Abstract 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 7,500 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.

中文翻译：

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加速老化过程中浸渍的 Nomex 纸 410 和 910 的机械性能变化

摘要 目前正在开发用于变压器设计的新材料。由于变压器的使用寿命现在由固体绝缘条件决定，为了从技术和经济的角度改进电气系统管理和规划，更好地了解老化动力学非常重要。本文总结了在热加速条件 (170 °C) 下用绝缘流体（Nynas Polaris 和 Luminol Tri）浸渍芳纶和纤维素/芳纶纸（Nomex 410 和 910）对其机械性能的影响的研究。发现 Nomex 410（100% 芳纶）在加速老化（约 7,500 小时）后仅显示出很小的拉伸强度变化（降低约 5%）。然而，其延伸能力显着降低（干湿 Nomex 410 降低约 45-70%，分别）到老化过程结束时，可能是由于水解。此外，水和芳纶氢键在高温下的相互作用产生断裂，然后这些键在间位芳纶纤维中随机重建，从而降低了其塑性变形能力。在 Nomex 910（芳纶增强纤维素）的情况下，它的机械性能比热升级牛皮纸 (TUK) 的机械性能保持更长的时间，这是通过拉伸指数的保留百分比测量的。然而，当使用拉伸指数代替保留百分比时，TUK 在初始阶段显示出比 Nomex 910 更高的拉伸指数值，而两种纸的值在第二阶段变得相似。只有在老化过程结束时，由于添加了芳纶纤维，Nomex 910 才比 TUK 纸更具优势。还发现 Nomex 910 的初始断裂，作为一种纤维层状复合纸，从复合材料的最薄弱部分开始，可能在中央纤维素层。断裂线遵循最弱的路径，避开芳纶纤维。本文中提出的结果可用作基准，以提高我们对电力变压器固体绝缘中使用的这些相对较新材料的老化和机械性能变化的理解。更好地了解芳纶纸的老化特性（热降解）应该有助于更好地评估新一代电力变压器组的状况。还发现 Nomex 910 的初始断裂，作为一种纤维层状复合纸，从复合材料的最薄弱部分开始，可能在中央纤维素层。断裂线遵循最弱的路径，避开芳纶纤维。本文中提出的结果可用作基准，以提高我们对电力变压器固体绝缘中使用的这些相对较新材料的老化和机械性能变化的理解。更好地了解芳纶纸的老化特性（热降解）应该有助于更好地评估新一代电力变压器组的状况。还发现 Nomex 910 的初始断裂，作为一种纤维层状复合纸，从复合材料的最薄弱部分开始，可能在中央纤维素层。断裂线遵循最弱的路径，避开芳纶纤维。本文中提出的结果可用作基准，以提高我们对电力变压器固体绝缘中使用的这些相对较新材料的老化和机械性能变化的理解。更好地了解芳纶纸的老化特性（热降解）应该有助于更好地评估新一代电力变压器组的状况。断裂线遵循最弱的路径，避开芳纶纤维。本文中提出的结果可用作基准，以提高我们对电力变压器固体绝缘中使用的这些相对较新材料的老化和机械性能变化的理解。更好地了解芳纶纸的老化特性（热降解）应该有助于更好地评估新一代电力变压器组的状况。断裂线遵循最弱的路径，避开芳纶纤维。本文中提出的结果可用作基准，以提高我们对电力变压器固体绝缘中使用的这些相对较新材料的老化和机械性能变化的理解。更好地了解芳纶纸的老化特性（热降解）应该有助于更好地评估新一代电力变压器组的状况。