导线贯通金属腔体端接负载电磁脉冲响应规律*

为分析金属导体贯通腔体时导体腔内端接负载电路的电磁脉冲耦合响应,基于时域有限积分方法的 电磁数值计算软件CST 建立了贯通导体端接负载电磁辐射响应耦合模型,研究了高斯脉冲作用条件下入射电场角 度、贯通孔径、外部导体长度、端接负载等对终端负载响应的作用规律,分析了耦合机理。基于GTEM 室搭建了实验 平台,在贯通导体两端开路条件下,通过测量腔体的屏蔽效能,与数值计算结果对比,两者吻合较好。结果表明:贯 通导体方向的电场分量大小对终端负载耦合电压影响显著;入射波长远大于贯通孔径时,贯通导体为主要耦合通 道;负载耦合响应与裸露导体长度、导体半径成正比;负载变化时,自身响应电压随阻值变化,而对另一端负载响应 电压影响不大,两端阻值变化导致负载响应电压波形的衰减振荡不同;容性或感性阻抗是影响响应电压及频率的关 键因素之一。     

双极天线的核电磁脉冲响应特性研究*

针对应用较为广泛的一种短波双极天线,利用CST 仿真分析了天线对高空核电磁脉冲(HEMP)的响应特性。计算了双极天线分别在自由空间和导体板上方时的天线端口开路及端接50 赘负载情况下的响应特性,得出了天线在两种情况下端口的感应电压时域和频域信号及负载的沉积能量,并探讨了其随电磁脉冲入射角兹、导体板半径R 和天线高度H 的变化规律。仿真结果对于实验方案的制定及天线系统防护具有重要指导意义。     

城市地区架空配电线路防雷性能影响因素研究

雷电活动对架空配电线路的安全稳定运行有着直接的影响。为降低配电线路雷击跳闸给城市地区供电造成的危害,文中对城市地区架空配电线路的防雷性能影响因素进行系统分析。根据雷电感应过电压的Hcidalen模型计算理论,建立了架空配电线路耐雷水平仿真计算模型,对不平衡绝缘、不同杆塔接地电阻、不同地面电阻率、有无避雷器和不同耦合地线装设情况下的线路耐雷水平进行计算分析,获得了不同因素对城市地区架空配电线路防雷性能的影响规律。文中研究成果可为城市地区架空配电线路的防雷设计及雷击跳闸率的降低提供有效的参考和指导。     

750kV输电线路下方感应电的原因分析及防范措施

750kV输电线路下方低电压等级线路及长行导体大量存在,在这些线路上作业时,作业人员常常容易忽视感应电的存在,感应电压电击伤亡事故屡屡发生,严重威胁人身安全。本文介绍了感应电压的产生机理,对交流感应电压进行了分析计算,并提出了在生产中对感应电应采取的措施,为停电检修线路人员避免感应电击提供参考。     

大规模光伏电站的防雷评估及雷击风险管理

对大规模光伏电站户外场的雷击感应电压原理进行分析,确定雷电电流波的数学模型,推导雷电冲击电流产生的瞬态电磁场分布。计算了单个光伏电池板上的感应电压,对金属边框和背面铝箔屏蔽层的影响因素进行分析,并通过有限元方法得到相应的衰减因子,计算出了有和没有金属边框这两种情况下的光伏电池板的雷击感应电压。最后给出整个光伏电池串的感应电压的计算方法,计算结果证实上述方法的可行性和有效性。     

端接非线性负载的不等长传输线瞬态分析

对时域有限差分(FDTD)法应用于不等长多导体传输线端接非线性负载的情况进行了介绍.首先给出了多导体传输线电报方程和差分公式;然后介绍了不等长传输线的仿真模型;在此基础上,最后通过建立端接非线性负载的不等长多导体传输线模型,对该情况下传输线两端的电压响应进行了分析.数值仿真结果说明了FDTD法解决此类问题的正确性和有效性,为不等长传输线瞬态分析的进一步研究打下了基础.     

基于单端正激变换的地线取电系统电源电路仿真设计

为解决输配电系统检测设备供电难题，设计了能够从输电线路架空地线取电系统电源电路，根据输电线路地线感应电压不稳定的特点，采用不可控整流桥和单端正激变换电路，结合闭环控制技术，设计并搭建了电路模型，通过分析在不同输入电压情况下电路的输出特性，验证了电路可行性，该电源电路实现了将9Ｖ~ 100Ｖ 可变交流输入转换为12Ｖ 稳定直流输出，并且通过拟合不同负载情况下电路输出功率特性曲线，分析得出电源电路输出功率稳定。     

TDSE方法用于多导体传输线端接动态元件的分析

利用时域空间扩展方法(TDSE)对多导体传输线端接动态元件的情况进行了分析，为电磁兼容分析提供了一种新的途径。利用该方法分别对由独立激励源和入射电磁波激励的传输线的终端感应电压和电流进行了分析。仿真结果表明：当传输线端接动态元件的时候，终端感应电压和电流的过渡过程时间将会变长。     

叠加定理在求解交流负载线中的应用

图解法常用于分析波形失真问题和估算最大不失真输出电压,其中交流负载线的求解和作图又是该方法的核心。为此,应用叠加定理对交流负载线方程的求解进行了探讨,证明了直接耦合放大电路的直流负载线和交流负载线相同、阻容耦合放大电路的直流负载线和交流负载线不同;提出了应用解析法计算最大不失真电压幅值、分析波形失真。与目前广泛采用由戴维宁定理求解交流负载线的方法相比,得出了由叠加定理求解交流负载线的三个优点。     

500kV交流输电线路组合绝缘配置探索

本文简要地介绍了500kV交流输电线路的不同组合绝缘配置方式,分析了复合绝缘子、玻璃绝缘子有限元模型的建立方法,在此基础上,针对导线下沉式和导线上扛式分别进行了计算及结果分析,得出各种组合绝缘配置的电压分布情况,并提出最佳绝缘配置方案,有效改善了绝缘子电压分布,减小了电场强度.     

