机房防雷电

目前正值雷雨季节，机房防雷电是大问题，机房防雷电分为直击雷和感应雷防护。对直击雷的防护主要由建筑物所装的避雷针完成；对感应雷的防护主要是防止由感应雷引起的雷电浪涌和其他原因引起的过电压。据统计，机房设备的雷击损坏95％以上是由感应雷击所引起，解决的办法通常是安装防雷器，防雷器应安装在所有外部线路（通信、供电等采用金属传输介质）进入机房内的设备端口，视具体情况采用1至3级防雷，检查机房设备接地的科学性、合理性、有效性很重要．以2004年鹤壁市机房设备遭雷击为例．分析如下：     

配电线路雷电感应过电压真型试验研究

首先比较了不同试验所采用的雷电测量手段,而后介绍了雷电过电压在线监测系统,并且根据真型试验方案搭建感应雷试验系统,模拟雷击过程在线路上产生的感应过电压,采集到了多次感应过电压波形;最后仿真计算了真型试验工况下的雷电感应过电压,其结果与真型试验结果吻合性较好。     

直线感应加速器聚焦段的模拟

介绍了直线感应加速器聚焦段的结构模型,成功地使用了非均匀网格模型,实现了对直线感应加速器聚焦段的三维数值建模。利用独立编写的螺线管线圈和磁透镜计算程序,将磁元件的场分布设置到三维模型中。模型结合PIC与FDTD方法模拟聚焦段内电子注的传输、聚焦过程,并将结果与文献做比较,验证了模拟的正确性。模拟结果对直线感应加速器聚焦段的调试有一定的指导意义,为试验调节节省开支。     

水平电流在双层大地中感应地电位的数值分析

从麦氏微分方程组出发，推导出双层大地模型下水平电流产生的感应地电位的公式，并利用该公式对一些典型情况进行了计算，分析限计算结果，给出了水平电流产生的感应地电位的一些重要性质。     

接地体附近导体对土壤中冲击电势分布的影响

模拟实际冲击接地实验的构架,采用时域有限差分(FDTD)方法建立计算模型,计算了雷电流冲击下接地体附近土壤中的冲击电势分布情况。计算结果表明:接地体周围土壤中存在的其它金属导体,将改变土壤中的电势分布,导致附近导体与接地体之间的电位差增大,而且,该电位差随土壤电阻率的增大而增大,与附近导体的形状体积也有关。接地体周围土壤中其它金属导体可能使得在所谓的安全距离上的安全裕量减少。     

扫描电子显微学中二次电子发射过程的蒙特卡洛模拟

利用蒙特卡洛模拟固体中电子散射轨迹的计算方法，系统地研究了扫描电镜中二次电子信号的发射过程。该模拟电子与固体相互作用的蒙特卡洛模型包含了级联二次电子产生的过程，并且采用光学介电函数方法描述电子的能量损失和相伴的二次电子激发。由于模拟计算可以给出背散射电子和二次电子的绝对产额，以及它们随加速电压和样品的原子序数的变化关系，因此可以用于模拟元素衬度和形貌衬度像。还计算得到了关于二次电子产生和发射的其它分布，并与实验结果作了比较。     

阶跃电压法确定产生寿命的计算公式

采用一个最近发展起来的产生区宽度模型，导出了描述阶跃电压作用下ＭＯＳ电容器的电容－时间瞬态特性方程，给出了阶跃电压法确定产生寿命的一个计算公式。     

无电极高频放电球形光源的阻抗

本文描述了决定感应耦合低压氩等离子体放电管阻抗的一种方法，设计应用于感应耦合荧光灯光源，它是一球形放电管，感应线圈绕在球形赤道表面。灯内氩气压力为100Pa，射频线圈电充的频率为10MHz。假定等离子体密度和电子温度是均匀的，易于得出电磁场的分析解。使用这个了解我们可以得到电子电流和等离子体阻抗的空间分丰的简便近似计算。给出了阻抗数据计算的结果并与实验结果比较。     

电视转播台的防雷

电视转播台的防雷刘继生电视转播台为了扩大服务范围，大多建在山顶附近视野良好的地点。因此，电视转播台极易受到直击雷、感应雷的冲击，以致损坏设备危及人身安全。从统计规律来看，铁塔和机房直接受到雷击的情况很少，大部分雷电冲击是经供电线路侵入。对供电线路进行...     

激光冲击强化残余应力的数值模拟研究

为了获得激光冲击强化诱导的残余应力场,采用数值模拟的方法,建立了单次激光冲击强化35CD4合金钢厚板2维轴对称有限元模型,对激光冲击过程中材料内部的能量变化、表面动态应力进行了分析,验证了显式动态求解时间选取的合理性,并讨论了模型网格单元尺寸、冲击压力空间分布模型选取对残余应力模拟结果的影响。结果表明,为了得到收敛的模拟结果,选用的网格单元尺寸应为0.03mm左右。单次圆斑激光冲击的残余应力计算结果与已知的实验测量结果吻合得较好。     

Measurements of the voltage induced on an overhead power line 20 mfrom triggered lightning

Voltages induced on a 448-m power distribution line by eleven return strokes in three lightning flashes artificially initiated 20 m from one end of the distribution line and the corresponding vertical electric fields at 500 m have been measured. Two types of induced-voltage waveforms were recorded: oscillatory and impulsive. The former exhibit peak values that range from tens of kilovolts to about 100 kV; the latter show peak voltages nearly an order of magnitude larger. Both types of induced voltage waveforms were observed to occur for different strokes within a single flash. Relatively successful modeling of the oscillatory voltage waveforms is presented. Modeling of the impulsive waveforms proved unsuccessful, probably due to those waveforms being in part associated with a failure, perhaps an unexpected flashover, in the measuring system     

