In order to elucidate mechanical impacts affecting the insulation strength of thermal-ageing oil-impregnated pressboards, we perform mechanical degradation experiments of impacting forces that are represented as the winding-suffered stresses on thermal-ageing oil-paper insulation in transient short-circuit of transformer. Water content, degree of polymerisation (DP), partial discharge inception voltage and AC breakdown field strength are tested and analysed for diverse thermal-ageing levels. An analytical model of mechanical degradation is established by relating dielectric breakdown strength to mechanical impact. Mechanical impacts result in less water content in thermal-aging oil-impregnated pressboards while causing reduction and increment of DP, respectively, in mildly and severely aged oil-impregnated pressboards. Partial discharge inception voltage and dielectric breakdown strength vary significantly with the numbers of impact cycles, showing a maximum value under low-intensity impact and decreasing monotonously under high-intensity impact. High-intensity mechanical impacts will evidently exacerbate the thermal deterioration process of oil-impregnated pressboards, which is primarily attributed to cellulose fibre fractures in pressboard cracks produced by equivalent tensile stress of mechanical impacts. It is acceptable for mildly aged oil-impregnated pressboards to suffer low-intensity mechanical impacts that will alleviate insulation degradation by restraining partial discharge in smaller oil-gaps and prolonging breakdown discharge pathways along impact-caused cracks.

中文翻译：

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机械冲击热老化油浸纸的绝缘劣化及断裂裂纹

为了阐明影响热老化油浸纸板绝缘强度的机械冲击，我们进行了冲击力的机械退化实验，冲击力表示为瞬态短路时热老化油纸绝缘的绕组承受应力。变压器。针对不同的热老化水平，对水分含量、聚合度 (DP)、局部放电起始电压和交流击穿场强进行了测试和分析。通过将介电击穿强度与机械冲击联系起来，建立了机械退化的分析模型。机械冲击导致热老化油浸纸板的含水量减少，同时导致轻度和严重老化油浸纸板的 DP 分别减少和增加。局部放电起始电压和介质击穿强度随冲击循环次数变化显着，在低强度冲击下呈现最大值，在高强度冲击下单调下降。高强度的机械冲击会明显加剧油浸纸板的热劣化过程，这主要归因于机械冲击等效拉伸应力产生的纸板裂纹中的纤维素纤维断裂。轻度老化的浸油纸板承受低强度机械冲击是可以接受的，这将通过限制较小油隙中的局部放电和延长冲击引起的裂缝的击穿放电路径来减轻绝缘劣化。