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2.8 Circuit Breaker Failure Protection
105
7ST6 Manual
E50417-G1176-C251-A3
Delay Times
When the initiate conditions are fulfilled, the associated timers
tBF1
(address
3904
)
and
tBF2
(address
3905
) are started. The circuit breaker pole(s) must open before
the associated time has elapsed. The device detects that the circuit breaker has
opened when the current drops below the dropout threshold
I> BF
(address
3902
).
With two-stage breaker failure protection, the trip command of the overhead contact
line protection is usually repeated, after a first time stage, to the feeder circuit breaker,
often via a second trip coil or set of trip coils, if the breaker has not responded to the
original trip command. The signal 1471
„BrkFailure TRIP“
is provided for this trip
command repetition. A second time stage monitors the response to this repeated trip
command and trips the breakers of the relevant bus-bar section with the signal 1484
„B/F s.ordProt“
, if the fault has not yet been cleared after this second time.
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