基于IEC标准雷电后续回击电磁场的计算

基于IEC标准雷电回击电流,用击穿电流和电晕电流两种成分对雷电后续回击标准电流进行拆分拟合.用一种新型脉冲函数表示回击中击穿电流,电晕电流用双指数函数表达.然后基于DU模型,合理地选取了两种电流成分的放电时间常数,并对雷电标准后续回击电磁场分布进行了计算,计算结果比较符合雷电回击电磁场测量波形的四个特征.     

雷电通道模型研究与应用

雷电的研究必须基于雷电本身,而闪电通道模型的建立可以很好地模仿自然雷电。通过建立逼真的雷电通道模型,可以更有效地研究雷电及开发雷电防护产品。通过对常见的雷电回击通道模型进行分析,重点阐述了雷电通道的工程模型,分析其中TL,TCS,BG和DU等模型之间的关系,并对其优劣做出比较。利用Matlab工数学软件分析了双指数模型与海德尔模型雷电流模型的波形和频谱,经对结果进行分析比较发现,海德尔模型相比双指数模型更符合实际的雷电流。     

地闪弯曲通道在不同观察尺度下的回击电磁场特征分析

基于偶极子法建立了弯曲通道中任意倾斜通道段产生雷电回击电磁场的三维计算模型, 给出了空间倾斜通道微元在柱坐标系下激发电磁场的解析表达式, 以此为基础, 研究了弯曲地闪通道的观察尺度对首次回击和后继回击电磁场计算的影响.结果表明:通道弯曲是导致雷电回击电磁场波形出现振荡的直接原因, 无论是首次回击还是后继回击, 近区电场基本上不会因为通道弯曲而出现振荡, 通道弯曲及其观察尺度也基本不会影响所计算回击电磁场初始峰值(近场区和过渡场区的电场波形为初始拐点)的上升时间, 但会影响回击电磁场波形的初始峰值(或初始拐点)、波形的振荡起伏程度以及波形的频谱能量分布, 且通道的观察尺度越小、观测点的距离越远、通道回击电流的上升时间越短, 对应回击电磁场波形中的振荡起伏越明显.     

回击速度对雷电电磁场近似关系的影响

为了探索雷电回击通道底部电流与回击电磁场之间的关系,基于TL模型在近场区和远场区对雷电电磁场近似表达式进行了推导,在此基础上研究了回击速度对底部电流和雷电电磁场之间近似性的影响。研究结果表明：在近场区电磁场与底部电流之间的差异主要集中在峰值部分,而在远场区二者之间的差异主要集中在峰值过后的下降沿部分,但无论在近场区还是远场区,二者之间的偏差均会随着回击速度的增大而减小,当回击速度接近光速时,二者波形几乎完全重合。在v=c时基于不同的电磁场成分对电磁场与底部电流之间的关系进行了推导,结果显示当v=c时近场近似与远场近似将统一为一个相同的表达式,且此表达式在推导过程中不存在任何近似,进一步证明了当v=c时,无论在近场区还是远场区地表电磁场波形与底部电流波形完全一致。     

用MCP 方程求解雷电分支通道辐射电磁场

在雷电科学研究和雷电防护技术开发中,闪电通道电磁场辐射特性建模一直是人们关注的重点。人 们常采用理想垂直通道进行建模,用各种解析和数值方法得到较为有效的结果,而研究带分支通道等精细通道结构 的则较少,因而垂直模型得到的场可能和实际测得场有一定偏差。文中基于运动带电粒子(MCP)方程计算了雷电 分支通道的回击电磁场,分别计算了辐射场、速度场与静电场分量以及总场。结果发现分支通道的存在导致了次峰 值的出现,波形与观测点位置、回击速度、分叉点高度等参数有关,运动带电粒子速度矢量的改变正好契合这一特 点,更能体现回击过程中的物理特性。相比于偶极子求解方法,该方法避免了回击电流的微分运算,是一种高效分 析雷电通道辐射场的方法。     

通道高度对雷电回击电磁场的影响研究

主要研究了雷电回击通道高度对回击电磁场的影响，同时选取不同通道高度基于BG、TL、MTLE、MULS和TCS五种雷电回击模型计算了雷电回击在不同水平距离产生的地面电磁场，指出了国外文献计算回击电磁场时在选取通道高度方面存在的问题，并作出了合理的解释。     

雷电斜向放电通道电磁场建模及计算

基于传输线模型,通过将柱坐标系进行旋转变换,建立了斜向放电通道电磁场模型;采用脉冲函数加双指数函数作为通道底部电流,从垂直放电通道电磁场的表达式中推导出斜向放电通道电磁场的计算公式;基于斜向放电通道电磁场模型,研究了不同角度对不同场区地表回击电磁场的影响,认为雷电放电通道越倾斜,雷电流对地面电磁场的影响就越明显。研究了不同回击速度对不同场区地表回击电磁场的影响,结果表明回击速度对电磁场的影响较为明显。     

