measure will ensure fast busbar protection tripping for faults within end fault region in
that feeder bay, while feeder CB is open.
However, it shall be noted that in order to utilize end fault protection feeder circuit breaker
status and its closing command must be connected to the binary inputs of busbar protection
scheme in order to be available for zone selection logic.
End fault protection logic can be easily done with the help of graphical configuration tool. One
stage (that is, 4
th
stage) from optionally available overcurrent protection can be used as
dedicated end fault protection for feeders with CT on the line side of the CB.
End fault protection is here explained for simple single busbar station. However the same
principles are applicable to almost all other station layouts. Moreover, under certain
circumstances, for stations with a transfer bus more extensive logic for end fault protection
implementation might be required.
6.1.3.8
Zone interconnection (Load transfer)
M12114-3 v4
In multiple busbar stations, with or without transfer bus, it is common requirement to use the
possibility of zone interconnection loading current in any feeder bay from one busbar to the
other(s). The sequence of operation during zone interconnection is normally as the following:
•
bus coupler or bus section bay is closed (that is, CB and both disconnectors).
•
feeder bay busbar disconnector to the busbar not already in service is then closed. The
switchgear interlocking system shall allow this only when the bus coupler breaker is
already closed. Depending on the thermal capacity of the feeder busbar disconnectors
(QB1 and QB2) 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 or bus section bay CB.
The zone interconnection has to be taken into consideration for the busbar differential
protection scheme, as each two busbar zones are interconnected together via two
disconnectors. The primary current split between busbars is then 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. For example, in two-zone applications, it leads to disconnect one zone
(normally zone B, and connect all feeders to other zone (normally zone A). At the same time the
current from the bus-coupler bay, which just circulates between zones, must be disconnected
from the measuring differential zone.
Similar situation regarding to busbar protection can occur between any busbar sections
interconnected via sectionalizing disconnector, see Figure
sectionalizer is closed, two separate protection zones becomes the 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 Zone Interconnection will be used to handle both situations. This
feature can be activated either externally via binary input or derived internally by built-in logic.
Especially in two-zone busbar protections, to internally activate such feature, the setting
ZoneSel shall be also considered. Consequently, the zone interconnection will be activated
internally only when 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 multiple internal differential zones
Section 6
1MRK 505 370-UEN D
Differential protection
108
Busbar protection REB670
Application manual
Summary of Contents for REB670 Series
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