外场激励下多导体传输线响应的节点导纳分析法

基于空间电磁场激励下的Taylor和Agrawal传输线模型,分别推导了Taylor 和Agrawal模型的均匀平面波激励下耦合多导体传输线终端响应的方程.将沿传输线分布的激励源等效为终端等效电流源,根据散射电压、入射电压和总电压的定义以及终端网络的边界条件,分别以传输线终端节点的总电压和散射电压为未知量,推导了均匀平面波激励下端接耦合多导体传输线的节点导纳方程.该方程为分析均匀平面波激励下含有复杂终端网络的传输线以及传输线网络的节点电压电流响应提供了简便途径,概念和计算过程简单,易于计算复杂传输线网络的节点电压.考虑大地的影响,本文全面阐述了传输线耦合电压响应分析过程,并验证了该方法的正确性.对含屏蔽地线的五导体传输线响应进行了数字仿真,并分析了地线对其他三导体响应的影响.     

架空传输线在电偶极子激励下的瞬态电磁响应

利用电磁拓扑学,将电偶极子产生的电磁场与架空传输线的电磁耦合问题进行拓扑分解,推导出用于同时求解传输线瞬态电压响应和空间电场的BLT方程.推导过程中引入电场的分量形式以解决入射场的方向性,考虑了传输线中差模电流和共模电流的辐射,并计及了由传输线初始状态引起的零输入响应.利用本文结果可有效地计算外部电磁场与传输线的耦合问题.     

电气系统中多导体传输线的瞬态电磁响应

连接电气系统的多导体传输线在电偶极子激励下的瞬态电磁响应分析是开展电力系统电磁干扰防护工作的基础。本文将复频域形式的BLT(Baum-Liu-Tesche)电流方程分解为电偶极子电磁场等效分布电压源与负载端电压两部分激励产生的响应之和,在此基础上利用拉普拉斯反变换得到了线性多导体传输线的时域终端电压-电流关系式,并将传输线的初始条件等效为线上的分布激励源,计及了由传输线初始状态产生的零输入响应。与数值算法结果的对比验证了所提出的传输线时域终端电压-电流关系式。最后,通过一个交直流供电系统计算例,说明了本文给出的方法可有效地计算外部电磁场与电气系统中多导体传输线的电磁耦合问题。     

变电站电磁脉冲耦合倾斜二次电缆数值分析

为了研究电磁脉冲耦合二次电缆的机理,基于电磁散射理论建立了脉冲场耦合传输线的三维倾斜时间域有限差分(FDTD)数值分析模型,推导出了三角形网格内的电磁场修正方程,进而计算了电磁脉冲激励下理想导体面上倾斜单导体传输线终端负载上的电流响应。结果表明,随着一端负载逐渐增大另一端负载上电流幅值逐渐减小,但反射逐渐增大。用电磁脉冲模拟器进行的实验验证结果表明,传输线终端负载上电流测量结果与计算结果比较符合,证明建立的三维倾斜FDTD数值模型可用于变电站电磁脉冲耦合二次电缆问题的研究。     

变电站瞬态电磁场耦合二次电缆数值方法研究

提出瞬态电磁场耦合细线问题的三维时域有限差分(finite-difference time-domain,FDTD)数值方法的一种改进模型。基于电磁散射理论推导出有限长直细导线终端以及拐角附近的电磁场分量的离散方程。利用改进模型计算电磁脉冲激励下双导体传输线终端负载上的电流电压响应,并进行实验验证。结果表明计算结果与实验结果吻合较好,说明改进的三维FDTD数值模型对研究瞬态场线感应问题是有效的,可用于变电站瞬态电磁场对二次电缆干扰问题的研究。     

HEMP场激励下交直流高压输电线耦合响应概率分布

应用蒙特卡罗法和传输线耦合响应节点导纳方程,分析了高空核电磁脉冲(HEMP)场激励下交流高压输电线和直流高压输电线耦合响应的分布规律.分析中将电磁波的入射参数,包括极化角、入射角和方位角,作为一组随机变量,并由计算机随机产生.应用瞬态外场激励下多导体传输线节点导纳方程分别分析端接传输线耦合电流和耦合电压响应峰值,并得出...     

