Comparison of results for the effective height and atmospheric electric field distribution surrounding a parallelepiped building with Franklin's rod and lightning protection rod JUS N. B4. 811

Atmospheric electric field distribution in the surroundings of building with lightning protection rod with and without horizontal circular loop is determined in this paper. Lightning protection rod having a circular loop is Serbian national standard (JUS N. B4. 811). The effective height of the building with lightning protection rod, as an important parameter for defining protection area, is also determined. Using the results it is noticed that lightning protection rod having a horizontal circular loop (JUS N. B4. 811) is better than Franklin's lightning protection rod, with equal height, for protecting buildings.     

Some issues concerning lightning strikes to communication towers

It is a usual phenomenon that lightning strikes tall communication towers. Some of the questions about lightning interaction with communication towers are dealt with in this paper. Can tall towers influence the incidence of lightning in the area where the tower is situated? Are the parameters of lightning, such as peak currents, influenced by the presence of the tower where lightning strikes? What would be the difference in the electric and magnetic field environment in the near vicinity of the tower and far from the tower when compared to the corresponding values with lightning striking level ground? Are lightning protection methods designed primarily to protect the communication equipment sufficient to prevent lightning surge transfer to nearby local networks? This paper addresses the above issues based on the analysis, models and observations made in the recent past and also using some simple calculations by the authors.     

直升机雷电间接效应数值仿真

为了提高直升机对雷电的防护能力,根据标准SAE-ARP5416A规定的试验方法在基于传输线矩阵法的CST Microwave Studio中搭建仿真环境,对"黑鹰"直升机采用注入大电流的方法来分析其遭遇雷击时的间接效应。分析了在不同雷电流路径下,直升机机体外部以及机体内部重点舱室的电磁场分布情况,同时对机体内部线缆耦合情况进行了分析。仿真结果表明:在不具备开展整机直升机雷电间接效应试验的条件下,该方法能够对直升机遭遇雷击时的间接效应进行有效分析,进而指导直升机的防雷设计。     

From an electron avalanche to the lightning discharge

The goal of this work is to describe qualitatively the physics of processes which begin with an electron avalanche and finish in a lightning discharge. A streamer model is considered that is based on studies of the recently discovered processes occurring in the prestreamer region. The investigation and analysis of these processes enabled making the conclusion that they are, in essence, the attendant processes, which ensure the electron avalanche-to-streamer transition, and may be interpreted as a manifestation of properties of a double charge layer exposed to the external electric field. The pressing problems of physical processes which form a lightning discharge are considered from the standpoint of new ideas about the mechanism of the streamer formation and growth. Causes of the emergence of coherent super-high-frequency radiation of a leader and the neutron production in a lightning discharge are revealed that have not been explained so far in the theory of gas discharge. Based also on new ideas about the lightning discharge, a simple ball-lightning model, providing answers to almost allquestions formulated from numerous observations on the behavior of ball lightning, is offered, and the need of a new design of lightning protection instead of the traditional rod is discussed.     

Statistical model of the lightning leader attraction to ground objects

A statistical model of the lightning channel attraction to ground objects is proposed based on the analysis of the available experimental data on the breakdown of long air gaps and the propagation of the lightning leader channel. The model allows one to estimate the probability of lightning interception by a lightning rod and of lightning damage of the protected object. Examples of calculating the probabilities of lightning strike to the lightning rod and neighboring areas are presented.     

Studies on characteristics of lightning generated currents in an interconnected lightning protection system

An in-depth knowledge about the characteristics of lightning generated currents will facilitate evaluation of the interception efficacy of lightning protection systems. In addition, it would aid in extraction of valuable statistics (from measured current data) on local lightning parameters. Incidentally, present day knowledge on characteristics of lightning induced current in typical lightning protection systems is rather limited. This is particularly true with closely interconnected protection systems, like the one employed in Indian Satellite Launch Pad-II. This system is taken as a specific example in the present study. Various aspects suggest that theoretical modelling would be the best possible approach for the intended work. From the survey of pertinent literature, it is concluded that electromagnetic modelling of lightning return-stroke with current source at the channel base is best suited for this study. Numerical electromagnetic code was used for the required electromagnetic field solution and Fourier transform techniques were employed for computing time-domain results. A validation for the numerical modelling is provided by laboratory experiments on a reduced scale model of the system. Apart from ascertaining the influence of various parameters, salient characteristics of tower base currents for different kinds of events are deduced. This knowledge can be used in identifying the type of event, as well as its approximate location. A method for estimation of injected stroke current has also been proposed.     

Mössbauer study of phase transition caused by oxidation in the temperature region from 20 to 1000°C in almandine garnets

A Mössbauer investigation has been carried out on garnets from Měděnec and Kti? (Czech Republic). Changes of Fe²⁺ and Fe³⁺ crystallographic sites were observed in these silicate garnets after temperature processing under oxidising atmosphere. The temperature processes were realised from 200 to 1000°C by 100 degrees. The results of Mössbauer experiments are compared with the results of the chemical analysis, X-ray diffraction, infrared spectroscopy, and magnetic susceptibility measurements.     

