电气毕业汇报资料2000字外文翻译.doc

-/ 毕业设计/论文 外 文 文 献 翻 译 院 系 机电与自动化学院 专 业 班 级 电气工程及其自动化1104班 姓　 名 原 文 出 处 T&D Conference and Exposition, 2014 IEEE PES,April 14-17,2014 评 分 指 导 教 师 华中科技大学武昌分校 2015 年 3月 1日 毕业设计/论文外文文献翻译要求： 1．外文文献翻译的内容应与毕业设计/论文课题相关。 2．外文文献翻译的字数：非英语专业学生应完成与毕业设计/论文课题内容相关的不少于2000汉字的外文文献翻译任务（其中，汉语言文学专业、艺术类专业不作要求），英语专业学生应完成不少于2000汉字的二外文献翻译任务。格式按《华中科技大学武昌分校本科毕业设计/论文撰写规范》的要求撰写。 3．外文文献翻译附于开题报告之后：第一部分为译文，第二部分为外文文献原文，译文与原文均需单独编制页码（底端居中）并注明出处。本附件为封面，封面上不得出现页码。 4．外文文献翻译原文由指导教师指定，同一指导教师指导的学生不得选用相同的外文原文。 I.引言 500kV输电线路总是位于绵延千里的荒野，接地设备在这里最容易遭受雷击。据中国国家电网公司近年来的生产运行分析，在所有的110KV〜500KV输变电设备跳闸中40%至70%的输电线路停运是雷击造成的。特别是在山区和有高频雷击或高阻抗的地方，线路故障较高[1-3]。它严重地影响到电网的保障性、安全性和供电的可靠性。因此降低雷击跳闸率是确保电力系统安全可靠的运行的重要任务。 不同的保护措施的应用目标和转化作用在不同的区域变化很大，其成本和难度[4-5]也是一样。然而，在工程实践中，仍然采用忽略了多样性的闪电转化的粗放管理，这将导致不理想的结果，需要进行一次改进。因此，取得完美的最终效果的关键是首先采取全面的研究，并与根据结果选择有较高的技术经济的转型战略。 本文旨在选择典型的防雷措施作为主要选择。首先，它们的优点和缺点是它们通过建立电几何模型（EGM）进行分析。在此基础上，采用了改进的层次分析法建立输电线路综合评价模型，并考虑每个塔的技术和经济因素，如跳闸率降低，工程造价，改造和维护难度来选择最佳措施。最后，选择在中国东部的电网公司的一条典型500kV输电线路作为例子来考察选择最佳措施的可行性。 II.输电线路防雷措施的技术和经济效益分析 在确定线路的防雷措施时，有几个因素要考虑，包括该系统的操作模式和自然条件，比如电压等级，线的重要度，线所在区域的闪电活动情况，地形特征和土壤电阻率。然后，按照当地的原有线路的运行经验和技术经济比较结果采取合理的保护措施。到目前为止，组装线避雷器，添加水平侧针，架空地线或耦合接地电线，降低接地电阻和增加绝缘水平架设等方法已被广泛应用于在减少雷电的致故障率，其中前两种方法是最常用的，它们详细的介绍在下文叙述[6-8]。 A.组装线避雷器的分析 当没有避雷器的传输线被雷电击中时，部分电流通过屏蔽线流动到下一个塔，而另一部分电流通过塔流向大地。如果塔顶的电压超过绝缘的闪络电压，绝缘字符串将发生闪络。避雷器可以避免雷电闪络是因为传输线通常的绝缘水平比穿过避雷器形成的残余电压高得多。当带避雷器的传输线被击中时，随着闪电电流值超过某个值，电流的分布将发生变化。因此，大多数的电流将通过避雷器流向相导线，然后流向相邻的塔。这就是避雷器的主要防雷特性。 现有的研究表明，线路避雷器在耐雷水平的提高上具有重要意义。如果线路避雷器装配在整个传输线路，理论上雷击跳闸率将下降到零。考虑到高成本和现有经济能力，避雷器应安装在高接地阻抗或容易发生震动的区域。如果有需要，也可以使用一些辅助方法来降低电阻。 B.加侧针的分析 在架空地线上添加水平侧针将提升架空地线的针的整体屏蔽性能，因为针比线更容易吸引雷电[9-10]。侧针和避雷针具有相同的效果。当雷电先导向下发展，侧针会扭曲自己周围的电场。因为电场的强度在侧针的顶部将达到最大值，雷电先导将发展到侧针。如果雷击输电线路，雷电流会通过相邻的塔放电。把侧针，接地线和大地看作的3D整体，侧针具有确定的保护范围，就如图1所示的EGM模型生动展示出来的那样。其中，AB和CD接地线和地面被保护的弧段，BC是传输线暴露出来的弧段，rs是雷击的距离。 对于雷电电流的典型振幅，如果整个暴露弧段在球体O的保护范围内，点P是被侧针完全屏蔽的。加上P和塔之间的距离，除非球O不能完全覆盖弧段，它即是所谓的最大保护距离。输电线路将不会被这个距离内被雷击。它随着针的长度和设置角度不同或电流振幅的变化而改变，因而该问题应全面地处理。 C.其它方法的分析 此外，对于提高在复杂地形的屏蔽效果，降低接地线保护角是最直接的方法。传输线建好后这个角度是固定的，但是，它并不容易改变。因此增加接地线的水平宽度是一个合适的辅助手段。 降低塔基电阻可以保护的范围小，但具有较高的实用性。在低土壤电阻率的地方原本的塔基电阻会得到充分利用。在减少接地电阻变得困难的区域，可以应用辐射接地连接器或接地减速器。 III.IAHP及其应用 A.基本理论 IAHP起源于由T.L.Saaty在20世纪70年代提出的层次分析法（AHP） [11]，它对各种因素进行了分层，并逐层比较了诸多相关因素。它提供了用于分析和预测对象的发展的定量基础，同时，避免了不均匀，强主观性和传统方法计算繁琐之类的问题。IAHP有两大特点。 （1） 使用三标度法来取代九规模的方法，以减少主观评价的影响。 （2） 使用最佳传输矩阵来构造判断矩阵，从而该权重可以直接获得而不需要通过均匀性的检查。 B.评价模型的构建 当使用IAHP分析问题时，我们应该分层问题并使它变得有条理，然后构造有层次结构的模型。这一个层次的元素对于下一个层次的相关元素起着主导作用，是下一个层次元素的其标准，它分为三个部分。 （1） 目标层。该层仅具有一个元素，它是所分析的问题预定的目标或所需的结果。 （2） 标准层。这一层包含了指导方针和需要考虑的实现目标的标准。最佳补偿需要考虑成本，效果，运行维护，谐波，操作冲击，噪声和故障率，响应时间。 （3） 测量层。此层包括了为了达到这些目标而选择的各种方法手段，既上文所述的TSC，SVC和STATCOM。 I.INTRODUCTION 500kV transmission lines are always located in the desert stretching thousands of miles, which is the grounded facility most likely to suffer lightning. According to the production operation analysis of State Grid Corporation of China in recent years, forty to seventy percent of transmission line outages are caused by lightning in the total number of the 110kV~500kV transmission equipment trip. Especially in mountainous and areas where there is a high frequency lightning or high resistance, line faults are higher [1-3]. It seriously impact on the grid security and the safety and reliability of the power supply. So lowering lightning tripping rate is an important task to ensure the safe and reliable operation of the power system. The application targets and transformation effects of different protective measures vary