Characteristics of lightning surges induced in telecommunication center in tropical area

The characteristics of lightning-induced surges in telecommunication equipment due to a direct lightning strike at a telecommunication center building or tower should be investigated to maintain the reliability of advanced telecommunication systems. In particular, investigations in tropical areas are important because these areas have many thunderstorm days. We observed lightning surges induced in a telecommunication building in Kuala Lumpur, Malaysia. The results show that the peak value occurrence frequency and waveforms of direct strike lightning surges were almost the same as those in a temperate area. The peak current relationships between the cables in the building and the tower legs indicate a strong correlation between the current at the tower legs, waveguide, power line, and outer and inner conductors of the coaxial cables. However, the peak value correlations between the tower leg currents and interface cable voltages were not strong. Based on the observation results, we obtained the correlation factors between the peak value at the observation point and the tower legs, and calculated the peak value at the interface cables as a function of the number of thunderstorm days.     

Improvement of the lightning shielding performance of overhead transmission lines by passive shield wires

This paper addresses a numerical electromagnetic analysis of the influence of installing passive shield wires "extra ground wires" (EGW) underneath the bottom phase conductor on the lightning shielding performance of 765-kV, 3-phase, double-circuit transmission lines. The method of moment (MOM) is employed to model the whole structure in three dimensions except the lightning channel. The lightning channel is simulated by the well-known transmission-line model (TLM), where the influence of the lightning-channel-generated electric and magnetic fields (EMF) are taken into account. The lightning shielding performance with and without EGW is introduced and discussed, without ac energization and due to three distinct lightning strokes, namely, the negative first, the negative subsequent and the positive strokes. The produced voltages and currents in the phase conductors and ground wires as well as the voltage across the insulators are computed, with and without the EGW, due to different lightning current waveforms, locations and inclination of the lightning channel, and return-stroke velocities. The introduction of such EGW results in a significant improvement of the shielding effectiveness by reducing the lightning-produced voltages and currents in the phase conductors as well as the voltage across the insulators. Accordingly, much lower transient overvoltages can be expected with less inadvertent outages of the lines, where the probabilities of flashover and back-flashover decrease, and the reliability enhances.     

Lightning induced transient voltages in presence of complexstructures and nonlinear loads

EMI induced in electronic circuits inside a building due to a lightning flash can be caused by either a direct strike to the lightning protection system or or by an indirect discharge in close proximity. This paper deals with the induced transient voltages on nonlinearly terminated metallic loops inside a building due to an indirect lightning strike. The conductive parts of the building (such as reinforcing bars in walls and floors, metallic beams), the lightning protection system, and the loops are simulated by an electric field integral equation in the time domain, with the nonlinear loads by a system of nodal equations. These two sets of equations allow a solution to be determined completely in the time domain. The proposed technique is validated by comparison with other referenced numerical techniques. Some results which show the effects of the conductive structural elements of the building on the induced transients are presented     

Magnetic fields and loop Voltages inside reduced- and full-scale structures produced by direct lightning strikes

This paper presents a numerical electromagnetic analysis of magnetic fields and loop voltages inside reduced- and full-scale lightning protection systems (LPSs) "structures" resulting from direct lightning strikes. The method of moments is employed to model the whole structure in three dimensions except the lightning channel. The lightning channel is simulated by the well-known transmission-line model (TL model), where the influence of the lightning-channel generated electric and magnetic fields are taken into account. Three distinct LPSs were modeled, namely, reduced-scale model with return conductors (RSRC), reduced-scale model with lightning channel (RSLC), and full-scale model with lightning channel (FS). The computed results of magnetic fields and magnetic-field derivatives were verified versus some experimental results for the RSRC model. In addition, the scale factor for all the measured quantities were also checked as functions of the geometrical scale factor for the positive and the negative first stroke currents. The lightning shielding performance with and without bonding was investigated for three distinct lightning stroke types, namely, the negative first, the negative subsequent, and the positive strokes. The voltages and currents generated in loops located inside the struck FS LPS were computed with and without bonding and grounding resistance and for different lightning current waveforms, locations and inclination of the lightning channel, and return stroke velocity.     

