【作者】 陈智；

【导师】 陈俊武；

【作者基本信息】 华中科技大学 ， 高电压与绝缘技术， 2007， 硕士

【摘要】 我国电网运行统计表明雷击引起的跳闸次数约占线路运行总跳闸次数的40%-70%,而广东省500kV直流输电线路雷击跳闸90%以上是由绕击跳闸引起的,这与目前绕击屏蔽设计方法有关系,如规程法等。近年来先导传播模型法的运用使绕击屏蔽研究取得了长足的进步,但以上研究均未考虑导线工作电压的影响,故无从解释前苏联超高压线路随着电压等级提高雷击跳闸率升高的现象。本文首先运用ATP-EMTP建立特高压直流输电线路、杆塔、绝缘子串伏秒特性等计算模型,对特高压直流输电线路三种形式的雷击过电压进行仿真计算,得出绕击的耐雷水平比雷击塔顶、雷击档距中央避雷线要低。与500kV直流输电线路的绕击耐雷水平相比较,发现绕击的小雷电流有入侵换流站的可能性,对设备绝缘存在威胁。其次,本文根据电磁场理论,建立了计及工作电压及杆塔高度的击距系数模型,计算得出随着导线工作电压的增加,相同雷电流大小、相同杆塔高度下,击距系数明显减小;先导对导线,先导对避雷线击距不能近似相等的结论。并辅以绕击实例计算说明,线路的绕击率随着极线工作电压的升高而增大,若不考虑工作电压的影响,有误判可能。随着极线工作电压的提高,以单侧地线、极线及雷电先导作为雷屏蔽的研究模型已满足不了工程实际的需要。作者以模拟电荷法为基础,将雷电先导、两侧地线、极线作为整体研究对象,考虑极线工作电压,计算下行先导垂直下行过程中各导线表面场强变化,运用Peek判据确定各导线对应的雷先导一级定位高度,合理解释了特高压直流线路中存在的正极线绕击概率较大等问题,提出对特高压直流线路绕击屏蔽的新观点:在特高压直流架空线路中,仅有负极线侧避雷线和正极线产生上行先导竞争拦截雷下行先导,正极线侧的避雷线屏蔽功能被削弱,没有起到完全保护正极线的作用。最后作者分析了上述整体模型的不足,提出了雷击屏蔽三维模型并进行探讨、研究、计算分析,得出与上述二维整体模型一致的结论。更多还原

【Abstract】 Statistics show that the rate of lightning strike flashover is about forty percent to seventy percent of total flashover in our power grid. In Guangdong province, the number of lightning shielding failure is ninety percent in the total number of lighting strike flashover on 500 kV HVDC overhead lines. It relates with the current design method, such as regulations and electrical geometric model(EGM). Lately, the study of lighting shielding failure has made a great progress with the use of leader progression model(LPM) and EGM. The study result shows that this models work well only in the transmission line of low voltage level. With the increasing of the voltage level of the transmission line, this model cannot describe the real circumstance of UHVDC transmission lines, which made problems to explain the polarity effect in the process of shielding failure. So this model cannot meet the use in the engineering field.First, the article builds the calculation model of UHV DC transmission lines, tower, insulators and so on. It simulates the three-form over voltage of lightning strikes on the UHV DC transmission lines and compares with 500kV DC transmission lines. It indicates the possibility of lower current-flow of lightning strike on the transmission lines invasion converter station, and the existence threat of the equipment insulation.Then, according to the electromagnetism field theory, a lightning simulation model and a striking distance factor computation model considering the working voltage and the height of the tower are created. The simulation results show that given the same lightning current and tower height and along with the increase of working voltage, the striking distance factor will obviously decrease, and the striking distance will certainly be different between that of leading lightning to the lead and that of leading lightning to the shield. The calculation of a lightning shielding failure example indicates that the rate of lightning shielding failure will increase as the working voltage increases, and could, therefore, lead to misjudge in the case without considering the working voltage.Along with the increase in working voltage, the lightning shielding failure model is composed by one side of shield wire,one side of transmission line and lightning downward leader will be unable to describe the real circumstance of UHVDC transmission lines, which made problems to explain the polarity effect in the process of shielding failure. So this model cannot meet the use in the engineering field. Then, the article bases on Charge Simulation Method, and takes the lightning leader, two shield wires and bundle conductors as a unified whole to research the lightning shielding failure. Also the author considers the working voltage and conductor bundles, calculating the surface electric field of the conductors and shield wires when the lightning leader develops downwards and calculating the electric field with the different distance between the lightning leader and overhead lines. When the conductors induce the upward leader which is decided by Peek equation, the height H that named as the first lightning height away the earth of the lightning downward leader will be determined. Then the author explains the lightning shielding failure problems in UHVDC rationally. It has more probability for lightning shielding failure if the working voltage is considered. Finally, the author puts forward a new viewpoint of UHVDC lightning shielding failure: in UHVDC overhead lines, only anode conductor and cathode side shield wire will initiate positive leader to compete with each other to intercept lightning leader, the shielding function of anode side shield wire will be weakened and plays no role in the protection of the anode conductor.Finally the author has analyzed the insufficiency of the overall model, and the lightning shielding three-dimensional model is proposed. The article carries it on the discussion, the research, the computation and the analysis. And then it obtains with the above two-dimensional overall model consistent conclusion.更多还原