ABB REB670 Applications Manual page 125

1MRK 505 337-UUS -
Application manual
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ANSI06000139 V1 EN
Figure 49: Busbar protection measuring and fault clearing boundaries
where:
1 is Busbar Protection measuring boundary determined by feeder CT locations
2 is Busbar Protection internal fault clearing boundary determined by feeder CB locations
3 is End fault region for feeders as shown in figure 48/B
4 is End fault region for feeders as shown in figure 48/C
In figure 49 single busbar station is shown. Two feeders on the left-hand side have CTs on
the line side of the breaker. The two feeders on the right-hand side of the busbar have CTs
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 location in feeder bays, busbar protection will detect all primary faults located
within measuring boundary determined by CT locations, see figure 49. However its
operation will only completely clear faults within clearing boundary determined by CB
locations as shown in figure 49. 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:
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Section 6
Differential protection
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