Siemens SENTRON - Circuit Breaker Parameters

Methods of implementing selectivity using circuit breakers
3.3 Current selectivity
Selectivity for 3VA molded case circuit breakers
20 Configuration Manual, 08/2016, A5E03603181010-01
3.3.1 Circuit breaker parameters
The following parameters are important for current selectivity:
● Setting of the instantaneous I release (I
i
)
The parameters of the L release (I
r
and t
r
) remain unchanged from the example given in
chapter "Selectivity in the overload zone (Page 15)".
The settings
of the instantaneous I release (I
i
) trip at different short-circuit currents in this
case:
● Setting of I release (I
i
) of 100 A circuit breaker = 500 A
● Setting of I release (I
i
) of 250 A circuit breaker = 2500 A
The effects are clearly illustrated in the current-time curve diagram, see below.
Note
Note the tolerance ranges
The tolerances of the operating currents and the delay times must be taken into account
when the parameters are set:
• Tolerances of setting values (I
r
, I
sd
, I
i
): ± 10 %
• Tolerances of delay times (t
r
, t
sd
): ± 10 %.