When biaxially oriented polypropylene film (BOPP) is aged at fields above about 480 MV/m, the film breaks down before the current density comes to steady state, i.e., after voltage application, the current drops for some tens of minutes, after which it starts to increase monotonically to breakdown over some minutes to tens of minutes. However, the average conductivity of BOPP at 480 MV/m is in the range of 10-16 S/m. This suggests that under these conditions in this relatively thin (~10 �m) film, aging, and probably current density, are local phenomena based on the statistics of morphology, impurity content, and �defects� in the film, but aging clearly involves a positive feedback mechanism. If the electrical properties are statistically independent on a scale of 10-10 m2 of surface, a 10 cm2 sample has 106 statistically independent paths through the sample, and aging/breakdown are dominated by the worst case path. A great deal more is known about the solid state properties and high field aging of polyethylene than polypropylene, but usually for much thicker samples where statistical variability through the sample will be much less. This presentation will bring together the experimental work in this area in the context of relevant theory in an attempt to discern material properties which are likely to be correlated with improved dielectric properties.

Overview of high field aging: Empirical knowledge and theoretical basis

246th National Meeting (2013)

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