Development of a positive creeping discharge along an aerial insulated wire

In high‐voltage aerial distribution systems, the insulated cables are supported by the binding wire with the post insulator at the utility pole. When a lightning strike occurs in the neighborhood of the insulated cable in an aerial power distribution system, inductive lightning surges invade the central line of the cable. Then, creeping discharges develop along the cable surface from the binding wire tip at the same time as flashover of the post insulator at a supporting point of the cable. If the cable insulator has weak points such as pinholes, a malfunction near the cable supporting point may occur, with melting of the wire due to punch‐through breakdown. To prevent such accidents, it is important to clarify the mechanism of the creeping discharge along the insulated cable caused by the lightning strike. The polarity of creeping discharges depends on the polarity of the inductive lightning surges, and the extension length and aspect of the discharge differ greatly depending on the discharge polarity. The development of these creeping discharges is attributed to complicated behavior of the positive and negative electric charges. In the present study, we examined in detail the development of a positive creeping discharge along a wire surface by using a high‐speed image converter camera. This paper describes the mechanism of development of a positive creeping discharge based on the experimental results. 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 173(3): 20–29, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20997     

Impulse creeping discharge characteristics in insulating oils with EHD function reinforced by added HFC gas components

The basic properties of electrohydrodynamic (EHD) pumping and dielectric strength were examined for two insulating oils, rapeseed ester oil and silicone oil, which were denatured by a bonding of hydrofluorocarbon (HFC)134a gas components decomposed using a barrier discharge reactor. In this work, the mechanism of a pure conduction pumping contributed to the evaluation of the electrical pumping in sample oils. Dielectric strength of oils was evaluated from the impulse creeping discharge characteristics and the 60 Hz breakdown voltage test. Experimental results revealed that the creation of radicals such as C-F and C-H in denatured oils led to a slight deterioration of the insulation ability compared to standard oils, but the pumping ability was reinforced significantly. Such additional EHD function may be utilized as a new cooling method in oil-filled power apparatuses in view of the dielectric strength.     

Characteristics of creeping discharge along aerial insulated wire under impulse voltages with various wave front durations

When lightning occurs in the neighborhood of outdoor high‐voltage distribution lines, creeping discharges propagate along the wire surface from the binding wire tip just after insulator flashover. These discharges give rise to various faults on distribution lines, for instance, disconnection and melting of wire, punch‐through breakdown, and so on. We must clarify the creeping discharge characteristics associated with various inductive lightning surges from the viewpoint of safety in high‐voltage distribution systems. In our previous paper, it was reported that the lengths and aspects of the negative creeping discharges were influenced by the wave front durations of impulse voltages applied to the central line with a grounded binding wire. The present study was performed to obtain more information on such creeping discharges. This paper describes the distinctive characteristics of a creeping discharge along the insulated wire surface when impulse voltages with various wave front durations are applied to the binding wire. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 158(3): 29–37, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20430     

一起110kV户外气体绝缘全封闭组合电器母线气室支撑绝缘子故障分析

本文分析了一起110kV户外气体绝缘全封闭组合电器母线气室导体支撑绝缘子击穿故障,找到了引起故障的原因,提出了解决及处理措施,为户外气体绝缘全封闭组合电器设备类似故障的处理提供了参考.     

GIS绝缘子表面固定金属颗粒放电特性研究

为研究气体绝缘开关设备中绝缘子表面固定金属颗粒的放电特性,在实验室建立了一套220kV电压等级的GIS局部放电检测平台,模拟GIS绝缘子表面固定金属颗粒放电模型,应用紫外成像技术、超声波检测技术和脉冲电流法对整个放电过程进行了检测。试验结果表明:光学检测法灵敏度很高,通过紫外光子数可以直观的反映放电的剧烈程度和放电位置;绝缘子表面固定金属颗粒的形状对放电剧烈程度有较大影响;在绝缘子缺陷处,随着放电的加剧,局部区域瞬间受热而膨胀,体积的剧烈变化引起了介质密度的瞬间变化,从而导致超声波信号不断增强。     

