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Changes in mechanical properties of impregnated Nomex papers 410 and 910 during accelerated aging

Arroyo Fernandez Oscar Henry, Jalbert Jocelyn, Rodriguez-Celis Esperanza, Duchesne Steve, Morin Brigitte et Fofana Issouf. (2020). Changes in mechanical properties of impregnated Nomex papers 410 and 910 during accelerated aging. Polymer Testing, 83, (106358), p. 1-13.

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URL officielle: https://doi.org/10.1016/j.polymertesting.2020.1063...

Résumé

New materials are currently being developed for applications in transformer design. With the useful life of transformers now determined by solid insulation conditions, a better understanding of aging kinetics is important in order to improve electrical system management and planning from the technical and economic points of view. This paper summarizes an investigation of the effects of impregnating aramid and cellulose/aramid papers (Nomex 410 and 910) with insulation fluids (Nynas Polaris and Luminol Tri) at thermally accelerated conditions (170 °C) on their mechanical properties. It was found that Nomex 410 (100% aramid) showed only a small change in tensile strength (~5% decrease) after accelerated aging (around 7500 h). However, its elongation capacity was significantly reduced (~45–70% decrease for dry and wet Nomex 410, respectively) by the end of the aging process, probably due to hydrolysis. In addition, the interaction between water and aramid hydrogen bonds at high temperatures produced the rupture and then, the randomly rebuilt of these bonds in meta-aramid fibres, thereby reducing its plastic deformation capacity. In the case of Nomex 910 (aramid enhanced cellulose), its mechanical properties were maintained for a longer time than those of thermally upgraded Kraft paper (TUK), as measured by the retained percentage of tensile index. However, when the tensile index was used instead of the retained percentage, TUK showed a higher tensile index value than Nomex 910 during the initial stage, while the values for both papers became similar during the second stage. It is only at the end of the aging process that Nomex 910 presented an advantage over TUK paper due to the addition of the aramid fibres. It was also found that the inception fractures in Nomex 910, as a fibrous layered composite paper, start in the weakest part of the composite, probably in the central cellulose layer. The fracture line follows the weakest path, avoiding the aramid fibres. The results presented in this paper can be used as a benchmark for improving our understanding of aging and changes in the mechanical properties of these relatively new materials used in the solid insulation of power transformers. A better understanding of the aging characteristics (thermal degradation) of aramid-based papers should help better assess the condition of the new generation of power transformer fleets.

Type de document:Article publié dans une revue avec comité d'évaluation
Volume:83
Numéro:106358
Pages:p. 1-13
Version évaluée par les pairs:Oui
Date:Mars 2020
Sujets:Sciences naturelles et génie > Génie > Génie des matériaux et génie métallurgique
Sciences naturelles et génie > Génie > Génie mécanique
Département, module, service et unité de recherche:Départements et modules > Département des sciences appliquées > Module d'ingénierie
Mots-clés:Nomex 410, Nomex 910, aramid, cellulosic insulation, power transformer, solid insulation, aramide, isolation cellulosique, transformateur de puissance, isolation solide
Déposé le:29 janv. 2020 21:52
Dernière modification:29 janv. 2020 21:52
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