Lightning activity during winter thunderstorm and leader progression in thundercloud

We have been studying lightning discharges by means of a UHF interferometer, and we show a comparison between lightning during winter thunderstorms are those during summer. The main objective of the comparison is further understanding of features of lightning during winter storms, especially of positive cloud to ground flashes. For this purpose we compare negative and positive flashes on UHF radiation and pulse density, and perform two‐dimensional mappings of UHF radiation sources. Moreover we show the three‐dimensional imaging for a cloud flash, and discuss the relationship between the altitude of leader progressions and atmospheric temperature profiles as a function of height. We also show the estimated velocity of leader progressions and find no discrepancy with the earlier results obtained by Proctor. © 2000 Scripta Technica, Electr Eng Jpn, 133(4): 71–78, 2000     

Observation of multiple stroke and multipoint discharges by means of UHF interference

Results of interferometric observations of cloud‐to‐ground flashes in Darwin (Australia) have been analyzed to investigate some features of the lightning phenomenon. Our study focused on comparison between multipoint and multiple negative cloud‐to‐ground flashes. The speed of leaders was estimated with submillisecond resolution for both multipoint and multiple strokes. Leaders preceding the first stroke in multiple‐stroke flashes progress in a stepped fashion, and their behavior exhibits the same features as leaders in multipoint flashes. The estimated average speed of the leaders is on the order of 10⁵ m/s, and the mean step length is found to be 96 m with a mean pause time of 73 μs. The running time of the leader found from results of these observations has a mean value of 89 μs. The duration of UHF radiation bursts generated by leaders propagating along previously formed channels ranges from 0.2 to 55.3 ms with a mean value of 7.5 ms. By contrast, the duration of UHF radiation in leaders preceding multipoint strokes ranges from 21.1 to 90.6 ms with a mean value of 47.5 ms. The time intervals between strokes that strike at the same point as the previous stroke range from 22.5 to 330.6 ms with a mean value of 75.1 ms, while intervals between strokes in multipoint flashes range from 55.6 to 633.7 ms with a mean value of 149.1 ms. All leaders preceding multipoint strokes start in the same region inside the cloud. © 2001 Scripta Technica, Electr Eng Jpn, 134(4): 62–69, 2001     

避雷针迎面先导发展物理过程仿真研究

开展避雷针迎面先导起始及发展过程的仿真研究对建立正确的雷电屏蔽分析模型具有重要意义。基于长间隙放电的物理机制,建立了包括正极性电晕起始与流注发展、先导起始、先导–流注体系发展等物理过程的迎面先导发展物理过程仿真模型,并使用实验室和自然雷电条件下的迎面先导发展过程观测结果对其进行了验证,最后采用该模型对避雷针迎面先导特性进行了分析讨论。结果表明:该模型的计算结果与实验室条件下和一次自然雷电条件下获得的正极性迎面先导发展过程观测结果相吻合;迎面先导起始时刻随着雷电流幅值和避雷针高度的增加而提前;避雷针迎面先导的发展过程主要受雷电流幅值、避雷针高度影响,其发展速度随着下行先导的趋近而逐渐增加;由实验室条件下的正极性棒–板间隙放电获得的先导起始特性直接用于自然雷电中正极性迎面先导起始的计算,以及在迎面先导发展过程的计算中假设迎面先导发展速度与下行先导发展速度成一固定比例是不合适的。     

Winter lightning on Japan Sea coast-development of measuring systemon progressing feature of lightning discharge

With the aid of recent optoelectronic techniques, the authors have developed a measuring instrument named ALPS (Automatic Lightning Discharge Progressing Feature Observation System) to determine the progress of lightning flashes. The progress velocities of stepped leaders for lightning in winter seasons were observed using the ALPS in the coastal area of the Japan Sea. The progress velocity of an individual step of a stepped leader can be expressed by a lognormal distribution and its mean value is 1.6×10⁶ m/s for upward leaders and 4.0×10⁶ m/s for downward leaders. The mean progress velocity of a total leader process is given as 0.8~2.7×10⁵ m/s for upward leaders and 2.9×10⁵ m/s for downward leaders     

