Relationship between Creeping Discharge along Aerial Insulated Cable and Duration of Wave Front of Inductive Lightning Surge

We report the results obtained on the developing characteristics of creeping discharges along the insulated cable surface under inductive lightning surge voltages with various durations of wave front. The aerial insulated cables, usually, are supported by the post insulator and the binding wire at the reinforced concrete pole. When a lightning strikes near by the aerial insulated cables, the overvoltage due to the inductive lightning surge invades to the central line of the cable. The creeping discharge can develop along the cable surface from the free end of the binding wire just after a flashover of the post insulator at the cable supporting point. This creeping discharge may give rise to the accidents such as a melting or snapping of the cable. An important subject to prevent these accidents is to clarify the characteristics of creeping discharge along the cable surface and the developing mechanism of discharges. In this study, the impulse voltages with various durations of wave front are applied to the central line of the wire as the inductive lightning surge. The length and aspect of positive and negative creeping discharges developing along the cable surface are measured using a still camera with an image intensifier, and the developing mechanisms of creeping discharges are discussed on the basis of the models which are proposed taking into account the obtained results.     

Positive Creeping Discharge along Aerial Insulated Wire Generated by Lightning Stroke

There are two causes, inductive lightning surge and direct lightning stroke, as the aerial insulated wire accidents accompanying lightning in a power distribution system. When the overvoltage due to the inductive lightning surge invades to the wire core, the creeping discharge can develop along the wire surface from the free end of the binding wire just after a flashover of the post insulator at the wire supporting point. This creeping discharge may give rise to the accidents such as a melting or snapping of the wire. The creeping discharge along the wire surface has the positive or negative polarity. Positive creeping discharge is restricted to the area where a positive lightning generates. Only a few examples have been reported on the positive creeping discharge, and its characteristic has many unsolved points. In the previous studies, we have observed the positive creeping discharges along the wire surface under the negative inductive lightning surge with the peak values in the range |V_m| ≤80 kV. In this study, the positive creeping discharges are examined newly in the range |V_m| > 80 kV. It is reported that the positive creeping discharges are greatly affected by the negative corona discharges generating from the wire surface in |V_m| ≥ 95 kV.     

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     

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     

架空电缆在10 kV线路应用中的探讨

通过对10kV架空绝缘导线(以下简称架空电缆)性能分析，指出架空电缆在线路运行中的可靠性、经济性以及架设施工、维修便利等方面都优于裸导线。为了进一步科学应用架空电缆，针对一些容易发生的问题，提出了相应的防止措施，重点介绍了国内外架空电缆的防雷技术和咸宁地区的防雷特点。     

The effects of steep-front, short-duration impulses on powerdistribution components

A line-type pulser has been developed to test the effects of steep-front, short-duration (SFSD) pulses on distribution components. The risetime is 50-100 ns and the pulse duration is on the order of 300 ns. Terminators often shattered or punctured rather than flashing over. The insulator flashover voltage is approximately 1.5 times CFO for standard lightning impulses. Arresters exhibit an inductive character, with the SFSD peak voltage at 10 kA approximately 4-5 times the 8-pulse×20-μs 10 kA discharge voltage. Polyethylene insulated cable has a characteristic degradation in which failure voltage decreases with number of SFSD pulses     

表面电荷积聚对冲击电压下绝缘子沿面放电的影响

绝缘子的表面缺陷会导致表面电荷积聚，使绝缘子表面的电场发生畸变，影响冲击电压下绝缘子的沿面放电。研究了表面电荷对绝缘子沿面放电进程的影响，发现表面电荷积聚可以降低绝缘子沿面放电的起始电压。外施冲击电压的极性与绝缘子表面电荷极性是否相同会影响绝缘子的电晕起始时刻、由流注向先导的转变时间间隔和流注电晕电流。表面电荷对GIS支撑绝缘子的50％冲击闪络电压和伏秒特性也有一定的影响。     

影响送电网安全运行的有关问题及对策

从设计、科研、运行、制造、材料等多方面分析了近年来影响送电网安全运行的风偏放电、雷击、OPGW断股等主要故障的原因、机理及影响因素。为增强电网抵御自然灾害及外因影响的能力,减少送电网的故障概率,针对上述故障应采取的措施是:注意线路相关设计参数的合理选择,线路微气候区气象资料的收集,采用V型串悬挂;增强绝缘水平,加装避雷线、线路避雷器,降低接地电阻,减小导线保护角;采用铝包钢线,安装雷击放电尖等。     

