2 Functions
120
7ST6 Manual
E50417-G1176-C251-A3
2.11
InRush Restraint
This function is optional, i.e. not included in all device variants.
When switching in equipment, especially transformers operating at weak load or no
load, high inrush currents may briefly occur which can cause unwanted pickup of pro-
tection functions. The inrush restraint feature allows to recognize such startup condi-
tions. The functions provides signals that block the protection functions, in order to
prevent overfunctioning when switching in transformers.
2.11.1 Functional Description
When switching in transformers, high inrush currents occur, which may amount to a
multiple of the rated transformer current, depending on the switch on moment.
Although the fundamental current is evaluated by filtering of the measured current,
overfunctioning during energization of the transformer may result if very short delay
times are set. In the inrush current there is a substantial portion of fundamental current
depending on the type and size of the transformer that is being energized.
The inrush restraint function generates an indication
„INRUSH detected“
for as
long as the inrush currents persists. This indication informs you that the inrush re-
straint feature has detected an inrush current.
With the parameters
Inrush DIS >=Z2
,
Inrush O/C
and
Inrush O/C BU
the
blocking of the respective protection functions can be switched on and off. The figure
below shows the logic diagram for the inrush restraint.
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