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1MRK 505 370-UEN D
2
1
IEC06000139 V1 EN-US
Figure 51:
where:
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2
3
4
Figure
51
located on the line side of the breaker, meanwhile two feeders on the right-hand side of the
busbar having CTs located on the busbar side of the breaker. It is assumed that busbar
protection is connected to all four set of CTs in this station.
Due to CT locations in feeder bays, busbar protection will detect all primary faults located
within measuring boundary determined by CT locations, see Figure 51. However its operation
will only completely clear faults within clearing boundary determined by CB locations as shown
in Figure 51. Obviously, the primary faults in-between these two boundaries do pose certain
practical problems.
First of all it shall be noted that there is no ideal solution for faults within end zone region in a
feeder bay, when the feeder breaker is closed. Such faults, within end fault region, will be then
cleared with additional time delay either by operation of local backup protection (that is,
feeder circuit breaker failure protection) or by operation of remote backup protection (that is,
remote ends zone 2 distance protection).
However, the overall busbar protection behavior can be improved for primary faults within end
fault regions, when feeder breaker is open. Under such circumstances the following actions
can be taken:
•
For feeders with CT on the line side of the circuit breaker (that is, the two feeders on the
left-hand side in Figure 51), 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 51), the current measurement can be disconnected from the
busbar protection zone some time after feeder CB opening (that is, after 400 ms). This
Busbar protection REB670
Application manual
ZA
QA1
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Busbar protection measuring and fault clearing boundaries
Busbar Protection measuring boundary determined by feeder CT locations
Busbar Protection internal fault clearing boundary determined by feeder CB locations
End fault region for feeders as shown in Figure 50/B
End fault region for feeders as shown in Figure 50/C
shows a single busbar station, where two feeders on the left-hand side having CTs
BI1
BI1
QA1
QA1
3
Differential protection
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xx06000139.vsd
Section 6
107
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