雷击风机叶片的跃变击距特性与定量表征

风机叶片对雷电的接闪是风机防雷研究中的关键内容,合理分析接闪时的击距特性意义重大。基于雷击过程的物理机制,将雷击发生时上、下行先导头部间的距离定义为跃变击距,并分析了多上行先导竞争对风机接闪和跃变击距的影响。基于先导起始和发展理论,根据下行先导的等效模型和稳定上行先导的判定方法建立了风机叶片接闪模型,利用该模型得到了随雷电流幅值变化的跃变击距公式,指出侧面距离等参数对跃变击距没有影响,实验和观测结果证明了模型的正确性。最后利用接闪模型提出了考虑稳定上行先导对周围电场畸变作用的对地击距公式,与其他学者计算的结果进行对比指出,现有对地击距公式或不适用于风机背景的防雷计算。     

预测竖直杆体的年雷击率

介绍了一种预测竖直杆体年雷击率的有效方法.该方法首先根据上行先导对下行先导的拦截条件推出竖直杆体的引雷空间边界方程,在这一引雷空间域内按雷击距作出杆体的受雷曲面,再从雷电流的概率分布出发给出雷击距累积概率密度函数的一般表达式.杆体的等值暴露面积是通过在受雷曲面上进行空间积分运算来获得的,其中下行先导定向取向角的随机性也被加以考虑,最后由雷击距累积概率密度函数和等值暴露面积来计算杆体的年雷击率.为了校验该方法的可行性,文中还将计算结果与实测结果进行了比较,比较表明,两者能基本取得一致.     

高压输电线路雷电绕击分析方法及模拟试验研究*

大量线路雷电跳闸故障统计资料显示,雷电绕击是引起电压等级为500 kV及以上输电线路雷击跳闸的主要原因。综述了几种有代表性的输电线路雷电绕击分析方法,并介绍了在南方电网昆明特高压基地开展的雷电绕击模拟试验研究。试验模拟了下行雷电先导接近线路时输电线路上行先导起始和发展的过程。试验结果表明,导线、地线会产生上行先导放电,且地线上行先导放电起始易于导线,导线、地线上行先导发展速度约为1.2～2.4 cm/?s。该结果可为雷电绕击分析提供了试验基础和物理参数。     

正极性上行先导特性的模拟试验方法

开展负极性雷电地闪过程中地面物体正极性上行先导特性的模拟试验研究是完善雷电屏蔽分析模型的基础,选择正确的模拟试验方法十分必要。分析了采用棒–棒、棒–板及板–棒等典型放电间隙结构的模拟试验方法的电场特征,研究了各种方法获得的正极性先导特性,并通过与自然雷电下的电场特征及上行先导特性进行对比,评价了各模拟试验方法的等价性。结果表明:采用棒–棒间隙和棒–板间隙无法模拟自然雷电下地面物体附近的电场空间分布特性;采用板–棒间隙可以模拟自然雷电下地面物体附近的电场空间分布特性,但传统的冲击电压发生器无法产生与自然雷电下行先导趋近地面过程中电场时变规律相同的冲击电压。因此,提出了研发一种基于电力电子技术、能够模拟自然雷电下电场时变规律的高压任意波形发生器,并结合板–棒间隙结构,形成正确有效的正极性上行先导特性模拟试验方法。     

对特高压直流线路绕击屏蔽的一种新观点

随着极线工作电压的提高,以单侧地线、极线及雷先导作为雷屏蔽研究模型已满足不了工程实际的需要。因此,以模拟电荷法为基础,将雷电先导、两侧地线、极线作为整体研究对象,考虑极线工作电压及极线分裂数,计算雷先导垂直下行过程中各导线表面场强变化,并运用Peek判据确定各导线对应的雷先导一级定位高度,合理解释特高压直流线路中存在的正极线绕击概率大的问题,提出了新的绕击屏蔽观点:特高压直流架空线路中仅负极线侧避雷线和正极线产生上行先导竞争拦截雷下行先导,正极线侧的避雷线屏蔽功能被削弱,未起到完全保护正极线的作用。     

基于随机理论的特高压输电线路雷电屏蔽模型(英文)

The operation data obtained abroad indicates that shielding failure in UHV transmission lines mostly accounts for the tripping-out accidents introduced by lightning striking the transmission line.Based on the discharge theories of long air gap and randomness theory,a leader progression model of lightning shielding failure is presented in this paper.The random characteristics of the downward and upward leader are simulated in this model.The ground slope angel is also considered in this model by using coordinate transformation.Moreover,the system voltage is also taken into consideration in this model.The simulation results show that the good agreement between this model and the field data.And the results suggest that return striking exist obviously in UHV transmission line.     

