189
ZA
ZB
289
989
189G
en06000086_ansi.vsd
152
ANSI06000086 V1 EN-US
Figure 45: Feeder bay layout when line disconnector position might be required
for busbar protection
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.
6.1.3.5 CT connection control
M12108-3 v4
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.
In applications where zone selection (that is, CT switching) is required (for
exampledouble or multiple busbar stations) all CTs will be permanently connected to
the analogue input module(s), as shown in Figure
63. Therefore, all necessary
switchingof currents will be performed in internal software logic.
In general, there are dedicated binary inputs available for one CT at each bay, to
control its current connection towards dif
ferential zones, based on operational status of
Section 6 1MRK 505 370-UUS A
Differential protection
120 Busbar protection REB670 2.2 ANSI
Application manual
To Next Page
Loading...
