Circuit Breaker Failure Protection
119
7SS52 V4 Manual
C53000-G1176-C182-3
5.3.5.2 Circuit Breaker Failure Protection during a Feeder Short-Circuit
In the event of a breaker failure following a feeder short-circuit, the fault current must
be interrupted by isolating the bus zone to which the affected feeder is allocated. The
breaker failure protection of the SIPROTEC 7SS52 V4 distributed busbar and breaker
failure protection is triggered by the TRIP command from the feeder protection. This
command can be detected for one phase with the binary inputs ”>CBF Lx”
(FNo. 7611,7612,7613/BU) or for three phases with the binary input
”>CBF 3-pole” (FNo. 7621/BU) in the bay unit.
BF OP MODE How the 7SS52 V4 protection system reacts after this depends on the breaker failure
protection mode, which is set with the parameter BF OP MODE (XX15/CU). It is set
individually for each feeder.
The following modes are available for the circuit breaker failure protection (CBF):
• I> query (1-stage CBF)
• TRIP repetition with overcurrent detection I> (2-stage CBF)
• Unbalancing (1-stage CBF)
• TRIP repetition with following unbalancing (2-stage CBF)
• TRIP by external CBF
2-stage CBF In the 2-stage CBF operating modes, a second bay-selective TRIP command is output
by the bay unit after the delay T-TRIP repeat (XX25/CU) has elapsed to provide in
any case for a trip of the circuit breaker. This can be useful, for instance, if the circuit
breaker has a second trip coil or a control circuit that is separate from the bay protec-
tion. The affected bus zone is not disconnected until a second, unsuccessful TRIP at-
tempt has been made. A prerequisite for a TRIP repeat is that the curcuit breaker is
ready for operation. That means a binary input ">CB not ready" (FNo. 7619/BU)
is not active.
Initiation by feeder
protection
In feeders with a double set of protection devices (main/back-up protection), the CBF
protection can be initiated both phase-selectively and 3-phase by the main or back-up
protection equipment. To do so, the binary inputs ">CBF Lx" (FNo. 7611,7612,
7613/BU) and/or ">CBF 3-pole" (FNo. 7621/BU) must be marshalled according-
ly. The CBF protection is started by the first signal that is detected.
Circuit breaker fail-
ure delay times
If a single-pole fault evolves to a multi-pole short-circuit before the delay set with the
parameter T-BF-1P (XX20/CU) has elapsed, the running process is aborted and a
delay time is started which is set with the parameter T-BF-mP (XX21/CU).
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