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     

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.     

Ground effects on induced voltages from nearby lightning

The lightning induced voltage on overhead lines from return strokes and it's dependency of a lossy ground is analyzed using a new, analytical vector potential formulation. Norton's (1937) approximation and the surface impedance approach are used to take loss effects into account. The surface impedance method predicts in general induced voltages in good agreement with Norton's approximation, but the accuracy of the method is dependent on the variation of the current along the lightning channel. Norton's method is compared with the exact Sommerfeld solution, showing a deviation <10% even for low conducting grounds and distances from 100-1000 m. The effect of stroke location and line termination is also analyzed, showing that a line terminated by it's characteristic impedance and excited by a return stroke at the prolongation of the line is especially sensitive to lossy ground effects. Strokes near the mid-point of an overhead line gives less loss effect than strokes at the end of the line. The surface impedance approximation is derived from Norton's method and the necessary assumptions are outlined     

Lightning-induced voltages at both ends of a 448-mpower-distribution line

Lightning-induced voltages due to return strokes in ground flashes beyond about 5 km were measured simultaneously at both ends of an unenergized 448-m power-distribution line. The measurements represent an extension of an earlier experiment on the same line in which voltages are obtained at only one end of the line. In addition to the induced voltage measurements, the causative lightning electric and magnetic fields are recorded. The voltage and field measurements are made as a function of the lightning direction and of the power-line termination. For both measured and idealized electric fields as inputs to a time-domain transmission-line coupling model, the authors calculate line voltages as a function of the incident angle of the lightning electromagnetic radiation and of the line termination. Measured and predicted voltages calculated from the coupling model with measured fields as inputs show, overall, good agreement in waveshape, but the predicted voltages are about a factor of three larger in amplitude. To the extent that the results can be compared, there is reasonable agreement with the earlier experiments on the same line     

Simulation models of a dissipative transmission line above a lossyground for a wide-frequency range. I. Single conductorconfiguration

The simulation model of a single conductor dissipative line above a lossy ground, based on the exact formulation of the Maxwell equations, is proposed for a wide frequency range. The transmission-line (TL) and fast-wave (FW) propagation constants of the line are computed by solving the modal equation coming from the continuity of the tangential component of the electric field at the air-wire interface. Three different expressions of the distributed line impedance and admittance are suggested with reference to different definitions of the line voltage. Moreover, logarithmic approximations of the Sommerfeld integrals are proposed in order to obtain an easy-to-implement formulation of the simulation models for use in computer codes. Comparisons between the proposed models and the Carson (1926) approach are carried out with reference to a single conductor line above a lossy earth, considering different values of the line geometrical parameters and ground conductivity and permittivity     

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.     

Lightning-Induced Voltage Over Lossy Ground by a Hybrid Electromagnetic Circuit Model Method With Cooray–Rubinstein Formula

This paper presents the calculation of lightning-induced voltages over lossy ground, generated by a lightning strike to a flat ground and a tall object. A hybrid electromagnetic circuit model method adopting an approximation formula, i.e., Cooray–Rubinstein expression, is employed in this paper. A comparison of the simulation results with experimental data shows that the Cooray–Rubinstein formula is still good enough for the calculation of a lightning-induced voltage. Electric fields calculated by the proposed method, and by equations derived by Master and Uman and a conventional dipole technique, are compared. The two approaches yield the same total electrical fields but different components of electrostatic, induction and radiation.      

Influence of a lossy ground on lightning-induced voltages onoverhead lines

A comprehensive study on the effect of a lossy ground on the induced voltages on overhead power lines by a nearby lightning strike is presented. The ground conductivity plays a role in both the evaluation of the lightning radiated fields and of the line parameters. To be calculated by means of a rigorous theory, both fields and line constants need important computation time, which, for the problem of interest, is still prohibitive. The aim of this paper is to discuss and analyze the various simplified approaches and techniques that have been proposed for the calculation of the fields and the line constants when the ground cannot be assumed as a perfectly conducting plane. Regarding the radiated electromagnetic field, it is shown that the horizontal electric field, the component which is most affected by the ground finite conductivity, can be calculated in an accurate way using the Cooray-Rubinstein simplified formula. The presence of an imperfectly conducting ground is included in the coupling equations by means of two additional terms: the longitudinal ground impedance and the transverse ground admittance, which are both frequency-dependent. The latter can generally be neglected for typical overhead lines, due to its small contribution to the overall transverse admittance of the line. Regarding the ground impedance, a comparison between several simplified expressions used in the literature is presented and the validity limits of these expressions are established. It is also shown that for typical overhead lines the wire impedance can be neglected as regard to the ground impedance     

Analytical formulation of lightning-induced voltages on multiconductor overhead lines above lossy ground

This paper presents analytical expressions for calculation of lightning-induced voltages (LIV) on multiconductor overhead lines above lossy ground. The transmission-line return-stroke model is used and the propagation effect on the electromagnetic field is approximated by the surface impedance method. Assuming a linear return-stroke current, the standard numerical integrations along the lightning channel and the overhead line are avoided, and the result is a fast and stable formulation that contains only a single convolution integral. The described method applies for distances between 100 m and 10 km and is valid the first few microseconds where the maximum LIV usually occurs. A simplified approach to how to include overhead line losses is also outlined. A model is proposed that can be included in the electromagnetic transients program ATP-EMTP for calculation of LIV in larger and practical systems.     

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。