Introduction
8
7SS52 V4 Manual
C53000-G1176-C182-3
Breaker failure
protection
The integrated circuit breaker failure protection (CBF) contains the following functions:
• In case of a busbar short-circuit, a breaker failure is detected by comparison of cur-
rent thresholds.
• In all operating modes of the circuit breaker failure protection, a bay-selective com-
mand is output by the bay units to trip the circuit breaker at the remote end (transfer
trip command).
• The external breaker failure protection can be started for one phase or for three
phases.
• The breaker failure protection can be started on 1 channel or, for extra reliability, on
2 channels. Both settings can be combined with a monitoring feature.
• Reduced response times in case of a circuit breaker malfunction
• Query of the circuit breaker position in case of low-current faults
• The circuit breaker failure protection function can be deactivated for test purposes.
The following modes are available for the circuit breaker failure protection:
• I> query:
After initiation by a TRIP command from the feeder protection, the 7SS52 V4
checks the feeder current. If the measured current stays above the set threshold af-
ter a set time has elapsed, the 7SS52 V4 issues zone-selective TRIP commands in
the bays considering the isolator replica.
• TRIP repetition with subsequent I> query:
When initiated by a TRIP command from the feeder protection, the 7SS52 V4 is-
sues a second TRIP command to the circuit breaker of the initiating feeder after a
set time delay. In case this second TRIP command is also unsuccessful, tripping as
per mode I>query is effected.
• Unbalancing:
After initiation by a TRIP command from the feeder protection, the
7SS52 V4 system checks the feeder current. If the measured current stays above
the set threshold after a set time has elapsed, the polarity of the current in this feed-
er is inverted by the 7SS52 V4 (unbalancing).
• TRIP repetition with subsequent unbalancing:
When initiated by a TRIP command from the feeder protection, the 7SS52 V4 is-
sues a second TRIP command to the circuit breaker of the initiating feeder after a
set time delay. In case this second TRIP command is also unsuccessful, tripping as
per mode Unbalancing is effected.
• TRIP by external CBF:
Where a separate circuit breaker failure protection is provided, the 7SS52 V4 can
generate zone-selective feeder trip commands utilizing the integrated isolator rep-
lica.
• TRIP repetition with subsequent unbalancing with pulse trigger or I>query:
This mode should be used when the CBF is triggered by the remote station. The
function is triggered by a trip command from the feeder protection at the remote
feeder terminal. The further proceeding is described in the modes TRIP repetition
with subsequent unbalancing and I>query.
• Low-current CBF:
This mode outputs a TRIP command even in the case of low-current faults (e.g. trip-
ping by Buchholz protection). After a settable time the circuit breaker position is
queried. A TRIP repetition also takes place with a low-current operating mode.
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