ABB Relion 670 Series Applications Manual page 114

Section 6
Differential protection
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ANSI06000139 V1 EN-US
Figure 52:
where:
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Figure 52
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 52. However its operation will only
completely clear faults within clearing boundary determined by CB locations as shown in Figure 52.
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 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
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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 51/B
End fault region for feeders as shown in Figure 51/C
shows a single busbar station, where two feeders on the left-hand side having CTs located on
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1MRK 505 370-UUS Rev. K
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Busbar protection REB670
Application manual