基于先导发展模型的舰艇避雷防护评估仿真

基于先导发展模型实现了海域上地闪先导2维数值放电模拟,完成了海域上地闪先导放电通道过程的图样采集。通过建立二维舰船模型,并根据相关标准对舰船模型进行避雷针的数量、高度、位置设定,对此模型进行雷电先导放电数值试验。经大量试验统计分析,舰船采用单根避雷针设计方案时,避雷针的高度较高,使得接闪概率明显增大,但在避雷针周围取得了较理想的防护效果;与单根设计方案相比,双根避雷针设计使得舰船整体结构高度降低,总的接闪次数有所减少,防护效果更佳。该评估方法可与长间隙放电试验和雷电观测互为补充,进一步完善了水面舰艇避雷系统防护评估检验技术,为舰艇的雷电防护提供理论基础。     

A new concept in lightning parameters measurement

Nowadays the electrical activity measured in tall objects has been widely characterized, but the collected data of lightning rods installed in buildings do not amount to enough to obtain reliable statistics. The measures stored at relatively few points are not representative of the different types of installations. Furthermore, the protection model applied for lightning air terminal installations is based on theoretical models. This paper describes the design of a micro-station to measure some lightning parameters in real lightning air terminal installations correlated to the nature of emplacement instead of triggering lightning or choosing points with a high number of lightning impacts.     

超高避雷针系统接闪效能的数值评估

针对目前超高避雷针系统日趋增多但现行标准又难以对其整体接闪效能进行有效评价的现状,基于亚网格技术发展了一种地物装置接闪效能数值评估方法,建立了超高避雷针系统接闪效能的数值评估模型,并对典型超高避雷针系统的接闪效能进行了数值评估实验,结果表明:超高避雷针系统接闪器顶端接闪概率最大,但其上部其他区域也可能遭受雷电的侧击,且接闪器上部遭受侧击的概率会随着侧击点高度的增加而增大。此外,雷击强度或雷云荷电强度对超高避雷针系统接闪器上各部分的接闪概率也有影响。雷击强度或雷云荷电强度越小,接闪器顶端的接闪概率越低,相应地接闪器上遭受侧击的概率越大,且侧击点的覆盖范围也会随之逐渐向接闪器的下部扩展。     

On the optimum rod geometry for practical lightning protection systems

The effectiveness of a lightning rod as a strike receptor has been the subject of a number of studies recently, particularly in relation to the influence of the tip radius of curvature. The evidence suggests that sharp-tipped rods are not as effective as those with a more blunt geometry. The overall aim of the present paper, as a major extension of previously published work, is to develop and implement a method for computing the “optimum” tip radius of any lightning rod installed on a structure of any given dimensions. Numerical modelling techniques were used to determine the optimum tip radius as a function of the rod length and to account for the difference in electric field intensification created by the placement of the rod in various positions on structures. The results show that the optimum tip radius has a significant dependence on the: (i) rod length, (ii) dimensions of the structure on which the rod is installed, and (iii) physical criterion used for the calculations. In general, the additional electric field intensification created by placing rods on structures, particularly when they are positioned near edges and corners, means that the tip radii required for optimum effectiveness are larger than their counterparts on the ground surface.     

A New Radioactive Lightning Protection

The protective zone of conventional lightning rod (Franklin's rod) is very small. In order to enlarge it, a greater number of such lightning rods can be set up or the Faraday cage employed. In the case of high objects or those covering large areas, this kind of protection is not economical. The use of radioactive sources for air ionization around the lightning rods enlarges the protective zone considerably. A comparison is given of the radioactive lightning rod, which use alpha emitters and are widely employed in some countries of western Europe and Africa, and the proposed radioactive lightning which uses a gamma radiation source.     

Application of fuzzy logic based expert system in preventive lightning protection

Preventive lightning protection (PLP) deals with situations, when risk of injury or damage caused by lightning strike is prevented not by primary or secondary lightning protection, but by the information of preventive measures. This paper represents, how an expert system can be used to help decision making to select appropriate measures in preventive protection. The system is used to approximate the relationship between the collected data and the actual risk level, the time after a risk reaches the critical limit, the speed of change of risk. The paper presents an example with different situations where the described method improves the prevention time.     

Characteristics of lightning flashes striking the CN Tower below its tip

It has been observed that tall structures are sometimes struck by lightning below their tops. This phenomenon necessitates the use of special procedures for the protection of tall structures from lightning hazards. This paper focuses on the analysis of lightning flashes that struck the CN Tower below its tip over an extended period of time (1991–2005). Through the use of video images recorded during the reporting period, it was found that out of 404 flashes to the tower, only 16 hit the tower below its tip (3.96%). The distance between the tower's tip and the strike location varied from 5.4 to 70 m. Statistical analysis of flash characteristics of strikes below the tower's tip generally shows that the flash duration and the number of strokes per flash are considerably lower than those for the majority of cases, when the tower is struck at its tip. Furthermore, a trend of decrease in flash duration is found as the distance between the tower's tip and the strike location increases. Therefore, based on the analysis of the available data, lightning strikes below the top of a tall structure do not seem to pose greater danger than strikes to the structure's top, assuming that the structure is also protected along its sides. It is hoped that the presented observations and statistical analyses will be of value in the development of sophisticated measures against lightning hazards at elevated objects.     

