Degradation assessment of nanostructured superhydrophobic insulating surfaces using multi-stress methods

This paper describes the electrical insulation property of modified superhydrophobic surfaces, which are prepared on epoxy based composites by using special nano-particles. After surface modification the samples exhibit an extreme unwettability with a static contact angle thetasges130deg. In order to investigate the long term stability under multiple stress, the specimens are subjected to electric fields and moisture in accelerated aging tests like modified-rotating-wheel-dipping-test (MRWDT), clean fog test and condensation test, according to the critical outdoor and indoor service conditions, respectively. It is shown that leakage current and effective power dissipation of contamination layers are significantly suppressed in the presence of superhydrophobic insulating surfaces. Thus, the pollution performance of the insulation systems can be enhanced to a great extent in clean fog test and MRWDT, whereas the insulating surfaces covered with nanoparticles seem to have no beneficial effect during the condensation experiments because of the different wetting mode. In addition, the impact of release agents and fillers on the surface superhydrophobicity is also examined in this study. Moreover, the surface analyses are employed to characterize the topographical change of the nanostructure in connection with the material degradation.     

恒压洁净雾环境中复合绝缘子表面泄漏电流特征参量分析

为有效地建立污闪与泄漏电流之间的关系,针对一种憎水性充分迁移的10 kV复合绝缘子试样,采用恒压洁净雾试验方法,分析了泄漏电流特征参量随受潮时间的长期变化特征,并讨论了泄漏电流各个特征参量与污闪之间的对应关系。结果表明：累积泄漏电流脉冲数目及累积放电量随时间的变化特性与试品是否发生污闪有对应关系,即发生闪络的试品其表面累积泄漏电流脉冲数目及累积放电量的上升速度均快于未闪络的试品。     

220kV三凤线N38塔地段污情分析

针对外绝缘配置的适应性进行了探讨,测定了产生严重串弧的绝缘子的等值附盐密度,结合在线监测到的泄漏电流、环境变化情况以及绝缘子表面积污不均匀分布试验,分析了等值附盐密度在划分污秽等级时的局限性,认为酸雾及沿海盐污等动态污秽虽然不以沉积方式滞留在绝缘子表面,但会加速外绝缘的降低;同时证实了环境相同、爬电距离和高度相等的情况下,瓷质双伞绝缘子的耐污水平优于钟罩玻璃绝缘子,涉及到有效利用系数的问题。为此,推荐使用采集到的相对湿度一泄漏电流曲线监视外绝缘的变化,用以指导外绝缘配置及状态管理。     

测量接地电流检测合成绝缘子污秽程度的可行性分析

通过对合成绝缘子体泄漏电流和表面泄漏电流分离测量,研究了合成绝缘子接地电流的特性,并将这两种泄漏电流与整体接地电流进行比较,同时分别研究了洁净和污秽合成绝缘子的接地电流。结果表明,污秽合成绝缘子整体接地电流与表面泄漏电流在幅值和波形上相同,因此可以通过测量绝缘子接地线上的电流来检测合成绝缘子的污秽程度。     

基于远程耦合法的绝缘子泄漏电流监测及局部放电识别

电缆终端绝缘子的实时状态监测可以有效保证电力电缆线路的安全运行。为了解决电缆终端绝缘子泄漏电流监测和放电识别的问题,本文提出了一种远程探测泄漏电流并且识别局部放电状态的方法。这种方法基于远程耦合磁场来探测泄漏电流,首先在实验室中测试典型临近干扰对电力电缆绝缘子监测的影响,并讨论了检测系统的鲁棒特性。试验是为了获取和分析五支不同清洁绝缘子(陶瓷、玻璃和硅橡胶三种材料制作)在盐雾条件下的泄漏电流,其中盐雾等级为10 g/L和40 g/L,电压等级为50%~300%的标称电压。本文还测试了通过清洁雾进行现场染污的绝缘子,为了证明检测系统和方法的有效性,在所有检测试验中都直接检测泄漏电流的数值。将直接检测得到的泄漏电流分为三类:正弦型泄漏电流、非正弦泄漏电流和放电。同时基于峰态分析远程感应得到的泄漏电流也可以分为三类。本文讨论了利用远程感应的泄漏电流峰态进行绝缘子放电识别的有效性,并证明了在典型干扰效应下检测系统是鲁棒的。     

