操作冲击电压下纳米改性变压器油中空间电荷分布特性和流注放电研究

发布时间：2018-06-01 04:40

本文选题：变压器油 + Kerr电光效应　；参考：《重庆大学》2014年博士论文

【摘要】：电力变压器作为电力系统中能量转换和传输的核心设备，其安全稳定运行关系着人们正常的生活和国家的经济命脉，由操作冲击导致的内绝缘放电将带来严重的后果。变压器油是一种绝缘性能优良的液体电介质，并已在电力变压器中广泛应用，随着我国特高压电网的快速发展，电力系统电压等级不断增加，为了节省生产成本的和空间资源，变压器本身逐渐紧凑化，这进一步增加了变压器绝缘的设计与制造难度；同时，变压器油中不可避免地存在空间电荷，空间电荷的出现不一定引起击穿，但能够通过畸变场强，影响变压器油的击穿强度。因此，需要从变压器油本身出发，提高其绝缘性能，这对提升变压器的绝缘水平和保障电力系统的安全运行具有重要的工程和理论研究价值。本文开展了变压器和纳米改性变压器油中电场和空间电荷分布的测量工作，对纳米改性变压器油的操作冲击击穿特性进行了试验研究、仿真模拟与理论分析。主要研究内容和相应的结论有： ①以高Kerr常数碳酸丙烯酯液体为载体，，分析了其中空间电荷分布的Kerr电光测量系统、测量原理，探索了液体中电场-光强图的成像规律，研制的Kerr电光测量系统为变压器油中电场和空间电荷分布的测量奠定了基础。为了提高电光测量的精度，对光路进行了优化以消除电场等倾线的干扰，得到了一种规范的空间电荷分布的测量系统及其反算方法。并最终利用该系统测量并得到了操作冲击电压下碳酸丙烯酯液体中空间电荷的注入水平及其分布的动态过程，其中CCD（Charge Coupled Device，电荷耦合元件）图像的灰度化处理和频域滤波等技术提高了液体中空间电荷的计算精度。对碳酸丙烯酯液体中空间电荷注入与输运过程进行了仿真，与试验测量结果对比后发现双电层理论和电化学反应过程分别能够很好地解释液体中空间电荷的注入与产生机理。 ②基于高Kerr常数碳酸丙烯酯液体中空间电荷的测量方法和数据处理方法，利用阵列型光探测量了低Kerr常数纯变压器油和纳米改性变压器油在操作冲击电压作用下的电场和空间电荷分布。试验发现平板不锈钢电极系统下的纳米改性变压器油的耐受电压比纯变压器油的高8.3%，利用阵列型光探测量结果解释了纳米变压器油的耐受电压提高的原因，即不锈钢平板电极间纳米改性变压器油中的双电极同性电荷注入现象更加明显，电极附近的电荷注入水平更高（纯变压器油和纳米改性变压器油空间电荷水平分别为0.010C/m3和0.036C/m3），空间电荷的屏蔽作用更好，从而使纳米改性变压器油具有更高的耐压特性。 ③研究了纳米改性变压器油中纳米粒子的自然稳定机制和被充电后的纳米粒子在电场作用下的迁移过程，对纳米粒子进行了表面改性试验、油中纳米粒子的分散性测试，结果表明，自然状态下经表面改性后的纳米粒子能够稳定的分散在变压器油中，直流电场下纳米粒子容易吸附到正电极，交流和操作冲击电压下的纳米改性变压器油中的纳米粒子也是稳定的。对介电型（Al2O3）、半导体型（TiO2）和导电型纳米粒子（Fe3O4）改性的变压器油在操作冲击电压作用下的击穿特性进行了测试，并与传统变压器油的击穿特性进行对比，结果表明，Al2O3、TiO2、Fe3O4纳米改性变压器油的正极性操作冲击击穿电压较纯油分别提高了35.9%、33.3%、44.3%，而负极性操作冲击下变压器的击穿电压分别只提高了11.5%、10.2%、8.12%，提高幅度较小。 ④从导电型纳米粒子与介电型纳米粒子在外加电场下的界面电荷特性入手，分析了它们对电子载流子的捕捉作用，得到了不同介电特性纳米粒子对流注发展过程影响的普适性规律，即不论是导电型纳米粒子还是介电型的纳米粒子，在电场作用下，其界面分别形成的感应电荷和极化电荷，都会产生电荷势垒，吸附变压器油击穿过程中流注中的电子，从而降低流注发展速率，提高了变压器油的击穿电压水平。纳米粒子对电子吸附的饱和电量与其电导率和介电常数有关，每个Al2O3、TiO2、Fe3O4纳米粒子分别能吸附的电子数为7.9e、11e、11.4e。 ⑤基于对变压器油中电荷载体的注入、产生、消失、复合、迁移等过程的理论分析和参数的确定，建立了变压器油中流注放电发展的场致分子电离模型，基于该模型得到的流注尺寸和流注发展速率与试验结果吻合，同时得到了流注通道内的电场、空间电荷、电位、温度分布等参数。纳米改性变压器油中纳米粒子对流注中电子的捕捉作用降低了流注发展速率和限制了流注尺寸，且流注头部的正离子、负离子、电子及空间电荷密度都有所提高，而流注通道中只有电子密度相对纯油中流注通道是降低的，原因是纳米粒子对电子的捕获作用降低了流注头部的电子数密度，为了维持流注的进一步发展，流注头部更多的中性分子会被电离。上述研究工作，为新型变压器油的研制提供了试验支持和理论依据，有利于大型电力变压器的内绝缘优化设计。
[Abstract]:Power transformer is the core equipment of energy conversion and transmission in power system. The safe and stable operation of power transformer is related to people's normal life and national economic lifeline. The internal insulation discharge caused by operation impact will bring serious consequences. Transformer oil is a kind of liquid dielectric with excellent insulation performance and has been in power transformer. With the rapid development of the UHV power grid in China, the voltage level of the power system is increasing. In order to save the production cost and the space resources, the transformer itself is gradually compact, which further increases the difficulty of the design and manufacture of the transformer insulation. At the same time, the space charge and space charge inevitably exist in the transformer oil. The appearance of the transformer does not necessarily cause breakdown, but it can affect the breakdown strength of transformer oil through the distortion field strength. Therefore, it is necessary to improve the insulation performance from the transformer oil itself, which is of great engineering and theoretical value for improving the insulation level of the transformer and ensuring the safe operation of the power system.
In this paper, the measurement of electric field and space charge distribution in transformer and nano modified transformer oil is carried out. The operation impact breakdown characteristics of nano modified transformer oil are studied, simulation and theoretical analysis are carried out. The main research content and the corresponding conclusions are as follows:
(1) using the high Kerr constant propylene carbonate liquid as the carrier, the Kerr electro-optic measurement system of the space charge distribution is analyzed, the measurement principle and the imaging law of the electric field intensity map in the liquid are explored. The developed Kerr electro-optic measurement system has laid the foundation for the measurement of the electric field and the space charge distribution in the transformer oil. The optical path was optimized to eliminate the interference of the electric field. A standard space charge distribution measurement system and its inverse method were obtained. Finally, the dynamic process of the injection level and distribution of the space charge in the propylene carbonate liquid under the operating impact voltage was measured and obtained, in which CCD (Cha) Rge Coupled Device, the gray-scale processing of the charge coupled element and the frequency domain filtering techniques have improved the calculation precision of the space charge in the liquid. The space charge injection and transport process in the propylene carbonate liquid is simulated. Explain the injection and generation mechanism of space charge in liquid.