in different regions, as well as the cost and difficulty [4-5]. In the engineering practice, however, the extensive management of lightning transformation ignoring the diversity is still adopted which results in the unsatisfactory effects and needs to be transformed once more. Therefore, taking the comprehensive research first and choosing the transformation strategy with higher technology economy according to the result is the key to perfect final effect. This paper aims to select typical lightning protection measures as primary options. Firstly, the advantages and disadvantages of them are analyzed by the establishment of electrical geometric model (EGM). On this basis, using the improved analytic hierarchy process to establish the comprehensive assessment model of transmission lines and choose the optimal measure of each tower considering technical and economic factors such as tripping rate reduction,engineering cost, reformation and maintenance difficulty. Finally, select one section of 500kV typical transmission line in East China Grid Corporation as an example to examine the feasibility of chosen optimal measures. II.TECHNICAL AND ECONOMIC EFFICIENCY ANALYSIS OF TRANSMISSION LINE LIGHTNING PROTECTION MEASURES When determining the line lightning protection, several factors should be taken into consideration, including the operating mode of the system, the natural condition like voltage grade and importance degree of line, lightning activities of line area, topographical features and soil resistivity. Then reasonable protective measures are adopted according to the local original line operating experience and technical economic comparison results. So far, assembling line arresters, adding horizontal side needles, the erection of overhead ground wires or coupled ground wires, reducing the ground resistance and increasing insulation level have been widely used in reducing failure rate of lightning, among which the first two methods are most commonly applied and the detailed introduction is presented as follows [6-8]. A.Analysis of Assembling Line Arrester When transmission lines without arresters are struck, part of current flow to next towers through shield wire, and another part flow to the earth through towers. Insulation strings will flashover if voltage of the tower top exceeds flashover voltage of insulation. Arresters avoid lightning flashovers since the usual insulation level of transmission lines is much higher than the residual voltage developed across arresters. When transmission lines with arresters are struck, distribution of current will change as lightning current value exceeds a certain value. Therefore, most current will flow to phase conductors through arresters, then to the adjacent towers. That’s the main lightning protection characteristic of arresters. The existing research indicates that line arrester has a great significance of improving lightning withstand level. If line arrester assembled in the whole transmission lines, the lightning trip rate can fall to zero theoretically. Considering the high cost and economic ability, it should be installed in high grounding resistance or easily shocked area. Some auxiliary methods to lower resistance can also be applied if possible. B.Analysis of Adding Side Needle Adding horizontal side needles on overhead ground wires will enhance the overall shielding performance of the overhead ground wire for needles are more easily attracting the