斜向通道地表雷电电磁脉冲场分布规律研究

通过分解电流微元偶极子并求解Maxwell方程组,得到了斜向通道雷电电磁脉冲(Lightning Electromagnetic Pulse,LMEP)场解析表达式;基于此斜向通道模型,研究了不同方位角和回击速度时的雷电电磁场分布规律.结果显示:近场区电场分量随方位角的变化规律要受到放电通道倾斜程度的影响,但是其他场区的电场分量和任意场区的磁场分量初始峰值均会随方位角的增加而减小;当回击速度改变时近场区电磁场分布规律保持不变,但在中间场和远场区电磁场初始峰值将随回击速度的增大而增大.     

紫峰大厦雷电流全波测量研究

雷电流是描述闪电放电最重要的物理量,对于雷电防护相关研究意义重大,因此,雷电流测量一直是雷电研究领域的基础性工作。为了获得自然雷电流全波波形,在南京第一高楼紫峰大厦(约450 m)楼顶的避雷针处安装了一套雷电流全波测量系统,用于长期检测雷击建筑物回击电流和建筑物上行先导电流。该系统包含两套子系统,分别由雷电流传感器、数据传输系统、数据采集系统、远程控制系统构成,能够同时测量回击电流和建筑物上行先导电流,对国内特别是华东地区高塔自然雷电流研究具有重大意义。首先对所安装的雷电流测量系统进行了介绍,对测得的两组上行先导电流波形进行了全面分析,得出高建筑物上行先导电流波形的相关特征。     

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。     

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.     

Measured and Modeled Horizontal Electric Field From Rocket-Triggered Lightning

This paper presents the results of experiments carried out with rocket-triggered lightning and the related theoretical analysis. It describes the test setup and presents the electric field waveform recorded at the earth surface alongside with the simultaneous measurement of the lightning return stroke current at the channel base. The relevant parameters that allow the validation of a model to correlate the two waveforms are presented, i.e., the return stroke velocity, the distance from the lightning channel base, and the earth parameters (resistivity and permittivity). A theoretical analysis is also presented, which models the phenomenon by the superposition of an induced and a conducted component, providing results that are in good agreement with the measurements. Finally, the paper presents a discussion about the range of validity of the theoretical model and analyzes the behavior of the two components of the electric field.      

Experimental study of lightning-induced voltage on an overhead wireover lossy ground

Experiments on the lightning-induced voltage on an overhead wire with a simulated lightning channel and a 1/20 reduced-scale model have been carried out on a lossy ground. This method is quite useful in testing various coupling models as repeated measurement along with a simple simulated lightning channel is possible. The electrical characteristics of the ground, indispensable in the calculation of the induced voltage over lossy ground, are evaluated through the comparison of the measured and the calculated horizontal electric field waveforms. The coupling model adopted in the numerical calculation of the induced voltage, including the terminations of a finite line, is verified by the good agreement of the measured and the calculated voltage waveforms. This result also verifies the usefulness of the measurement of the horizontal electric field waveform in assessing the ground conductivity in the frequency range of interest     

On Representation of Lightning Return Stroke as a Lossy Monopole Antenna With Inductive Loading

In this paper, a modification of the antenna theory (AT) model of the lightning return stroke to include inductive loading is presented. The distributed inductive energy-storing elements are used in the modified AT model (designated as ATIL model, where IL stands for inductive loading) to control the propagation speed of the upward traveling current wave without using an artificial, higher permittivity dielectric medium, as done in the original AT model. The variation of the propagation speed along the channel is also considered in the proposed model. As in the original AT model, resistive loading is used to account for the current attenuation with height. Numerical solution of the electric field integral equation in the time domain using the with appropriate boundary conditions yields a time-space distribution of current along the lightning channel. This current distribution and the resultant electromagnetic fields for the ATIL model are compared with those predicted by other time-domain and frequency-domain electromagnetic models. The current distribution predicted by the ATIL model exhibits features (such as current dispersion) that are more consistent with optical observations of lightning compared to the predictions of the original AT model.     

栅格式排气孔雷电电磁效应机理分析北大核心CSCD

飞行器上存在不可避免的孔缝,使得飞机遭受雷击后电磁场从孔缝处透射。文章研究了飞机上真实孔缝结构——栅格式排气孔对飞行器内部电磁场的影响,选择传输线矩阵时域求解器分析了不同雷电流波形(A和H)下排气孔以及排气孔周围蒙皮材料变化时的电磁场分布情况。结果表明:沿孔缝表面垂直向内会有一定的电磁场透射,向内超过200 mm以后,电磁场透射强度低于外部电磁场的1.5%,因此其影响范围主要在200 mm以内;蒙皮材料不同时,距排气孔较近的地方,内部电磁场差异较小,距排气孔较远的地方,内部的电磁场差异较大。     

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.