ABB RELION 670 Series Applications Manual page 114

Section 6
Differential protection
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ANSI06000139 V1 EN-US
Figure 49: Busbar protection measuring and fault clearing boundaries
where:
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In figure
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:
• 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
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is Busbar Protection measuring boundary determined by feeder CT locations
is Busbar Protection internal fault clearing boundary determined by feeder CB locations
is End fault region for feeders as shown in figure 48/B
is End fault region for feeders as shown in figure 48/C
49 single busbar station is shown. Two feeders on the left-hand side have CTs on the line
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1MRK 505 337-UUS A
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Application manual