基于FDTD的GIS中电磁波传播特性仿真研究与分析

该文采用时域有限差分法研究电磁波信号在GIS中的传播特性,从而为GIS局放超高频在线检测提供借鉴与参考。首先参照GIS实际试验装置进行建模,然后分别研究了激励源脉冲宽度与幅值对电磁波传播的影响、电磁波在GIS筒体内传播的时延特性、GIS结构变化对电磁传播特性的影响。仿真结果表明,电磁波信号幅值与衰减速度与激励源的脉冲宽度与幅值关系密切,利用此特征可以帮助判别局放源的种类和严重程度;电磁波信号在GIS内传播时呈现明显的时延和幅值衰减特性,此特征有利于进行局放源的定位;GIS结构变化对电磁波的幅值及信号特征均有影响,因此应按传播特性选择传感器放置点,以取得更好的检测效果。     

基于改进Agrawal模型和FDTD法的感应雷过电压算法

为了计算架空配电线路雷电感应过电压,利用Nucci提出的雷电回击通道模型(MTLE模型),计算雷电回击电流产生的空间电磁场,采用Cooray-Rubinstein公式计算大地电导率影响的水平电场分量,并改进Agrawal场线耦合模型,建立架空配电线路雷电感应过电压方程,基于时域有限差分(FDTD)法,计算10 kV架空线路的雷电感应过电压数值。结果表明,大地电导率对计算结果影响较大,大地电导率使线路上的感应电压幅值降低接近20 kV;不同回击传播速率也影响感应雷过电压的数值。定量计算雷电感应过电压,需要分析各种因素对计算感应雷击过电压的影响,完善计算方法,保障计算准确性,使理论与计算方法适用于实际的配电线路防雷设计,提供有价值的参考依据。     

地震波斜入射对高拱坝地震反应的影响

高坝地震反应分析通常假定地震波垂直入射,在显式有限元法结合黏弹性人工边界的时域波动分析方法的基础上,建立了三维平面地震波倾斜入射的输入方法。采用所建立的斜入射输入方法,研究了地震波斜入射对小湾拱坝地震反应的影响。分析结果表明：与垂直入射相比,地震波倾斜入射可能显著增加对拱坝抗震安全性起控制作用部位位移、速度、加速度反应的频谱幅值放大系数,应该在拱坝地震反应分析中考虑地震波斜入射的影响。     

变压器绕组内局部放电UHF电磁波传播过程研究

采用时域有限差分(FDTD)法,研究了变压器绕组内部局部放电的特高频(UHF)电磁波向外辐射的传播路径和衰减情况。根据一台220 kV变压器的尺寸建立了铁芯绕组仿真模型,利用自适应网格法剖分模型空间,给出了用于模拟局部放电的高斯电流元,置于同一铁芯柱上的高低压绕组之间;仿真了UHF电磁波向外辐射的过程;分析了沿绕组径向和轴向的放电源产生的UHF电磁波向外辐射的传播路径和衰减情况。仿真结果表明:当放电源沿绕组径向时,UHF电磁波主要经过高压绕组的饼间油道传出,相对无绕组情况下衰减3.4 dB。当放电源沿绕组轴向时,UHF电磁波主要经过高低压绕组间的油道传出,相对无绕组情况下衰减1.2 dB。     

基于黏弹性边界的地震波斜入射方法研究

地震动输入的形式的选取是计算水工建筑物地震反应的重要问题。本文在前人工作的基础上,采用工程波动理论,总结推导出基于黏弹性边界的二维P波和VS波的等效荷载计算公式,进而施加在人工边界上,实现地震波的斜输入。通过斜输入算例表明,本文的黏弹性边界地震波斜输入方法很好反映P波和VS波的斜入射情况,具有较高的精度,能够有效应用于地震斜输入过程中结构与地基的相互作用的计算中。     

