ABB RELION 670 Series Applications Manual page 107

1MRK 505 337-UUS A
Line disconnector replica
The line disconnector position from a feeder bay might be required for busbar protection under
certain circumstances. Typical example is when the line disconnector 989 and associated
grounding switch QC1 are located between CT and protected busbar as indicated in figure 42.
189 289
152
989
en06000086_ansi.vsd
ANSI06000086 V1 EN-US
Figure 42: Feeder bay layout when line disconnector position might be required for busbar
Such feeder set-up can be often found in GIS stations where cable CTs are used for busbar
protection. If in such feeder the line disconnector 989 is open and then immediately the grounding
switch 189G is closed before the busbar disconnectors 189G & 289 are open there is a danger to
get current unbalance into the zone differential measurement under following circumstances:
• In case of parallel lines zero sequence mutual coupling can induce zero sequence current into
the grounded line especially during externalground-faults.
• In case of cable feeder the stored energy in the cable will be discharged through the
grounding switch at the moment of its closing.
In order to avoid such problems for busbar protection the status of line disconnector can be
monitored by busbar protection and CT measurement can be disconnected from both differential
zones as soon line disconnector is open. Similar functionality can be obtained by instead
monitoring the position of feeder breaker 152. In such case the breaker closing signal shall be
connected to busbar protection as well.
6.1.3.8 Zone selection features
The IED offers an extremely effective solution for stations where zone selection (that is, CT
switching) is required. This is possible due to the software facility, which gives full and easy
control over all CT inputs connected to the IED. The philosophy is to allow every CT input to be
individually controlled by a setting parameter. This parameter called
configured for every CT input. This parameter, for every bay, can be set to only one of the
following five alternatives:
FIXEDtoZA
1.
FIXEDtoZB
2.
FIXEDtoZA&-ZB
3.
4. CtrlIncludes
CtrlExcludes
5.
Application manual
ZA
ZB
189G
protection
Section 6
Differential protection
SEMOD127523-82 v3
ZoneSel can be individually
M12108-3 v3
101