【作者】 张丽娜；

【导师】 赵彤；

【作者基本信息】 山东大学 ， 高电压与绝缘技术， 2014， 硕士

【摘要】 特高压直流穿墙套管作为特高压直流输电系统的重要设备,在电力的经济传送、灵活分配和安全使用中具有关键的作用。然而高压套管也有双刃性的特点,如果它的绝缘性破坏,不但无法起到保护作用,还会对其他设备乃至其周围的电力运行起到破坏作用。目前我国已可制造整流变压器等高端设备,但是±800kV及以上等级(如±1000kV和±1100kV)的高压直流套管等其他高端设备仍大部分依赖于进口,究其原因是这些特高压直流高端设备存在着诸如局部放电、介电性能、耐热性能等难以解决的绝缘问题,使得特高压直流穿墙套管的绝缘优化设计一直是一个难题。研究特高压直流穿墙套管的困难之一是空间电荷问题,在运行过程中套管会承受直流、交流、极性反转等多种激励条件,无论何种工况下,空间电荷的存在、转移、甚至是消失都会畸变绝缘介质内部的电场分布,极易导致材料的绝缘破坏甚至击穿。在直流电压下空间电荷更容易积累,特别是对于极性反转等特殊工况条件,空间电荷效应最为明显,空间电荷的积累会造成局部电场强度急剧增高,畸变的电场极易使绝缘结构发生破坏和击穿,严重威胁高压套管的安全稳定运行。因此,有必要对特高压直流穿墙套管在强电场环境下的电场分布和空间电荷效应展开深入研究。探究解决高压直流穿墙套管的绝缘问题的办法,除了研制和分析新的绝缘材料之外,还有必要对套管进行电场分布分析,在此基础上再展开绝缘结构的优化。本文利用有限元电场分析软件对±1000kV直流穿墙套管的电场分布进行了研究。首先,以±1000kV特高压直流穿墙套管为研究对象,利用有限元分析软件ElecNet建立了考虑空间电荷分布的特高压穿墙套管的结构模型。然后,研究分析了直流稳态、交流稳态和极性反转瞬态过程中空间电荷与电场变化的内在关系,用空间电荷理论解释了不同工况下电场强度分布的变化。针对温度场对电场分布的影响,本文将温度梯度加载到特高压直流穿墙套管的电场计算模型中,分析了温度因素对套管内部电场强度分布的影响。此外,还将软件仿真电场分布和实测热场分布相结合,提出了一种间接测量电场分布特性的方法。基于对±1000kV直流穿墙套管电场分布的计算和分析,本文深入探究了改善套管电场分布的方法,对套管的绝缘系统设计与优化展开了研究。分别针对套管的电容芯子、均压环、内电极和应力锥这几个关键部位进行了结构分析和尺寸优化,为套管的设计研制提供了有价值的参考依据。本文研究了特高压直流穿墙套管在不同工况下考虑空间电荷影响的电场分布,并对套管的绝缘系统进行了分析和优化。这对特高压直流高端设备的研制,以及特高压直流输电技术的发展,都具有重要的应用价值、经济价值和社会效益。更多还原

【Abstract】 UHV (Ultra-high voltage) DC (direct current) wall bushing is an import ant equipment of UHV DC transmission system. It plays a key role in the economic transfer, flexible allocation and safe usage of power. However, the UHV DC wall bushing is a double-edged sword. Because if the insulation is damaged, the bushing not only has no protective effect, but also may cau se damage to other equipments and the surrounding electric power operation. At present our country has the technical strength to make rectification trans formers and other high-end equipments already, but±800kV DC wall bushin gs, higher voltage (such as±1000kV and±1100kV) DC wall bushings and o ther high-end equipments still rely on foreign imports mostly. The reason is that there are a lot of difficult to solve the insulation problems such as pa rtial discharge, dielectric properties and heat-resistant properties of these UH V DC high-end equipments, which makes the insulation design and optimiza tion of the UHV DC wall bushing a difficult problem.One of the problems of researching the UHV DC wall bushing is the s pace charge effects. The+1000kV DC wall bushing under planning bears n ot only the normal DC and AC operating voltage, but also the polarity reve rsal impulse voltage which appears in the process of phase commutation. Sp ace charge always exists widely under various work conditions. The existen ce, transfer, and even disappearance of space charge would distort the electri c field distribution inside the insulating medium, and thus the material can be damaged in early stage and finally breakdown. In DC electric field, espe cially during polarity reversal, the accumulation of space charges will distort electric field distribution in polymer seriously, and thus threaten the safe o peration of UHV DC wall bushing. Therefore, it is necessary to research the electric field distribution and space charge effects of the UHV DC wall bu shing in a strong electric field condition.To find a useful solution to resolve the problems of insulation, not onl y new insulation materials should be researched and developed, but also the electric field analysis of the bushing, and further insulation construction opt imization are necessary. In this paper, the electric field distribution of±100OkV DC wall bushing is analyzed by using the finite element software. First ly, a finite element model for±1000kV DC wall bushing is established by the commercial software ElecNet, to analyze the electric field distribution un der DC, AC and polarity reversal conditions especially considering the space charge effects. The change of the electric field distribution under different working conditions is explained with the theory of space charge. Secondly, t he electric field distribution with thermal stress is also calculated in this pap er to incorporate the influence of the dielectric temperature gradients. Beside s, the software simulation of electric field distribution and the measured ther mal field distribution are combined in this paper to propose an indirect met hod of measuring the electric field distribution. Finally, based on the electric field analysis of±1000kV DC wall bushing, the methods of improving th e electric field distribution and insulation construction optimization are explo red. The structural analysis and size optimization of the capacitor core, gradi ng ring, inner electrode and stress cone of the bushing are respectively rese arched. The research results provide useful reference for further design and development of UHV DC wall bushings.In this paper, the electric field distribution under different conditions wi th considering the space charge effects, and the insulation construction optim ization of±1000kV DC wall bushing are analyzed. The research has import ant applications, economic value and social benefits for the design and devel opment of UHV DC high-end equipments, and the development of UHV D C transmission technology.更多还原