A Modified Version of the Rolling Sphere Method

The calculation of the striking distance can estimate the probability of lightning strike on a structure and thereby evaluate the effectiveness of a lightning protection system (LPS). The dimensioning and the positioning of air-termination on structures is often performed with the Rolling Sphere Method (RSM). RSM originated from the electric power transmission industry and is based on the well-known Electrogeometric Model (EGM). The EGM relates striking distance to the prospective peak stroke current. To apply this technique, an imaginary sphere is rolled over the structure. All surface contact points are deemed to require protection, whilst the unaffected volumes are deemed to be protected. The main drawback of this method is that it disregards the upward leaders? development and assumes the same probability for attachment to the ground, to a structure, and to a LPS. The proposed model is based on physical phenomena leading to the formation and the development of positive upward leader in the field produced by the negative downward leader charge distribution and by some other competing upward leaders. Its purpose is to develop a 3-D numerical model in order to improve the interception efficiency of the Lightning Protection System.     

利用先导通道三维空间结构研究的先导发展速度

先导发展长度与速度是描述先导发展过程的重要参数,也是近年国内外研究热点。电荷耦合高速摄像机的广泛应用为研究先导发展速度提供了有力工具。为定量研究先导发展速度,利用2台电荷耦合高速摄像机对长空气放电过程进行同步拍摄结果,利用图像处理方法重建了长空气间隙放电先导通道发展过程的三维结构。对12m棒-板间隙在正极性操作冲击电压下先导发展过程进行观测后,基于先导通道三维空间结构的时域演变,将先导发展方式分为平稳发展与"突跳"2种方式。在此基础上定量分析了先导发展的一维轴向速度、二维路径速度以及三维空间速度。研究结果表明,在12m棒-板间隙的先导平均一维轴向发展速度为1.8cm/μs,平均二维路径速度为2.03cm/μs,平均三维空间速度为2.3cm/μs;先导通道发生"突跳"时,先导通道长度瞬时剧烈增大,发展速度瞬时剧烈增大,发展速度分散性很大,在10～30cm/μs。     

基于引雷空间理论的水平接闪器年雷击率预测方法

介绍了一种基于引雷空间理论的水平接闪器年雷击率的预测方法。该方法考虑了水平接闪器的引雷空间域和雷电下行先导随机取向角的影响,加权处理了不同雷电极性下的等值受雷面积,根据等值受雷面积和地面落雷密度对水平接闪器的年雷击率作出预测,该方法明显改善了定量计算精度和有效性,预测结果与实测结果基本一致。     

考虑先导发展随机性的输电线路雷击仿真模型

随着电压等级的升高,由雷电绕击而引起的线路跳闸事故所占比例越来越大。为准确评价线路的绕击耐雷性能,考虑先导发展随机性,运用模拟电荷法,建立了输电线路雷屏蔽性能的雷击仿真模型。仿真结果表明:随着下行先导随机发展的方向由靠近输电线路变为远离输电线路,雷击目的物也由地线逐渐转变为导线,并最终变为大地;相比地线,导线上的上行先导较难产生。算得的对地击距与IEEE推荐的击距公式一致,绕击概率与雷击模拟实验结果相符,证实了模型的可信性。     

特高压交流输电线路的雷电屏蔽分析模型

绕击是引起超高压、特高压输电线路雷击跳闸的主要原因。将低电压等级输电线路绕击防护经验直接外推至更高电压等级时具有一定的局限性,可能导致新建线路的绕击耐雷性能显著低于预期值。基于先导发展的绕击分析模型细致地考虑了影响雷击发展物理过程各种因素的影响,较传统工程化分析方法更适用于新建电压等级线路的绕击性能评估。但由于对雷击物理过程和长间隙放电机理认识的不足,不同时期不同学者对雷击过程描述所采用的模型和方法不尽相同,若将现有学者所提出的绕击分析模型直接用于工程中,不同分析模型所得结果差异较大。为此,通过对比现有的雷电观测资料,认为Cooray提出的下行先导通道模型与最新的雷电观测结果比较相符;对迎面先导起始工程判据的对比分析结果表明,当导线对地高度10.0 m时,Rizk感应电压法和临界电晕半径法计算得的先导起始电压结果一致,外推至实际导线对地高度时,Rizk感应电压法的计算结果与长间隙放电理论相违背;同时依据长间隙放电理论,提出了下行先导和迎面先导的相对速度比近似等于迎面先导通道单位长度电压降与导线感应电压增量之比的迎面先导持续发展条件,建立了基于Schwarz-Christoffel变换的能考虑任意地形的2维特高压输电线路雷电屏蔽分析模型;该分析模型解释了传统先导发展模型无法解释的特高压输电线路ZMP2和ZBS2型杆塔的中相屏蔽问题。计算结果表明,在典型的平原、斜坡和山顶地形下,ZMP2和ZBS2型杆塔的绕击跳闸率低于设计预期值0.1次/(100 km.a)。     

