This paper presents both an experimental study and a theoretical discussion on the relevant faults resulting from progressive creeping discharge. Pressboard ageing, voltage amplitude, and pressboard type are configured to generate the faults under divergent creeping stresses. The fault progression is recorded by high-resolution camera, partial discharge (PD) device, and optic-fiber thermometer. The damaged pressboards are scrutinized by microscopy and image-processing techniques, and gas chromatography is used to analyze the gas compositions. The progression of internal treeing shows distinct stages of different interface phenomena, such as spark discharge, white marks, and bubbling effect, as well as varying discharge patterns. In contrast, the progression of surface tracking is a simple but hardly noticeable process due to the PD disappearance. The internal carbonization channels are believed the fundamental causes of the interface phenomena pertinent to internal treeing. A theoretical model is proposed to expound the development of the internal carbonization channels, which considers the charge emission, the pressboard pyrolysis, and the percolation theory. The failure mode of internal treeing is schematically illustrated using a four-phase model, and the effects of thermal ageing and field distribution on surface tracking are discussed. Lastly, a detailed comparison is made between internal treeing and surface tracking in terms of the occurrence condition, initiation mechanism, growth driver, and growth characteristics.

中文翻译：

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发散交流电压下的油/纸板沿面放电研究——第 2 部分：内部树化和表面漏电起痕


本文对渐进式沿面放电引起的相关故障进行了实验研究和理论讨论。纸板老化、电压幅度和纸板类型被配置为在不同的蠕变应力下生成故障。高分辨率摄像机、局部放电 (PD) 装置和光纤温度计记录故障进展情况。通过显微镜和图像处理技术对损坏的纸板进行检查，并使用气相色谱法分析气体成分。内部树化的进展显示出不同界面现象的不同阶段，例如火花放电、白痕和起泡效应，以及不同的放电模式。相比之下，由于 PD 消失，表面跟踪的进展是一个简单但几乎不引人注目的过程。内部碳化通道被认为是与内部树化相关的界面现象的根本原因。提出了一个理论模型来阐述内部碳化通道的发展，该模型考虑了电荷发射、纸板热解和渗滤理论。使用四相模型示意性地说明了内部树化的失效模式，并讨论了热老化和场分布对表面跟踪的影响。最后，从发生条件、引发机制、生长驱动力和生长特征等方面对内部树化和表面追踪进行了详细的比较。