Applications of polymeric outdoor insulation in Japan

Intensive research and development concerning the application of polymeric outdoor insulations in Japan started about 10 years ago. Research on applying polymeric insulating materials to power systems covers various fields such as insulators and interphase spacers for overhead transmission lines, polymer housing of bushing and surge arresters for substation apparatus, insulators and interphase spacers for distribution lines and insulators for railways. Polymeric insulators and housings for electric power systems are being evaluated to extend their use, focusing on insulation characteristics such as withstand voltage against salt contamination and deterioration through prolonged use. For railways, trial uses of polymeric insulators have been started on commercial lines     

弯曲电极结构对真空中氧化铝陶瓷沿面闪络耐压的影响

氧化铝陶瓷以其良好的绝缘性能广泛应用于高压真空器件,起到绝缘和支撑作用,但氧化铝陶瓷的沿面闪络现象严重制约了其耐压性能。分析了阴极金属-陶瓷-真空三结合处电场局部增强的原因,对阴极金属电极结构对柱状氧化铝陶瓷三结合处电场分布影响进行了仿真和单次脉冲耐压试验研究,给出了不同电极情况下,氧化铝陶瓷的耐压结果。结果表明,弯曲电极结构能有效减弱氧化铝陶瓷三结合处的电场强度,并且随着金属电极弯曲长度的增加而明显减小;相对于平板电极,弯曲电极的平均最高耐压提高了45%。     

Effects of manganese and chromium doping on the surface properties of alumina insulators

Bulk doping was taken into consideration to improve the surface voltage hold-off performance of alumina insulators in vacuum. The as-blended 95% alumina powder was selected as initial powder to be doped with proper Cr₂O₃ and MnCO₃. The results of properties measurements and experiments showed that samples doped with proper Cr₂O₃ and MnCO₃ possessed better surface properties compared with original 95% alumina insulators. The doped samples displayed higher surface breakdown strength and performed better metallization properties after being metallized through a newly designed method. Both the surface resistivity and the secondary electron emission coefficient of alumina were decreased significantly after manganese and chromium doping, which resulted in the improvement of surface insulating performance. In addition, some points concerning the influences of manganese and chromium doping on the structures and properties of alumina insulators were also briefly discussed upon analyses on composition and structure of ceramic samples.     

Influence of surface roughness on the charging of insulating spacers in vacuum

This paper describes the charging phenomena of cylindrical insulators made of PMMA, PTFE, or Al₂O₃ under ramped and stepped dc voltage. It is primarily concerned with the influence of surface roughness on the formation of charging for various insulating spacers. By using an electrostatic probe located on the cathode, we conducted real‐time observations of the electric field induced by the surface charge. It was found that the surface roughness positively affects the charging, which becomes more pronounced in insulators polished to a higher degree. Furthermore, polished insulators are characterized by a shorter time lag. These results show the importance of surface treatment for insulating spacers in vacuum. © 2001 Scripta Technica, Electr Eng Jpn, 135(3): 16–25, 2001     

Influence of sintering temperature on the flashover performance of alumina insulators in vacuum

This paper reports on the influence of sintering conditions on the flashover/pre-flashover characteristics of alumina insulators in vacuum under an impulse voltage. Four kinds of alumina insulator were studied, which were prepared using the same formula with different sintering conditions. The surface pre-flashover and flashover phenomena of different samples in vacuum have been observed under impulse voltage. Based on the experimental results, the characteristics of pre-flashover and flashover vary with different kinds of test samples. It was found that the insulators with a higher sintering temperature had a lower flashover voltage, and more active preflashover. From a scanning electron microscope (SEM) analysis of alumina insulators, we conclude that the methods of preparing alumina samples can affect their microstructure resulting in a change in the pre-flashover and flashover performance as alumina insulators.     