基于长间隙放电研究雷电屏蔽问题的进展

长间隙放电是研究地面物体雷电屏蔽问题的最有效手段之一。首先介绍了国内外在雷电击距、直击雷防护措施的屏蔽性能试验和雷电迎面先导过程研究3个方面所取得的进展,并结合最新开展的长达6 m间隙尺度的放电试验观测,对现阶段上述3个方面研究所存在的问题进行了分析。认为基于雷电击距建立的电气几何模型(electric geometry model,EGM)仅适用于小尺度目标物的雷电屏蔽性能分析,现有的雷电屏蔽模拟试验方法仅能近似模拟不存在雷电迎面先导时的雷击过程,无法完全证明以提前流注发射模型装置为代表的非传统防雷装置具有比传统措施更优越的屏蔽性能。大尺度目标物的雷电屏蔽问题应聚焦于雷电迎面先导过程的研究,建立并完善雷电迎面先导过程的模拟试验方法和物理仿真模型。     

Artificial Initiation of Lightning in Thunderclouds by Model Hydrometeor Groups

Basic provisions of the scientific and engineering fundamentals of the methods of an artificial initiation of the downward lightning and intracloud lightning by the model hydrometeor arrays have been formulated. The key role played by the model hydrometeor size and form on the probability of an artificial initiation of the downward lightning and intracloud lightning has been established. Volume hydrometeors of centimeter size are tailored for such goals. Dividing of the model hydrometeors on the five classes differing on the electric field amplification coefficient has been proposed. Model hydrometeors with the amplification coefficient from 5 to 19 will be the most optimal for an artificial lightning initiation. It was found that the requirements for the sizes and parameters of the model hydrometeor families and to the places of their introduction in a thundercloud will be determined in most by the effect of the earlier appearance of the avalanche corona on the hydrometeors. It discharges the nearest parts of the thunderstorm cells leading to the local decreasing of the field strength, probability of the streamer corona initiation, and its transition into the volume leader. It was determined that the combining of the model hydrometeors in the group by the dielectric string or tape and the simultaneous introduction in thundercloud of some hydrometeor arrays will significantly increase the probability of the artificial initiation of the intracloud lightning and lightning “cloud–ground,” and the successful discharging of a thundercloud. Moreover, the minimal linear sizes of separate hydrometeor groups should be more than several dozens of centimeters. Some variants of the disposition of the model hydrometeor groups in a thundercloud (near the bottom boundary of the thunderstorm cell, inside the thunderstorm cell, and in the space between the thunderstorm cells) when the most optimal conditions for the initiation of the intracloud lightning and lightning “cloud—ground” are provided, have been proposed.     

Simulation of energized Franklin rods for lightning protection

In this paper, the onset criterion of the upward streamers from an energized Franklin rod is formulated as a function of the geometry of the rod and the height and current of the downward leader. The electric field in the vicinity of the lightning rod is calculated using the charge simulation technique. The dependency of the radius of protection on the amplitude of the pulse voltage applied to the Franklin rod, the downward leader current, and the tip radius and height of the rod is investigated     

导线电压对电气几何模型的雷电击距的影响

使用击距描述的电气几何模型广泛用于输电线路的雷电绕击分析。由于没有考虑导线工作电压的影响，导致其分析超高压及特高压输电线路的雷电绕击概率与实际运行数据存在一定的偏差。本文采用基于电磁场理论和模拟电荷法的雷电先导发展模型模拟向下发展的雷电先导的发展过程，分析了雷电击距与雷电流、导体高度和导体电压之间的关系，提出了考虑工作电压后水平导体雷电击距的修正方法。     

肃雷暴云电荷分布和闪电特征的个体差异

分析观测的资料表明,虽然甘肃地区雷暴云的电结构普遍呈三级结构,云底部存在一分布相当广的正电荷层,但不同雷暴中的闪电类型及闪电行为特征往往有较大差异。有些雷暴没有负地闪,而有些雷暴过程中却有负地闪;有些雷暴中的负地闪全为C型,有些则既有C型,又有P型。不同雷暴中闪电情况的不同,与雷暴云的个体差异性有关。