输电线路下击暴流强风荷载最不利工况研究

Study on Critical Load Cases for Transmission Lines under Downburst

对流天气引起的下击暴流已经成为我国中东部地区输电线路风灾破坏的主要原因。下击暴流风场的特异性造成现有规范无法适用,开展下击暴流输电线路设计风荷载的研究成为提高电网安全性亟待开展的课题。介绍了下击暴流的数学风场模型并用于计算输电线路风荷载,采用非线性有限元方法对杆塔受到的导线风荷载开展了风场及线路结构参数分析,着重考察了最大导线风荷载对应工况。研究结果表明:(1)直线塔与耐张塔最大横向荷载值相同,但后者最大纵向荷载值显著大于前者;(2)直线塔的最大横向荷载和纵向荷载塔位分别出现于八跨输电线路的端部和次端部直线塔,耐张塔则出现于四跨输电线路;(3)最大导线风荷载与出流直径、中心相对位置、塔位及跨数密切相关,均存在特定的最不利工况。通过对风荷载影响因素和分布规律的总结,最终给出了三种代表性最不利导线风荷载工况的归一化风场参数,为输电线路抗下击暴流导线风荷载的合理取值提供了数据支撑。

A mathematical wind field model for downburst is introduced and applied to calculate the distributions of wind loads on transmission lines.The wind field and structural parameters analysis for the downburst and multi-spanned transmission lines are performed to investigate the critical cases of the conductor wind load acting on the tower using the nonlinear finite element method.The result shows that:(1)the maximum lateral load value of the tangent tower is the same as that of the tension tower,however,the maximum longitudinal load value of the latter is significantly larger than that of the former;(2)The maximum lateral and longitudinal conductor wind loads of the tangent tower ap-pear at the end and sub-end of the eight-span transmission line,while the maximum longitudinal loads of the tension tower appears in the four-span transmission line;(3)The maximum conductor wind loads are affected by the downburst diameter,the relative position between the center of downburst and the target tower,as well as the number of spans.Therefore,there exist specific most unfavorable cases for both lateral and longitudinal conductor wind loads on tangent or tension towers.By summa-rizing the above parameter analysis,a set of normalized wind field parameters for three critical cases of most unfavorable transmission line wind loads are proposed,which will provide an important analyti-cal basis for the reasonable determination of the design value of the conductor wind loads under down-burst.