Leakage current

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Leakage current is a leakage current that flows along the surface of an insulating material .

While the internal insulation properties of an insulating material are determined by its specific electrical resistance , the current conduction on its surface can differ significantly from this, even if the dielectric strength of an air gap of the same length is not yet achieved.

The tracking resistance characterizes these properties of insulating materials. She will u. a. determined by their water absorption capacity and their behavior in the event of pre-discharges or creeping discharges (resistance to ultraviolet radiation and thermal stress).

Some insulating materials decompose at high temperatures into conductive materials (e.g. hard paper to graphite ) or have a high water absorption; these substances usually also have high leakage currents or low leakage current strengths.

Another effect is the adsorption of water on the surface (known from the insulating material glass ).

Leakage in insulating materials can be represented by water-repellent ( hydrophobic ) coating or impregnation to reduce (z. B. waxes , paraffin ).

In the case of very high-resistance signals (e.g. input signals from charge amplifiers , instrument amplifiers , FET operational amplifiers ), the flow of leakage currents can be prevented by so-called guard rings placed around the connections , which must be at the same potential as the signal.

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