Zone Interconnection (Load Transfer) - ABB REB670 Applications Manual

Section 6
Differential protection
6.1.3.8
130
• For feeders with CT on the line side of the circuit breaker (that is, the two feeders
on the left-hand side in Figure 52), 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, the two feeders
on the right-hand side in Figure 52), 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 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
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.

Zone interconnection (Load transfer)

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 (189 and 289) the opening of the bus coupler circuit breaker is
th
stage) from optionally available overcurrent protection can
1MRK 505 370-UUS A
M12114-3 v4
Busbar protection REB670 2.2 ANSI
Application manual