The electric field uniformity imposes a significant effect on the breakdown mechanisms of dielectric liquids. In general, breakdown is dominated by streamer initiation under uniform field, while it is dominated by streamer propagation under non-uniform field. This paper presents a study on identifying and quantifying the transition field factor boundary, represented by the field enhancement factor $f$ , between the two dominating breakdown mechanisms. The methods for deducing the transition field factor boundary are introduced. The first method from our previous study was developed by measuring and processing both the streamer initiation and breakdown voltages. In this paper, a new method is developed by only processing the breakdown voltage data. Based on the breakdown results reproduced from the literature, the transition field factor boundaries are derived for the mineral oil under both positive and negative lightning impulses. It is found that the negative transition field factor boundary is lower than the positive one. A four-region model is proposed to describe the effect of impulse polarity on breakdown mechanisms of dielectric liquids and to interpret the transition of breakdown mechanisms with respect to the field uniformity.

中文翻译：

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电场均匀性对雷电冲击下电介质液体击穿机理的影响

电场均匀性对介电液体的击穿机制有显着影响。一般情况下，击穿以均匀场下的流注起始为主，而在非均匀场下以流注传播为主。本文提出了一项关于识别和量化过渡场因子边界的研究，以场增强因子为代表。$f$ ，在两种主要的击穿机制之间。介绍了推导过渡场因子边界的方法。我们之前研究的第一种方法是通过测量和处理流注启动电压和击穿电压而开发的。在本文中，通过仅处理击穿电压数据开发了一种新方法。根据文献中再现的击穿结果，推导出矿物油在正负闪电脉冲下的过渡场因子边界。发现负过渡场因子边界低于正过渡场因子边界。提出了一个四区域模型来描述脉冲极性对介电液体击穿机制的影响，并解释击穿机制相对于场均匀性的转变。