盆式绝缘子存在自由金属颗粒时的电场分析及其对沿面闪络的影响

为研究气体绝缘全封闭式组合电器(GIS)中盆式绝缘子表面存在自由金属颗粒时的沿面电场分布及其对沿面闪络的影响,建立了800k V盆式绝缘子三维结构模型,采用有限元法对盆式绝缘子存在大小、位置及形状不同的自由金属颗粒时分别在工频电压、雷电冲击电压及快速暂态过电压(VFTO)作用下的电场进行了分析。给出了不同情况下盆式绝缘子的沿面电场分布、沿面法向和切向电场强度分布曲线及电场强度最大值。通过与不存在缺陷时的闪络场强作对比分析,为GIS的绝缘设计提供参考。     

标准雷电压下750kV复合横担暂态电场计算

电力设备在雷电冲击电压下的暂态电场分布多采用求解雷电冲击峰值电压下的静电场分布来近似替代。因此,研究了750kV复合横担在雷电压下的暂态电场分布,提出了暂态电场分布的分频域计算方法;试验测量并定量拟合了复合横担各材料的介电谱数据,得到了暂态电场计算中各材料在雷电压各直流分量及各谐波分量下的计算参数;计算分析了750kV复合横担在标准雷电压下的暂态电场分布,对比分析了传统方法与分频域方法在雷电压峰值时刻的计算结果。研究发现:两种方法所得复合横担各组件承受电压相近,各金具表面最高场强的差值百分比在0.58%~2.92%之间,绝缘子护套端部表面场强最大差值百分比接近18%,支柱绝缘子内部场强差值百分比在–4%~6%之间。该研究可修正传统方法的计算结果,并为复合横担的绝缘设计提供计算依据。     

雷电过电压下绝缘子串电场分布特性研究

为了研究雷电过电压下绝缘子串的电场分布特性,使用电磁暂态仿真软件(ATP-EMTP)计算雷电绕击、反击事故绝缘子串端部的过电压情况,并通过ANSYS有限元仿真软件建立绝缘子串二维模型,将过电压计算结果作为边界条件在ANSYS中进行电场求解。计算出雷电绕击、反击事故发生时复合绝缘子串的沿面及轴向电场分布情况,并与正常工况下绝缘子串的电场分布进行对比分析。结果表明:雷电绕击、反击事故使绝缘子串端部产生过电压,大幅提高了绝缘子串沿面和端部的电场强度,同时绝缘子串的电位和电场分布发生明显畸变,造成绝缘子串发生电晕放电,电气性能降低。     

雷电冲击电压下GIS盆式绝缘子暂态电场分析

GIS盆式绝缘子在雷电压下的暂态电场分布对其安全运行至关重要。工程上一般忽略雷电压下盆式绝缘子盆体材料转向极化的建立时间,采用工频电压下的静电场来近似替代雷电压下的暂态电场。为此利用建立的盆式绝缘子暂态电场数学模型,联合基于LM算法的介电谱分析方法,实现了盆式绝缘子的暂态电场计算,得出了盆式绝缘子屏蔽罩表面、盆体表面以及盆体与中心导杆界面等关键位置的暂态电场分布规律,对比了传统方法的计算结果,发现传统方法下凹面屏蔽罩以及盆体表面处场强最高值均高于暂态电场结果,差值分别为-2.2%、-1.21%和-4.37%;盆体与中心导杆界面处场强最高值在2种方法下相差相对较大,差值为4.46%。该方法能够在计算时间成本可接受的前提下,更精确地掌握GIS盆式绝缘子各关键位置的电场分布,为GIS盆式绝缘子的绝缘设计提供计算分析依据。     

40.5kV真空断路器灭弧室内的暂态电场计算

计算了40.5kV真空断路器开断空载变压器时由复燃和截流引起的暂态过电压.通过离散的傅里叶变换获得暂态过电压的三个主要频率分量,以此作为真空断路器的边界条件,首次对真空断路器灭弧室内的暂态电场采用有限元方法进行了计算.给出了灭弧室内的暂态电场分布,电场强度的最大值、发生时间及典型位置的电场强度随时间变化的曲线.讨论了暂态电场的一些特征,为真空断路器的绝缘设计提供参考.     

合成绝缘子沿面电场计算与均压环优化设置的研究

介绍了计算合成绝缘子沿面场强的简化模型;在此模型的基础上,给出了利用二次插值有限元法计算合成绝缘子沿面电场的分布情况结果,并对不同安装参数下均压环对合成绝缘子沿面电场强度的影响进行计算研究,最终给出了不同电压等级下有效改善绝缘子电场分布的均压环推荐参数。     

