Electrical aging of polyurethane under ac voltage

The electrical aging of polyurethane under ac voltage has been investigated using Weibull statistical analysis. It is shown that the time to breakdown characteristic (V-t) of this polymer includes three zones corresponding, respectively, to the youth defects, the statistical dispersion of the intrinsic defects, and the real aging of the polymer. The variation of slope of the V-t curve is related to the change of the degradation mechanism. This degradation is governed by the action of partial discharges according to three stages: (1) the appearance of very fast discharges within the cavities; (2) the initiation of discharges resulting of a very thin layer of oxidation products; and (3) the formation of crystals having small dimensions leading to degradation by electrical tree. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008