Siemens SIPROTEC 7SA522 Manual page 301

Figure 2-122 Current flow monitoring with plausibility currents 3·I
Processing of the
Circuit Breaker
Auxiliary Contacts
7SA522 Manual
C53000-G1176-C155-3
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 2.20.1). 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 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 auxil-
iary contact does not (yet) indicate that the circuit breaker has opened (Figure 2-123).
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 trip.
It is possible to disable the auxiliary contact criterion. If you set the parameter switch
&KN %5. &217$&7 (Figure 2-125 top) to 12, 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.
Figure 2-123 Interlock of the auxiliary contact criterion - example for phase L1
On the other hand, current flow is not a reliable criterion for proper operation of the
circuit breaker for faults which do not cause detectable current flow (e.g. Buchholz pro-
tection). Information regarding the position of the circuit breaker auxiliary contacts is
required in these cases to check the correct response of the circuit breaker. This is ac-
complished through binary input ´!%) 6WDUW ZR ,µ FNo. 1439
2.18 Circuit breaker failure protection (optional)
and 3·I
0 2
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