含分布源传输线方程的时域求解

变电站内雷击、故障和开关操作引起的瞬态电磁脉冲通过空间耦合作用在二次电缆上产生的感应电压和电流将干扰终端保护、自动装置等设备,感应电压和电流的大小可通过含分布源的传输线方程算出。均匀传输线在频域可方便求解,但非均匀传输线方程,在频域求解会很困难。为此运用时域有限差分法FDTD在时间和一维空间离散求解传输线方程,考虑到外界电磁脉冲对传输线的耦合,将其表示为分布源,从而算出终端负载的响应。计算与频域两种算法的结果吻合,验证了此算法适用于非均匀传输线方程的求解。     

确定非均匀传输线网络时域灵敏度的伴随网络法

基于模量分析、特征值灵敏度和数值逆拉普拉斯变换技术，提出采用伴随网络法计算含有耦合均匀与非均匀传输线网络的时域灵敏度。通过求解原网络方程和伴随方程，可一次计算出任意输出对网络元件以及传输线电气参数的灵敏度，与扰动法相比效率更高。通过仿真实例与采用扰动法的计算结果进行比较，验证了所提方法和公式的正确性。     

基于BLT方程的电磁干扰建模

为了解决场线耦合下传输线负载端响应问题,基于BLT方程建模思想,利用电磁拓扑概念中的管道和节点概念构建了计算的物理模型;利用场线耦合、传输线理论结合叠加原理推导了线上负载干扰的计算方法;利用辐射场空间传播、传输线散射理论结合叠加原理推导了空间场的计算方法;对节点处的电压方程进行合并、整理得到了类似BLT方程的矩阵方程。计算结果表明,该分析方法不仅可计算传输线负载响应,还可计算空间电磁场。与其它论文计算结果的比较证实其模型、推导、计算的正确性。     

斜阶跃场源瞬变电磁法的全程视电阻率数值计算

推导了斜阶跃场源激励下采样零时刻在发射电流关断处的均匀导电半空间瞬变响应解析式,分析了斜阶跃场源激励下的磁场、感应电压与视电阻率的对应关系,指出用感应电压定义的全程视电阻率可能存在无解或多解的情况。提出了一种全程视电阻率直接计算方法,将发射电流关断时间作为系统参数参与视电阻率的计算,可以方便地计算出中心回线装置下测量目标的全程视电阻率。理论模型的分析与Electromagnetic Model Analysis软件计算数据的比较证明了这种数值算法的可行性。不同于常规数据校正算法,提出的全程视电阻率直接算法具有更小的误差和更快的计算速度,由于斜阶跃场源技术的成熟,该算法具有一定的应用价值。     

A Distributed Circuit Model for Power-Line Communications

This paper presents a computational efficient distributed circuit model for broadband power-line communications (PLC) in the frequency range of 1 to 30 MHz. The model is derived based on the full wave approach and it takes into account the mutual coupling between the power lines, the effect of the ground plane and the discontinuity along the lines (e.g., PLC line bent with an arbitrary angle and the terminations). To derive the distributed circuit model, the PLC lines were divided into many small elements with each element treated as a dipole antenna. The electromagnetic fields along the power lines were considered as the summation of the field of these elements solved by the boundary conditions at the air-conductor and the air-ground interfaces from which the explicit expressions of the per-unit-length circuit parameters were obtained. To check the accuracy of our proposed model, the current distributions along PLC lines excited by an external source were determined using the chain matrix approach. Common-mode current is calculated with the transmission line equations. The agreement between our theoretical calculations with the experimental data as well as with full wave approach shows the validity and applicability of our proposed model for such PLC applications.     

Transient characteristics of power cables: a new approach based on Poynting's theorem

Frequency-dependent transmission line parameters are analysed using Poynting's theorem. Using the general formulation of impedance and admittance matrices and solution for electromagnetic field vectors, wave propagation characteristics of the transmission line are obtained. The method is particularly useful for power cables, in which electromagnetic effects such as the proximity effect and electromagnetic shielding are strong. Calculations of underground eccentric cable characteristics illustrate the method. New formulae for inductances and conductor internal impedances are derived and new results for the propagation constant are given.     