高电压等级真空灭弧室绝缘结构的研究

为了解真空灭弧室的绝缘性能,通过对72.5kV真空灭弧室试品的冲击耐压试验以发现规律、分析其影响因素并改进绝缘结构。试验表明,其内部绝缘击穿并非发生在触头间隙,而是触头背部与主屏蔽罩间的间隙放电。增大触头边缘与背部过渡处的圆弧半径后,提高了耐压水平。进一步提出126kV真空灭弧室内部绝缘结构的设计方案,计算了电场分布情况并用真空灭弧室绝缘击穿的统计特性分析其耐压特性。     

Surface switching characteristics of variable permittivity dielectrics

Flashover voltage, lifetimes, and switch performance of insulators utilizing square thin and thick film electrodes were examined to determine the viability of using thin electrodes for reliable surface discharge switching. Gold, silver, and platinum were sputtered (0.25 /spl mu/m) and screen printed (15 /spl mu/m) onto Al/sub 2/O/sub 3/, TiO/sub 2/, and modified BaTiO/sub 3/ (MBT), then tested in air at 10/sup 5/ Pa, under vacuum (10/sup -3/ torr), and while immersed in an insulating fluid, SF-2 (manufactured by 3M). For the measured range of 0.5 to 3 mm in air, the flashover voltage for all three insulators was found to have a linear dependence on the electrode separation distance with 15 /spl mu/m thick screen printed electrodes and a square root dependence with 0.25 /spl mu/m thick sputtered electrodes. Delay times of approximately 20 ns with a corresponding jitter of 6 ns were observed across all three insulators under triggered flashover. Insulators in air with sputtered electrodes had lifetimes of approximately 5 flashovers for dc flashover and 40 for triggered flashover. Screen printed TiO/sub 2/ and MBT had dc lifetimes of approximately 10 flashovers in air, and 3 flashovers in vacuum and SF-2. Screen printed TiO/sub 2/ and MBT had triggered lifetimes of greater than 200 flashovers in air, and <3 flashovers in vacuum and SF-2. Screen printed Al/sub 2/O/sub 3/ had dc and triggered lifetimes of greater than 200 flashovers in air, vacuum and SF-2. Insulator failure during dc flashover was determined to be due to the formation of a conductive channel between the anode and cathode. Formation of the channel was attributed to insulator thermal and dielectric properties and the presence of vaporized electrode species in the gap region during flashover.     

Optimizing the performance of flat-surface, high-gradient vacuum insulators

High-gradient insulators (HGI) are periodic assemblies of conducting and insulating layers that have been shown to withstand higher pulsed voltages in vacuum than homogeneous insulators of the same length. We carried out calculations and experimental studies to understand the effect of geometry on the performance of well-conditioned, flat-surface HGI assemblies. We tested stacks with several different values of I/M (where I is the axial length of an insulating layer and M is the length of a metal layer). The experiments showed that HGI performance was substantially better than conventional insulators for I/M<3 and somewhat worse for I/M>3. Numerical calculations of electron orbits showed: 1) that the electric fields in HGI assemblies may have the favorable property of sweeping charged particles away from the surface and 2) that electron multiplication on the surface is suppressed when I/M<3.     

Complex Permittivity Spectra of Various Insulating Polymers at Ultrawide‐Band Frequencies

Nowadays, trials to use even higher frequencies are pursued to realize high‐speed wireless communications. In order to respond to such a trend, dielectric properties of insulating polymers at high frequencies have to be clarified, although the importance of clarifying low‐frequency properties is still very high, especially for use as high‐voltage insulators. In this regard, complex permittivity spectra from 10 mHz to 4.0 THz were obtained for various insulating polymers. The spectra obtained in the very wide frequency range are important, because they can be a valuable database and they provide various pieces of important information on dielectric characteristics.     

真空绝缘堆的电场仿真

真空绝缘堆是脉冲功率系统的重要部件,承担着绝缘支撑以及不同氛围隔离的重要作用,往往也是整个系统的薄弱环节之一.笔者对真空中绝缘堆的不同绝缘结构进行了电场仿真分析,探讨了金属极板的层数、绝缘层与金属极板的位置、两者的比例、绝缘子的角度、电极嵌入对真空绝缘堆电场分布的影响.仿真结果表明:加入金属极板改变了绝缘子表面的电场分...     