Attenuation by a lightning protection system of induced voltagesdue to direct strikes to a building

This paper deals with induced transient voltages on electric circuits inside a protected building due to direct lightning strikes. The prediction of these overvoltages is a mandatory requirement for every EMC design of the installations inside the stricken building. The maximum level of expected transients and the efficiency of their attenuation by different configurations of a lightning protection system (LPS) are evaluated by a new simplified approach. The results are compared with those obtained by a complete circuit prediction model. A loop transfer impedance is defined as the ratio between the open end voltage induced in metal loops and the injected lightning current. This impedance is used to set the upper and lower bounds of the frequency spectra of the voltages induced in the loops internal to the building. The results are helpful in locating critical positions of circuits and devices within the volume protected by a LPS     

加速电荷法快速求解雷击高塔辐射电场

雷击高塔时会在周围形成很强的电磁场,分析高塔辐射电磁场对雷电研究和雷电防护具有重要意义。就电磁场中的辐射电场部分,根据加速运动电荷产生辐射电场的基本原理,将雷电流等效为运动电荷,分别计算MTLE(Modified Transmission Line with Exponential Decay,回击电流随高度以指数减小)回击通道和高塔中电流产生的辐射电场,进而得出雷击高塔总辐射电场。结果表明,高塔辐射电场在总辐射电场中所占比例很大,在初始时间总辐射电场波形不断振荡出现多个峰值,然后缓慢下降,其多次振荡波形主要取决于高塔中雷电流的多次反射和透射过程。高塔上方回击通道对辐射电场有一定的贡献,提高了总辐射电场的首次峰值,使得电场强度幅值得以增加。加速电荷方法直接给出了每个过程所辐射出的电场,避免了常规计算方法中复杂电流的积分和微分运算过程,也有助于理解雷击高塔辐射机理。     

A coplanar-waveguide system for cells exposure during electrophysiological recordings

In order to investigate the biological effects of microwave electromagnetic (EM) fields as those emitted from mobile telecommunication equipment, a suitable exposure system has been designed. The system is specific for real-time acquisition of membrane ionic currents in a biological cell, i.e., patch-clamp recordings. Both numerical and experimental characterizations are considered, in terms of EM field and specific absorption rate (SAR) distribution in the Petri dish containing the biological target. Results show a good efficiency of the system in terms of SAR induced in the sample by incident input power.     

缝隙天线阵双站电磁散射的混合法

利用矩量法（ＭＯＭ）和等效边缘电磁流方法（ＥＥＣｓ）研究波导馈电的缝隙天线阵的双站散射问题。从理论和计算上分析,等效边缘电磁流方法可以计算有限尺寸的导体平板沿任意方向上的双站散射（包括边缘绕射场）,而矩量法可以考虑波导缝隙天线阵的散射与耦合问题,使它们混合便可以解决有限尺寸缝隙在线阵的散射问题。实际计算表明,方法是切实可行的。     

Computation of Transient Overvoltages in Low-Voltage Installations During Direct Strikes to Different Lightning Protection Systems

This paper presents a numerical electromagnetic analysis of loop-termination voltages inside an outer lightning protection system (LPS) resulting from direct lightning strikes. The method of moments is combined with the transmission line model, and employed to model the whole structure in three dimensions and the lightning channel, respectively. Three distinct standard LPS classes and a nonstandard LPS are modeled, namely, LPS1, LPS2, and LPS4, and LPS0, respectively. All cases are simulated using the negative subsequent stroke current at lightning protection level II according to IEC 62305-1. Three distinct current waveforms are selected in order to simulate the variety of different current rises. Three single-phase parallel vertical loops are simulated inside the struck LPS. The results reveal that reducing the LPS mesh width improves its shielding performance, where this may be a basic method to damp the lightning-induced voltages with little dependency on the strike location, and without any appreciable effect of the LPS material. The variation of the lightning-current front shows that the loop-termination voltages are altered within a factor of about 2. Existence and interconnection of extra protective earthing, e.g., via information technology cables, and the value and type of the loop-termination impedance also have significant influence on such voltages.     

移动通信铁塔直击雷电流分布的研究

为研究雷击移动通信基站铁塔的电流分布特性,提出了一种全新的电路方法,创建了一个描述铁塔及其接地网构成的网络系统的电路模型。分析了铁塔上的雷电流分布及铁塔的冲击阻抗特性。仿真表明:铁塔及天线电缆屏蔽层上的雷电流分布情况与铁塔结构及雷击位置有关,但几乎不受大地电阻率的影响;而且,任意位置的直击雷在接地网对称位置的接地体上产生几乎相同的入地电流;"铁塔—接地网"网络的整体电阻和电抗随雷击点距地面高度的增加会有略微增大,其中电抗的变化比电阻的略大。研究成果为雷电防护设计提供了重要参考。     

An Approximate Time-Domain Formula for the Calculation of the Horizontal Electric Field from Lightning

This paper presents an approximate formula to calculate the horizontal electric field from lightning, considering finitely conducting earth. The formula is represented by an analytical expression in the time domain, which is useful for the calculation of lightning-induced voltages on power and telecommunication lines, without the need of domain transformations. The paper also compares the results of the formula with the results obtained from frequency-domain techniques, namely the numerical calculation of Sommerfeld's integrals and the Cooray-Rubinstein's formula. The comparison is favorable for a wide range of distances from the lightning channel and values of earth's conductivity. The horizontal electric field calculated by the formula is composed of two components of opposed polarities, one due to the return stroke charge and the other due to the return stroke current, resulting in an electric field with a bipolar wave shape. The charge component prevails in the region close to the lightning channel, while the current component prevails in the region far from it.     

