The effects of water immersion on the electrical properties of miniature XLPE cables

Abstract

On trouvera dans cet article les resultats de recherches sur les effets de rimmersion dans l'eau de cables miniatures. Des mesures ont ete effectuees sur la capacite, le taux de dissipation et la tension de rupture de cables immerges dans l'eau a differentes temperatures et soumis a des tensions et des frequences variables. La tension de rupture diminue en deux etapes: la premiere etape correspond a la croissance d'arborescences noeuds papillon ou saturation de Tisolation vis-a-vis de l'eau, et la deuxieme etape a l'apparition d'arborescences de l'eau a partir de la surface. La frequence a eu pour effet d'accelerer le vieillissement de facon notable entre 60 Hz et 400 Hz, mais entre 400 Hz et 1 kHz l'effet s'est avere minime.The results of an investigation into the effects of water immersion on the electrical properties of miniature cables are reported. The capacitance, dissipation factor, and breakdown voltage of cables immersed in water at different temperatures and subjected to various voltages and frequencies were measured. The breakdown voltage decreased in two stages, the first stage corresponding to the growth bf bow-tie trees or saturation of the insulation with water and the second stage with the occurrence of surface-originating water trees. The frequency accelerated ageing was significant between 60 Hz and 400 Hz but there was little effect between 400 Hz and 1 kHz.

Studies on the aging processes of polymers in electrical systems

“…The presence of ions and morphological changes in the treed material, implied changes in electrical properties, for example a reduced resistivity has been observed for aged cables, but it is difficult to correlate this change with either the tree length or to factors affecting the tree growth 46) . An increase of 1.5 to 1.8% of the permittivity of a miniature cable was correlated to the increase of the volume fraction of water in XLPE 47) , a mean permittivity of 2.8 was found by Filppini's team 48) . We have investigated three kinds of polyethylene where water trees were grown in the so called water-needle experiment in which the liquid electrode was NaCl or KI.…”