On the interception of lightning flashes by power transmission lines

The design of the lightning protection system LPS of transmission lines is based on the well known electro-geometrical model. The electro-geometrical model assumes that the first point on a power transmission line that will come within striking distance of the tip of a down-coming stepped leader channel is the strike point of the lightning flash. The model neglects almost all of the physics associated with the lightning attachment.Nowadays, as it is possible to use modern hardware and software tools and several different numerical methods, it is feasible to apply the physics of the discharge process to the study of lightning attachment. Such models take into account the movement of the downward and the resulting upward leaders from different points on the structures under consideration.In this paper, a procedure based on lightning physics was used to analyze the lightning attachment phenomena in EHV transmission lines of 230 kV and 500 kV and the results were compared with the predictions of the electro-geometrical method.     

Numerical simulations of thunderstorm-induced corona processes near lightning rods installed on grounded structures

For the purpose of estimating the efficacy of a lightning rod, the current of a corona was numerically calculated from a rod placed (i) centrally on the roof of a vertical grounded cylindrical structure, a model of a man-made object, and (ii) at the top of a grounded hemispherical structure of large radius, such as a hill or mountain. The calculations were carried out for a slowly varying thundercloud electric field and when this field was enhanced by the charge of an approaching downward leader. In case (i), variation of the ratio between the height and radius of the cylindrical structure leads to a variation in the (a) corona current from the tip of the rod over a wide range and (b) distance from which lightning is attached to the rod. In case (ii), it is shown that, contrary to the case of rods installed on the ground surface, a slowly rising thundercloud electric field can be sufficient to initiate streamers and upward leaders from rods tens of meters in height installed on the top of tall, grounded, hemispherical structures. When the thundercloud electric field is enhanced by the charge of an approaching downward leader, the discharge processes near the rod depend on its length and the height of the tip of the downward leader relative to the top of the hemispherical structure, but are almost independent of the hemisphere radius.     

基于分形理论的飞机雷击初始附着点的数值模拟

飞机雷击附着点的确定能够为飞机防雷设计提供依据,是飞机雷击区域划分和飞机各部件进行雷电试验鉴定的先决条件.本文提出了一种基于分形理论的飞机雷击初始附着点数值模拟的新方法.该方法首先依据标准SAE-ARP5416中有关飞机雷击附着点试验的规定,确定放电间隙、雷电起始坐标、飞机姿态和放电次数等参数,然后根据分形理论,使用电介质击穿模型模拟符合自然界雷电物理机理和几何特征的雷电先导分形发展过程,同时考虑飞机自身触发双向先导的情况,最终得到飞机的雷击附着点分布.通过本文方法仿真模拟得到飞机F-4雷击附着点的分布概率,并分别与该飞机飞行实验和实验室高压放电实验测试得到的真实雷击附着点的概率分布情况比较,结果基本吻合,验证了该方法的有效性.研究结果为飞机雷击附着点仿真模拟提供了一个有潜力的方法,可作为飞机防雷设计和今后开展相关研究工作的基础.     

Evaluation of parameters influencing the lightning performance of communication towers by numerical modeling and experimental tests

This paper analyzes the effective parameters on lightning performance. The effects of tower height, breakdown electric field threshold, the ground slope of installation place, and the effect of the trees around the tower are investigated. A 3-D numerical analysis model is proposed to determine the number of direct lightning strokes to antennas. The communication tower, lightning rod, downward descending leader and upward leaders are modeled by different shapes of charges. Finally, a small-scale communication tower was built and tested in a high voltage laboratory. The experimental tests were consistent with the simulation results verifying the merits of the proposed method.     

Application of charge simulation method for investigation of effects of the trees on lightning protection of structures

The paper deals with the principles of lightning protection of structures. The principles have been formulated on the base of application of charge simulation method (CSM) in order to investigate the effects of trees on lightning protection of buildings. The simulation results and laboratory test on scale model demonstrate the benefit of this method of computation lightning protection for structures.     

Identification of lightning vulnerability points on complex grounded structures

The identification of the most vulnerable points on a given structure to be struck by lightning is an important issue on the design of a reliable lightning protection system. Traditionally, these lightning strike points are identified using the rolling sphere method, through an empirical correlation with the prospective peak return stroke current. However, field observations in Kuala Lumpur and Singapore have shown that the points where lightning flashes strike buildings also depend on the height and geometry of the structure. Since a lightning strike point is believed to be the place on a grounded structure where a propagating upward leader is first initiated, a physical leader inception model is used here to estimate the background electric field required to initiate a stable upward leader from the corners of some complex buildings. The computed location of the points from where leaders are incepted are compared with the damaged points on buildings struck by lightning. The observed lightning strike points coincide rather well with the corners of the buildings which are characterized by lower leader inception electric fields. Furthermore, it is found that the geometry of the buildings significantly influences the conditions necessary to initiate upward leaders and, therefore, the location of the most likely strike points.