Influence des arborescences d'eau sur les propriétés diélectriques des polymères

Abstract : The water trees reduce the dielectric strength of the synthetic insulation of electrical cables. The mechanisms proposed for their growth is not very well understood. Moreover, to choose new materials, with a better résistance to the propagation of water trees, \ve need pertinent criteria based on a better knowledge of the phenomenon. To analyse the water tree composition and for finding the characterisation parameters correlated with their composition, vve hâve examined the growth of individual water trees in watei -needle polyéthylène sample, in différent expérimental conditions (type and concentration of ions in solution, frequency of the voltage). The concentration of water and SO^ and N(V ions in the water tree was analysed by Fourier transform infrared microspectroscopy on water tree slices. The analysis was made for différent distances from the water tree initiation point and for varions times of voltage application. This study shows that in polyéthylène the water tree opacity, determined in the visible light, is well correlated with the présence of water. We hâve deduced that the opacity can be considered as a pertinent factor to characterise the water tree résistance of materials. In addition, for a given ion. there is a constant ratio between the ions concentration and water concentration in water tree. independently of the initial solution concentration. Depending on the nature of the ions, the ions concentration in water inside a water tree is twice to ten times greater than in the initial solution. The results obtained confirm that the mechanism of water tree growth is based on the displacement of the ions and water under the electric fiekl.
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Oana Irina Visata. Influence des arborescences d'eau sur les propriétés diélectriques des polymères. Energie électrique. Université Joseph Fourier (Grenoble I), 2001. Français. ⟨tel-01611306⟩

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