Fault Between Transformer Terminals And Incoming Feeder Circuit Breaker - Siemens SENTRON Configuration Manual

5.2.2

Fault between transformer terminals and incoming feeder circuit breaker

Symmetrical fault current distribution
The instantaneous short-circuit release (I release) must be set in such a way that its value is
higher than the partial short-circuit currents I
incoming feeder circuit breaker carrying the total short-circuit current
instantaneously on a secondary-side terminal short-circuit on the transformer. The circuit
breakers in the incoming feeders without a fault remain closed because of the delay time t
set on the S release.
K = 30 kA / 15 kA = 2 is the ideal characteristic displacement factor for the transformer
t-I
circuit breakers Q2 and Q3 of the fault-free incoming feeders.
①
Characteristic displacement factor
②
Total short-circuit current
Selectivity for 3VA molded case circuit breakers
Configuration Manual, 08/2016, A5E03603181010-01
Selectivity with parallel incoming feeders
5.2 Selectivity with three identical incoming feeders
of a transformer. This means that only that
k-Ti
ever trips
kΣ
sd
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