流动状态下工程纯油绝缘介质的放电特性与击穿机理及影响因素研究

The insulation characteristic of pure liquid dielectrics usedin engineeringunder flow conditionis different from that ofits static state. The basic engineering and theoryproblems aboutits discharge progress and breakdown mechanismalso can not be explainedsatisfactorilyby classical small bridgetheory.Hence, in this project, the general information of transformer oil passages, such as impurity property, particle size, oil velocity, oil temperature, oil electrical field distribution,etc.will be collected and analyzed.Theexperimental platformwill becompletedand the the technical problemsabout how to produce, control and detect the suspended impurity particle in pure oilwill be resolved.Then the motion characteristic of flowing suspended impurity particle under external electrical fieldwill be obtainedand themotion regularity will also bedescribed quantitatively.After that, the partial discharge characteristic and its influence factors of flowing insulated liquidwill be studiedand the developing progress of partial dischargewill be revealed.Afeatureparameter will be proposedto present different kinds of partial discharge and the spectrogram used to recognize partial discharge pattern will also beestablished. In addition, the research mainly focus on insulation tolerace,breakdown progress and influence factors of flowing transformer oil with suspended impurity particles. And it will establish the discharge model forpure liquid dielectricsused in engineeringunder flow conditionand explore its breakdown mechanism and conditions. These efforts can initially set up the discharge theory of pure liquid insulating medium under flow condition and it can also beused to design more reasonable oil passage structure to improve internal insulating property and provide the theoretical and experimental guideline for large-scale transformer safe operation.

针对工程纯流动液体绝缘介质的绝缘特性有别于静止状态、且无法用经典小桥理论圆满解释其放电过程与击穿机理的基础与工程问题，收集并分析实际运行下变压器油道中的杂质性质、微粒尺寸、油流速度、油温范围以及油道电场等综合信息，完善实验平台，解决试验中产生、控制和观测油中悬移杂质微粒的技术难题，获取流动状态下不同悬移杂质微粒受外电场影响的运动特性，定量描述其运动规律，研究流动状态下悬移微粒杂质产生PD的特征及影响因素，揭示其PD的发展变化规律，提出表征不同PD形式的特征量，构建辨识PD模式的谱图。同时，重点研究含有悬移杂质微粒的变压器油在流动状态下的绝缘耐受特性、击穿过程及影响因素，构建流动状态下工程纯液体介质放电模型，探索击穿机理和条件，初步建立流动状态下工程纯液体绝缘介质的放电理论，为大型电力变压器的绝缘安全运行或用设计更加合理的油道结构来提升内绝缘性能给出理论和实验依据。

解释工程用变压器油击穿过程的“小桥理论”是以绝缘油处于静止状态为前提，但在变压器实际运行过程中，由于强迫油循环或温差产生热对流的存在，绝缘油常常处于流动状态，使得经典“小桥理论”无法适用。针对这一基础与工程问题，本项目根据大型变压器典型油道结构与电场分布，设计了变压器油流实验模拟平台，能够进行不同流速大小、杂质种类、微粒含量、尺寸以及不同温度下的局部放电和击穿实验；深入分析了杂质微粒在流动绝缘油中的受力情况，分别建立了金属微粒、悬移气泡的运动和变形物理仿真模型，获取了不同影响因素下，悬移杂质在油道中的运动规律、分布特点和对电场畸变情况；通过大量实验，研究了不同杂质种类、含量、流速和温度等影响因素下变压器油局部放电和击穿特性，发现流动状态下变压器油绝缘特性相比于静止状态有明显提升，结合悬移杂质的运动规律与分布特点，揭示了金属微粒与电极、金属微粒间相互碰撞以及气泡变形对流动变压器油绝缘特性的作用机制；梳理出流动液体电介质中金属微粒引发局部放电的四种类型和悬移气泡引发局部放电的两种类型，根据含悬移杂质微粒时流动变压器油局部放电与击穿特性的关联关系，初步建立了由微放电触发油隙击穿的流动工程液体电介质击穿物理模型。本项目的研究成果为通过调整油流速的方法来提高变压器内绝缘性能提供了理论依据与技术保障，同时进一步发展了液体绝缘介质的放电和击穿理论。