Functions
124
7SS52 V4 Manual
C53000-G1176-C182-3
Initiation by
external CBF
If the operating mode
is set with the parameter
(
XX15/CU
),
the breaker failure is detected by an external device. On activation of the configured
binary inputs of the bay unit "
>CBF Lx
" (
FNo. 7611, 7612, 7613/BU
) or
"
>CBF 3-pole
" (
FNo. 7621/BU
), the protection system trips without delay the bus-
bar to which the bay with the faulted circuit breaker is connected. The central unit eval-
uates for this the isolator replica.
Low-current mode
In the presence of low-current faults (e.g. trip by the Buchholz protection of the trans-
former), the necessary threshold for a current-controlled mode may not be reached.
Therefore, it is not ensured that the circuit breaker failure protection is activated.
(
XX16/CU
) ensures that circuit breaker failure protec-
tion is provided nevertheless. After a set time
(
XX22/CU
) has elapsed, and
if the circuit breaker is closed, a busbar TRIP command for the affected bus zone is
issued.
If the feeder current exceeds this one with the parameter
(
XX18/CU
) adjusted
limiting value, the low-current mode is blocked. Logic of the current release see Figure
5-21, page 120.
With the operating modes
and
, to be set with the param-
XX15/CU
), this function has no influence. For more information on
the operating modes, please refer to the setting notes in Chapter 5.3.6, page 128.
As with other operating modes of the breaker failure protection, the tripping consists
of two stages, i.e. a first stage as "TRIP repetition" on the local breaker and a second
stage for the tripping of the busbar. The parameter
XX25/CU
),
which is also used for the current-controlled stages of the breaker failure protection, is
used in the central unit to delay the first stage.
The following figure shows the logic of the low-current operating mode of the breaker
failure protection:
Note
In this operating mode, always work with breaker failure protection triggering and re-
leasing (2 BI) since there is no further protection by a current check (refer to Chapter
5.3.5.1, page 117).
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