表层非线性电导盆式绝缘子表面电荷分布与沿面放电特性

盆式绝缘子表面电荷积聚是影响直流气体绝缘输电管道(direct current gas insulated transmission line,DC-GIL)电场分布与沿面闪络的重要因素,因此探究绝缘子表面电荷积聚机理并提出调控方法,进而改善绝缘子沿面电场分布具有重要意义。该文搭建缩尺直流GIL绝缘子试验平台,研究不同Si C质量分数(23.1%、37.5%、47.4%)的非线性电导涂层对直流电压、金属微粒附着和极性反转工况下盆式绝缘子表面电荷分布与沿面闪络特性的影响规律。结果表明：环氧基Al₂O₃绝缘子的表面电荷极性取决于气固侧电流密度博弈结果,具有显著的场强依赖特性;非线性电导涂层可以自适应调控直流GIL绝缘子的表面电荷与沿面电场分布,显著提高不同工况下的沿面闪络电压。该文的研究结果为高可靠性直流GIL绝缘子的研发提供了一种潜在的解决方案。     

非线性电导涂层对直流GIL绝缘子空间/表面电荷和沿面电场的调控研究

空间/表面电荷积聚是导致直流GIL绝缘子沿面闪络电压降低的潜在原因,涂敷非线性电导涂层是提升沿面绝缘性能的有效方法。本文建立了电场依赖性非线性电导涂层对绝缘子空间/表面电荷及沿面电场调控的数学模型,综合考虑了绝缘气体电流密度以及绝缘子固体电导率与电场强度的非线性关系,通过该模型研究了温度梯度分布下绝缘子内部电荷的分布规律,以及非线性电导涂层对绝缘子表面电荷积聚的影响机制。结果表明：非线性电导涂层对空间电荷消散有明显的促进作用,高压电极附近的同极性电荷主导了表面电荷分布;由于表面电荷分布和切向电场的改善,绝缘子的沿面闪络性能得到提高;在绝缘子与涂层界面之间会积聚正电荷,并从高压电极向地电极逐步递减。     

高压GIS功能梯度绝缘子交/直流电场优化与沿面闪络抑制

在双极高压直流(high voltagedirect current,HVDC)系统中,气体绝缘金属封闭开关设备(gas-insulated switchgears,GIS)可能承受交-直流混合电压。为了提高盆式绝缘子的沿面耐电性能,该文提出了基于多维功能梯度材料(multi-dimensional functionally-graded material,MFGM)的绝缘子交、直流电场协同优化方法,制备了兼具体介电常数梯度材料(ε-functionally gradient materials,ε-FGM)和表面非线性电导材料(surface nonlinear conductivity materials,SNCM)的MFGM绝缘子,并在直流、交流和交-直流混合电压下开展电场仿真计算与沿面闪络测试。结果表明：直流电压下MFGM绝缘子的凸面中心区域积聚同极性表面电荷,而周围区域积聚异极性表面电荷,使高压三结合点处的电场强度较常规绝缘子降低25%,沿面闪络电压提升约14.5%;交流电压下,MFGM绝缘子的沿面电场畸变较常规绝缘子降低21%,沿面闪络电压提升约18%;交-直流混合电压下,...     

HVDC电缆电场分布影响因素的仿真研究

电场分布是决定电缆绝缘短时耐压能力和长期运行可靠性的关键因素。HVDC电缆稳定运行时,绝缘材料的电导率决定电场分布,在较高温度梯度分布下有可能出现电场分布翻转现象。由于电缆绝缘材料的非线性电导率是温度及电场的函数,在投入运行和电压极性反转时HVDC电缆暂态电场分布更为复杂。为此,采用多物理场耦合软件仿真研究了绝缘材料非线性电导属性对不同温度梯度、不同施压方式下电缆绝缘稳态和暂态电场的影响规律。仿真结果发现:当绝缘材料非线性属性确定,绝缘内温度梯度越高,稳态时电场分布翻转现象越严重;电压反转过程暂态电场最大值与电压极性反转时间密切相关,反转时间越短暂态最大电场越高,且暂态最大电场的位置越靠近导体屏蔽。仿真结果同时表明:降低材料电导活化能和提高材料电导率对电场依赖性有利于在温度梯度下对电缆绝缘稳态和暂态电场分布的控制。根据仿真研究结果,建议在HVDC电缆料研发时应采取有效的调控手段降低材料电导活化能和提高场致增强型电导的场强依赖系数;而在HVDC电缆设计时,要特别关注温度梯度效应和极性反转过程中的暂态电场分布问题。     

