Vieillissement thermique des gaines PE et PVC de câbles électriques

Abstract : In France, about 35% of the electric connections are buried. These connections are, among other, constituted of synthetic cables where the insulating system is a polymer. The high costs for replacing the underground electrical cables make their lifetime prediction an important economic and strategic challenge. However, the outer sheath is the first barrier protecting the cable against water penetration. It is also considered as the most sensitive component with respect to ageing. For this reason, the thermal ageing of two types of sheaths of synthetic electrical cables used in the underground electricity network have been studied between 80 and 160 °C in air. In the case of PE sheath, it is observed a violent polymer oxidation as soon as the totality of antioxidants disappears by evaporation and chemical consumption. In contrast, in the case of PVC sheath, it is observed a progressive disappearance of plasticizer by evaporation, leading to polymer vitrification and its embrittlement when the mass fraction of plasticizer reaches a critical value of the order of 8%. Oxidation and cracking induce a loss of water sealing of the sheath. From this moment, it is suspected that water will induce corrosion and local breaking of metallic screen and, thereafter, the formation of water treeing inside the electrical insulator leading cable breakdown. A kinetic model for sheath thermal ageing has been derived from all these physical and chemical mechanisms. This model allows to predict the sheath lifetime (by sealing loss) as long as the diffusivity of molecular adjuvants (antioxidants and plasticizers) is negligible.
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Submitted on : Monday, September 30, 2013 - 11:55:59 AM
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Inès Mkacher. Vieillissement thermique des gaines PE et PVC de câbles électriques. Sciences de l'ingénieur [physics]. Arts et Métiers ParisTech, 2012. Français. ⟨NNT : 2012ENAM0034⟩. ⟨pastel-00867609⟩

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