变压器局部放电UHF信号传播特性的仿真分析

特高频(UHF)技术通过检测局部放电辐射电磁波信号来实现对设备局部放电的检测,抗干扰能力强,检测灵敏度高,是一种基于空间电磁场耦合的局部放电测试技术,能够实现真正意义上的局部放电在线检测,因此在变压器局部放电检测领域取得了日益广泛的关注及研究。由于变压器内部结构复杂,各种金属结构件都会对辐射电磁波的传播产生影响,因此变压器局部放电UHF检测技术有必要研究变压器内部电磁波的传播规律。为此在对变压器内部结构进行合理简化的基础上完成了变压器典型结构的计算机建模,以高斯电流元模拟局部放电源,合理设置各类仿真参数,利用时域有限差分法(FDTD)对特高频电磁波在变压器内部的传播特性进行了仿真分析。仿真结果给出辐射电磁波信号在铁心绕组之间的传播特点,铁心对电磁波传播造成的衰减和畸变作用,并通过时域及频域波形的对比给出不同脉宽、不同幅值电磁波信号在铁心绕组结构中传播的特点。     

基于时域有限差分方法的污秽绝缘子局部放电频谱分析

绝缘子污秽问题一直是困扰电力安全生产的难题之一。为此,采用超高频(ultra-high frequency,UHF)法仿真和测量了绝缘子污秽放电情况,并对其放电频谱进行了分析。首先运用时域有限差分软件XFDTD对污秽绝缘子的放电过程进行了仿真,得到其电磁波的时域波形,再经快速Fourier变换(fast Fourier transform,FFT)得到放电频谱,并研究了污秽程度对绝缘子放电的影响规律,得出了重污秽绝缘子的电磁辐射大于中污秽绝缘子的电磁辐射的结论。然后,针对不同人工污秽程度的绝缘子,测量绝缘子局部放电电磁辐射在680～9 400MHz频率范围内的电磁波频谱。分析测量数据时,采用了分频段分幅值统计所处区间数据个数的统计方法来处理数据,结果表明:在各个区间内重污秽绝缘子的数据个数大于轻污秽绝缘子的数据个数,得到其潜在规律,初步通过比较区分了绝缘子的污秽程度。进一步可建立不同污秽等级绝缘子的电磁波辐射特性数据库,判断绝缘子的污秽情况。     

金属球电磁散射特性FDTD混合并行算法研究

研究金属球电磁散射特性与MPI OpenMP混合并行FDTD算法,可为金属目标和其他复杂介质目标的电磁散射特性及大数据计算提供一定的理论依据和方法借鉴。采用FDTD方法分析了自由空间中金属球的电磁特性,利用Fortran软件实现了金属球数据建模,得到了远场区电场分量和雷达散射截面的波形曲线,实现了MPI OpenMP混合并行FDTD计算。实验表明,计算结果与现有实验数据非常吻合,且该并行方法是正确的,具有良好的加速比和效率。     

开关柜内局部放电电磁波特性分析

为了研究开关柜中局部放电产生的电磁波特性分布,基于有限元差分法理论,利用三维全波电磁仿真软件XFDTD对最易发生故障的电缆室进行仿真分析。分析结果表明局部放电引起的电磁波以球面波的形式向四周传播,由电磁波感应生成的电场强度在柜门缝隙处最强,呈现出衰减振荡的波形,同时检测的感应电压与电场强度波形相似,考虑到实际传感器的差异性,提出感应电压的归一化处理,通过多点检测有效地实现了局部放电的定位。     

屏蔽分析中的三维FDTD细孔缝模型

研究了时域有限差分(Finite-Difference Time-Domain, FDTD)法的三维细孔缝模拟问题,推导出基于CP(Contour Path)法的三维细孔缝仿真算法.在不同孔缝宽度模型下,分别利用细化网格和容性细孔缝(Compacitive Thin-Slot Formalism ,C-TSF)两种算法验证三维CP细孔缝模型的精度和适应性.结果表明该CP模型在缝宽较大时精度较好,和C-TSF算法相结合在分析细孔缝电子机箱屏蔽问题时应避免使用细化网格.     

