Nowadays, polymers are widely used in most of the high voltage equipment, e.g., power transformers, insulators, capacitors, reactors, surge arresters, current and voltage sensors, bushings, power cables and terminations. When structural factors were considered alongside the statistics, no clear trends emerged to indicate that either the compositional or morphological variations were reflected in the short-term electrical failure processes. In view of the principal application area of this material, the breakdown strength of each of the above systems was then measured and the whole data set was analysed statistically. Where extensive crosslinking occurred prior to crystallization, the resulting gel inhibited structural development, such that only a few small, isolated sheaves were able to form at 102 ☌. Some crosslinking also occurred at 150 ☌, but over a much longer timescale. Further addition of dicumyl peroxide (DCP) resulted in the rapid formation of a crosslinked network at 200 ☌.
At higher temperatures, sheaf-like lamellar aggregates developed, which were much smaller and much more numerous than in the case of the virgin polymer. Inclusion of the antioxidant resulted in greatly increased nucleation densities, such that, at low temperatures, no evidence of spherulitic organisation remained. In the virgin polymer, a space-filling banded spherulitic morphology was found to develop at low temperatures (102 ☌ and below) whereas, at higher temperatures, only a few isolated axialites were observed. In all three of these systems, multiple melting transitions were observed, as a result of molecular fractionation effects during crystallization.
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All materials were based upon a single polymer, that is commonly used in high voltage applications, but with different additives.
#20 question gridable bubble sheet series#
A series of low density polyethylene systems has been studied with respect to structural evolution and short-term dielectric breakdown behaviour.
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