Transient analysis of nonuniform lossy transmission lines with frequency dependent parameters

An s-domain method for transient analysis of lossy, frequency dependent nonuniform transmission lines having parameters arbitrary varying with space is presented. Nonuniform line is divided into adequate number of sections which are then assumed uniform. The terminal equation for the nonuniform line is calculated by using the terminal equations of the uniform line sections. By using the boundary conditions, total response in s-domain is obtained. Fast inverse Laplace transform is used for frequency to time domain conversion. In one of the examples, the step response of an open ended nonuniform line is obtained and the results are compared with those obtained by lattice-diagram technique. The effect of number of sections is investigated and it is concluded that for sufficiently large number of sections, the results approach to the analytical solutions which can be obtained only for very special nonuniform lines. In the second example, the method is applied for the calculation of transmission tower lightning surge response.     

Numerical electromagnetic field analysis on lightning surgeresponse of tower with shield wire

Lightning surge characteristics of a transmission line comprising a tower, a shield wire and phase conductors are studied with the help of NEC-2. A tower struck by a lightning stroke behaves as an antenna until a traveling wave makes several roundtrips in the tower. During this interval, the tower footing impedance appears to be higher than the footing resistance, and the coupling coefficient between a shield wire and a phase conductor is much lower than that in the TEM mode. These affect the estimation of insulator voltages of transmission towers subject to lightning currents having short rise times. On the basis of these findings, the parameters in the multistory tower model, which has been used widely in EMTP multi-conductor analyzes, are newly proposed     

同塔多回输电线路相导线布置形式研究

明确了同塔多回输电线路地面工频电场、自然功率和线路阻抗等参数的工程计算方法,针对规划的330kV同塔四回输电线路,重点研究了同塔多回输电线路相导线布置形式与地面工频电场、自然功率和线路阻抗的关系,通过计算、分析对同塔多回输电线路的相导线布置形式进行合理选择,对同塔多回输电线路的设计与建设具有一定的指导意义。     

特高压输电线路地面最大工频电场强度和导线最大弧垂特性

研究特高压输电线路几何参数与地面最大工频电场强度的关系和地面最大工频电场强度的特点,给出2种基本分裂导线排列方式的导线最小对地高度和走廊宽度。分析特高压输电导线运行温度和最大弧垂的特点。从特高压输电导线最大弧垂变化和输电运行方式两方面,讨论特高压输电导线地面最大工频电场强度限值10~12 kV/m的安全与经济的合理性。最后,提出特高压2种基本杆塔结构(猫头塔和酒杯塔)的几何参数供参考。     

超高压输电塔在覆冰断线作用下的动力响应

以某500 kV典型输电线路的塔-线体系为模型,借助非线性有限元软件ANSYS/LS-DYNA,在不考虑导线与地面碰撞接触的情况下,模拟不均匀覆冰工况下,四分裂子导线同时断裂、相继断裂两种工况下,断线冲击荷载对输电塔的动力效应.分析结果显示,塔头上的应力和位移动力效应明显,采用拟静力法计算断线冲击荷载是偏于不安全的.     

采用六相输电技术优化双回高压输电线路电磁环境的研究

随着输电线路电压等级的提升,特高压线路电磁环境问题已成为决定其杆塔尺寸的主要因素之一。文中对1 000 k V特高压双回线路和六相578 k V线路的电磁环境进行了计算和比较,结果显示采用同样的塔头和呼高情况下,六相线路的电磁环境优于三相线路。文中还研究了六相线路电磁环境随呼高的变化规律,地线及距地面最高的两根输电线的表面场强随呼高降低而降低,其余导体表面场强随呼高降低而增加;线路下方地面附近工频电场强度、无线电干扰及可听噪声均随着呼高的降低而增加。相比于同等相电压等级的三相线路,其导线表面电场强度更小。因此,六相输电可有效改善双回交流线路的电磁环境。     

特高压交流同塔双回输电塔地震模拟振动台试验

为了分析地震作用下导、地线质量对特高压输电塔动力特性及其地震反应的影响,进行了特高压输电塔模型的地震模拟振动台试验。以某特高压输变电工程为背景,依据振动台试验相似理论,严格模拟了1 000kV特高压交流同塔双回输电塔,进行了不锈钢塔架模型的设计与制作。同时,针对地线及8分裂导线进行了相应的简化,制作了8个等效集中质量块悬挂在绝缘子下端用以模拟导地线质量。选取4种不同类型的地震动输入,针对单塔及单塔悬挂集中质量进行了8度罕遇烈度下的动力响应测试。试验发现,输电塔地震反应受所选地震激励类型影响较大;悬挂集中质量块后该型输电塔顺线路方向自振频率降低了5.7%,横线路方向自振频率降低了3.9%;单塔悬挂集中质量块后地震反应有所降低。导、地线质量的存在降低了输电塔的地震响应。     

