This situation only means that for this particular bay its busbar disconnectors are closed and
therefore zone interconnection switching is happening in the station.
When zone switching feature is activated inside the IED, each individual bay current will behave
in the predetermined way. In six-zone busbar differential protection, it is internally determined
how a bay CT should behave during zone interconnection, depending the bay is a feeder or a
bus coupler or section bay. In two-zone busbar differential protections, it is determined by the
end user with a settable setting
ZoneSwitching
. This parameter, for every bay, can be set to
only one of the following three alternatives
•
ForceOut
•
ForceIn
•
Conditionally
If for a particular CT input setting parameter
ZoneSwitching
is set to
ForceOut
, then this CT
input will be disconnected from both the differential zones, regardless of any other set value
or active binary input, while zone switching feature is active within the IED. This setting is
typically used for bus coupler bay in double busbar stations.
If for a particular CT input setting parameter
ZoneSwitching
is set to
ForceIn
, then this CT
input will be connected to both the differential zones, regardless of any other set value or
active binary input, while zone switching feature is active within the IED. This setting is
typically used for all feeders bay in a station with two single zone interconnected by a
sectionalizing disconnector.
If for a particular CT input setting parameter
ZoneSwitching
is set to
Conditionally
, then this
CT input will be connected to both the differential zones only if it was included to any of the
two zones for 2ms before the zone switching feature was activated. This setting is typically
used for all feeders bay in double busbar stations. With this setting all feeder bays, which were
not connected to any of the two zones before the zone interconnection activation (that is, out
for scheduled maintenance), will not either be included during zone interconnection.
This practically means that for double busbar station, when zone switching feature is active, all
feeder bays will be connected to both differential zones, while bus coupler CT will be
disconnected from both zones. In this way simple but effective solution is formed. It is as well
important to notice that all necessary changes in the individual bay tripping arrangements will
be automatically performed within the internal logic.
A dedicated binary signal will be immediately activated in the internal logic when zone
interconnection feature is activated. If this feature is active longer than the pre-set time
separate alarm binary signal is activated, in order to alarm the station personnel about such
operating conditions.
ZoneInterconnection
feature can be disabled by a parameter setting for
substation arrangements where it is not required that is, single busbar stations, one-and-half
breaker stations and so on.
6.1.3.9 Tripping arrangements
M12116-3 v3
Tripping circuit arrangement
The contact outputs are of medium duty type. It is possible to use them to directly trip the
individual bay circuit breakers. This solution is suitable for all types of station arrangements.
The internal zone selection logic provides individual bay trip signals in the internal software
and no external relay for this purpose are required. This arrangement insures correct trip
signal distribution to all circuit breakers in case of busbar protection operation or individual
bay breaker failure protection operation. Breaker failure protection can be internal or external
to the IED.
1MRK 505 370-UEN D Section 6
Differential protection
Busbar protection REB670 109
Application manual
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