Siemens SENTRON - Circuit Breaker Parameters

Methods of implementing selectivity using circuit breakers
3.2 Selectivity in the overload zone
Selectivity for 3VA molded case circuit breakers
Configuration Manual, 08/2016, A5E03603181010-01
17
3.2.2 Circuit breaker parameters
In order to ensure selectivity, the protection parameters of the LI protective function must be
set appropriately for the given situation.
The following parameters are important for the overload zone:
● Settings of the inverse-time delay L release (I
r
)
● Delay time of the inverse-time delay L release (t
r
)
The inverse-time delay L release (I
r
) trips at the following overload currents when the
settings shown in the table are applied:
● Setting at L release (I
r
) of 100 A circuit breaker = 100 A
● Setting at L release (I
r
) of 250 A circuit breaker = 250 A
The delay time of the L release (t
r
) ensures that there is a sufficient distance (i.e. no contact)
between the characteristics of the two circuit breakers in the overload zone.
The setting of the instantaneous I release (I
i
) trips in the short-circuit zone. This value has
been set to 1000 A for both circuit breakers. Since this parameter has no relevance in the
overload zone, it will not be discussed in any detail until later on.
Note
Note the tolerance ranges
The tolerances of the setting values 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 %