Zone Interconnection (Load Transfer) - ABB REB670 Applications Manual

Section 6
Differential protection
6.1.3.11
120
• For feeders with CT on the line side of the circuit breaker (that is, two feeders on the
left-hand side in figure 49), the current measurement can be disconnected from the
busbar protection zone some time after feeder CB opening (for example, 400 ms for
transformer and cable feeders or longest autoreclosing dead time +300 ms for
overhead line feeders). At the same time, appropriately set and fast (that is, typically
40 ms time delayed) overcurrent protection shall be enabled to detect fault within end
fault region. Any operation of this overcurrent protection shall only issue inter-trip
command to the remote feeder end CB. Such overcurrent 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.
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One stage (that is, 4 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. However, under certain
circumstances, for stations with a transfer bus more extensive logic for end fault
protection implementation might be required.

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
1MRK 505 337-UUS -
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