Effect of Hydrophobicity on Electric Field Distribution and Discharges Along Various Wetted Hydrophobic Surfaces

According to hydrophobicity and hydrophobicity transfer studies on silicone rubber surfaces, although the silicone rubber can transfer its hydrophobicity to various contaminants deposited on its surface, the hydrophobic states of water droplets on clean silicone rubber surfaces and on various contaminated silicone rubber surfaces were found to be different based on evaluation by contact angle measurement. Furthermore, surface discharge and aging of materials decreases the hydrophobicity of the surface. Focused on the difference of hydrophobicity and the effect of water droplets on the hydrophobic contaminated surfaces, some contrastive computations and tests of water droplets on various surfaces were carried out in this study. The results showed that the water droplets existing on the surface of silicone rubber materials might change the electric field and voltage distribution along the surface, and even reduced the initial voltage of the corona discharge, which was verified with a comparison test on a high voltage side of polymer insulator monitored by a photomultiplier tube (PMT) system. Since the leakage current provides much useful information to diagnose the state of outdoor insulation, this study investigates the time and frequency distributions of surface discharges on ceramic insulators, new room temperature vulcanized (RTV) silicone rubber coated insulators and aging RTV insulators with various hydrophobic states with the short time Fourier transform and Gabor transform methods. Then a correlation was found between the distribution of the spectrum of surface discharges and hydrophobicity via the joint time and frequency analysis of discharges on various hydrophobic surfaces.     

Frequency characteristics of leakage current waveforms of anartificially polluted suspension insulator

In order to establish a method for monitoring contamination in insulators based on leakage current waveforms and their frequency characteristics, the leakage current waveforms and frequency characteristics of an artificially polluted 180 mm diameter cap and pin type insulator were investigated by the wet contaminant and the clean fog methods at fixed applied voltages. As a result it was found that leakage current waveforms become similar to the symmetrical wave when strong local arcs occur; hence, the intensity of the odd order of harmonic components, e.g. 50, 150, and 250 Hz, is high. Furthermore, it was clarified that the transition of the leakage current waveforms, until flashover occurs, is classified into six stages and that a threshold exists by which the occurrence of flashover can be predicted     

Influence of fog parameters on the aging of HTV silicone rubber

Testing of outdoor insulators in a fog chamber is universally used. Many factors affect the generation of fog. Fog parameters such as the pressure of the compressed air and the water flow rate feeding the nozzles to form the fog, as well as the size and the speed of the fog droplets impinging on the surface of the insulators, play a major role in the outcome of electrical performance tests. In order to be able to compare test results from different laboratories, the conditions of fog generation should be defined unambiguously and clearly. In the present paper relationships between air pressure, water flow rate and air speed which are related to the distribution and the speed of the fog droplets, are determined as a function of distance from the IEEE-IEC standard nozzles forming the fog. The distribution of different fog droplet sizes is measured. The influence of the fog parameters on the aging characteristics of surface resistance, surface roughness, leakage current and surface hydrophobicity of high temperature vulcanized (HTV) silicone rubber are presented     

An instrument for insulation conditions detection of roof insulator on high-speed-train

With the rapid development of high-speed-railway, environment around high voltage device on train roof becomes very complicated. Most train accidents happened due to occurrence of flashover on roof insulator, but the insulation condition estimation of insulator in such environment is much difficult. To ensure the insulation property of electric equipment, and guarantee the operation safety of high-speed-train, here established an instrument with high reliability which can on-line monitor insulation condition of roof insulator and give out advanced alarm before the incipient insulator flashover. The instrument consists of three parts, Data Acquisition & Sensor, Data Processing and Back Processing. Anti-interference and protection methods are processed to Rogowski coil sensor for better leakage current signal. To avoid the fluctuation from railway power supply, four modules are set to filter the power supply waveform. Through laboratory measurement, it is shown that the leakage current and the impedance angle can be detected by the instrument accurately. From the comparison of leakage current and impedance angle results under different moisture condition and the alarm operation when leakage current value reached threshold, this instrument can give out enough information for staff to understand the insulation condition of insulator.     