基于有限元的超高压输电线路电场的数值分析与测量

为探讨500 k V超高压输电线路下的电场分布问题,在验证了有限元电磁场分析软件Ansoft maxwell的有效性后,建立了同塔双回输电线路模型。主要分析与研究了相导线对地高度、分裂导线结构尺寸等因素对电场特性的影响,以及线路发生故障或停电检修时电场分布的变化规律,这为降低输电线路周围电场和对电磁环境的优化提供理论依据和方法,同时对停电检修线路注意事项提供一定的参考。     

1000 kV级交流特高压输电线路导线最小对地距离研究

导线最小对地距离的取值是特高压输电线路设计过程中需要考虑的关键因素之一。通过总结国外特高压输电线路的相关研究成果,结合我国超高压输电线路的设计经验,提出了把"最大地面电场强度限值"作为我国交流特高压线路导线最小对地距离的选取原则。基于逐步镜像法建立了特高压架空线下空间电场的数学模型,并按照不同区域地面电场控制指标的要求,通过计算确定了1000 kV级交流特高压单回和同塔双回输电线路导线在相应区域下的最小对地距离。研究了线路运行电压、相间距离、分裂导线结构、导体布置形式和双回路相序布置方式等因素对导线最小对地距离取值的影响规律。     

紧凑型输电线异型分裂导线周围工频电场研究

基于二维有限元法研究紧凑型输电线路分裂导线周围工频电场并探讨提高计算精度的方法,计算对比了500 kV紧凑型线路导线表面最大平均电场强度和线路下方距地面1 m处的最大电场强度和走廊宽度,考虑了几种子导线异型排列方式。计算得出,子导线椭圆短轴水平排列优于对称排列,杆塔高度可适当降低。     

甘肃炳-和-银330kV输电线路带电作业试验研究

采用真型模拟塔对甘肃炳-和-银330kV三分裂输电线路工程的ZMS1型猫头直线塔进行了4种带电作业方式的试验研究。通过模拟人在塔窗中不同位置时的操作冲击放电电压以及修正的高海拔参数,校核了各种带电作业方式的危险率和安全距离。研究表明,有3种带电作业方式是安全可行的:①人乘绝缘斗从塔侧进入中相导线;②人沿水平硬梯从塔侧进入中相导线;③人通过软梯从中相导线悬挂点以外3m处由地面向上进入中相,然后沿中相导线进入中相悬挂点。在该线路上进行带电作业时,推荐相对地最小安全距离不小于2.1m。     

特高压直流直线塔断线荷载分析

导(地)线断线严重影响输电线路的安全运行。针对特高压直流线路的特点,采用ABAQUS软件建立了分裂导线连续档断线模型。通过有限元分析,求得V型绝缘子串的摆幅、冲击荷载以及各相导线的断线荷载。通过与断线荷载理论计算结果比较可知:我国现有线路规程关于断线荷载的取值是合理的,按规程设计线路在一定程度上能够抑制倒塔事故的发生。     

Practical method for evaluating ground fault current distributionin station, towers and ground wire

The paper presents an original analytical procedure which enables a quick and, for practical purposes sufficiently accurate evaluation of the significant parts of the ground fault current, for a fault at any of the towers of a transmission line of an arbitrary number of spans. The advantages of the method are the simplicity and accuracy of the formulae for solving uniform ladder circuits of any size (from one up to an infinite number of pis) and any terminal conditions. The formulae are obtained by applying the “general equations of the line represented by discrete parameters” on a specific electrical circuit formed by a transmission line ground wire during ground faults. The presented method is suitable for analyses aimed at evaluating the maximum substation grounding system fault current, at selecting the ground wire capable of withstanding the fault currents and at the prediction of step and touch voltages near transmission towers     

避雷线分流对杆塔接地电阻测量的影响

采用电流-电压三极法测量架空线路杆塔的工频接地电阻时,架空避雷线对注入杆塔地网的测量电流具有分流作用,从而影响接地电阻的测量精度。建立了架空避雷线对注入杆塔地网的测量电流的分流模型,分析了避雷线分流的程度和影响分流效果的因素及其影响规律。结果表明：（1）避雷线分流所占比重可以达到60%以上,当测量杆塔接地电阻较大、非测量杆塔接地电阻较小、测量杆塔为变电站出线上的前2座杆塔时,避雷线分流效果更明显;（2）仅考虑分流电流大小对杆塔接地电阻测量的影响是不够的,忽略分流电流与测量电流的相角差同样会造成较大的测量误差,导致接地电阻的测量值偏高。     

