ABB RELION 670 Series Applications Manual page 115

1MRK 505 337-UUS A
protection is often called end fault protection in relay literature. It shall be noted that at the
same time busbar protection will remain stable (that is, selective) for such fault.
• For feeders with CT on the bus side of the circuit breaker (that is, two feeders on the right-
hand side in figure 49), the current measurement can be disconnected from the busbar
protection zone some time after feeder CB opening (that is, after 400 ms). This measure will
insure 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. Please refer to Zone Selection section for more info.
End fault protection logic can be easily done with help of graphical configuration tool. One stage
(that is, 4
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. However, under certain circumstances,
for stations with a transfer bus more extensive logic for end fault protection implementation
might be required.
6.1.3.11 Zone interconnection (Load transfer)
In double busbar stations or double busbar with transfer bus stations it is common requirement
to use the possibility of zone interconnection of load current in any feeder bay from one busbar to
the other. The sequence of operation during zone interconnection is normally as the following:
• bus coupler 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 (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
Application manual
th
stage) from optionally available overcurrent protection can be used as dedicated end
ZoneInterconnection will be used to handle both situations. This feature can
Section 6
Differential protection
M12114-3 v3
109