【作者】 涂愈明；

【导师】 肖达川； 江缉光；

【作者基本信息】 清华大学 ， 理论电工， 1998， 博士

【摘要】 国内外己发现多起由于变压器油流静电带电引发的恶性事故。变压器油流静电带电问题己成为影响500kV及以上电压等级大型电力变压器安全运行的关键因素，引起国际有关学术组织和广大研究人员的极大关注和兴趣。变压器油流带电问题受到油速、油温、外加交流电场、油和固体绝缘材料性质等多种因素的影响，涉及到静电学、流体力学、电化学和材料学等多个学科，同时问题本身又具有很大的分散性。因此，深入开展变压器油流带电问题的研究具有重要的理论意义和实际意义。 迄今为止，对于超高压变压器复杂油道结构中的油流带电现象，还没有一个既能考虑油道中油的流动对起电的影响，又能考虑外加交流电场对油流起电的影响的计算模型见诸报导：也还没有一个既在几何结构上，又在电荷的产生和泄放规律上可模拟超高压变压器下端部实际油道中的油流带电现象的实验模型见诸报导，填补这两方面的空白正是本文工作的目的。本文工作的主要内容及所取得的主要成果归纳如下： 首先，在综合考虑油流的流动作用和外加交流电场的电动作用两种作用机制的前提下，针对油流的紊流状态，推导出油中电荷密度方程的两种约束条件，解决了以往求解电荷密度方程时所面临的，必须人为给定油／纸界面电荷密度的困难。由此建立的计算模型小仅可以考虑油流速率、油的电导率、温度和外加交流电场等重要因素对油流带电程度的影响，而且还可计及流体运动粘度以及油中离子的性质(如离子迁移率和扩散系数）等其它因素的作用。 其次，针对油流带电问题中媒质运动的特点，提出用混合格式的有限差分算法以及迎风有限元算法求解变压器油流静电带电问题的电荷密度方程，解决了采用中心格式有限差分法和常规有限元法求解电荷密度方程所引起的数值解易失真振荡问题。 第三，针对超高压变压器下端部油速高、交流电场大，易引发油流带电事故的特点，提取出具有扁矩形截面的均匀油道模型进行了透彻的理论计算分析。在此基础上，设计了具有扁矩形截面、可改变串并联结构的三层油道实验模型。该模型可以外加较高的交流电压以研究交流电场对油流起电的影响。低压极板设计成七块分立电极的结构，可以测试沿流动路径不同部位的泄漏电流。 第四，在理论分析的基础上，合理周密地设计了实验内容、实验步骤、测试方法和防干扰措施，使实验具有较好的重复性。并且，根据收集箱的电流泄放规律提出了一种简便有效的研究交流电场对油流带电影响的方法。 第五，对于所设计的油道模型，实验测试结果和理论计算结果两者基本吻合。研究中得出的关于油流流速、流态、油温和外加交流电场等因素对油流带电影响的结论对超高压变压器的设计、运行具有指导意义。更多还原

【Abstract】 Serious faults of electric breakdown due to the static electrification owing to oil flow in extreme high voltage(EHV) power transfonners have been reported both inland and abroad. The static electrification problem for large power transformers with voltage higher than 500 kV has become one of the key factors threatening the transformer safe performance, and it has caused great interest and concern of the related academic organizations and researchers all over the world. The static electrification owing to oil flow is under the influence of oil velocity, oil temperature, applied AC field and characteristics of insulating materials involved. To deal with this problem, it is required a combination of the knowledge of electrostatics, hydromechanics, electro-chemistry and insulating materials. Besides, the problem itself is of great diversity. Hence it is of great theoretical interest and industrial significance to study this problem. Up to now, for the complicated oil-path structure of EHV transformers, there is no mathematical model which can be applied to deal with the effects of both the flow- induced charge in the oil-path and AC field-induced charge, no laboratory model which can be used to investigate the static electrification phenomena at the bottom of the transformers. The purpose of this dissertation work is aimed at solving these problems. The main work and achievements in the dissertation are as follows: 1. By taking both the flow-induced and the AC field-induced charge effects into consideration, two groups of constraint conditions are obtained for solving the electrical charge density equation under the condition of turbulent flow state in the oil. Thus the difficulty of obtaining the unknown charge density at the oil/paper interface is avoided. By this model, the influences of oil velocity, oil conductivity, oil temperature, applied AC field, oil viscosity and the effects of ions in the oil such as ion mobility and diffusion coefficients can be determined. 2. Owing to the feature of existing moving medium in the related problem, the finite difference algorithm with combined scheme and the finite-element algorithm with up-wind scheme are applied for solving the charge density equation to avoid the irregular oscillating phenomena in the numerical solution obtained by the finite difference algorithm with central scheme or the conventional finite-element algorithm. 3. The fault caused by static electrification usually occurs at the bottom of transformers where high oil velocity and strong AC field appear. To take this phenomenon into consideration, a simplified model with uniformly flat rectangular section is analyzed theoretically. Then a 3-layer laboratory model with uniformly flat rectangular section for experimental study is designed carefully, and the layers of the model can be put in series or in parallel. High AC voltage can be applied for studying the effect of AC field with the model. The low-voltage electrode is made into an electrically insulated 7-section plate, hence the leakage current at different parts along the oil path can be measured. 4. Based on the theoretical analysis, the experiment with the laboratory model are well organized and designed, so that the tests are carried out smoothly and successfully, and the results in the experiment are highly repeatable. According to the way of leakage current in the small collecting tank, a simple and effective method is proposed to study the influence of strong AC field upon the st更多还原