重复频率双极性电压下环氧/电极界面电荷行为与介质损伤研究

In the 21st century, domestic and international power transmission and distribution systems are developing towards a high proportion of power electronic equipment, while the insulation system of power electronic equipment has a high failure rate and a short lifetime under its typical operating voltage, repetition frequency bipolar square-wave voltage. The interface between dielectric and electrode is the starting point for insulation damage, especially under high frequency bipolar voltage. During charge injection and extraction process at the interface, the energy released by the charge recombination and detrapping changes the dielectric molecular structure, significantly affecting the dielectric properties, and leading the surface layer of the dielectric to a weak point of insulation. In this project, power electronic transformer used epoxy resin was chosen to study the charge behavior and dielectric damage of the epoxy/electrode interface under repetitive frequency bipolar-square wave voltage. The relationship between charge behavior and voltage waveform was investigated by using the bipolar charge transport model. The relationship between the voltage waveform at the interface and the molecular chain damage of epoxy dielectric was established. The interaction between molecular chain damage process in epoxy resin and evolution of interface charge behavior was studied. This project reveals the degradation mechanism of epoxy resin dielectric under repetitive frequency bipolar-square wave voltage, and provides theoretical basis and experimental basis for insulation design of power electronic equipment.

21世纪国内外电力输配系统正朝着高比例电力电子装备方向发展，而电力电子装备在其典型运行电压——重复频率双极性方波电压下绝缘系统失效快、故障率高、设计寿命短。界面是造成绝缘损伤的起始点，尤其是在频率较高的双极性电压作用下。介质/电极界面处电荷注入与抽出过程中，电荷复合与脱陷行为释放的能量造成介质分子链结构损伤，影响介质介电性能，使介质表层演变成绝缘系统中的薄弱环节。本项目以电力电子变压器用环氧绝缘材料为对象，研究重复频率双极性方波均匀电场下环氧/电极界面的电荷行为与介质损伤。采用双极性电荷输运模型研究界面处电荷行为的数量特性与能量特性和电压波形的关系；表征该类电压作用后环氧介质分子链损伤特征，建立其与电压波形的关系；研究环氧介质分子链损伤与界面电荷行为的相互作用关系。本项目揭示了环氧介质在重复频率双极性方波均匀电场下劣化“潜伏期”的损伤机制，可为电力电子装备绝缘设计提供理论基础和实验依据。

新型电力系统与电力设备越来越多的面临复杂电压下的电气绝缘问题。其中，重复频率双极性方波电压作用下的绝缘失效快、故障率高、设计寿命短。本项目以环氧绝缘为研究对象，聚焦重复频率双极性方波电压下环氧绝缘的电荷行为与介质损伤问题开展研究。首先，项目研究了环氧/电极界面处电荷行为与重复频率双极性方波电压波形的关系。获得了环氧绝缘的电荷输运参数和电荷陷阱特性，开发了双极性方波电压下绝缘介质电荷输运模型，得到了环氧/电极界面处的电荷积聚量、电荷注入深度与能量释放特征。然后，项目研究了环氧介质分子链损伤与重复频率双极性方波电压波形的关系。搭建了双极性方波电压老化平台，获得了不同老化程度的环氧绝缘样品，分析了其基础理化性能的演变规律，表征了样品表面形貌特征与化学结构的演变，分析了环氧绝缘样品的表层劣化特征与机制；此外，还获得了环氧绝缘电树枝劣化与电晕劣化的规律与双极性方波电压波形的关系，获得了绝缘/电极界面气隙对电树枝劣化规律的影响。最后，项目研究了环氧介质分子链损伤与界面电荷行为的关系。通过量子化学软件建立了环氧绝缘分子链模型，获得了环氧绝缘的能级结构与静电势，获得了分子链断裂位置对能级结构和静电势的影响，并通过能级结构、绝缘/电极电接触机制分析了分子链损伤与界面电荷行为的相互作用；表征了不同老化程度的环氧绝缘样品的击穿特性，揭示了交、直流击穿特性差异的原因，提出了以直流击穿场强作为电老化“潜伏期”特征量的评价方法；表征了环氧绝缘经双极性方波电压老化后的空间电荷、表面电荷陷阱和电荷注入特性，获得了分子链损伤和界面电荷行为耦合作用下固体绝缘的劣化规律与机制。本项目揭示了环氧绝缘介质在重复频率双极性方波电压下的劣化机制，及其与界面电荷行为的关联。可为承受复杂电压波形的绝缘材料和绝缘结构的设计提供理论基础和实验依据。

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