A study of partial discharges from water droplets on a siliconerubber insulating surface

This paper presents measurements of partial discharge (PD) from water droplets on a silicone rubber insulating surface in an ac field. Tests are done by placing droplets on the surface using a micro-pipette, and by condensing water in a controlled humidity chamber. The field enhancement factor due to droplets placed on the insulation surface is experimentally and numerically determined. Values in the range of 3.8 to 6.3 are obtained depending on the size and number of droplets. The time resolved analysis of PD from water condensation indicates a threshold field, between 3.0 and 3.5 kV/cm, above which the PD activity increases with time, and brings the insulation to a surface breakdown. The corresponding field enhancement factor obtained for the condensation experiments is between 5.8 and 6.8. The results therefore suggest that the PD activity on the hydrophobic surface can be used effectively to learn about the insulation surface conditions     

紫外光辐照交联聚乙烯在电缆行业中的应用及进展

结合近年来在聚乙烯紫外光引发交联及其工业应用研究的系统工作,评述了该领域的研究进展和取得的主要突破性成果．简要介绍了聚乙烯本体光交联的强化引发体系和光交联机理。最后还介绍了光交联聚乙烯电力电缆的绝缘材料和产品的性能指标以及新的进展。     

智能端子箱防凝露控制器的研制与试验研究

提出了一种智能型户外端子箱防凝露控制方法,通过同时采集箱内、外温湿度信息,将两组信息进行智能处理,得出加热器和排风扇的控制条件判定,达到端子箱主动防凝露的目的。研制出了整套智能防凝露试验装置,并在多个变电站进行了长时间的现场试验,获得了良好的效果。与传统的加热除湿装置比较,本装置直接控制箱内露点条件,具备良好温湿度控制曲线和平稳的控制性能;采用低功率远红外加热器配合小排量风扇的控制方式替代目前普遍使用的单一电加热器,除湿快,箱内温升小,加热时间短,节能效果非常显著。     

超高分子量聚乙烯用作低温电缆绝缘的试验研究

为了解决固体合成绝缘材料低温下的脆裂问题,本文研究了超高分子量聚乙烯用作低温电缆绝缘层的可能性。通过试验比较了各种电缆绝缘材料在低温下的脆裂情况,并在液氮温区中测定了 UHMW-PE 的电气绝缘性能。试验结果是满意的。     

基于COMSOL仿真分析的环网柜湿度控制

环网柜在潮湿凝露的环境下长期运行会导致设备的绝缘强度下降,从而易发生放电、击穿等故障,进一步造成设备的使用寿命缩短,因此需要保证良好的环网柜运行环境。半导体冷凝除湿是新兴的除湿技术,通过将水分冷凝后排出柜体,可控制柜内湿度。利用COMSOL仿真软件对半导体冷凝除湿进行模拟,将柜内的气流场、温度场及水分传输3个物理场进行耦合,研究安装除湿器后柜内的流场、温度、相对湿度的分布变化以及除湿器安装位置对除湿效果的影响。结果表明：加装除湿器后,环网柜内温度变化不大,相对湿度在11 h左右可从90%降至50%,且除湿器安装在柜体底部的除湿效果最优,仿真结果得到了实验验证。给出的除湿器的安装位置对环网柜内温度、湿度的分布变化及对除湿效果的影响可供环网柜内安装除湿器时参考。     

基于COMSOL仿真分析的环网柜湿度控制

环网柜在潮湿凝露的环境下长期运行会导致设备的绝缘强度下降,从而易发生放电、击穿等故障,进一步造成设备的使用寿命缩短,因此需要保证良好的环网柜运行环境。半导体冷凝除湿是新兴的除湿技术,通过将水分冷凝后排出柜体,可控制柜内湿度。利用COMSOL仿真软件对半导体冷凝除湿进行模拟,将柜内的气流场、温度场及水分传输3个物理场进行耦合,研究安装除湿器后柜内的流场、温度、相对湿度的分布变化以及除湿器安装位置对除湿效果的影响。结果表明：加装除湿器后,环网柜内温度变化不大,相对湿度在11 h左右可从90%降至50%,且除湿器安装在柜体底部的除湿效果最优,仿真结果得到了实验验证。给出的除湿器的安装位置对环网柜内温度、湿度的分布变化及对除湿效果的影响可供环网柜内安装除湿器时参考。     

