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。     

弯曲通道长度及倾斜角度对雷电电磁场影响研究

为了得到弯曲通道雷电电磁脉冲场的分布特性,将电流微源偶极子进行水平分解和垂直分解,利用偶极子法对弯曲通道产生电磁场的表达式进行了推导.在此基础上就底部回击通道长度以及上部回击通道倾斜角度对地表电磁场的影响规律进行了相关研究.研究结果表明,弯曲通道的电磁场峰值主要取决于底部放电通道的长度,在中间场和远场区底部通道越长对应的电磁场幅值越小;而倾斜角度对近场区电磁场影响极小,在中间场和远场区电磁场幅值会随着倾斜角度的增加而降低,且距离越远倾斜角度对电磁场幅值的影响越明显.     

雷电通道水平电场影响因素分析

影响雷电通道产生的水平电场因素众多,分析其影响因素对电力系统的雷电防护具有重要意义。文中利用运动电荷电磁场方程求解得到闪电回击通道的水平电场和方位磁场,并结合C-R 算法,得到了有限电导率地面上方的水平电场。依据运动电荷电磁场方程的特征分析了不同回击速度、不同距离、不同电导率对雷击产生的水平电场的影响。得出以下结论:水平电场随回击速度增大而减小;水平电场波形呈双极性特征且水平距离越大或电导率越小负向偏移越明显。这些研究结论为输电线路雷电过电压计算打下良好的基础。与其他方法相比,本文方法可以避免远距离电磁场计算中的震荡问题和积分方程的奇异问题。     

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.     

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。     

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。     

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.     

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。     

LEMP 空间表达式求解及分布规律研究

利用偶极子理论对Maxwell方程组进行了求解,得到了垂直通道与斜向通道模型的雷电电磁场解析表达式。基于此表达式分析了不同高度处雷电电磁场的空间分布规律。研究结果表明,在垂直通道与斜向通道模型中,垂直电场和磁场受观测点高度的影响随水平距离的增加而减小,但是对水平电场而言,在垂直通道模型中其初始峰值随着观测点高度增加而增加,在斜向通道模型中,当观测点在通道下方时电场峰值随着观测点高度的增加而增加,当观测点在通道上方时高度越高电场峰值越小。     

基于脉冲函数电流模型对闪电回击电磁场的计算

基于一种新的描述回击通道底部电流的脉冲函数模型，利用偶极子法对距离回击通道底部不同距离处的LEMP进行了计算，把几种闪电回击的工程模型的计算结果与实测结果进行了比较，表明MTLL模型能够与实际结果更为吻合。     

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.     

Coupled Field Inside Shielding Enclosure With an Aperture Due to Nearby Lightning

Due to a nearby lightning return stroke, the coupled electromagnetic (EM) fields inside a rectangular shielding enclosure, on the finitely conducting ground, with an aperture in one wall are calculated numerically by using the finite-difference time-domain (FDTD) method. First, the near fields generated by the return stroke are obtained in two-dimensional (2-D) cylindrical coordinates by the FDTD method. Then, the coupled fields inside a rectangular shielding enclosure are calculated in three-dimensional (3-D) rectangular coordinates through the total field-scattered field connecting boundary, with the sources obtained by coordinates transformations of the return stroke near fields     

Couplage entre le champ électromagnétique rayonné par un coup de foudre et une ligne de télécommunication aérienne ou enterrée

This paper describes the determination of the current induced by a lightning discharge on a telecommunications cable using a transmission line theory. The electromagnetic field due to the return stroke is calculated by modeling the channel by a vertical antenna situated above a perfectly conducting ground. The electromagnetic coupling to a telecommunications line is then determined by introducing the finite conductivity of the ground into the transmission line model. Examples are given for various positions of the lightning discharge with respect to telecommunications cable. A comparison with results obtained during the last experiment at Saint-Privat-d’Allier is also presented. To get the response of a buried cable the authors first determine the propagation constant and the primary parameters of the line. The reference for the voltage is also analysed. The authors show that the choice of the origin at the infinity allows to take into account the energy propagating in the ground parallel to the cable.     

Note on the fields of an upward-traveling current wave pulse

The so-called transmission-line model for an upward-traveling lightning stroke is often employed by the atmospheric and electromagnetic compatibility community. Simple expressions are obtained for the radiation fields of an idealized lightning channel. The model is an attenuated traveling current, which is perpendicular to a perfectly conducting ground plane. The enhancement of the radiation field at higher elevation angles is confirmed following Krider's (1992) prediction     

Analyse du champ électromagnétique dû à une décharge de foudre dans les domaines temporel et fréquentiel

The paper presents an analysis in the time and in the frequency domain of the electromagnetic field originated by negative lightning return strokes, calculated at ground level. The analysis is performed on the basis of the « Transmission Line » model modified by the authors, which gives results in good agreement with experimental data. The influence of several parameters which deeply affect the time waveshape and the frequency spectra of the electromagnetic field has been investigated. These parameters are : the rise time and the peak value of the lightning current pulse, its velocity of propagation and the rate of decreasing of the intensity of the current pulse propagating along the channel. The influence of other parameters such as the lightning channel height and the distance of the observation point is also analyzed. It is shown that the height of the channel does not affect practically the electromagnetic field. Two simplified expressions of the electromagnetic field used for the calculation of overvoltages induced on transmission lines are discussed in order to assess their validity limits.     

Analysis of lightning-radiated electromagnetic fields in the vicinity of lossy ground

An antenna theory (AT) approach in the frequency domain is presented to compute electromagnetic fields radiated by a lightning return stroke. The lightning channel is modeled as a lossy-wire monopole antenna (a wire antenna with distributed resistance) energized by a current source at its base, and the ground is modeled as a lossy half-space. The method of moments is used for solving the governing electric field integral equation (EFIE) in the frequency domain. The resultant current distribution along the channel is used to calculate electromagnetic fields at different distances from the channel. All field components are evaluated using a rapid but accurate procedure based on a new approximation of Sommerfeld integrals. In contrast with the previous models, the approach proposed here is characterized by a self-consistent treatment of different field components in air or on the surface of a lossy half-space. It is shown that the omission of surface wave terms in the general field equations, as done in the perfect-ground approximation, can strongly affect model-predicted field components.