220 kV玻璃绝缘子并联间隙雷电冲击放电路径研究

绝缘子并联间隙可以保护绝缘子不受电弧损伤,提高供电可靠性,但试点应用中发现并联间隙存在失效情况。为获取并联间隙结构参数对保护效果的影响,对220 kV玻璃绝缘子不同结构尺寸并联间隙开展了雷电冲击闪络特性试验,获取各间隙试品的雷电冲击50%放电电压与保护效果,并对电弧路径进行了分析,给出了并联间隙失效的可能解释。试验结果表明：Z/Z0值越小、Xc与Xp值越大,并联间隙保护效果越好,所选220 kV并联间隙Z/Z0小于0.875后保护效果趋于稳定。雷电冲击电压作用下,并联间隙两侧电极均会出现先导,先导发展过程受径向电场作用向绝缘子串弯曲,可能是U50电压下发生沿面闪络的主要原因。     

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。     

特高压绝缘子串冲击电压放电特性研究

对 L XP- 30 0玻璃绝缘子串和 XP- 4 0 0瓷绝缘子串进行了雷电冲击和操作冲击电压试验 ,对特高压合成绝缘子进行了操作冲击电压试验 ,获得了其 5 0 %放电电压的相关数据。试验结果表明 ,玻璃绝缘子操作冲击临界波前时间为180～ 2 80μs且随绝缘子片数增加而增加     

合成绝缘子悬挂方式对雷电冲击特性影响

试验研究了合成绝缘子并联和V型悬挂方式对耐雷电冲击特性的影响并运用有限元软件计算了绝缘子串周围电场分布,结果表明并联绝缘子串间击穿电压较单串时低,而型串的影响很小。认为绝缘子串悬挂方式对绝缘子串之间电场分布变化的影响是造成击穿电压变化的原因。     

Insulation properties and degradation mechanism of insulating spacers in gas insulated switchgear (GIS) for repeated/long voltage application

Gas insulated switchgear (GIS) has been increasingly being used in recent years and high reliability and rational insulation design are required. This research provided V-N characteristics (the dielectric breakdown voltage versus number of repetitions characteristics) regarding the internal insulation and creeping insulation of the epoxy spacer, which are the main insulation elements of GIS, in order to help set LIWV (lightning impulse withstand voltage) and SIWV (switching impulse withstand voltage). The insulation strength decreased the most when the lighting impulse voltage was applied to internal insulation of the spacer, however, taking the absolute values into consideration, it turned out that the impact of frequent surges is slight. In the experiment in which alternating current voltage is applied for a long period of time, it was found that there is no decline in the insulation properties even after the voltage is applied for the equivalent of 30 years when the electric field intensity is 12 kVrms/mm or less although the combination with the multiple lightning impulse application may bring about damages to the spacer insulation. The degradation mechanism caused by generation of micro-pits was also understood through simultaneous microscopic observation of the surface and of the interface between the electrode and epoxy     

负极性冲击电晕的微观数学物理模型

本文建立的负极性冲击电晕的微观数学物理模型考虑了电晕发展的一些主要物理过程,例如电子碰撞电离、光电离、电子附着、正负电荷的迁移等。通过数值模拟计算得到冲击电晕的外特性——伏库特性,与已有的实验结果基本吻合;并计算出冲击电晕发展过程中高压输电线附近电场的分布及其随时间的变化。该模型的建立对加深冲击电晕物理过程的认识,更好地进行雷电过电压分析与优化绝缘配合是有意义的。     

Deterioration characteristics of insulating spacer model in repeating impulse voltage

To discuss the UHV GIS test voltage, the deterioration characteristics of the GIS insulating spacer model were studied by repeating lightning or switching impulse voltage. The deterioration factor indicating the decrease of lightning or switching impulse breakdown voltage applied up to 1000 times was found to be 35.7/45.5. The relationship between the partial discharge inception voltage and the breakdown voltage after 1000 impulse applications was also studied. It was found that the partial discharge inception voltage increases despite a decrease in breakdown voltage due to the impulse voltage. In addition, to elucidate the deterioration phenomenon, a study was made of the breakdown characteristics of models with various boundary conditions between the electrode and epoxy resin, as well as the relationship between the boundary conditions. Microdischarge was also studied. The results of the investigation suggest that the deterioration by repeating voltage is caused by microdischarge due to electric field intensification on microprotrusions of the electrode surface.     

Application of functionally graded material for solid insulator in gaseous insulation system

Functionally graded materials (FGM) have spatial distribution of a material property in order to achieve efficient stress control. An application of the FGM to a solid insulator (spacer) for a gaseous insulation system, like gas insulated switchgear, is expected to improve electric field (E-field) distribution around the spacer. In this paper, we describe the applicability of the FGM spacer to gas insulated power equipment. In the FGM spacer, we gave spatial distribution of dielectric permittivity to control the E-field distribution inside and outside the spacer. This paper includes following key results for the applications of the FGM. Firstly, E-field simulation results when applying the FGM by a finite element method are presented, in which we show the effective reduction of the maximum field strength by applying the FGM. Next, a fabrication technique of the FGM spacer sample with not only step-by-step but also continuous changes of permittivity is presented by use of centrifugal force. Finally, dielectric breakdown tests using FGM samples which are accurately controlled the spatial distribution of permittivity are carried out under lightning impulse voltage applications. The test result indicates the increase of breakdown voltage (BDV). From these results, we verified the applicability and the fabrication technique of FGM spacer for improvement of the dielectric strength in the gaseous insulation system.     