尘土中可溶性盐对电路板绝缘失效的影响

随着电子设备的小型化,印制电路板的导线间距变小,使得导线间电化学迁移失效问题更加突出。同时,大气污染严重,尘土颗粒沉积吸附在电路板上,其中的可溶性盐会改变电路板表面吸附水膜的离子浓度,从而改变线间绝缘失效机理和失效时间。使用浸银Y形电路板,采用不同浓度氯化钠溶液和尘土溶液水滴实验的方法来研究电路板表面存在可溶性盐溶液的情况下导线间绝缘失效特征与失效时间的变化规律。发现随着溶液离子浓度的升高,电路板绝缘失效机理由电化学迁移转变为离子性导电,失效时间呈现先减小后增大再陡降的趋势。存在促进阳极金属快速形成电化学迁移的可溶性盐溶液浓度Ca、由电路板阳极金属离子迁移形成晶枝导电向离子导电为主导转换的盐溶液浓度Cb及直至完全抑制电化学迁移的盐浓度Cc。     

Extinction of spherulites and improvement of polyethylene properties by the use of lithium carbonate

Polyethylene (PE) consists of nonpolar molecular chains having simple structural units. Physically, this polymer is so stable and flexible that it is widely used for insulation of electric wires and power cables, as well as for fabrication of various molded products. The crystalline texture and the presence of spherulites are major factors determining the mechanical and electrical properties of polyethylene. For the purpose of improving these properties of PE, the spherulites are eliminated completely by heat mixing of PE with Li₂CO₃. PE processed in this manner is free of spherulites, has a uniform structure and excellent electrical, mechanical, and thermal properties, such as short treeing length, high dielectric breakdown strength, and high tearing impact strength. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 148(2): 22–38, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10296     

Electric field computation in wet cable insulation using finite element approach

Accurate assessment of cable insulation conditions can be achieved by implementing advanced diagnostic and simulation techniques that assist the measurement and monitoring of the properties related to aging and failure of the insulation system. It is well recognized that the electric field distribution is the dominant factor in the initiation of degradation process in the insulation system. In such a system, and due to the presence of pollutants such as water or moisture, local field enhancement occurs resulting in field stress values enough to cause local breakdown of the insulation. The finite element simulation technique is used to evaluate the electric field inside the power cable. A model that illustrates the water-dielectric interface within the cable insulation system is proposed. The difficulties associated with the building of such a model, which contains elliptically shaped water particles and unusually configured insulation areas, are illustrated. Finally, the link between the local field concentration in the vicinity of water particles and the possibility of insulation failure, which can be developed to a complete breakdown, is discussed.     

高压方波脉冲下局部放电的相位分布特征

针对局部放电可导致变频电机绝缘过早损坏这一问题,笔者分别在方波脉冲下和工频下,对匝间绝缘电磁线进行了老化试验和局部放电测量,主要对脉冲电压下局部放电的相位分布特征进行分析,并与工频下进行了对比。结果表明:脉冲条件下,随老化时间的增长,放电相位呈展宽趋势且出现明显的离散特征;高相位放电的出现是部分缺陷迅速发展的标志,是绝缘失效的先兆。     

一种户外端子箱驱潮防腐监控新技术的研究与应用

提出了一种户外端子箱驱潮防腐集中分散监控方法,通过实时采集箱内、外温湿度、和金属腐蚀过程中,薄层电解质液膜下电化学电池的电流信息,应用大气环境金属腐蚀临界湿度、和金属结露的原理,得出加热部件、送风部件、抽湿排水部件的控制策略,达到端子箱自动驱潮防腐的目的.研制出了端子箱驱潮防腐集中分散监控系统,该系统与常规的加热除湿装置比较,既能实时监测户外端子箱内金属腐蚀行为和结露情况,又能科学地进行控制策略优化.由于采用了ACM大气电偶电化学过程监测技术,简化了不同大气环境地域污染物及金属腐蚀程度的测定工作,通过现场运行,具有良好的驱潮防腐效果,有效地延长端子箱内设备的使用寿命.     

