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Breaker failure protection (BFP)
Start BFP
Relay
time
CB Opening time
30 ms
40 ms
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The breaker-failure protection will be started by a general signal, or in some cases phase
selective signals, either from an external protection, or internally from a protection trip
signal in the terminal.
The breaker receiving the original protection trip command can be retripped from the
BFP. The retrip can be controlled by a current check, or carried out as a direct retrip
without any current check. The direct retrip can be used, because the breaker-to-trip has
already received a tripping command, and the direct retrip does not cause any unselec-
tive tripping
The use of retrip, limits the extent of unwanted power disconnection in case of an acci-
dental start of the BFP at work in the initiating circuits, with the primary circuit in ser-
vice and the load above the set current level.
The back-up trip is sent to the adjacent circuit breakers in order to clear the fault and
disconnect the failing circuit breaker.
Normal
CB Opening
Margin
20 ms
BFP
Time
CB Opening time
<10 ms
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Retrip
General trip
original CB
adjacent CB
110 ms
Marginal
40 ms
BFP
20 ms
time
<10 ms
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150 ms
125
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