Siemens SIPROTEC 7SS523 V3.2 Manual page 183

Maintenance mode
5.9.4 Overcurrent-Controlled TRIP command
Caution!
Bus bar protection with transfer bus
The transfer bus condition is characterized by the status:
Line disconnector Q9 open, respectively all bus bar disconnectors open and transfer bus dis-
connector Q7 closed.
If the feeder is in transfer busbar operation, the feeder must not be put "out of service".
During disconnector revisions the feedback does not correspond to the switching sta-
tus of the disconnectors (e.g. with maintenance of the auxiliary contacts or switched
off power supply for disconnector position signal).
In such a case, the existing isolator status is frozen during maintenance and main-
tained until the maintenance function is finished. The start of the maintenance mode
and the switching off of the isolator status indication are usually done simultaneously.
To prevent erroneous annunciations, there is a short delay of 0.5 s for the responses
and the signalling of auxiliary voltage failure. The protection function, however, re-
mains fully operational. It is also possible to exclude individual switchgear of a bay unit
from the maintenance mode via the parameters Maint. Iso or Maint. CB
(XX51A/CU to XX56A/CU).
The main points to observe for maintenance mode are:
• In 2-bay couplers, maintenance must be selected for one coupler bay only.
• To ensure a selective functioning of the protection, the isolator status must not be
changed during maintenance mode; this is because the individual protection zones
are managed on the basis of the frozen isolator replica.
• The circuit breaker monitoring and the isolator status monitoring are closed.
• A warning annunciation "IsoProhib/Maint" (FNo. 10471/CU) is output
throughout the maintenance work.
The SIPROTEC 7SS52 V4 distributed busbar and breaker failure protection provides
the possibility, in the event of a busbar short-circuit, to disconnect only those feeders
which carry currents exceeding a set level. This threshold can be set individually for
each bay with the parameter I>TRIP (XX13/CU) (Figure 5-39, page 165).
7SS52 V4 Manual
C53000-G1176-C182-1
Protection General
167