Description
2.2 Electronic components
3WJ Air Circuit breakers
Operating Instructions, 12/2022, L1V30828903001-01
51
2.2.5.3 ST: Short-time delay short-circuit release (Short time), S tripping
With the electronic trip units, tripping caused by a short-circuit current Isd can be delayed by
t
sd.
This enables selectivity with respect to short-circuit protection in switchgear with more than
one grading level.
Isd = (1.25 / 1.5 / 2 / 2.5 / 3 / 4 / 6 / 8 / 10 / 12) x In
1)
/ 0.1 / 0.2 / 0.3 / 0.4 s
The delay time 0.02 s is not a grading time.
In this setting, the motor protection function is activated.
With the setting value tsd = 0 s, the ETU350WJ and ETU360WJ electronic trip units can support
instantaneous short-circuit protection with a variable response value that is lower than the
fixed response value I
i.
Motor protection function
A special protection function for electromotive drives is activated with the Circuit Breaker
setting t
sd= (0.02 s). This prevents the short-time delay short-circuit release from
responding to the inrush peak of electric motors. At the same time, phase-failure protection is
activated and the time constant for the internal, arithmetic simulation of the warming and
cooling process is switched from plant protection to motor protection.
ETU350WJ and ETU360WJ:
When motor protection is active, the time-lag class is also set in such a way that, regardless of
the default setting t
R = 10 s, the tripping time for overload protection is 11.2 s @ 7 x IR, which
means that it lies within the tolerance band of class 20 (6 < t
p ≤ 20 s).
2.2.5.4 INST: Instantaneous short-circuit release (Instantaneous), I-tripping
Exceeding the setting value Ii causes the Circuit Breaker to trip instantaneously.
i
n
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