High‐current lightning discharges in winter

Lightning electric‐field waveforms related to power line faults in winter have been identified. Most of those waveforms appear to be associated with upward lightning discharges with absolute peak currents of over 100 kA. They are quite different from common return‐stroke waveforms, and the lightning discharges which produce these characteristic waveforms are called GC (Ground to Cloud) flashes. These high‐current lightning discharges are distributed around the coastline in different ways depending on their polarities. The spatial distributions of high‐current lightning discharges around Japan are also investigated. It is revealed that the region of Honshu Island along the coastline of the Sea of Japan belongs to the area in which the density of high‐current lightning flashes is the highest in Japan through the year. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 170(1): 8–15, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20874     

Breakdown characteristics of gas‐insulated switchgear for nonstandard lightning impulse waveforms under nonuniform electric field

To improve the insulation specification of gas‐insulated switchgear (GIS), it is necessary to recognize the insulation characteristics of SF₆ gas during actual surges (called nonstandard lightning impulse waveforms) occurring at field substations. The authors observed the insulation characteristics of SF₆ gas gap under various types of nonstandard lightning impulse waveforms and compared them quantitatively with those obtained with standard lightning impulse waveforms. The experimental results were used to derive an evaluation method for real surges, which was applied to typical surges for various UHV and 500‐kV systems. In the preceding study, therefore, only the case of a quasi‐uniform electric field (with a typical range of field utilization factors in the bus of a GIS) was investigated. In the present investigation, the insulation characteristics of an SF₆ gas gap for a nonuniform electric field were observed experimentally and an evaluation method for converting nonstandard lightning impulse waveforms equivalently to the standard lightning impulse waveform was investigated. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 177(1): 11–18, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21144     

输电线路杆塔接地的防雷分析

介绍输电线路在防雷中对杆塔接地的要求和降低杆塔接地电阻的措施，及其措施的装置在以后维护中的注意事项。     

复合光纤架空地线在不同接地方式下的放电路径选择特性

复合光纤架空地线(optical fiber composite overhead ground wire,OPGW)由于具有防雷和光纤通信功能,在交直流输电线路上得到了广泛应用。当前OPGW采用逐基接地而普通地线采用分段绝缘一点接地的接地方式,这种不平衡的接地方式使得OPGW更容易遭雷击而出现断股和掉线事故以致影响光纤通信。为此,采用缩微模型试验研究了OPGW和普通地线在全绝缘、分段绝缘一点接地和逐基接地等3种接地方式对放电路径选择特性的影响,试验结果表明,地线采用逐基接地时放电路径选择概率最高,而全绝缘时最低,试验结论和现场统计数据得到规律相符。为了降低OPGW遭雷击的概率,需要改变OPGW的接地方式或采取适当保护措施。     

Initiation of lightning in thunderclouds with the use of artificial clouds of charged aerosol

Results of the experimental simulation of lightning initiation processes in thunderclouds by large hydrometeor arrays using artificial clouds of charged water aerosol of negative and positive polarity are presented in this paper. A significant influence of the hydrometeor arrays on the discharge initiation and propagation between the charged cloud and the ground is shown. It is found that cloud polarity has a significant influence on the probability of discharge initiation by the hydrometeor array. It is established that hydrometeors have the most pronounced influence on the discharge initiation in positively charged aerosol clouds. Character types of the discharge phenomena initiated by the hydrometeors in the clouds of negative and positive polarity are found: cloud discharges, channel discharges, and diffuse discharges. It is established that the characteristic frequency ranges in the wavelet spectrum of electromagnetic radiation of such discharge phenomena initiated by hydrometeors have greater values for a negative polarity of a cloud than for a positive one. It is found that the characteristics of the current impulse of the main stage of the discharge between the cloud and the ground forming with the participation of hydrometeors differ from the analogous characteristics for cases in which hydrometeors are absent in the gap between the charged cloud and the ground. Thus, using artificial clouds of charged aerosol opens new possibilities for investigation of the processes of lightning initiation in thunderclouds.     