反激式变换器电磁辐射的FDTD仿真与分析

开关电源电磁辐射发射容易超出EMC标准限值,有必要对其形成机理、特性和预测进行研究。本文在建立电容、变压器、PCB引线、半导体开关等元器件模型基础上,对Flyback开关电源进行了时域有限差分(FDTD)建模,仿真研究了其在开放空间中远场电磁辐射的分布和规律。仿真结果表明开关电源输入/输出电缆是电磁辐射的主要影响因素,并验证了共模电感对远场电磁辐射的抑制作用。     

An FDTD analysis of electromagnetic fields caused by electrostatic discharge between metals with ferrite material attachments

The transient electromagnetic fields due to electrostatic discharge (ESD) between charged metals have wide‐band frequency spectra up to the microwave region, which create a serious malfunction for high‐tech information devices. For the above ESD fields, we previously analyzed them, using the finite‐difference time‐domain (FDTD) method, and showed that the metals enhance the field level according to the metal dimension. From the standpoint of reducing such ESD fields, the electromagnetic fields caused by the spark between the metals with ferrite core attachments were investigated. The FDTD method was also used to compute the ESD fields. An FDTD algorithm for the magnetic field inside the ferrite core was newly derived. The results show that the cores attached near the spark gap considerably reduce the magnetic field level, which is also confirmed experimentally. © 2001 Scripta Technica, Electr Eng Jpn, 138(1): 34–41, 2002     

Efficient analysis of ridged cavity by modal FDTD method

A modal finite‐difference time‐domain (FDTD) method is extended for the analysis of ridged cavities, which are uniform in the z‐direction. Assuming that the end surfaces of cavity are the perfect conductor, thus, the fields along the z‐axis can be described by k_z. Therefore, three‐dimensional (3‐D) problems can be simulated by the use of a two‐dimensional model. Besides, to achieve a faster computation, the field components are expressed by two pairs of equations—sine and cosine. To validate the utility and efficiency of proposed method, we analyzed two ridged cavities. Numerical results show that less than one‐tenth memory and CPU requirements are needed by the modal FDTD as compared with conventional 3‐D FDTD method. Copyright © 2012 John Wiley & Sons, Ltd.     

Absorption of electromagnetic wave by inhomogeneous, unmagnetized plasma

In this article, a novel and normalized Z-transform finite-difference time-domain (ZTFDTD) method is presented. This method uses a more general form of Maxwell’s equations using the E, H, D fields. The iterative model of D-E-H-D can be obtained by using the Z-transform resulted frequency-dependent formula between D and E. The advantages of the ZTFDTD consist in that the discrete equations are simple, the results are precise, easy to program and capable of dealing with the key technologies of finite-difference time-domain (FDTD), such as absorbing boundary conditions (uniaxial anisotropic perfectly matched layer, UPML) and near-to-far-field transformation. The ZTFDTD method is then used to simulate the interaction of electromagnetic wave with plasma. Using a simplified two-dimensional model, the stealth effect of inhomogeneous, unmagnetized plasma is studied both in different electron densities of plasma, different electromagnetic wave frequencies and different plasma collision frequencies. The numerical results indicate that plasma stealth is effective in theory and a reasonable selection with the plasma parameters that can greatly enhance the effectiveness of plasma stealth. __________ Translated from Journal of Huazhong University of Science and Technology (Nature Science Edition), 2006, 35(6): 57–59 [译自: 华中科技大学学报(自然科学版)]     

Stabilization control of multi‐machine power systems by adaptive power system stabilizer using frequency domain analysis

To improve electric power system transient stability, synchronous generators are generally equipped with controllers such as AVR, PSS, and GOV. Fixed parameter controllers degrade control performance, since various oscillation modes occur depending on system conditions. This paper presents an adaptive power system stabilizer (PSS) using frequency domain analysis for improving the transient stability of a multimachine system. In the proposed method, first, the frequency components of the generator swings are detected by the FFT. The conventional PSS parameters are tuned online by a fuzzy controller and frequency domain analysis. We verify the proposed adaptive PSS using frequency domain analysis, which can damp the generator swings effectively. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 142(2): 10–20, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10129