lightning strikes than lines [9-10]. The side needles have the same effect as lightning rods. When the lightning leader proceeds down, the side needle will distort the electric field around itself. Because the strength of electric field will reach the maximum value at the top of the side needle, the lightning leader will proceed to the side needle. If lightning strikes the transmission lines, lightning current will discharges through the tower adjacent. Regarding the side needle, grounding wire and ground as a 3D entirety, the side needle has a certain scope of protection which is vividly shown in EGM model as Fig.1. Where, AB and CD are shielding bows of grounding wire and ground, BC is exposed bow of transmission line, rs is striking distance. For the typical amplitude of lightning current, point P is completely shielded by side needle if the whole exposed bow is inside the protection scope of sphere O. Add the distance between P and tower unless sphere O can’t entirely cover the bow, which is called the maximum protection distance. Transmission lines will not be shocked within this distance. It varies along with the needle length and setting angle differs or current amplitude changes, thus the problem should be treated comprehensively. C.Analysis of other methods Furthermore, reduction of grounding wire protection angle is the most direct method to improve shielding effect in complex terrain. The angle is fixed when transmission lines are set up, however, it can’t be changed easily. So adding the horizontal width of grounding wire is an appropriate auxiliary. Reduction of tower footing resistance has small range of protection but high practicality. The natural footing resistance would be fully used in low soil resistivity. In the areas where reduction of ground resistance tends to be difficult, radiative ground connectors or ground reducers can be applied. III.IAHP AND ITS APPLICATION A.Fundamental Theory The IAHP is originated from Analytic hierarchy process (AHP) brought up by T. L. Saaty in 1970s [11], which stratifies a variety of factors, and compares many associated factors layer-by-layer. It provides quantitative basis for analysis and prediction of the object development, meanwhile, avoids the problems such as nonuniformity, strong subjectivity and fussy calculation of traditional methods. IAHP has two main characteristics. (1) Use the three scale method to replace the nine scale method to reduce the subjective influence of evaluating. (2) Use the optimal transfer matrix to construct judgement matrix, from which the weights can be obtained directly without uniformity checking. B.Construction of Evaluation Model When using IAHP to analyze problems, we should methodize and stratify the problems, then construct a structure model with hierarchy. A hierarchy of elements plays a dominant role to the related elements of next level as the criterion, which is divided into three parts. (1) Target layer. This layer has only one element, which is the predetermined goal or desired result of analyzed problem. (2) Criterion layer. This layer contains guidelines and standards that need consideration to achieve goals. The optimal compensation needs to consider cost, effect, operation maintenance, harmonic, switching impulse, noise and fault rate, response time. (3) Measure layer. This layer includes a variety of measures to choose from in order to achieve the goals, which are TSC, SVC and STATCOM mentioned before.