Ct Disconnection For Bus Section And Bus Coupler Current Transformer Cores - ABB REB670 Applications Manual

1MRK 505 337-UUS -
6.1.3.9
Application manual
This setting is typically used for feeder bays in double busbar single breaker stations in
order to form proper busbar disconnector replica. It is especially suitable when only
normally closed (that is, b) auxiliary contact from the busbar disconnector(s) is available
to the IED. For more information please refer to figure 63.
In applications where zone selection (that is, CT switching) is required (for example
double or multiple busbar stations) all CTs will be permanently connected to the analogue
input module(s), as shown in figure 62. Therefore, all necessary switching of currents will
be performed in internal software logic.
CT disconnection for bus section and bus coupler current transformer
cores
In practice there are three different solutions for bus section or bus coupler bay layout.
First solution is with two sets of main CTs, which are located on both sides of the circuit
breaker, as shown in figure 43.
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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
Differential protection
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