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Chapter 3
Behaviour of the Isolation Unit
3.8
Automatic adaptation of switching thresholds to the mains power
conditions
A distinction can be made between an overreaction of the ENS and an un-
controlled island effect. In the case of an overreaction by the ENS, the
power supply remains available after disconnection of the feeding point
from the mains.
If an overreaction is detected, the switching threshold for the next shut-
down is adapted to a value which is a little above the current threshold
value that has lead to a shutdown.
Before the switching threshold is adapted to a less sensitive value, the
ENS31 switches off briefly in order to check whether the power supply is
still available. The threshold is only changed to a less sensitive value
when it is recognised that the situation does not concern an uncontrolled
island effect. In the case of stable, undisturbed mains supply feeding
points, the switching threshold is slowly set to a value (i.e. over several
days) which is about double that of the recurrent fluctuations which oc-
curred (safety clearance). As a result of this automatic adaptation to the
mains power conditions, safety is considerably increased without limiting
the availability of the system.
If the interference level repeatedly exceeds the switching threshold, the
switching threshold is incremented and the slow adaptation begins again
from the start.
Page 12 of 20
switching threshold
interference level
Product Description ENS31
Version: A.02
Issue: 20.09.2005
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