Siemens SENTRON Configuration Manual page 67

①
Total short-circuit current
Figure 5-6 Selectivity with an incoming feeder short-circuit in the center busbar section
The displacement factor of the tripping characteristics K
With a total short-circuit current = 30 kA and
the partial short-circuit currents of the circuit breakers Q1, Q4, Q3 and Q5 = 15 kA,
the displacement factor K
The displacement factor K
because
the total short-circuit current = 30 kA and
the partial short-circuit current of the incoming feeder circuit breaker = 30 kA
The tripping characteristics of the instantaneous releases are far to the right of the total
short-circuit current in the case of circuit breakers Q1, Q3, Q4 and Q5 and are therefore not
shown in the diagram.
Protective response
Circuit breaker Q2 trips instantaneously, the contacts of circuit breakers Q1, Q3 – Q5 remain
closed.
Selectivity for 3VA molded case circuit breakers
Configuration Manual, 08/2016, A5E03603181010-01
= 2
t-I
= 1 for the incoming feeder circuit breaker Q2, however,
t-I
Selectivity with parallel incoming feeders
5.3 Selectivity with bus-couplers
is as follows:
t-I
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