500 kV直流GIL支撑绝缘子的电场优化

随着电网建设的日益深入,直流气体绝缘金属封闭输电管道(GIL)由于可用在高电压、大容量的场合,用作经济的长距离输电线路而被提上研究日程。直流GIL支撑绝缘子的沿面闪络很大程度上是由表面电荷积聚引起的。直流下GIL的内部稳态电场分布主要受环氧树脂固体绝缘的电导率和形状控制。以500 kV直流GIL为计算模型,借助COMSOL软件,研究了GIL中支撑绝缘子的形状、体积电导率和表面电导率对电场分布的影响。研究认为,半圆锥式绝缘子的电场分布是最优化的,绝缘子的体积电导率对其电场分布影响不大,通过控制绝缘子表面电导率,可以控制和优化直流GIL中绝缘子沿面电场分布。     

环氧树脂非线性电导复合材料表面电荷与沿面闪络特性研究

针对直流气体绝缘金属封闭开关设备(GIS)盆式绝缘子表面电荷积累与沿面闪络的问题,制备了不同Si C质量分数的环氧树脂非线性电导复合材料,研究了Si C含量对Si C/环氧树脂非线性电导复合材料的体电导率、表面电荷、沿面闪络电压等相关特性的影响。结果表明:Si C质量分数大于50%的环氧树脂复合材料试样在高电场下呈现非线性电导特性。随着Si C含量和外加直流电场强度的增加,Si C/环氧树脂复合材料的表面电位增加量明显下降。Si C质量分数大于50%的环氧树脂复合材料在高电场下对其表面电荷积累具有抑制作用,减少了沿面闪络现象的发生。     

SiC掺杂对直流电缆附件用硅橡胶材料非线性电导特性的优化研究

电气设备部件的性能提升不仅要依靠传统几何方法来改善绝缘结构,更要侧重于对绝缘材料自身性能的优化。该文通过实验研究了碳化硅（SiC）/硅橡胶复合材料的直流电导特性和直流击穿特性。随着温度升高,SiC晶格散射会阻碍载流子迁移,宏观上表现为电导特性非线性系数降低,而更多高能载流子的出现则会使非线性区阈值场强减小。随着SiC体积分数及粒径的增加,复合材料直流击穿场强虽有一定程度降低,但整体仍满足运行设计要求。在兼顾关键位置电场分布、损耗功率及局部温升的条件下,该文通过仿真探究了非线性电导特性参数的合理范围,所制备的掺杂10%体积分数SiC/硅橡胶复合材料作为应力锥增强绝缘参与电场调控,可有效改善电缆终端内部电场强度分布,应力锥导体锥面处电场强度降低幅度达到50%。该研究结果有望从材料改性角度为提升电缆附件性能提供思路。     

非线性材料在气-固界面电荷调控中的潜在应用可行性分析及验证

盆式绝缘子表面电荷累积可能导致高压直流HVDC(high-voltage direct current)气体绝缘设备绝缘子附近电场畸变。基于非线性材料具有根据外界电场变化而自适应调节其电导的特性,本文探究了碳化硅(SiC)在绝缘子气-固界面电荷调控的应用可行性,验证了掺杂SiC的环氧基材料电荷消散性能,研究了掺杂不同质量分数SiC的绝缘子的直流沿面闪络特性。结果表明,SiC掺杂的环氧基绝缘材料具备电导非线性特征;当SiC质量分数超过20%,盆式绝缘子沿面闪络性能得以提升;而支柱绝缘子的直流性能随掺杂量升高而降低。     

表层介电功能梯度绝缘子的介电常数分布优化

电场分布是决定复合绝缘系统耐电性能的关键因素之一,为改善气体绝缘开关设备(GIS)绝缘子的沿面电场分布进而提升其闪络电压,提出了表层介电功能梯度绝缘子(SFGM)的设计概念及其介电参数分布优化方法。针对盆式绝缘子,以分别提升绝缘子凹面和凸面的沿面电场分布均匀度为优化目标,利用迭代算法自适应调整各表层的介电常数,以获得最优的介电常数分布。对比研究了介电常数分布取值无约束及有约束条件下,绝缘子的沿面电场及表层介电常数分布。结果表明:无约束条件下经过5次迭代,绝缘子凹面沿面电场不均匀系数由4.26下降到1.12,场强集中区域从高压三结合点处转移至地电极侧绝缘子内部,整体耐电性能提升;有约束条件下,表层介电常数最大值被钳制,绝缘子凹面沿面电场不均匀系数由4.26下降到1.84。交流闪络实验结果表明,优化后的SFGM圆台绝缘子的放电起始电压和闪络电压分别提升了20%和21%,进一步验证了基于迭代法的SFGM绝缘子设计具有优异的电场分布调控效果。     

