Study by electron microscopy investigations (TEM, SEM, ED, HVEM) of treeing (from pre-breakdown to breakdown) induced by accelerated methods

In this paper we have studied the evolution of treeing (from pre-breakdown to breakdown) induced by accelerated methods-like electron or laser beam irradiation-in polyethylene. The growth of treeing is very closely related to the structural changes of polyethylene observed by different electron microscopy investigations-like transmission electron microscopy, high voltage electron microscopy, scanning electron microscopy etc.-and thus we consider that it can be used as an ageing indicator. The increased role of polymers in the field of high technologies requires the structural study of dielectric. The polyethylene (linear thermoplastic polymer) is used like cable isolation in the nuclear power plants. The polyethylene has very good dielectric properties and good stability of its properties in usual conditions. Pre-breakdown, treeing discharge and breakdown phenomena in polyethylene are particularly sensitive to the conditions of samples such as specimen defects (especially at the surface), nature of beam, ambient medium, temperature, time and the mode in which the phenomenon occurs. The authors would also suggest that more attention should be given to the study of influence of the surface defects, impurities, specimen geometry, temperature and especially the transformations of the structure in the presence of breakdown phenomenon.