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2 Functions
112
7ST6 Manual
E50417-G1176-C251-A3
Figure 2-31
Simplified operation scheme of the defrosting protection operating on the differ-
ential current principle
In addition to the current transformer in the infeed of the overhead contact line
I
,
which is shared with the other protection functions, another current transformer is
needed for the defrosting current flowing back. This transformer is connected to the
I
x
input.
Note
In auto-transformer systems, the negative feeder current IF- is measured as well. If
the negative feeder has its own current transformer, this current need not be consid-
ered, as the current IF- is very low in the special defrosting switching state.
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