EM fields associated with lightning channels: on the effect oftortuosity and branching

Usually the electric and magnetic fields associated with lightning have been computed by assuming the lightning current to be contained in a straight vertical channel of negligible cross section above a flat perfectly conducting plane. Such a model, which does not take into account that real lightning is characterized by tortuosity and branching, is not able to justify the fine structure of the fields radiated by lightning discharges whose time-domain behavior exhibits a jagged shape with remarkable spectral content in several bands of practical interest. In this work the effect of channel tortuosity and branching is investigated by adopting a suitable numerical technique. The discharge channel has been regarded as a fractal antenna whose associated EM field has been evaluated by superimposing the contribution of the single line radiators composing the whole channel. Such a field has been compared with that generated by a simple dipole antenna in order to study the influence of the fractal nature of the channel on the generated EM fields. The relationship between the fractal dimension of the discharge channel and the fractal dimension of the generated time domain EM fields has been considered and the influence played on such a relationship by the distance between EM source and observation point has also been studied by analyzing the fields evaluated at far and close distances     

Reduction of Lightning-Induced Magnetic Fields and Voltages Inside Struck Double-Layer Grid-Like Shields

This paper presents a numerical analysis of the reduction of lightning-induced magnetic fields and voltages inside double-layer grid-like spatial shields typically used in reinforced concrete buildings, e.g., nuclear power plants. The calculations are performed with the CONCEPT computer code, which solves Maxwell's equations using the method of moments in the frequency domain. The computer code is extended with the well-known transmission line model (TL-model) in order to simulate direct lightning strikes. The structure under study comprises a cubic cage of 2 m side length having single- or double-layer grid-like spatial shields with square meshes of 0.25 m width. Three lightning-channel attachment points are considered at the cage roof, namely, the center, the midedge, and the corner. The simulated lightning currents are the positive, the negative first, and the negative subsequent strokes at lightning protection level I (LPL I) according to the international standard series IEC 62305. The computed quantities comprise the currents through some selected wires of the grid-like spatial shields, the magnetic fields, the magnetic-field derivatives, and the induced voltage across a typical installation loop inside the shield. The results of the single-layer shield are compared to those of the double-layer one to evaluate the additional reduction of the latter shield.      

Evaluation of lightning location data employing measurements of direct strikes to a radio tower

A lightning location systems (LLS) provides large scale information for lightning strikes to ground. In addition to the event time and strike point position, the LLS gives estimates for the lightning peak current. For the end user of LLS data it is important to know the technical limits of the applied network in terms of detection efficiency, accuracy of the stroke location and peak current estimate. To establish a ground truth reference for comparison of natural lightning current parameters and the data of ALDIS (Austrian Lightning Detection & Information System), a telecommunication tower on Gaisberg near the city of Salzburg (Austria) was instrumented for direct lightning current measurement. Since the start of the tower experiment in 1998 we have recorded more than 200 lightning flashes to the tower. Based on the analysis of the current waveforms nearly all of them are so called upward initiated discharges. GPS time synchronization of both data sets allows a precise correlation of individual events measured at the tower and reported by the lightning location network.     

一维FSS电磁散射宽带特性的快速计算

基于渐近波形估计（AWE）技术和矩量法（MOM），快速分析了一维频率选择表面（FSS）的宽带电磁散射特性，首先采用MOM法将平面波照射下FSS的电场积分方程（EFIE）转化为关于感应电流的矩阵方程，并由该方程确定频率导数矩阵方程（MEFD）；再在所考虑的频带内的某一给定频率处求解MEFD，得到给定频率处的频率导数感应电流；最后根据Pade逼近理论由给定频率处的频率导数感应电流确定周期性结构在任意频率入射波照射下的感应电流，根据FSS上的感应电流及谱域Floquet谐波模计算FSS的电磁散射宽带特性，计算结果表明，AWE能有效逼近MOM逐点扫描计算的结果，同时在计算速度上可加快十几倍。     