Three winding transformer s-domain model for modal analysis of electrical networks

This paper describes an s-domain sequence model for three winding transformers to be used in modal analysis of ac networks. The model takes into account off-nominal tap positions and the phase shifts among the windings. The main contribution of this proposed model is to complete the set of s-domain models of electrical system components already developed (loads, transmission lines, generators, harmonic filters, shunt elements) suitable for modal analysis of complex electrical networks. Modal analysis provides an important set of system information that is hard to be obtained using the conventional time simulation and frequency response methods. This information may be effectively used to improve the harmonic performance of electrical networks, to build linear equivalents for harmonic and electromagnetic transient studies and to perform linear dynamic performance analysis.     

同塔双回直流输电线路的感应电压仿真研究

随着对输电能力需求的扩大,同塔双回输电技术不仅在交流输电领域应用广泛,而且在直流输电领域也逐渐得到了应用。针对同塔双回直流输电线路之间电磁耦合带来的感应电压问题,采用雷电流仿真模型、杆塔多波阻抗模型和绝缘子先导闪络模型。并建立雷电绕击故障计算模型和接地故障计算模型,对不同运行电压、导线排列方式、土壤电阻率以及排列间距等对同塔双回直流输电线路感应电压的影响进行分析,以溪洛渡直流工程为参考．研究在不同运行方式、输送功率以及加装线路避雷器情况下,同塔双回线路间的电磁耦合特性。在对溪洛渡工程实例采用ATP—EMTP进行仿真的基础上,分别对雷电绕击和接地故障2种情形下的感应电压进行计算。比较并得出了影响线路间感应电压的主要因素。     

A Contribution to the Frequency Analysis and Transient Response of Power Transformer Windings

Abstract—This article proposes a new approach to study the frequency response and the transient analysis of power transformer windings. For improved accuracy, the suggested model includes, among other equivalent circuit elements, the mutual magnetic couplings between any winding turn and all others. This implies that the equivalent inductance of any considered turn will be a location-dependent parameter. Accordingly, the winding will be analyzed as a non-uniform transmission line. Through the application of a recursive circuit reduction technique, a closed-form Laplace s-domain analytical expression for the winding's input impedance can be obtained for any neutral treatment. The resulting expression can be used to determine the winding's series and parallel resonance frequencies. The s-domain expression for the input impedance, in connection with the numerical inverse Laplace transform, will be utilized for determination of the winding's time-domain transient response for any input voltage or current time waveform. Accuracy increases with the assumed number of winding sections, which can be even increased to the actual number of turns, limited only by the available computation resources. The results of case studies are in good agreement with those available in the literature using the time-domain solution of the simultaneous differential equations in the state variables.     

同塔双回500kV高压直流线路感应过电压研究

为研究同塔双回500 kV高压直流线路在不同极线布置方式下对接地故障的过电压水平以及直流过电压大小的影响,根据实际工程参数,采用电磁暂态仿真软件PSCAD建立500 kV高压直流输电模型。模拟单极线路接地故障,得到不同极线布置方式在健全极线路上产生的过电压水平及分布情况,得出接地故障时最优的极导线排列方式。通过仿真分析了接地电阻,直流滤波器结构,直流线路安装避雷器以及线路参数等措施对直流过电压大小的影响。研究表明,改变直流滤波器结构,线路装设避雷器等措施可以有效的降低过电压水平。     

广东500kV同塔四回线路相序排列的选择

文章对采用水平型杆塔、各回路导线呈垂直排列的500kV同塔四回线路参数的不平衡度进行了分析,比较了不同相序排列下的潜供电流和恢复电压、感应电压和感应电流。对于杆塔内侧的五邑—南沙和江门—顺德线路,采用相序3时的感应电压和感应电流仅为采用相序1时的50%左右,其潜供电流和恢复电压也有所降低;而对于杆塔外侧的台山—上稔和糯扎渡—顺德线路,采用相序3时的电磁耦合感应电压和感应电压也低于采用相序1时的情况,其静电耦合感应电压和感应电流、潜供电流和恢复电压则差别不大。为此,推荐广东500kV同塔四回线路采用相序3排列方式。     

基于逐次镜像法的特高压同塔双回交流输电线路工频电场分析

采用逐次镜像法计算1000kV交流同塔双回输电线路导线表面电场强度和线路下方距地面1m处最大电场强度,根据一些文献给出地面场强控制指标计算了线路最低对地距离和走廊宽度。计算结果可给我国特高压交流输电线路设计工程提供参考。