直流叠加冲击电压下HVDC电缆暂态电场分布特性研究

运行中的HVDC电缆除了承受正常工作电压作用外,同时可能承受雷电和操作冲击电压的作用,因此在进行电缆绝缘结构设计时既要考虑稳态直流电场分布又要考虑冲击电压下暂态电场分布。由于HVDC电缆绝缘的电导率是电场及温度的函数,使得HVDC电缆在遭受雷电、操作冲击电压冲击时暂态电场分布更为复杂。为此,该文采用多物理场耦合软件COMSOL Multiphysics仿真研究了温度梯度、施压方式以及绝缘材料非线性电导属性对直流叠加冲击电压下电缆绝缘中暂态电场的影响规律。研究结果表明:直流叠加冲击电压时,暂态最大场强始终出现在电缆绝缘内屏蔽表面;当电缆结构、绝缘材料非线性属性和外加冲击电压幅值确定时,随绝缘内温度梯度的提高,直流叠加同极性冲击电压时暂态最大场强减小,而叠加反极性冲击电压时暂态最大场强却逐渐增大;降低材料电导活化能和提高电场依赖系数可有效改善暂态电场分布,降低暂态最大电场波的幅值并缩短波头和波尾时间。     

Optimization of a post-type spacer in a gas insulated system under three-dimensional conditions

This paper describes the optimization of a post-type spacer in a gas insulated system. The electric field calculation and the optimization have been performed in three-dimensional conditions. We have utilized the boundary element method to calculate the electric field distributions and the Marquardt method to improve the profile of the spacer so as to minimize the maximal electric field on the spacer surface. The optimization has been performed for spacers with cylindrical column, circular, and elliptical cross-sections, respectively. We have varied additional parameters, such as the permittivity of a spacer and the radius ratio of an inner conductor and a sheath. For elliptical cross-section spacers, the optimization has reduced the maximal value of the total field strength up to 35%, and the maximal value of the tangential field strength up to 56% compared with the respective maximal field without a spacer.     

换流变压器极性反转非线性电场分析

换流变压器绝缘材料电导率受电场强度、温度和压力等因素影响,即呈现非线性特性。为了考查非线性对换流变压器极性反转电场分布的影响,针对电导率对电场强度的非线性,对绝缘纸板和油的电导率非线性特性进行了数值拟合,并用于分析1台±500kV换流变压器的非线性极性反转电场。线性和非线性媒质条件下的计算结果表明,考虑1min极性反转的过程时,线性媒质中反转完成时刻的油中最大电场强度值同瞬间完成极性反转的数值结果几乎相同,而非线性条件下反转完成时刻的油中最大电场强度值要比瞬间完成极性反转的数值结果小50%。针对这一现象,进一步对非线性条件下空间电荷加速重新分布的过程进行了分析。     

Modeling of epoxy resin spacers for the 1 MV DC gas insulated line of ITER neutral beam injector system

The spacers for the Gas Insulated Transmission Line for the ITER neutral beam injector will be designed to withstand the operating voltage of 1 MV dc. Electric charging processes of the spacer surface are then expected to play an important role in the final electric field distribution. Aim of the paper is to investigate the effects of the different conductivity properties of the SF6-Spacer insulating structures on the surface charge set-up, and to identify a procedure to minimize this charge. Based on the most updated literature, the paper presents and discusses the results of two newly developed simulation tools: the first consisting of a quasi-static non linear model for epoxy spacer based on finite element method code ANSYS?, the other consisting of a spacer profile optimization package, whose kernel is based on a genetic algorithm. The numerical tools have been applied to post and disk spacer models of the gas insulated line; in particular, the optimization package has been used on the disk spacer, and the comparison between un-optimized and optimized spacer in terms of electric charge accumulated are presented and discussed.     

非线性均压材料的设计理论与参数调控

具有非线性电学参数的材料,其电导率或介电常数能够随着空间电场做出自适应的改变,从而达到智能改善绝缘介质空间电场分布均匀性的效果,可用于缓解高压设备局部集中的高电场。目前,国内外已经能够制备出具有高稳定水平的非线性电导特性的材料,如以氧化锌压敏微球为填料,以绝缘材料为基体的复合物。该文详细综述了国际上对于非线性电导材料均压的设计理论,介绍了如何根据实际改善电场分布的需求选择非线性均压材料的参数。在此基础上,总结国际上学者对于在材料制备过程中调控材料非线性参数以满足均压设计需求的研究工作。本文也对非线性均压材料在应用于实际高压设备方面的进展做了简单介绍。     