Steep Impulse Voltage Characteristics of Suspension Insulators

Transmission and distribution lines are sometimes struck by lightning and there is some risk of electrical puncture of suspension insulators due to high and steep lightning surge voltage. When the insulators suffer from steep lightning surge voltages, the solid insulating body of the insulators sometimes is punctured before external flashover in the air occurs. These characteristics were investigated on the insulators in the laboratory by using different steep impulse voltages. From the investigation results, both V-t characteristics of external flashover and internal puncture were obtained on the insulators. It was found that the puncture of the insulators is a matter of probability, depending on the dimensions of the insulators, steep impulse voltages and number of impulse voltage applications. Especially, the effect of number of voltage applications on puncture probability was clarified and partial damage by a small number of voltage applications was verified before complete puncture occurred. Based on the study results, an empirical equation relating to probability of puncture (P), impulse voltage (V) and number of voltage applications (N) was established.     

真空中典型沿面绝缘结构的电场分析

在高电压作用下,由复合绝缘介质构成的沿面绝缘结构的耐电强度远低于其绝缘材料自身的击穿场强,这一现象与其电场的分布特点密切相关。笔者针对真空中平行平板、平面和棒-板电极系统等多种典型沿面绝缘结构的电场分布进行了仿真计算,探讨了电极-介质结合处的间隙、圆台形绝缘子的圆锥角角度、平面电极的高度以及绝缘子介电常数等因素对电场分布的影响。仿真结果表明,接触间隙的存在导致局部电场的加强和电场方向的变化,间隙宽度越大、高度越小,间隙处电场畸变越大;圆锥角越大,绝缘子的介电常数越大,场强畸变也越大。该分析结果有利于真空中沿面绝缘结构的设计。     

Electrostatic painting of insulating surfaces

The purpose of this work was to develop methods for painting insulating surfaces by the conventional electrostatic painting technique used to coat conducting samples. This technique is not applicable to insulators since the charges carried by the paint accumulate on insulating targets, thereby preventing a proper coating. A detailed investigation of the decay of charges deposited on insulators by a corona discharge simulating the charged paint has confirmed that a grounded counterelectrode (CE) on the back face of the sample speeds up the decay and that the better the contact, the faster the decay. Because a material CE with proper contacts is inconvenient for painting in production configuration, it was suggested that ionized air might behave as a satisfactory CE. Several ionizers have been tested, and good coatings have been obtained, provided that the flows of paint and ionized air are well separated. The possibility of self-creation of ionized air by the voltage of the early paint deposit has also been successfully tested     

HV design of vacuum components

We discuss a number of practical implications from recent studies on HVDC design concepts for vacuum components. These studies dealt with microwave tube technology. The conclusions, however, are valid for a wide range of components. The goal of this work is to provide a scientific basis for the design of HVDC vacuum components. From a study of breakdown and emission mechanisms, and from the measured insulating performance of many different geometries, we have derived guidelines for the design of, for example, insulators and cables. It is further shown how conditioning procedures and operating conditions (operating pressure, insulator charging) should be reflected in the design. We discuss a number of practical implications regarding insulator design, conditioning, vacuum vs. air operation, HV cables in vacuum and potting     

Common insulating properties in insulating materials

Insulating materials exist in a variety of different forms, including gas, liquid, solid, and vacuum, and different forms of insulating materials have significantly different dielectric strengths and insulating properties. Power transmission/substation facilities for UHV AC and 500 kV DC power transmission and 500 kV underground power transmission facilities have been designed and constructed by taking advantage of the insulating properties of various insulating materials and structures so that they conform to the demanded insulation specifications. Conventionally, insulating material technology has been developed by making a close study of apparatuses and insulating materials individually. In this paper, as a new attempt, the insulating properties of various insulating materials/apparatuses are cross-sectionally compared and examined from an entirely new viewpoint through the assessment of commonalities and differences between them. A listing of lightning impulse and AC dielectric strength data is prepared and systematically positioned from the standpoint of material and structure, and compared and evaluated in a unified way from the viewpoint of typical indices of insulating properties including the "n" value of the V-t characteristic, Weibull parameters, and impulse ratio. Further, an insulation assessment of apparatuses is systematically made with consideration given to their sizes and structures as well as the insulating materials themselves. As a result, it was found, for example, that the design field strengths of power capacitors were high and those of generators were not, and there was a noticeable difference in design field strength between SF/sub 6/ gas insulated apparatuses and oil-immersed transformers. It is expected that the analysis conducted from an entirely new angle may provide a new approach to the development of apparatus insulation technology and to the rationalization of insulation design.     

