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Mode of operation
4
4 - 18
Siemens AG
⋅
May 1998
4.6
Circuit-breaker failure protection
The circuit-breaker failure protection in the 7SS52
detects a failure of the circuit-breaker either in the
event of a feeder short-circuit or a busbar short-cirĆ
cuit.
1. In the event of a circuit breaker failure with a feeĆ
der short-circuit, the bus section to which the feeĆ
der with the defective breaker is allocated, is seĆ
lectively isolated.
In addition a transfer trip signal is issued in order
to trip the remote feeder terminal, too.
2. In the event of a circuit breaker failure with a busĆ
bar short-circuit, the infeed from the remote feeĆ
der terminal has to be interrupted. For this purĆ
pose the 7SS52 issues a transfer trip signal.
For the breaker failure protection function, the 7SS52
offers separate setting parameters for the differential
protection characteristic "STAB.FAC:BF" (
DA
6202/ZE
) and "
>DIFF:BF" (
DA 6203/ZE
).
4.6.1
Circuit-breaker failure protection during
a feeder short-circuit
If a circuit breaker failure occurs after a feeder short-
circuit, then the bus section with the corresponding
feeder has to be isolated. The breaker failure protecĆ
tion in the 7SS52 is activated by a TRIP command
from the feeder protection, which is connected to a
binary input "CBF Lx" (
FNr. 7020, 7021, 7022/FE
) of
the bay unit.
The following reaction by the protection system
7SS52 depends on the operation mode "CBF-OP
Axx" (
DA 6601
to
6648/ZE
), selected for each feeder.
Following variants of CBF-operation are utilised:
1. Current sensor
2. Trip repetition with current sensor
3. Unbalancing (1-stage CBF)
4. Trip repetition with following unbalancing (2-stage
CBF)
5. Trip repetition with following unbalancing for pulse
trigger
6. TRIP from external CBF
The parameter "CBF-BE-MODE" (
DA 6201/ZE
) defiĆ
nes for all feeders whether the CBF-initiation is trigĆ
gered only by the feeder-selective binary input "CBF
Lx" (1-channel) or after additional evaluation of a seĆ
cond binary input "CBF-release" (2-channel). The
2-channel initiation increases the security of the cirĆ
cuit breaker failure protection function. The function
of the additionally selectable supervision is explained
in chapter 4.7.8.5. The TRIP command is always supĆ
plemented by a transfer trip command.
4.6.1.1 Breaker failure protection with current
sensor
Initiation of the circuit breaker failure protection
(CBF-) function is effected by the TRIP command
from the feeder protection. In the operation mode
"current sensor", the feeder current is monitored for
exceeding the threshold I>CBF (
DA 67xx/ZE)
in the
course of the delay time T-CBF (
DA 6204/ZE
).
When this condition is fulfilled, then the 7SS52 issues
a three-phase TRIP command to isolate the bus secĆ
tion with the feeder that has initiated the CBF after
the time T>CBF has elapsed.
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Summary of Contents for SIPROTEC 7SS52
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