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 Vb and dielectric strength Fb, 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