Femtosecond ultraviolet laser pulse induced lightning discharges ingases

Ultraviolet pulses of 200 fs duration and low energy (≈0.2 mJ) have a sufficiently high peak power to ionize oxygen and nitrogen by three- and four-photon ionization, respectively. It is shown that the resultant ionization channel induces a lightning like discharge at half of the natural self-breakdown voltage in nitrogen or air. The laser triggered discharging process is studied by monitoring the voltage between two planar electrodes. The effects of oxygen on the induced breakdown is investigated. A complete theoretical model is presented to simulate: (1) the electron seeding; and (2) the evolution of the plasma of electron-ion in the applied field. The results of the theory verified by small scale experiments-are used to simulate the process of laser triggered lightning in atmosphere, and helps to define the parameters of a laser system for lightning protection     

Comparison of lightning and a long laboratory spark

Long laboratory sparks are often considered to be miniature lightning. The salient properties of 4-m sparks created by impulse breakdown between a negative rod and a grounded plane by the Westinghouse Trafford 6.4 MV impulse generator are compared with those properties of natural lightning. In particular, a comparison is made of the luminous processes associated with breakdown, the current, voltage, power, and energy inputs to the discharges, the radiated visible spectra, the temperature, electron density, and pressure in the discharge channels, the absolute broad-band radiation in the visible and near infrared wavelength range, and the radiated acoustic signals. The spark return stroke most resembles a weak subsequent stroke in a multiple stroke lightning flash. The leader processes of the spark differ considerably from those of lightning.     

基于方向分形维的高频雷达抑制雷电干扰研究

远区雷电是高频雷达的主要干扰源之一,需要加以抑制。该文根据雷电干扰的奇异性提出了通过计算方向分形维在分维上来区分雷电干扰和杂波信号。根据雷电干扰的瞬时分布特点提出分段计算背景均值形成门限检测雷电干扰。最后通过建立线性预测的全极点自回归模型来恢复雷电干扰所在位置上的杂波信号,达到干扰抑制的目的。实测数据处理结果表明了该文方法是有效的。     

浅议变电站PT二次回路中性点安装过电压保护的重要性

近年来,变电站设备因遭受雷击或输电线路雷电侵入波而导致绝缘损坏的事故时有发生,由于雷电冲击传递过电压将对二次绕组绝缘耐受电压造成很大的威胁,因此,在电压互感器二次回路中性点就地安装过电压保护措施具有重要的意义。本文对电压互感器二次中性点安装过电压保护的必要性进行分析研究。     

简析氧化锌避雷器带电测试技术及应用

氧化锌避雷器是一种保护性能优越、耐污秽、质量轻、阀片性能稳定的避雷设备。利用氧化锌良好的非线性伏安特性,使在正常工作电压时流过避雷器的电流极小;当过电压作用时,电阻急剧下降,泄放过电压的能量,达到保护的效果。这种避雷器和传统避雷器的差异是它没有放电间隙,利用氧化锌的非线性特性起到泄流和开断的作用。文章从氧化锌避雷器的带电测试技术方面对其现场测试应用进行了简要说明分析。     

Voltages induced on overhead lines by dart leaders and subsequentreturn strokes in natural and rocket-triggered lightning

The voltages induced by nearby lightning strikes are a major cause of outages in power distribution systems. We compute such voltages taking into account the effects of the dart leaders that precede subsequent return strokes in both natural and rocket-triggered discharges. The results show that for stroke locations that are approximately alone, the line prolongation, the leader electric field change has a significant influence on the amplitude and shape of the induced voltages. The taking into account of the leader field in the coupling mechanism results in an improved agreement between theory and experimental induced voltage data from close triggered lightning obtained in 1986 on a test line at the NASA Kennedy Space Center     

基于组合匹配的低残压宽带雷电防护方法研究

为提高四分之一波长微带线雷电保护器的带宽,降低输出残压,提出了分节微带线与串联电感的组合匹配设计方法. 仿真分析了四分之一波长微带线避雷器的不足,通过对分节微带线、串联电感的仿真优化,拓展了雷电保护电路的带宽,仿真结果表明防护电路在1 GHz到3 GHz内具有良好的电压驻波比即宽带特性. 利用电压梯度法实现器件间的组合匹配,防护电路实测结果表明,在注入组合波波形为1.2/50 μs & 8/20 μs,电压峰值为10 kV的雷电磁脉冲下,输出残压为79 V. 通过组合匹配方法设计的防护电路具有频带宽、残压低、易于调谐的特点,可用于天馈雷电防护.     

Lightning-induced voltages in a satellite launch-pad protection system

Modern satellite launch pads are provided with lightning protection systems to take care of direct lightning strike to the satellite launch vehicle during the launch preparation period. This paper presents the results of the study on induced voltage on the conductors interlinking the towers of such a protection system due to a nearby lightning strike. The variation in the induced voltages with lightning-strike distances as well as ground conductivities are studied and the results presented in the paper. It has been seen that the waveshape of the induced voltage depends on conductor height and striking distance, whereas the ground conductivity has negligible effect on the induced voltage.     

滤波器在中波防雷中的设计与应用

提出了一种基于现有调配网络的发射机防雷设计方案,主要应用带通滤波器的幅频特性实现对雷电电压分量的衰减;应用其群时延特性,在微秒级时间段里让其两侧实现明显的电位差,让二级钳压装置以皮秒级的速度对雷电电压再次泄放并钳制在一个与发射机输出电压可比拟的范围,从而达到对发射机保护的目的。并用频率范围在800～1 400 kHz,12 000 V的高压正弦波形进行测试。从EDA仿真软件的结果来看,此测试效果比较理想。