Salt fog testing of polymer housed surge arresters

This paper deals with the evaluation of the insulation design of polymer housed surge arresters for distribution lines. Five commercial designs were tested in a salt fog chamber for 9 cycles using a cycle consisting of 120 hours of salt fog that was followed by a 48 hour rest period for a total of 1280 hours of salt fog. In these tests, the specification for the 1000-hour salt fog test in IEC 1109 for composite insulators was used as a guide. The results demonstrate that a comprehensive evaluation of the external and internal insulation design of polymer housed surge arresters can be obtained by performing a salt fog test, and as such, the test can be considered as a useful design test. Suggestions for improvements in the insulation design of all polymer housed surge arresters evaluated are given in the paper     

基于吸附势理论的SF6高压电器设备气体绝缘状态预测

SF6气体的相对湿度可以直观地反映SF6高压电器设备的绝缘状态。因为相对湿度值随温度变化,所以不同温度的离线相对湿度要根据在线监测得到的相对湿度换算得到,这一过程必须考虑设备对水分的吸附作用。文中在吸附势理论的基础上,采用吸附势与吸附空间的关系曲线作为描述SF6高压电器设备对水分吸附作用的特性曲线,并给出了曲线的制定方法及流程。在实时在线监测的基础上,利用特性曲线推导了温度变化时SF6气体相对湿度的离线计算算法。以离线相对湿度作为预测气体绝缘状态的依据,并在实验室进行了模拟实验。     

Analysis of electrical insulator surfaces by X-ray photoelectronspectroscopy

Our earlier studies centered on understanding the incipient failure mechanism in polyethylene (PE) as an insulation material. The results simulated conditions not measured in routine manufacturing or electric utility test procedures. These findings indicated that detectable changes with pure PE can occur on the surface of cavities (artificially produced), as observed by X-ray photoelectron spectroscopy (XPS). Because the prior studies were done with pure PE and cavities that were made for easy XPS analysis, the question remained “would the findings from the earlier inquiry be relevant to materials used by the electrical utilities?” To answer this question PE insulation was analyzed from a series of commercial type cables that had undergone long-term testing. Occasionally oxygen was found by XPS on the interior surfaces of the more highly stressed PE cable samples. The estimated amount of oxygen was lower than that often found previously. The oxygenated carbon species were similar to those found previously, i.e., alcohols and/or ethers and carbonyls. Some outgassing, probably hydrocarbons, of the PE was observed. The role, if any, of these outgassing components on the failure of PE as an insulation material is unclear     

Failure mechanism of the interturn insulation of low voltageelectric machines fed by pulse-controlled inverters

Partial discharges (PDs) occur in the air-filled gaps of enameled wires that are touching. They erode the insulation and consequently lead to an interturn breakdown. This paper describes the failure mechanism of low voltage interturn insulation as a consequence of PDs and shows why and how it is influenced by the insulation design, temperature, and the applied voltage. Understanding the failure mechanism leads to better founded maximal permissible stresses and a proper design of the interturn insulation to avoid premature drive failures     

