2 Functions
118
7ST6 Manual
E50417-G1176-C251-A3
Note
For the setting of the pickup current, the setting of the differential protection delay must
be taken into account. If the delay of the TRIP signal for the differential protection is
set in such a way that transient states occurring on switching on the defrosting current
have not yet entirely decayed, the pickup current must be set to approx. 10 % more
than the maximum transient current that is possible at this moment.
The slope
4304
k
to be set results from possible amplitude or angle errors of the
current transformers used.
The trip delay time following a pickup
4303
T ID>
is set in such a way that transient
states on switching on the defrosting current have completely decayed after that time.
Typical values for these decay times are about 200 ms. This time constant is reduced
by resistances in the current path.
Backup Protection
The backup protection of the defrosting protection function has two definite-time over-
current stages. The high-current stage is set to approx. 10 % more than the transient
current that is to be expected when switching on the defrosting current. This current
is set at address
4306
IX>>
. The delay of the stage is set at address
4307
T IX>>
without delay, or with a short delay of approx. 100 ms.
The pickup value of the overcurrent stage is set at address
4308
IX>
to approx. 10 %
more than the expected continuous defrosting current. The delay of the overcurrent
stage is set to approx. 100 ms more than the decay times of the transient states that
occur when switching on the defrosting current.
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