POLYMER FILMS DEGRADATION AND BREAKDOWN IN HIGH VOLTAGE AC FIELDS

Konstantinos Theodosiou - Isidoros Vitellas - Ioannis Gialas - Dimosthenis P. Agoris

   This paper examines the mechanism of electrical degradation and breakdown of polymeric insulating films as a sequence of electron injection by Fowler-Nordheim tunnelling, and macro-ion bond scission resulting in the creation of another macro-ion and a free radical. This is a thermo-fluctuational process which involves the action of the stretching force by the local electric field. Breakdown initiation starts when an electron following a Poole-Frenkel hopping mechanism, is accelerated in a hole with sufficiently large dimensions. Experiments were executed for measuring the breakdown AC voltage V_b and dielectric strength F_b, with voltage rising rate 3kV/sec, in order to examine their relation with specimen thickness d and hence to derive a steady state breakdown criterion. An attempt of prediction of the polymer lifetime is also taking place.

Keywords: polymer, degradation, conduction, tunnelling, micro-voids, macromolecules

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