Measurement of magnetic fields inside single- and double-Layer reinforced concrete buildings during Simulated lightning currents

This paper presents measurements of the voltages, the magnetic fields and the magnetic-field derivatives inside a structure simulating reinforced concrete buildings. The test structure comprises a cubic cage of 2-m side length with single- or double-layer reinforced grids. The injected lightning currents simulate the positive, the negative first and the negative subsequent return strokes with amplitudes of /spl sim/ 77, 16, and 4.8 kA, respectively. Three distinct points of the lightning stroke impact to the structure roof are considered, namely, the center, the mid-edge and the corner. In the case of a single-layer cage, the results reveal that slow-rising magnetic-field components are generated inside the structure for various lightning currents. This effect becomes dominant for the case of the double-layer cage. For all the simulated currents, striking to the structure corner induces the lowest voltage across it, but gives the highest values for both the resultant magnetic fields and the magnetic-field derivatives. For all striking points, the magnetic fields have the highest values for positive strokes, while the negative subsequent strokes give the highest amplitude of the resultant magnetic-field derivatives and roof-to-floor voltages. Compared to the case of a single-layer cage for the negative subsequent strokes, the use of a double-layer cage shows a considerable mitigation of the voltage across the structure, and a moderate mitigation of both the resultant magnetic fields and the magnetic-field derivatives.     

Etude des perturbations induites par une décharge orageuse sur un câble de télécommunication

Experimental results presented in this paper show the waveform and magnitude of the interference signals that occur on a telecommunication cable located nearby a lightning discharge. The measurements were performed at Saint-Privat-d’Allier (France). We then study the current induced in the outer shield of aerial cables of several lengths and in the common mode voltages which appear on the load impedances. We also give a few results obtained from a buried cable. We will compare experimental results and theoretical predictions that are based on the computation of the electric field radiated by the lightning current and on the coupling of the electric field with the wire structure. This last point is approached through the transmission line theory.     

Influence of Independent Towers and Transmission Lines on Lightning Return Stroke Current and Associated Fields

The influence of elevated objects, when they are hit by lightning, on the measured lightning currents and associated fields is studied. For the present study, an electromagnetic model of return strokes with the help of NEC-4 is employed. Cases of strokes to ground, to independent towers, and to a transmission line are compared and the validity of comparison is discussed. The influence of the independent tower of 70 m in height, which simulates Berger's tower, on the peaks of currents is negligible even for the fast-rising current, which corresponds to a subsequent return-stroke current. The shape of the lightning current at the top of a transmission line is less influenced than that at the top of an independent tower of the same height. Elevated objects significantly decrease the amplitude of vertical electric fields in a close range. If the ground conductivity is infinite, the peak amplitude of electromagnetic field at a distant range will be significantly increased by the presence of an elevated object. In actual cases of finitely conducting ground, however, the increase of the peak field is limited due to the propagation effect.     

Investigation of the Electromagnetic Interference Threat Posed by a Wireless Network Inside a Passenger Aircraft

Recent years have witnessed an incisive push to allow the use of wireless networks inside passenger aircraft. Research was recently conducted to investigate the internal electromagnetic (EM) environment excited by a wireless network inside a passenger aircraft to provide quantification of the ensuing EM interference threat. An airbus A319 EM model was developed and validated using experimental data and analytical techniques. The validated model was applied to the investigation of an 800 MHz cellular network. The peak electric field strength inside each of the A319 EM models examined was much less than the most severe RTCA/DO-160D radiated susceptibility test levels. The current coupled to a cable running along the length of the fuselage was much less than the minimum operating parameters of an extremely sensitive avionic system (e.g., strain sensor). The results obtained help to quantify and reinforce the conclusion of the major research efforts that the likelihood of interference with flight critical systems is low. The model presented herein can be easily adapted to study EM propagation for various types of wireless network and aircraft configurations, and the modeling approach employed could be of potential use in modeling other large, complex structures.     

Lightning-induced voltages on overhead lines

A modeling procedure that permits calculation of lightning-induced voltages on overhead lines starting from the channel-base current is discussed. The procedure makes use of a coupling model already presented in the literature, based on transmission line theory, for field-to-overhead line coupling calculations. Both models are discussed and compared with experimental results. The hypothesis of perfect conducting ground, used to analyze the voltages induced on an overhead line by a nearby lightning return stroke with a striking point equidistant from the line terminations, and the limits of its validity are determined. A comparison shows that peak value and maximum front steepness of the induced voltages calculated using other lightning return-stroke models differ. It is also shown that another coupling model used in the power-lightning literature by several other authors may result in a less accurate estimation of the induced voltages