(2) based on the measurement method and data processing method of space charge in high Kerr constant propylene carbonate liquid, the electric field and space charge distribution of low Kerr constant pure transformer oil and nano modified transformer oil under operating impact voltage are measured by array type optical probe. The nano modification of the plate stainless steel electrode system is found in the experiment. The tolerance voltage of the transformer oil is 8.3% higher than that of the pure transformer oil. The reason for the increase of the tolerance voltage of the nano transformer oil is explained by the result of the array optical probe measurement, that is, the double electrode same-sex charge injection phenomenon in the nano modified transformer oil between the stainless steel plate electrodes is more obvious, and the charge injection level near the electrode is higher (pure variable pressure). The space charge level of the oil and nano modified transformer oil is 0.010C/m3 and 0.036C/m3 respectively. The shielding effect of space charge is better, which makes the nano modified transformer oil have higher pressure resistance.
The natural stability mechanism of nano particles in the nano modified transformer oil and the migration process of the charged nanoparticles under the action of the electric field are studied. The surface modification of the nanoparticles and the dispersion test of the nanoparticles in the oil have been tested. The results show that the surface modified nanoparticles can be dispersed steadily in the natural state. In the transformer oil, the nanoparticles are easy to adsorb to the positive electrode in the DC electric field. The nanoparticles in the nano modified transformer oil under the shock voltage are also stable. The breakdown characteristics of the transformer oil of the dielectric type (Al2O3), the semi conductor (TiO2) and the conductive nano particles (Fe3O4) modified by the operating impulse voltage The results show that the impact breakdown voltage of Al2O3, TiO2, Fe3O4 modified transformer oil is increased by 35.9%, 33.3%, 44.3% respectively compared with the pure oil, and the breakdown voltage of transformer is increased by 11.5%, 10.2%, 8.12%, respectively. Smaller.
(4) from the interface charge characteristics of conductive nanoparticles and dielectric nanoparticles under the applied electric field, the capture effect of them on the electron carrier is analyzed. The universal law of the influence of different dielectric properties on the flow development process is obtained, that is, whether the conductive nanoparticles or the dielectric nanoparticles are in the field. Under the action of the electric field, the induction charge and the polarized charge formed by the interface respectively produce the charge barrier, which adsorb the electrons in the flow injection during the breakdown of the transformer oil, thus reducing the rate of the flow development and improving the breakdown voltage level of the transformer oil. The saturation of the electron absorption by the nanoparticles is related to the electrical conductivity and dielectric constant. The number of electrons adsorbed by each Al2O3, TiO2 and Fe3O4 nanoparticles is 7.9e, 11e, 11.4e., respectively.
Based on the theoretical analysis and parameters determination of the injection, generation, disappearance, recombination, migration and other processes of charge carrier in transformer oil, a field induced molecular ionization model for the development of streamer discharge in transformer oil is established. The flow size and speed of flow injection based on this model coincide with the experimental results. At the same time, the flow channel is obtained in the flow channel. The electric field, space charge, potential, temperature distribution and other parameters. The capture effect of the electrons in the nanoparticles in the nano modified transformer oil reduces the rate of flow development and limits the flow size, and the positive ion, negative ion, electron and space charge density of the flow head are improved, while only the electron density in the flow channel is relative to the flow. The flow channel in pure oil is reduced because the electron capture of nanoparticles reduces the number density of the electron in the head of the flow. In order to maintain the further development of the flow injection, more neutral molecules on the head of the streamer will be ionized.
The above research work provides experimental support and theoretical basis for the development of new transformer oil, and is conducive to the optimization design of internal insulation for large power transformers.
【学位授予单位】：重庆大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TM41

【参考文献】