Prospective method of lightning protection schemes in distribution system

Grounding wires and enclosed ZnO elements have been incorporated generally in 6.6‐kV distribution systems by TEPCO for the reduction of lightning overvoltages. At present, the reliability to lightning surges is tolerably good. However, the facility of grounding wires is not inexpensive and its maintenance is hard due to corrosion and disconnection in some areas. A typical model simulating TEPCO field adopting enclosed ZnO elements has been developed and we have evaluated relative failure risks systematically according to conditions with and without grounding wires against lightning overvoltages. Two kinds of failures discussed in the paper are the flashover of insulation and the overduty of ZnO elements, and two kinds of induced and direct lightning overvoltages are studied in flashover. The greatest problem with no grounding wire is the increase of ZnO elements' duty, but it was demonstrated that a short partial grounding wire around ZnO elements or the selection of heavier ZnO elements provides a solution. The main objectives of this study are to clarify the relative failure risks systematically according to realistic field conditions, the risk of small stroke currents having long duration to ZnO elements' duty, and countermeasures against ZnO elements' overduty. © 1999 Scripta Technica, Electr Eng Jpn, 127(1): 1–10, 1999     

基于ARM的开关柜环境湿度检测及除湿系统

针对传统开关柜、接线端子以及电子元器件容易受环境影响,潮湿的空气进入柜体接触到电子设备形成凝露,降低了绝缘性能,造成事故,同时不能实时智能控制处理,造成资源浪费。设计了基于ARM的新型开关柜环境湿度检测及除湿系统。该系统以STM32为核心,利用湿度传感器网络检测湿度参数,通过RS485传递参数数据,上位机实时显示数据,设置阈值参数,控制中心作出除湿处理。该系统通过4组数据与高精度湿度检测仪器对比,最小相对误差为0.06%,最大相对误差0.1%,准确度为0.1。能够真实呈现开关柜内的湿度状况。在48 min内,根据无有本除湿系统对比,湿度分别下降到67.2%和50%。从实验结果来看,系统准确度高,实时准确显示柜内湿度,智能除湿效果明显,能很好地检测处理开关柜环境湿度。     

Model of Inception and Growth of Damage from Microvoids in Polyethylene-based Materials for HVDC Cables. 1. Theoretical Approach

A comprehensive physical aging and life model is presented for damage inception and growth in polymeric insulation, starting at the level of microscopic cavities, that are known to be one of the most severe factors limiting design electric field and life of cable insulation. Degradation within a polyethylene-based material for HVDC cables is considered as a hot-electron induced bond-breaking process that cumulates with time into the polymer matrix at microvoid-polymer interface, fed by subsequent electron avalanches generated in microvoids. By this way, a conductive pit is formed, that may exceed eventually a critical size for the start-up of a rapid failure mechanism, thereby leading ultimately to electrical breakdown. The model, essentially based on the physical and microstructural characteristics of the insulation, is virtually free from disposable parameters. It is shown to reproduce qualitatively the dependence of insulation time to failure on applied field, temperature and cavity size and to fit quantitatively experimental times-to-failure relevant to PE-based materials in typical working conditions for HVDC cables. The first part of this paper presents the theoretical background and the derivation of model equations, as well as their discussion. The second part deals with parametric investigation and data fitting.     

海洋石油开采平台35 kV开关装置绝缘的参数

分析了滩海环境对陆地用中压开关设备绝缘性能的影响后确定了海洋平台用 35kV开关柜爬电比距、空气间隙等外绝缘性能参数。用加大空气间隙、提高爬电比距、采用复合绝缘等措施提高抗污绝缘能力开发的 35kV开关装置的 3年成功运行证明这些措施适于盐雾重污染地区的开关柜。     

Evaluation of medium voltage enameled wire exposed to fast repetitive voltage pulses

The paper describes the investigation of the failure mechanisms of medium voltage inter-turn insulation, as a consequence of pulse aging. To study the performance and failure behaviour of enameled wires, models of inter-turn insulation are prepared with enameled wires having polyimide and nano-filled coatings. The aging of such bar samples is attained by sinusoidal (60Hz), fast repetitive unipolar voltage pulses, and high frequency AC waveforms. To establish the residual strength of the bar samples, DC breakdown voltages are determined before and after the aging. In addition, the thermally stimulated depolarization current (TSDC) is used to provide information about the relaxation processes, such as the disorientation of the dipoles and the release of charges from the trapping sites in enameled wires. The various trapping levels, which have discrete energy differences with distinct peaks in the thermograms, are discussed in terms of space charge polarization