Selectivity for 3VA molded case circuit breakers
Configuration Manual, 08/2016, A5E03603181010-01
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Selectivity with parallel incoming feeders
5
Selectivity with parallel incoming feeders can be implemented in various different scenarios.
The following scenarios are presented in this chapter:
● Selectivity with two identical incoming feeders
● Selectivity with three identical incoming feeders
● Selectivity with incoming feeders connected in parallel via bus-couplers
Total short-circuit current and current scale
If multiple transformers are operated on a common busbar, the following applies:
The partial short-circuit currents I
K-Ti
of the incoming feeders are added together to produce
the total short-circuit current I
kΣ
in a faulty feeder.
The total short-circuit current I
kΣ
forms the basis for the current scale in the grading diagram.
This offers the advantage of making the selectivity conditions more favorable for all
protective devices downstream of the incoming feeder circuit breaker. This applies to all
types of fault.
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