ABB Relion REB500, Product Manual, Page: 17 / 50

Distributed busbar protection REB500 1MRK 505 352-BEN
Product version: 8.2 Issued: 2016-03-01
Revision: -
ABB 17
Conversely, during the opening movement, the N/O
contact must not open before the isolator main contact
gap exceeds its flashover point.
If this is not the case, i.e. the contact signals ‘no longer
closed’ beforehand, then the N/C contact may not signal
“OPEN” before the flashover point has been exceeded. In
such cases a Not Open=Closed scheme might be
applicable.
Figure 11. Switching sequence of the auxiliary contacts
that control the busbar replica
Circuit-breaker replica
When the circuit-breaker replica is read in the feeder or
the bus-tie breaker, the circuit-breaker CLOSE command
must also be connected.
Main current transformer
The algorithms and stabilization features used make the
busbar protection largely insensitive to CT saturation
phenomena. Main CTs types TPS (B.S. class x), TPX,
TPY, 5P. or 10P. are permissible.
TPX, TPY and TPZ CTs may be mixed within one
substation in phase-fault schemes. The relatively low CT
performance needed for the busbar protection makes it
possible for it to share protection cores with other
protection devices.
Current transformer requirements for stability during
external faults (Busbar protection)
The minimum CT requirements for 3-phase systems are
determined by the maximum fault current. The effective
accuracy limit factor (
′
) must be checked to ensure the
stability of the busbar protection during external faults.
The rated accuracy limit factor is given by the CT
manufacturer. Taking account of the burden and the CT
losses, the effective accuracy limit factor
′
becomes:
= ⋅
+
+
where:
rated accuracy limit factor
rated CT power
CT losses
burden at rated current
In the case of schemes with phase-by-phase
measurement,
′
must satisfy the following inequalities:
≥
5 ⋅
≥ 10 for ≤ 120 ms
≥ 20 for 120 ms ≤ ≤ 300 ms
where:
max. primary through-fault current
rated primary CT current
DC time constant
Pick-up for internal faults
In the case of internal busbar faults, CT saturation is less
likely, because each CT only conducts the current of its
own feeder. Should nevertheless CT saturation be
possible, it is important to check that the minimum fault
current exceeds the setting for
.