ABB RELION 670 Series Applications Manual page 109

1MRK 505 337-UUS A
1
ANSI01000013 V1 EN-US
Figure 43: Example of station with two sets of main CTs in the bus-section bay
This is the most expensive, but good solution for busbar protection. Two differential zones
overlapping across the bus-section or bus-coupler circuit breaker. All faults in the overlapping
zone will be instantly tripped by both zones irrespective of the section/coupler circuit breaker
status. However with modern busbar protection it is possible to disconnect both CTs from the
relevant zones when the bus-section or bus-coupler circuit breaker is open. This will insure that if
internal fault happen, in the overlapping zone, while breaker is open, only the faulty zone will be
tripped while other busbar section will remain in service. However, due to low probability of such
fault happening, while the breaker is open, such special considerations are typically not included in
the busbar protection scheme for this type of stations. In such application the bus section or bus
coupler current transformers shall be wired just to two separate current input of the IED. Then in
the parameter setting tool (PST) for the corresponding bays the parameter
FIXEDtoZA in one bay and FIXEDtoZB in another bay. This will insure that these currents are given
to both differential zones.
When live tank circuit breakers are used, owing to the high cost of the HV current transformer
often only one current transformer is available in bus-section or bus-coupler bay. The suggested
solution in such applications is shown in figure 44.
Application manual
ZA
2 8
ZB
BS
1 2
Differential protection
8
en01000013_ansi.vsd
ZoneSel shall be set to
Section 6
103