交流电压下绝缘子附近导电微粒运动特性

在施加交流电压条件下,对楔形布置的电极间聚四氟乙烯(PTFE)绝缘子附近自由导电微粒运动进行了实验观察.通过对微粒运动过程进行摄像和记录微粒起始运动电压,讨论球形导电微粒和线形导电微粒的运动特性.对不同外形绝缘子附近导电微粒运动规律进行了分析,认为绝缘子的存在能够降低微粒运动起始电压,并且能够吸引部分球形导电微粒沿电极表面滚动到达绝缘子表面;当绝缘子表面与接地电极夹角为锐角时绝缘子附近的微粒运动起始电压会显著降低.对绝缘子存在情况下的楔形电极间电场进行计算,并对微粒运动规律做出了合理的解释.     

Computation methods for one-dimensional bipolar charge injection

Kerr electrooptic field-mapping measurements have shown strong space charge effects in high-voltage stressed dielectrics, where the magnitude and sign of injected charge depends on electrode material. With appropriate choice of electrode material combinations and voltage polarity is possible to have uncharged, unipolar positively or negatively charged, or bipolar charged dielectrics. The bipolar homocharge case lowers the electric field at both electrodes due to space-charge shielding, and thus allows a higher voltage without breakdown. Using charge-transport analysis the authors consider the general case of charge injection from both electrodes and solve time and space dependences of the electric field and charge distributions and the time dependences of the terminal voltage and current. This analysis extends earlier work by including nonequilibrium charge dissociation and recombination so that the effective ohmic conductivity is not constant but varies with time and position due to local net charge density. Specific cases discussed are the open-circuit voltage decay of an initially charged capacitor, the charging and discharging by a Marx generator, and alternating voltage excitations     

Phenomena and mechanism of electric charges on spacers in gas insulated switchgears

The phenomenon of accumulated charges on solid insulator surfaces is one of the critical parameters to consider at the insulation design stage, for AC electric power equipment as well as for DC equipment, so it is important to investigate the characteristics and predominant factors underlying various charging mechanisms. Several researches related to this theme have been reported, but independently, and cross-sectional comparison and evaluation from a unified viewpoint are meaningful. In this paper, the resistance of solid insulator is first discussed, showing that the resistances found by diverse measurements are in a fairly good agreement under similar conditions of the temperature and electric field. Next, three kinds of electric charging mechanisms, i.e. volume conduction, surface conduction and electric field emission are characterized in terms of the time constant, applied voltage and charge distribution. Then, eight cases of recent measurements on the charging time are investigated and their charging mechanisms are classified. Electric field emissions are likely to occur with model spacers made in routine GIS manufacturing process at the electric field level used. Further, three examples in cases with metallic particles are introduced, of simulating charge from edge on the tank, spacer surface charging phenomena, and influence of charge on spacer surface flashover. It is expected that this paper wilt be helpful for understanding charging phenomena e.g. on insulation spacers in gas insulated switchgears     

Motion behavior and deactivation method of free-conducting particle around spacer between diverging conducting plates under DC voltage in atmospheric air

This paper deals with free conducting particle motion around different shaped spacers between diverging conducting plates under DC voltage in atmospheric air. Spherical particle motion was observed experimentally and the results were discussed on the basis of the electrostatic force acting on the particle with and without spacer. The results show that a particle around a spacer tends to move laterally towards or away from the spacer towards higher field regions, depending on the spacer configuration. It lifts at higher field positions and sometimes adheres to the spacer. The effects of spacer angle and spacer material (permittivity) on free conducting particle motion are also discussed. For comparing the results obtained with a sphere, a wire particle motion around different shaped spacers is also investigated. The obtained results suggest one of the methods to prevent/suppress the conducting particle from approaching or adhering to spacers, is to reduce the field strength in the vicinity of the triple junction of gas, solid dielectric and electrode in gas insulated system (GIS).     

大型电机定子线棒防晕层电场的有限元研究

大型电机定子线棒防晕层的电场计算,对优化防晕设计、提高线棒耐压水平意义重大.本文在分析传统方法基础上,提出了非线性防晕层电场计算的新型有限元方法,该方法不含空气域,大幅减小了建模尺寸,并提高求解效率和准确率.对不同额定电压下的防晕层表面电位、场强及损耗密度进行了计算,结果表明:随着电压升高,防晕层的表面电位、场强和损耗密度峰值分布均出现向防晕末端移动现象;转角内侧的损耗密度明显大于外侧,最大值一般出现在中低阻交界面的内侧棱角处.通过电老化试验和阻容链算法的验证,该有限元方法能够满足工程防晕设计精度,并可对三维电场进行定位分析,为存在表面电阻率的有限元电场计算提供了求解思路