Circuit Breaker Failure Protection
125
7SS52 V4 Manual
C53000-G1176-C182-1
Figure 5-26 Circuit breaker failure protection for busbar faults
5.3.5.4 Failure of the Bus Coupler Circuit Breaker
If a busbar short-circuit occurs with the bus coupler closed (Figure 5-27, page 125), a
TRIP command is issued to all related feeders of this zone and to the coupling bay
units. (1)
Thus bus zone BZ A is isolated and the healthy bus zone BZ B stays in service.
In the event of a failure of the bus coupler circuit breaker, the busbar protection has to
disconnect bus zone BZ B, too (single unbalancing to BZ B).
If the current continues to flow in a coupler unit after the time set with the parameter
T-BF-mP (XX21/CU), the coupler current is set to zero.
The trip criterion is thus fulfilled and bus zone BZ B is isolated, too. (2)
In the case of a breaker failure of the circuit breaker in the bus coupler bay (internal
breaker failure), the alarm "TRIP BF M" (10436/CU) is issued.
Figure 5-27 Fault on bus zone BZ A and failure of the bus coupler circuit breaker
5.3.5.5 Circuit Breaker Not Ready
For the detection of malfunctions in the tripping mechanism of the feeder circuit break-
er, the bay unit is provided with a binary input ">CB not ready" (FNo. 7619/BU).
If a breaker failure occurs while a signal is present at this binary input, the breaker fail-
ure protection uses the delay time T-BF CB fault (XX24/CU) instead of the time
set with the parameters T-BF-1P (XX20/CU) and T-BF-mP (XX21/CU).
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