Whqs-500型HVDC换流站带电清扫装置性能试验

对HVDC换流站使用的Whqs．500型直流污秽带电清扫装置的绝缘杆、绝缘软管（含清洗液）、绝缘绳等三大部件进行电气和机械性能试验,验证了各部件的安全性。对装置整机进行耐压和泄漏电流试验,验证了装置的整机安全性。现场实际运行试验表明,该带电清扫装置操作灵活方便,清扫效果良好,可以实现对带电HVDC换流站内污秽支柱绝缘子的清扫。     

A study on the ageing process for polyester resin using improved Weibull statistics

Surface tracking on organic solid insulators is one of the main reasons for failure in high voltage systems. Due to various factors, such as humidity, pollution, ice load, increase in local voltage, etc., it is hard to estime the lifetime of an insulator. For many years, Weibull statistics have been widely used and accepted as a successful mathematical method of predicting the remaining lifetime of an insulating material. The basic reliability function can perform well for predefined conditions. However, it might be insufficient in lifetime prediction in multi-variable conditions. In this research, a model based on improved Weibull statistics is proposed for estimating the breakdown time of polymeric insulation material. By using appropriate parameters, this improved model can estimate the remaining lifetime within a reasonable accuracy in varying external conditions such as voltages, contaminant flow rates and applied load. To determine the model parameters, several tests are performed according to the IEC 587 accelerated inclined plane tracking test method by investigating the breakdown times of polyesters under various external conditions generated artificially in the laboratory. The calculated results are found to be in good agreement with the experimental data.     

Depression of insulator charging in vacuum by partial mechanical processing

It has been clarified by researchers that insulators having contact angles, e.g. plusmn45 deg with regard to the plane electrodes, is hard to acquire charge when they are exposed to high voltages in vacuum. For example, an insulator in the shape of a truncated frustum is free from charging. However, since such insulator has inevitably large volume, it obstructs the compactness. On the other hand, roughening insulator surface is also effective to prevent the surface from charging. In this case, the cost for roughening the entire surface may be high when the insulator is large. In this paper we review our previous investigation results and describe new experimental results aimed at developing feasible and compact insulators used in vacuum. Surface charging characteristics of partially and mechanically processed insulators have been studied for this purpose. That is, the charging phenomena when such insulators are exposed to a ramped DC or AC voltage have been observed by using a capacitive probe embedded in the cathode. Firstly, we describe of a partially roughened cylindrical insulator, where the height of the roughened surface measured from the cathode is varied keeping the total length constant. Secondly, we describe a cylindrical insulator having a truncated conical frustum or a chamfer at its cathode-side end. Based on these experimental and simulation results we prove that the partial mechanical processing is effective to control and suppress the insulator charging in vacuum.     

1 000 kV级交流输电线路用复合绝缘子可行性探讨

简要阐述了我国目前AC、DC复合绝缘子的发展现状,提出了1000kV级交流复合绝缘子向>400kN的高强度等级发展,进一步改进结构完善配方提高复合绝缘子的可靠性及复合绝缘子绝缘距离的确定方法,并结合我国运行经验和对防污闪技术的认识,建议在c、d、e级特别是在d、e级污秽等级优先选用复合绝缘子。     

低气压下直流正极性冰电极电晕特性研究

覆冰将改变绝缘介质的放电过程，导致电力系统绝缘性能下降，为深入研究覆冰绝缘子串中空气间隙的电晕放电特性，基于冰棱-冰板电极系统，通过脉冲电流传感器和紫外线成像仪CoroCAM IV+揭示了气压对起晕电压、放电模式、放电波形及其幅值等的影响。通过数学分析提出表征不同大气压下不同间隙长度时起晕电压的修正公式，分析和讨论气压对放电脉冲及其幅值的影响。理论分析表明，随着气压的降低，覆冰空气间隙起晕电压呈幂函数或指数函数降低，特征指数同间隙长度相关。试验结果与理论分析一致，进一步揭示了覆冰环境下电晕放电的特性。