Treeing, electrical breakdown polymers

Tree formation n. The generation of a treelike void structure in a transparent plastic by electron bombardment at a point on the surface. The effect in acrylic blocks is dramatically decorative. Similar breakdown structures form in dielectrics subjected to strong electric fields, eventually penetrating the dielectric and causing a short circuit. Ku CC, Liepins R (1987) Electrical properties of polymers. Hanser Publishers, New York. Seanor DA (1982) Electrical conduction in polymers. Academic Press, New York. 

The wide use of polymers in the electrical industry arises from their excellent electrical insulation and dielectric isolation properties. However, these are dependent upon the polymer permeation properties. For instance, the sheathing of cables and wires is sensitive to the presence of water in the polymer. It has been shown that the most common form of insulation breakdown arises from electrochemical treeing. This arises from the simultaneous effects of an electric field and moisture present in the shielding, either initially present or by permeation. 

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