复合绝缘子接地电流的测量及其特性研究

目前检测复合绝缘子污秽状况的主要方法是泄漏电流法。这种方法需要在绝缘子上加装电流传感器,加大了测量难度和危险性。文章提出了通过测量绝缘子接地电流来检测复合绝缘子表面污秽程度的方法.对复合绝缘子的接地电流特性进行了研究,分别建立了复合绝缘子接地电流、体泄漏电流和表面泄漏电流的测试回路,对洁净和污秽条件下复合绝缘子上述3种电流进行了测量和比较分析。试验结果表明：污秽条件下复合绝缘子接地电流及表面泄漏电流的幅值比洁净条件下的都有明显增大,而且增大的幅度基本相同,而波形上谐波成分大大减小,但体泄漏电流基本没有变化。因此,通过测量复合绝缘子接地线上的接地电流可以用于检测出复合绝缘子的污秽程度。     

Evaluation of insulation performance of polymeric surface using a novel separation technique of leakage current

This paper describes a novel method to separate the leakage current, obtained in polymeric materials during a salt fog aging test, into three components of conductive current, corona discharge current and dry band arc discharge current. First, we investigated that the relationship between optical emissions due to discharges and a leakage current. Based on experimentally defined discharge types, the separation of the leakage current was carried out. Finally, the polymer surface was analyzed using an electron spectroscopy for chemical analysis (ESCA), and the change in the polymeric constituents was evaluated. The results showed that the cumulative charges due to the dry band arc discharge and the corona discharge to the total charge were about 20 and 10%, respectively. It was also found that a high temperature vulcanized (HTV) silicone rubber could retain its insulation performance better than a room temperature vulcanized (RTV).     

Effects of saline-water flow rate and air speed on leakage currentin RTV coatings

Room temperature vulcanizing (RTV) silicone rubber is increasingly being used to coat porcelain and glass insulators in order to improve their electrical performance in the presence of pollution and moisture. A study of the dependence of leakage current, pulse current count and total charge flowing across the surface of RTV on the flow rate of the saline water and on the compressed air pressure used to create the salt-fog is reported. The fog was directed at the insulating rods either from one or two sides. The RTV was fabricated from polydimethylsiloxane polymer, a filler of alumina trihydrate (ATH), a polymerization catalyst and fumed silica reinforcer, all dispersed in 1,1,1-trichlomethane solvent. The saline water flow rate was varied in the range 0.4 to 2.0 l/min. The compressed air pressure at the input of the fog nozzles was varied from 0.20 to 0.63 MPa. The air speed at the surface of the insulating rods was found to depend linearly on the air pressure measured at the inlet to the nozzles and varied in the range 3 to 14 km/hr. The leakage current increased with increasing flow rate and increasing air speed. This is attributed to the increased loss of hydrophobicity with a larger quantity of saline fog and a larger impact velocities of fog droplets interacting with the surface of the RTV coating     

Analysis of Surface Degradation of Silicone Rubber Insulation Due to Tracking Under Different Voltage Profiles

Tracking is basically a carbonaceous process. In the present study, the tracking phenomenon in silicone rubber material has been studied under AC and DC voltage. The influence of applied voltage magnitude, conductivity, and flow rate of the contaminant on tracking, were analyzed. It is observed that the tracking is more severe under DC voltages. The tracking time is less under negative DC voltage compared to the positive DC voltage. The tracking mechanism is explained in detail. The leakage current during the tracking studies was measured and its trends were analyzed by using the moving average technique. The leakage current magnitude is high with thermally aged specimens when compared to the virgin specimen, irrespective of the type of applied voltage. It is realized that the tracking time and the leakage current magnitude shows an inverse relationship. In addition, the surface condition of the insulation material was analyzed with the water aged specimen and the diffusion coefficient of the material was calculated. The reduction in contact angle of the specimen has direct impact in the reduction of its tracking time. The tensile test and DMA test results indicate that thermal aging of the specimen alter the mechanical properties of the material. The activation energy of the material was calculated through DMA studies, indicating that materials with high activation energy show an increase in tracking time of the specimen.     

