ABB REB670 Applications Manual page 127

1MRK 505 337-UUS -
Application manual
(189 and 289) the opening of the bus coupler circuit breaker is sometimes interlocked
while both busbar disconnectors within one of the feeder bays are closed.
• opening of the feeder bay busbar disconnector originally closed. The load is now
transferred from one to other bus.
• opening of bus coupler CB.
The zone interconnection has to be taken into consideration for the busbar differential
protection scheme, as the two busbar zones are interconnected together via two
disconnectors. The primary current split between the two busbars is not known and the
two separate measuring zones cannot be maintained.
In conventional, analog busbar protection systems the solutions have been to, by extensive
zone switching IEDs, disconnect one zone (normally zone B) and to connect all feeders to
other zone (normally zone A). At the same time the current from the bus-coupler bay,
which just circulates between two zones, must be disconnected from the measuring
differential zone.
Similar situation regarding busbar protection can occur between two single busbar
sections interconnected via sectionalizing disconnector, as shown in figure 54. When
sectionalizer is closed then two separate protection zones becomes one and busbar
protection must be able to dynamically handle this.
Due to the numerical design the IED can manage this situation in an elegant and simple
way. Internal feature called ZoneInterconnection will be used to handle both situations.
This feature can be activated either externally via binary input or derived internally by
built-in logic. Internally, this "zone switching" feature will be activated if the following
conditions are met:
• bays have parameter ZoneSel set to either CtrlInclude or CtrlExcludes
• internal zone selection logic concludes that this particular bay shall be
simultaneously connected to both internal differential zones
This situation only means that for this particular bay both 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 as dictated by a parameter 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
Section 6
Differential protection
121