Flutuações de composição em um elastomero dieletrico processado por extrusão

AUTOR(ES)
DATA DE PUBLICAÇÃO

1988

RESUMO

Dielectric polymer materials, such as the elastomers based on poly(ethylene/propylene/1,4-hexadiene), also called EPDM or ethylene-propylene rubbers, are normally used for the electric insulation of hiqh voltage cables. The dielectric strength of these materiaIs is one of the most significant properties for the evaluation of their performance, as a function of the operation conditions (electric stress and temperature) and of the environment. Prior work showed that dielectric breakdown does not occur randomly: the ruptures are preferentially found at certain locations of the dielectric. This suggested that some non-uniformity could exist in the insuIation, perhaps in its chemical composition. In order to check this assumption, an analysis was performed of the distribution of some EPDM components on cable samples (138 kV). Several physico-chemical analysis techniques were used for the monitoring of the components, such as: photoacoustic spectroscopy, X-ray fluorescence, mass spectrometry, and thermogravimetry. The results showed composition fluctuations of the rubber among samples taken from different points of the dielectric, some relative variations were: kaolin 5.7%, lead oxide (minium) 8.7%, zinc oxide 13.8% and paraffin is lost from 20% to 40% of weight. Kaolin is a reinforcement and filling charge, lead and zinc oxides and the antioxidant are rubber stabilizing agents, and paraffin is a processing agent. These variations were assigned to: i) point-to-point chanqes in the composition of the dielectric compound; ii) point-to-point changes in the thermophysical properties of the compounds. The fluctuations in composition and thermal properties of the compound caused dielectric constant fluctuations from point-to-point. As a consequence, some insulation points are subject to higher electric stresses than other points, and are more susceptible to dielectric breakdown. The results obtained lead to the planning of further work, in order to check the assumption of correlation between locations with higher breakdown frequency and locations with lack or excess of one or more compound constituents.

ASSUNTO(S)

elastomeros processo de extrusão

ACESSO AO ARTIGO

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