'(& )( )'& &) ( &!& ")& &$(( $# Ć %&( $# #)" &&#$
Mode of operation
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Siemens AG ⋅ May 1998
4.7 Ancillary Functions
The ancillary functions of the 7SS52 busbar/circuit
breaker failure protection include:
D Overcurrent controlled trip command
D Minimum duration of the trip command
D Detection of short-circuits in the "dead zone" of
the bus coupler
D Detection of CLOSE command in the bus coupler
D Event logging
D Storage of short-circuit data for fault recording
D Monitoring functions.
#"! ! !
The busbar protection 7SS52 provides the possibility,
in the event of a busbar short-circuit, to only disconĆ
nect those feeders which carry currents exceeding a
set level. The limit values can be set individually for
each bay > TRIP BAYxx ( $$).If this funcĆ
tion is not required, the particular bay setting is set to
the value "0". The setting values are always referred
to the feeder CT's nominal current.
!# !
The 7SS52 differentiates between a TRIP command
due to a busbar fault (BB-TRIP) and a TRIP command
due to breaker failure (BF-TRIP).
In the event of a busbar TRIP the breaker failure proĆ
tection time delay (CBF time delay) is startet. If TRIP
release is not given within the CBF time delay (via BI
of the bay unit), then no TRIP command is generated
and the status "missing TRIP release" is indicated
feeder-selective.
The missing "TRIP release" does not influence the
internal CBF processing. If the feeder current is still
measured after the CBF time delay, then the opposite
line terminal is tripped by a transfer signal.
This function is activated by parameter .
" "! ! !
The 7SS52 extends the feeder-related TRIP comĆ
mands to a set time duration
T-TRIP-DUR ( ). This extensions ensures
that the circuit breakers trip reliably.
If the feeder current persists after the minimum duraĆ
tion has elapsed and the threshold > CBF Axx (
$$) is exceeded, then the TRIP command is
maintained.
feeder current
TRIP by internal
busbar protection
P -CBF
$$
&
P T-TRIP-DUR
reset TRIP and
transfer trip command
t1
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