Methods of implementing selectivity using circuit breakers
3.6 Dynamic selectivity
Selectivity for 3VA molded case circuit breakers
40 Configuration Manual, 08/2016, A5E03603181010-01
3.6 Dynamic selectivity
Dynamic selectivity is fundamentally different to current and time selectivity.
Circuit breakers suitable for this application
Molded case circuit breakers are used to implement dynamic selectivity because it is a
concept that utilizes the current-limiting properties of these devices (see chapter
"Implementation of dynamic selectivity (Page 41)").
It is not meaningful to depl
oy air circuit breakers in dynamic selectivity systems because
these devices are so-called "zero-current interrupters" that are not capable of current-limiting
tripping behavior. It is however possible to combine downstream molded case circuit
breakers with upstream air circuit breakers and this solution can be beneficial in certain
situations.
Combinations of current-limiting molded case circuit breakers with fuses or circuit breakers
that also have current-limiting capabilities are also possible in dynamic selectivity systems.
Dynamic selectivity zone
In current and time selectivity systems, the parameters or tripping characteristics of the
upstream and downstream current-limiting circuit breakers are set specifically for the
purpose of implementing selectivity. Whether total or partial selectivity has been achieved
can be verified by mapping the tripping characteristics. This verification is possible, however,
only if the current curve does not deviate from the sinusoidal shape. This applies to tripping
characteristics only in the zone above 100 ms.
① Dynamic selectivity zone
Figure 3-11 Tripping characteristics and dynamic selectivity
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