饱和受潮条件下的绝缘子泄漏电流特性

空气湿度的大小直接影响到绝缘子表面污层的润湿情况,进而影响泄漏电流的特性。为此,针对目前电力系统大量使用的多种绝缘子,采用固体污层法试验研究了绝缘子在饱和受潮条件下的泄漏电流特性。在简要介绍了试验装置后详细分析了泄漏电流与染污程度、受潮状态、爬电比距等因素的关系,并建立了泄漏电流最大值与等值盐密、污闪电压梯度、运行电压、绝缘子串长、雾浓度之间的对应关系。这些基础规律的研究,可为绝缘子泄漏电流监测系统的正确预警和专家系统的正确分析奠定基础。     

人工盐雾环境下硅橡胶绝缘子泄漏电流的研究

在超声波盐雾发生装置模拟的盐雾环境下,采用高压直流电源测试研究环境相对湿度和盐雾电导率对硅橡胶绝缘子表面泄漏电流的影响,试验结果表明,绝缘子的泄漏电流主要取决于试验环境的相对湿度和盐雾电导率。     

复合绝缘子表面湿润特性建模分析

研究复合绝缘子在雾中的湿润特性有利于分析污闪机理,根据污闪试验中泄漏电流工频分量幅值的变化,利用一次分段曲线简化和替代原有数据,总结了描述复合绝缘子湿润过程的数学模型并针对两种初始憎水性状态对比研究了不同温度情况下的湿润特性。结果发现:低温雾中复合绝缘子的湿润模型是由湿润、过渡、烘干等过程重复组成,而室温下雾的强冷凝作用导致表面持续湿润并放电,湿润或烘干过程并不明显,使得湿润模型可仅存在过渡过程;此外,憎水性有效地抑制了泄漏电流工频分量的幅值,即有效地减轻了污层的湿润程度并延缓了达到第一次饱和湿润的时间,最终使得耐受电压(耐受时间)要高于(长于)丧失憎水性的情况。     

污秽绝缘子泄漏电流特性研究

为提高泄漏电流评估绝缘子污秽度的可靠性,综述了污秽绝缘子泄漏电流特性问题20余年的研究成果,其内容包括临闪前泄漏电流和污闪电压的关系;在运行电压下及绝缘子表面污层饱和受潮时泄漏电流和放电现象间的关系;泄漏电流和等值附盐密度(ESDD)、绝缘子形状、片数、污秽状况以及污闪电压的关系;以及在绝缘子表面污层未达到饱和受潮条件时泄漏电流和雾浓度、相对湿度、ESDD间关系的研究。基于泄漏电流与其他污秽度参数之间关系的研究开发出在实验室及变电站测量多参量泄漏电流的仪器,并在现场测量了大量泄漏电流及气象条件的数据。根据研究成果提出了利用运行电压下的泄漏电流最大值进行污闪预警的方法。     

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     

基于图像识别的绝缘材料憎水表面凝露形貌表征 及其对放电发展影响研究

凝露是造成电气设备绝缘劣化或损坏,影响电力系统安全稳定运行的主要危害之一。在相同凝露条件下不同表面产生的凝露在形貌上存在差异,对其放电发展的影响不同。提出了一种基于图像识别的湿区占比和凝露平均接触面积等特征形貌参数对沿面放电影响的表征方法,采用3种涂覆有不同憎水涂层的试验样品进行憎水性测试,在分析测定了不同样品表面憎水性的基础上,通过相关试验研究了不同憎水表面下凝露液滴的发展过程及分布规律,并分析了凝露形貌参数对闪络电压的影响。结果表明,CSS涂层、P-EL88涂层和无涂层样品表面静态接触角分别为103.17°、91.60°、80.77°,在0.01的显著水平下湿区占比和液滴平均接触面积对凝露闪络电压的Pearson相关系数分别为-0.989和-0.696,凝露闪络电压受湿区占比和液滴平均接触面积联合影响。     

温度湿度可控的小雾室研制

针对目前国内大型雾室温度及湿度不可控,研究环境因素对绝缘子污层受潮过程的影响存在困难的现状,介绍了一种温度及湿度可以准确控制的小雾室系统,用于研究绝缘子表层污秽的受潮过程。介绍了温湿度可控小雾室的研制过程,通过硬件调节和软件控制的手段,实现了雾室内的温湿度准确快速控制。该小雾室能模拟绝缘子所处的环境,实现温度和湿度的自动调节控制,相对湿度控制范围是从当前环境相对湿度至99%,波动<3%;温度控制范围是从当前环境温度至50°C,波动<1°C。泄漏电流可以反映绝缘子的表面受潮状况,结合泄漏电流监测手段,在此小雾室中进行了一系列污层受潮试验研究,初步探索了温湿度对绝缘子表层污秽受潮过程的影响。试验证实,该套小雾室系统控制温湿度的效果良好,可以用于绝缘子污层受潮过程研究。