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Functions

6-250 7SA6 Manual

C53000-G1176-C156-2

Figure 6-122 Current flow monitoring with the plausibility currents 3·I

and 3·I

Processing of the

Circuit Breaker

Auxiliary Contacts

The position of the circuit breaker is derived from the central function control of the de-

vice (refer also to Section 6.22.2). Evaluation of the breaker auxiliary contacts is car-

riedoutinthebreakerfailureprotectionfunctiononlywhenthecurrentflowmonitoring

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 auxiliary contact does not (yet) indicate that

the circuit breaker has opened (Figure 6-123). This gives preference to the more reli-

able 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

Chk BRK CONTACT (Figure 6-125 above) 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.

I> &

Current

criterion

3902 I> BF

L1>

L2>

L3>

plausi-

bility

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