Bubbles, as typical defects of oil–paper insulation systems, pose a great threat to the insulation state. In this article, the characteristics and mechanisms of the partial discharge (PD) inception, evolution, and induced breakdown of bubbles embedded between oil-impregnated paper (OIP) layers are investigated. The results show that the PD inception has a significant statistical time delay due to the lack of free electrons. The PD inception time delay (PDTD) follows an exponential distribution and leads to the large dispersion of the PD inception voltage (PDIV), which follows a Weibull distribution. The changes in PD behavior [charge, repetition rate, pulse current waveform, and phase-resolved PD (PRPD)] over time all show two separable stages (stages 1 and 2). The continuous recording of bubble area and gas composition under PD reveals that the evolution of bubble PD is attributed to the change in gas composition rather than the change in surface conditions as believed by researchers. The OIP breakdown induced by bubble PD indicates two breakdown modes, fast and slow, which correspond to direct-induced breakdown in stage 1 and cumulative-damage breakdown in stage 2. The former occurs because of the severe distortion of the electric field by the space charge at the head of the discharge channel inside the bubble, whereas the latter occurs because of the gradual deterioration of the OIP due to the continuous PD action. This study increases our understanding of the mechanisms of bubble discharge and of oil–paper insulation deterioration, and it provides guidance for fault diagnoses.

中文翻译：

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含气泡油纸的局部放电特性及劣化机理

气泡作为油纸绝缘系统的典型缺陷，对绝缘状态构成极大威胁。在本文中，研究了浸油纸 (OIP) 层之间嵌入的气泡的局部放电 (PD) 开始、演变和诱导破裂的特征和机制。结果表明，由于缺乏自由电子，PD 起始具有显着的统计时间延迟。PD 起始时间延迟 (PDTD) 遵循指数分布并导致 PD 起始电压 (PDIV) 的大分散，其遵循 Weibull 分布。PD 行为 [充电、重复率、脉冲电流波形和相位分辨 PD (PRPD)] 随时间的变化都显示出两个可分离的阶段（阶段 1 和 2）。PD下气泡面积和气体成分的连续记录表明，气泡PD的演变归因于气体成分的变化，而不是研究人员认为的表面条件的变化。气泡 PD 引起的 OIP 击穿表现为快速和慢速两种击穿模式，分别对应于第一阶段的直接诱导击穿和第二阶段的累积损伤击穿。前者是由于空间对电场的严重畸变而发生的。在气泡内部放电通道的头部充电，而后者是由于连续的 PD 作用导致 OIP 逐渐恶化而发生的。这项研究增加了我们对气泡放电和油纸绝缘劣化机理的理解，并为故障诊断提供了指导。