Selectivity with parallel incoming feeders
5.3 Selectivity with bus-couplers
Selectivity for 3VA molded case circuit breakers
Configuration Manual, 08/2016, A5E03603181010-01
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5.3 Selectivity with bus-couplers
If circuit breakers with over-current releases are installed in bus-couplers, the following can
be achieved:
● Fastest possible clearance of busbar faults
● Fault restriction to the respective busbar section
● Relieving the feeders of the effects of high total short-circuit currents.
Two parallel incoming feeders
With two parallel incoming feeders, only the partial short-circuit current of one transformer
ever flows through the bus-coupler. Selectivity between an incoming feeder circuit breaker
and the bus-coupler can thus only be achieved by time grading.
Three parallel incoming feeders
In configurations with three parallel incoming feeders or more, the partial short-circuit
currents flowing through the bus-couplers are dependent on the fault location (fault in the
outer or center section of the busbar).
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