Electrode conditioning characteristics in vacuum under impulse voltage application in nonuniform electric field

In this paper, we quantitatively investigated the impulse conditioning mechanism under nonuniform electric field electrodes in a vacuum. A negative standard lightning impulse voltage was applied between rod and plane electrodes whose materials were Cu-Cr, stainless steel and Cu and the gap lengths were d=5 and 10 mm, respectively. Experimental results revealed the transition of the breakdown (BD) sport region on the rod electrode and the corresponding BD field strength in the conditioning process. As a result, we found that the BD spot region started at the tip of the rod electrode and moved to the wider region of the rod electrode with lower electric field as the shots of the voltage application increased before the saturation of the BD voltage. Finally, by analyzing the results with an electric field strength, we propose that "the conditioning degree" along the electrode surface distributed directly proportional to the electric field distribution under a nonuniform electric field in a vacuum, irrespective of the electrode materials     

正极性雷电冲击电压下流注起始特性研究

流注是长空气间隙放电的主要过程,其起始特性具有重要的理论价值与广泛的工程应用。以往对直流电压作用下流注起始特性的研究较多,对冲击电压特别是电压上升率较大的雷电冲击电压下流注起始特性研究很少。采用基于光电集成技术的高压侧电流测量系统与空间电场测量系统,对1 m棒–板间隙在正极性雷电冲击电压下流注起始特性进行研究,提出了新的流注起始观测手段,获得不同半径棒电极、不同电压上升率下的流注起始电压与场强,拟合得到考虑电压变化率的流注起始场强判据,并验证了所提出判据的广泛适用性。另外,还对正极性雷电冲击电压作用下流注起始时延的变化规律进行研究,定量测量了流注的起始时延,为研究流注起始时延的概率分布奠定基础。     

冲击电压下不同温度油中空间电荷迁移对电场分布影响

冲击电压下油中空间电场分布对于变压器内部绝缘优化设计至关重要,现有设计方法没有考虑温度和空间电荷迁移对电场的影响。为了研究温度对空间电荷迁移特性的影响,搭建温度可控的冲击电压下油中电场测量平台,测量雷电冲击电压下25℃、50℃、60℃均匀电场的油中空间电场分布,分析空间电荷对油中电场的影响。实验结果表明:随着温度的增加,60℃时油中场强峰值比25℃时下降了5.2%;50℃时油中场强分布在0.60μs时提前达到稳定阶段。温度升高后,电子漂移速度最大是25℃下的1.8倍,迁移率最大是25℃下的2.0倍,温度升高引起电子迁移率、漂移速度的增加导致了上述现象。该文研究结果为变压器绝缘优化设计提供了实验依据。     

The influence of wave front duration of impulse voltage on creeping discharges along aerial insulated wire

In high‐voltage aerial distribution systems, creeping discharges progress along the cable surface from the free end of the binding wire when overvoltages caused by a lightning surge have invaded the central line of an insulated cable. Consequently, various accidents such as punch‐through breakdown, melting, or snapping of a cable, often occur at these systems. In our previous studies, it has been clarified that the lengths and aspects of creeping discharges under a 1.2/50 µ s impulse voltage condition can be markedly affected by changes in the electric field strength on the cable surface. However, lightning impulse surges which may invade the central line of a cable have various wave front durations. This will further complicate creeping discharge phenomena due to lightning. In this paper, we report the influence of the wave front duration on both the lengths and the aspects of the creeping discharges which progress on the cable on application of lightning impulse voltages. It has been shown that the behavior of negative creeping discharges reveals pronounced changes in response to the duration of the wave front of the applied voltage. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 147(2): 30–38, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10263     

Distortion-free measurement of high impulse voltages

It is shown that every high voltage divider has a limited bandwidth of some MHz, resulting in a limitation for the measurement of front oscillations or front-chopped lightning impulse voltages. It is pointed out that a voltage divider can be easily calibrated and can be constructed to prevent EMC-problems during impulse voltage measurement. Using a spherical electric field sensor with optoelectronic data transmission, a voltage measurement system with an upper bandwidth of 25 MHz has been constructed. The advantage of this system is the distortion-free measurement of all impulse test voltages in any circuit. After a short review of the principle and characteristics of the sensor, some practical applications are highlighted, showing that it can improve high-voltage measurement     

BOOK REVIEW

ABSTRACT

This paper presents a new mathematical model of impulse corona for the analysis of lightning transients on overhead transmission lines. The corona ionization zone is simulated equivalently in a symmetrical and cylindrical configuration, and the conductor under corona is placed at the axis of the cylinder. Charge, electric field and voltage drop are related macroscopically in the model. Multilayer space charges, their development and their displacement are also taken into account. The input variable is the applied voltage and the total charge is obtained through the computational procedure of the model. The model parameters may be determinted with several measured data under the traditional lightning waveshapes, then the model can produce q-v curves under the realistic lightning waveshapes. A reasonable agreement is shown between the results from the model and from the experiments.