Functions
202
7SS52 V4 Manual
C53000-G1176-C182-3
5.18
Backup Breaker Failure Protection in the Bay Unit
5.18.1 Functional Description
If an overcurrent protection function is provided as backup protection in the bay unit,
and if the backup breaker failure protection function of the bay unit has been activated
with the parameter
B
ackUp CBF
(
3901/BU
), a separate breaker failure protection
can be initiated by the bay unit. As an alternative, the binary inputs of the bay unit can
be used to activate ”
>b.u. CBF on
” (
FNo. 1401/BU
) and deactivate
(”
>b.u. CBF off”
(
FNo. 1402/BU
)) this breaker failure protection function. The
annunciation ”
b.u. CBF act.
” (
FNo. 1453/BU
) signals that the function is active.
With the function turned off, the annunciation ”
b.u. CBF off
” (
FNo. 1451/BU
) will
appear. The various blocking options for the backup breaker failure protection are
shown in
Figure 5-43, page 203 and Figure 5-46, page 205. The backup breaker fail-
ure protection works independently of the busbar protection function and remains ac-
tive even if the link to the central unit is interrupted or if the bay unit is set with the pa-
rameter
(
XX12/CU
.
The breaker failure protection picks up as soon as the O/C protection issues a trip
command, and one or more of the 3 phase currents have reached the current thresh-
old. This threshold can be set with the parameter
B
.U.CBF-I
(
3911/BU
). The TRIP
command ”
CBF Trp.rp.3p
” (
FNo. 7632/BU
) of the breaker failure protection is is-
sued as soon as the delay time
B.U.CBF-T
(
3912/BU
) has expired. If the pickup of
the breaker failure protection is cleared before this time has elapsed, no TRIP com-
mand is issued. The pickup is cleared if the current drops below the threshold. If the
TRIP command issued by the breaker failure protection does not result in disconnec-
tion of a system fault, and if the bay unit is linked with the central unit, the main CBF
protection function is initiated after the delay time
(
XX21/CU
) has elapsed.
This allows to issue a transfer trip command to all feeders of the faulted bus zone, pro-
vided that the tripping conditions for the configured operating mode are fulfilled.
3 binary inputs are provided for phase-selective initiation of the CBF protection, and
one binary input for 3-pole initiation. Phase-selective initiation is only possible if exact-
ly one of the phase-selective binary inputs is active. If several phase-selective binary
inputs are active, a single-pole start is carried out. Each initiation starts an individual
time stage. After this time stage has elapsed, the TRIP command is issued. The delay
time is set independently of the type of initiation with the parameter
B.U.CBF-T
(
3912
/
BU
) as well. After the TRIP command, the CBF main protection function is initi-
ated, just as in the case of initiation by the overcurrent protection. Please note that the
delay time for this is always set with the parameter
(
XX21/CU
), even if the
first initiation was single-phase.
To provide more security when the CBF protection is initiated by binary input, signals
at the release inputs are required for a successful initiation. These release inputs are
identical with those used for the CBF main protection function. There is one release
input for 1-phase initiation, and one release input for 3-phase initiation.
Note
Release inputs that are not marshalled are disregarded.
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