REG 316*4 1MRB520049-Uen / Rev. B ABB Switzerland Ltd
4-45
4.2.7.8. ‘End Fault Trip’
While in the case of a fault between a circuit-breaker and a sin-
gle set of c.t’s, the circuit-breaker may not fail, the affect on the
power system and the action that has to be taken are the same
as if the circuit-breaker had failed.
Where there is only a single set of c.t’s on the busbar side of a
circuit-breaker, the zones of protection do not overlap and a fault
between the circuit-breaker and the c.t’s is seen as a line fault,
although it belongs to the busbar zone and persists after the cir-
cuit-breaker has been tripped. The breaker failure protection’s
‘End Fault Trip’ logic ultimately clears such faults at the end of
the second time step.
This logic is enabled if the breaker is open and the current de-
tectors are still picked up, indicating a fault between the breaker
and the c.t’s. The speed of tripping is determined by the time
delay setting.
Depending on whether the single set of c.t’s is on the line side or
bus side of the circuit-breaker, either the section of busbar or the
circuit-breaker at the remote end of the line is tripped.
4.2.7.9. ‘External Trip’
This function has been included to make the breaker fail protec-
tion more user-friendly and reduce the amount of systems engi-
neering required. It generates an instantaneous trip when either
of the following inputs is activated:
· The input connected to the second time steps of other
breaker fail protection devices in the station.
· The input connected to the end fault outputs of other breaker
fail protection devices in the station.
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