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Siemens AG ⋅ May 1998
The 7SS52 has an integrated circuit breaker failure
protection (CBF).
D Six modes are available:
1. Current sensor
After initiation by a TRIP command from the feeĆ
der protection, this signal is checked in the 7SS52
for reset. If the measured current stays above the
set threshold after a set time has elapsed, then
zone-selective TRIP commands will be issued in
the bays considering the isolator replica in the
7SS52.
2. TRIP repetition with current sensor
When initiated by a TRIP command from the feeĆ
der protection, the 7SS52 issues a TRIP command
to the circuit breaker of the initiating feeder after a
set time delay. In case this second TRIP command
is also unsuccessful, tripping as per mode 1 is efĆ
fected.
3. Unbalancing
After initiation by a TRIP command from the feeĆ
der protection, this signal is checked in the 7SS52
for reset. If the measured current stays above the
set threshold after a set time has elapsed, then
the polarity of the current in this feeder is inverted
(unbalancing). For this function a dedicated set of
parameters is available.
4. TRIP repetition with subsequent unbalancing
When initiated by a TRIP command from the feeĆ
der protection, the 7SS52 issues a TRIP comĆ
mand to the circuit breaker of the initiating feeder
after a set time delay. In case this second TRIP
command is also unsuccessful, unbalancing as per
mode 3 is initiated.
5. TRIP repetition with subsequent unbalancing with
pulse trigger
The function is triggered by a trip command from
the feeder protection at the remote feeder termiĆ
nal.
The proceeding is described in mode 4.
This mode is used for remote transmission of the
CBF-initiating signal.
6. TRIP by external CBF
In case of a separate circuit breaker failure protecĆ
tion the 7SS52 can generate zone-selective feeder
TRIP command utilizing the integrated isolator reĆ
plica.
D Recognition of a breaker failure in case of a busbar
short-circuit by current limit value comparison.
D For all CBF modes, a feeder-selective command
to trip the circuit breaker at the remote feeder terĆ
minal (transfer trip) is issued by the bay units
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