Transmission line tower models in frequency domain

This paper proposes a transmission line tower model in frequency domain for back-flashover analysis, which has a uniform characteristic impedance and a uniform propagation constant. Most conventional tower models are constructed as a constant and uniform parameter transmission line that is independent of frequency. However, the authors' models have the frequency dependency of the characteristic impedance and the propagation constant to express the frequency characteristic of the transmission line tower. Two models, a cylinder model and a four-frames model, were investigated to simulate the tower. Their surge responses were computed by numerical electromagnetic field analysis based on the moment method. From the results, the two-port circuit constants were calculated in the frequency domain, and the characteristic impedance and the propagation constant are derived from them. The complex artificial oscillations appeared in frequency dependency of the parameters because the parameters were calculated numerically. The equations with analytical form were obtained by approximating with a smooth curve to the oscillations. It is possible for the equations to represent the transmission line constants as a function of geometrical parameters such as the tower height and the radius. Close agreement was found between the surge response computed by the numerical electromagnetic field analysis and the result calculated by inverse Laplace transformation of the analytical equations. To prove the model, the experimental results were compared with the computed ones of the cylinder model that has arms, and it was shown that the new model agrees closer with the experiment than conventional transmission line models.     

Effect of transformer sizes and neutral treatments on theelectromagnetic transients in transformer substations

This paper deals with the electromagnetic transients in transformer substations. The substation can have more than one transformer. Generally, these parallel-connected transformers can be of different sizes and neutral treatment. The substation is fed from a high-voltage overhead transmission line (or cable). Emphasis is given to the substation terminal voltage, the transformers' neutral voltages (if their neutrals are not directly earthed) as well as the internal distribution of transient voltages along the transformers' windings, following a typical external double-exponential surge voltage. The distributed parameter transient analysis is done in the s-domain, and then followed by a numerical Laplace inverse transform technique to get the distributions in time domain     

Animations of electromagnetic transients in power transmission lines by means of the two-dimensional numerical Laplace transform

This paper presents the use of animations of the wave propagation phenomena on power transmission lines as a valuable tool for research and educational purposes. These animations are generated from data obtained by transient analysis in the frequency domain applying the two dimensional numerical Laplace transform. Since the line electrical parameters are defined in the frequency domain, the frequency dependence of such parameters is directly taken into account. These animations allow an insightful illustration of how travelling waves propagate along transmission lines during an electromagnetic transient, making them a useful tool to determine transient overvoltages that occur at internal points along power transmission lines. In the educational field, using these animations in electrical engineering courses can help students to have a better understanding of the traveling wave concept and how it differs from the circuit theory. In addition, it allows detailed comparison of the wave propagation along lines under different conditions, such as type of excitation, type of load, introduction of losses, etc.     

基于DSP处理器的架空输电线波参数测试方法

基于分布参数电路理论,应用电报方程,推导出架空输电线三相全耦合传输线方程,并确定了二相回路传输线方程波参数与全耦合传输线波参数的关系。介绍了用数字信号处理器DSP(Digital Signal Processor)和单相正弦信号源确定二相回路传输线方程波参数．进而整定三相一地耦合传输线渡参数的原理与方法,并给出了电压相量测试电路的硬件实现。模型线路上的实验表明该测试方法原理正确,测试精度高。     

变频供电对电缆绝缘性能影响的研究

分析了变频长线供电波反射过电压的产生机理、影响因素及对电缆绝缘性能的危害及变频长线供电波反射过电压高频振荡的产生机理;在理解PWM脉冲传输机理的基础上,计算研究了变频器输出电压波形的上升下降时间、供电电缆的长度、供电电缆的波阻抗及系统负载匹配关系对过电压的影响程度;提出了抑制波反射过电压的措施.现场应用结果表明,达到了较好地消除波反射过电压的目的,保证了供电系统的可靠运行.     

DTS中长距离输电线路的电磁暂态仿真

提出了一种对高压交流长距离输电线路进行电磁暂态模拟的方法，并将春用于调度员培训仿真器（DTS）中。为保证DTS仿真的精度和速度，采用了对高压交流长距离均匀传输线采用电磁暂态模型，网络其他部分仍然采用常规机电暂态模型的混合暂态仿真方法，简单算例和实际等例结果证实了所提方法的正确性和有效性。