架空输电线路雷击监测系统

为解决电力输电线路雷电绕击与反击事故难以辨别的问题,提出在架空输电线路的绝缘子串悬挂金具处和杆塔横担下方竖杆处安装Rogowski型电流传感器,并根据2个传感器输出电流的极性关系判别绝缘闪络类型。以单片机为核心开发了输电线路雷击监测系统,线路监测终端通过无线接力传输模式与变电站监控主站传输数据;在输电线路遭受雷击时,发送雷击类型、杆塔位置等信息,自动形成雷击数据库。系统软件分为终端部分软件和变电站主控制室系统软件,终端软件采用C语言编程。该监测系统已在110kV线投入运行。     

Effect of shielded distribution cable on very fast transients

Fast transients in power systems can be generated by switching of vacuum and SF₆ insulated devices as well as by solid state devices such as those used in variable speed drives. Transients with ns risetimes can be generated which, in a cable-connected system, propagate down the cable to inductive devices such as motors and transformers. In general, the amplitude of such surges is not out of the ordinary; however, the very short risetime can cause unacceptable voltages across the first turn of an inductive device. A cable with high frequency loss does not generally decrease the amplitude of such surges appreciably but can lengthen the risetime substantially by absorbing high frequency energy from the surge. This reduces the voltage across the first turn of inductive devices and thereby protects them from damage and failure caused by such surges. In the present contribution, we quantify the high frequency losses and effect thereof on very fast transients for four types of shielded, 15 kV distribution cable, three made from various EPR compounds and one made from TR-XLPE     

计算特高杆塔雷击响应的感应电荷准静法

雷击杆塔引起的过电压是导致输电线路事故的原因之一 ,需要尽量准确估计 ,而特高杆塔系统上传播的雷电波是球面波 ,为避免建立等效电路的困难建立了雷击杆塔、地线、导线系统响应分析的数学模型 ,提出了感应电荷准静法 ,用电磁场理论确定绝缘子串两端电压。分析对位参考点和分流问题后提出了新计算分流系数法。研究发现杆塔电位包括可变的抵消分量和雷电单极电荷引起的恒定分量两部分。感应电荷准静法计算杆塔模型的冲击响应与NEC 2的计算结果基本一致。     

架空绝缘线路过电压保护技术的应用

为优选成本低、效果好的架空绝缘线的防雷技术措施,统计和比较了国内大量采取的过电压保护器和放电绝缘子2种架空绝缘线路防雷技术措施的防雷害应用效果。运行经验证实:线路安装过电压保护器或放电绝缘子等技术措施,可有效防止架空绝缘线路发生雷击断线事故和降低雷击导致线路开关跳闸概率,且安装方便,技术经济性较好。     

配电绝缘线路的防雷研究

雷击断线事故是应用绝缘导线中最突出的一个问题。从绝缘导线雷击断线的机理入手，介绍了国内外对绝缘导线防止雷击断线和雷击跳闸的研究成果。防雷支柱绝缘子能从根本上解决绝缘导线雷击断线的问题，介绍了该种防雷支柱绝缘子的特点和应用情况。     

配电绝缘线路的防雷研究

雷击断线事故是应用绝缘导线中最突出的一个问题。从绝缘导线雷击断线的机理入手,介绍了国内外对绝缘导线防止雷击断线和雷击跳闸的研究成果。防雷支柱绝缘子能从根本上解决绝缘导线雷击断线的问题,介绍了该种防雷支柱绝缘子的特点和应用情况。     

Insulation characteristics of SF6 gas for nonstandard impulse voltage polarity reversal pulse waveforms

Evaluation of insulation strength for lightning surge that actually enters into substations is important in estimating insulation reliability of gas‐insulated equipment. The standard lightning impulse voltage (1.2/50 µs) is used for factory tests. However, the actual lightning surge waveforms in substations are complex and are usually superimposed with various oscillations. Insulation characteristics of SF₆ gas as a function of such complex voltages have not been sufficiently clarified. This paper deals with gap breakdown characteristics in SF₆ gas under submicrosecond pulses. Breakdown voltages are lower under a polarity reversal condition than under a monopolarity condition. The cause of this difference is discussed while observing discharge propagation using an image converter camera. The electrode size effect is also discussed. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 146(4): 18–25, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10246