聚氯乙烯绝缘电线表面为何有“电”

聚氯乙烯绝缘电线若其表面附着一些导电脏物和在潮湿环境下带电使用时 ,用验电笔接触其表面 ,发现电笔氖管发光闪烁 ,用户认为电线“漏电”,电线质量有问题 ,不能安全使用。该文介绍了针对这情况进行调查及试验 ,认为电线质量并无问题 ,而是由极微量的电容电流引起的 ,并不危及人身安全 ,用户可安心使用。     

10 kV架空绝缘导线应用中存在的问题及对策

针对10kV架空绝缘导线运行中常见的问题,从设计方面分析了防雷措施不足、线路金具选用不当、档距过大等原因,并提出了对策。从施工方面分析了施工机具不当、施工操作对绝缘破坏严重等原因,提出解决的措施。     

500kV气体绝缘金属封闭开关设备盆式绝缘子放电故障原因分析

本文介绍了某±800kV换流站恢复送电过程中发生放电故障的500kV气体绝缘金属封闭开关设备盆式绝缘子现场解体情况,结合继电保护动作分析,追溯设备出厂试验结果,并对盆式绝缘子进行了电场模拟分析,最终确定了盆式绝缘子放电故障原因.     

Effects of a barrier on creeping discharge characteristics in SF6 and N2 gases under pulse voltages

This paper describes the effect of a barrier on creeping discharge characteristics in SF₆, N₂, and their mixtures. The barrier height effect on the discharge voltage was investigated under a positive pulse voltage. The discharge voltage increased with increasing barrier height in SF₆ gas. On the other hand, the discharge voltage hardly changed with the barrier height in N₂ gas. In order to clarify the mechanism of the initial creeping corona, it was observed by optical techniques, including an ultra-high-speed electronic imaging system (IMACON 468). The creeping corona path revealed differences in images at various barrier heights. The accumulated charge induced on the barrier by the initial corona in SF₆ gas was able to suppress the development of the later creeping corona, in contrast with N₂ gas. © 1998 Scripta Technica, Electr Eng Jpn, 125(4): 1–8, 1998     

Impulse partial discharge and breakdown characteristics of rod–plane gaps in air and N2 gases

In response to growing environmental concerns, we attempted to develop switchgear without using SF₆ gas. In our research, we used compressed air and pure N₂ as an electrical insulation gas, because of their low global warming potential. In this paper, we examined the impulse breakdown and impulse partial discharge characteristics under various conditions related to nonuniformity of the electric field. The experimental results show that the breakdown voltage (BDV) of air is higher than that of pure N₂ gas under highly nonuniform field conditions in the rod–plane gap. On the other hand, the discharge inception voltage of air and N₂ were almost the same. Furthermore, first partial discharge (PD), leader discharge, and its transition to the breakdown were successfully observed through the measurement of discharge current and light emissions under impulse voltage application. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 148(3): 36–43, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10277     

Effects of ambient humidity and temperature on partial discharge characteristics of conventional and nanocomposite enameled magnet wires

Effects of ambient humidity and temperature on partial discharge (PD) characteristics in twisted pairs with conventional and nanocomposite enameled magnet wires have been investigated. Measurements of the PD inception voltage (PDIV) and the apparent PD charge were performed by applying an ac sinusoidal waveform voltage of 60 Hz to the twisted pair. The observed PDIV in this study can be classified into the following three behaviors. First, the PDIV in both wires decreases with increasing relative humidity (RH) at low temperature. Secondly, the PDIV in both wires slightly increases when increasing the RH at high temperature. Thus, there is a certain value of the absolute humidity to determine the lowest PDIV in both cases with the conventional and nanocomposite enameled wires. Thirdly, the PDIV in the conventional enameled wire significantly decreases at the RH of 95 %, while the decrease rate of that in the nanocomposite enameled wire is relatively small. The observed PD phenomena are discussed in terms of material characterization of the enameled wires such as changes in permittivity due to moisture absorption and wettabilitiy under voltage application.     

