.16.1). The evaluation of
the breaker auxiliary contacts is carried out in the breaker failure protection function
only when the current flow monitoring has not picked up. Once the current flow crite-
rion 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 aux-
iliary contact does not (yet) indicate that the circuit breaker has opened (Figure 2-64).
This gives preference to the more reliable current criterion and avoids overfunctioning
due to a defect e.g. in the auxiliary contact mechanism or circuit. This interlock feature
is provided for each individual phase as well as for three-pole tripping.
It is possible to disable the auxiliary contact criterion. If you set the parameter switch
Chk BRK CONTACT (Figure 2-66 top) to NO, the 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.
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