小波变换去噪在绝缘子污秽放电声发射监测中的应用

研究了绝缘子污秽放电声发射监测中用小波变换进行信号提纯与消噪的实现问题。在大量绝缘子污秽放电声发射试验基础上,分析总结了污秽放电声发射信号的共有特点。并提出一种基于声发射信号小波变换的小波基选取方法。采用选取的最优小波函数rbio3.9对声发射信号进行频谱分析,提取了声信号的特征频带,并对重构后的信号进行二重小波分解消噪。两组声发射信号的小波变换消噪结果表明,小波变换提高了信号信噪分离结果的可靠性,有效地降低了噪声对污秽放电声发射信号的影响。     

小波变换去噪在绝缘子污秽放电声发射监测中的应用

研究了绝缘子污秽放电声发射监测中用小波变换进行信号提纯与消噪的实现问题.在大量绝缘子污秽放电声发射试验基础上,分析总结了污秽放电声发射信号的共有特点.并提出一种基于声发射信号小波变换的小波基选取方法.采用选取的最优小波函数rbio3.9对声发射信号进行频谱分析,提取了声信号的特征频带,并对重构后的信号进行二重小波分解消噪.两组声发射信号的小波变换消噪结果表明,小波变换提高了信号信噪分离结果的可靠性,有效地降低了噪声对污秽放电声发射信号的影响.     

Study on mathematical model for VHF partial discharge of typical insulated defects in GIS

Very high frequency (VHF) measurement is a valid technique for partial discharge (PD) detection, and PD mathematical models are very important to study PD denoising and waveshape pattern recognition etc. However, these mathematical models based on the traditional PD measurement have been established according to RC or LCR resistance detection so that they are not suitable for VHF measurements. PD signals are detected based on four typical physical models of defects in gas insulated substation (GIS) using VHF method. The VHF PD mathematical models are established, and the principles and methods of establishment are summarized. Furthermore, the parameters of the mathematical models are given and the validity of PD mathematical model is proved by fitting error, power spectrum and time-frequency analysis. Results show that the VHF PD mathematical models can facilitate theoretical simulation of different insulated defects by using the values of given parameters. In the end, applications of the VHF PD mathematical models and complex wavelet transform for extracting the relevant signals from a white noise background are illustrated     

绝缘操作杆表面状态与沿面放电关系试验研究

绝缘操作杆作为带电作业中重要操作工具,其是否处于良好的绝缘状态对确保带电作业人员和设备安全具有重要意义。本文通过不同测量方法检测绝缘操作杆表面存在的典型缺陷,通过电介质谱和沿面放电特性试验对高阻性缺陷检测的有效性进行验证。结果表明：在温度为25℃,相对湿度为68.1%的环境中,受潮状态下绝缘操作杆表面绝缘电阻值比干燥状态下绝缘操作杆表面绝缘电阻值下降了60.1%。干燥状态下绝缘操作杆的介质损耗角正切小于0.01。利用石墨模拟不同碳化位置对于沿面放电电压的影响,通过沿面放电试验得到,当两电极中存在贯通性缺陷时,沿面放电电压会严重下降。通过研究结果提出基于绝缘操作杆表面电阻或介质损耗特性的操作杆绝缘性能评估方法。     

基于GK模糊聚类和LS-SVC的GIS局部放电类型识别

局部放电可以反映气体绝缘组合电器(Gas Insulated Switchgear,GIS)内部的绝缘缺陷,对正确识别GIS的放电类型具有重要意义。在GIS重症监护系统研究平台上人工设置4种GIS的典型缺陷。基于4种缺陷不同电压等级下的局部放电样本数据,提取局部放电灰度图像的分析特性作为识别特征量。同时考虑到现场干扰对局部放电信号的影响,利用GK模糊聚类算法对分形特征量进一步处理,以提取隔离干扰后的分析特征量。最后设计了基于LS-SVC的局部放电模式识别器。试验结果表明所提方法能有效识别GIS放电类型,比人工神经网络方法具有识别率高、稳定性好的优点。