高土壤电阻率地区发电厂、变电站接地设计

【作者】 刘湘莅；

【导师】 王克文；

【作者基本信息】 郑州大学 ， 电力系统及其自动化， 2003， 硕士

【摘要】 电力系统的安全运行有两方面要求，一是要确保人身和设备的安全，二是要维护电力系统的可靠运行，这都与接地装置的设计密切相关。以往的电力规程中，在接触电势、跨步电压满足的前提下，发电厂、变电所的接地电阻小于0.5Ω即可。而在新的电力规程《交流电气装置的接地》(DL／T621-1997)中，对接地电阻提出了更高的要求；另一方面，随着电力系统规模的不断扩大，短路电流随之增加，也加大了接地设计的难度。在高土壤电阻率区，这一问题更加突出，因此就要采用各种措施降低接地电阻。 目前主要采用的降阻措施有增大接地网的面积、引外接地、增设垂直接地极、换土以及使用化学元素降阻剂等，但每种措施都有一定的适用条件，在实际工程中往往出现这种情况：不考虑电力系统外部环境、地理位置、地质等条件而任意采用降阻措施，这不仅有很大的盲目性，达不到降阻效果，而且会给系统的安全运行带来隐患。 本文简单介绍了常规的接地计算，在第三章重点研究了垂直接地极法。以往的做法通常是增设短垂直接地极，本文参阅了大量文献，在接地网参数软件CDEGS数值计算的基础上，着重分析了长、短两种垂直接地极的接地特性，长垂直接地极对水平网散流有抑制作用，降阻效果明显，短垂直接地极则效果不明显。另外，增设长垂直极后，大部分故障电流通过垂直极流入大地，相应减少了水平导体的散流量，因此地表面的水平方向电流密度大大减少，造成水平方向电场的强度大大降低，从而可以降低接触电势和跨步电压。文章随后探讨了增设长垂直极后复合地网的计算公式，并详细论述了长垂直接地极敷设位置、根数、深度的选择及施工方法。 本文第四章先简单介绍了降阻剂的特性、分类及降阻原理，然后探讨了加入降阻剂后接地电阻的各种计算和降阻剂的用量公式。针对目前降阻剂市场较为混乱的现状，文章重点阐述了降阻剂的选择，应注意降阻剂的降阻特性、腐蚀性和稳定性。最后对降阻剂的施工方法进行了说明。 摘要 第五章中，本文简单介绍了其它几种降阻措施，如外延法，水下接地网法等，简要说明了计算公式。 目前工程中采用的降阻措施很多，但最忌讳的是不因地制宜而盲目选用，不仅事倍功半，有时还会起到反作用。本文通过对各种降阻措施的研究、分析，归纳出各自的降阻特性、适用范围，并澄清了一些较为普遍的错误做法，在电力系统的实际工程中具有一定的意义。更多还原

【Abstract】 The basic demands for electric power system safe operation are to ensure the personnel and equipment safety, and the reliable system operation. These demands are much close related with the design of grounding system. According to the previous power system design standards, it is only required that the grounding resistance on the step voltage and touch voltage is less than 0.5 Ohm. However, in the newly published standard "Grounding for AC electrical installations" (DL/T621-1997), higher demands for grounding resistance are put forward. Moreover, short-circuit current increases largely with the growth of power network, which also multiply the difficulties of grounding system design. In the area of high soil resistivity, this problem is even more evident. Therefore, it is necessary to take effective measures to reduce the grounding resistance.Up till now, the principle measures adopted are as follows: expanding the area of grounding net, increasing grounding rod, soil renewal and use of chemical preparation etc. In the practice of engineering, it is very common to take measures on resistance reduction willfully, neglecting investigation of external conditions, geographic location and geology conditions. These measures often do not meet the requirements and even bring dangers to safe operation of electric power systems.In this thesis, the conventional approaches for grounding computation are briefly introduced. In Chapter 3, it lays special stress on analyzing the Vertical Grounding Rod (VGR) method. In the past, Short VGR was widely used. Based on lots of references and the computational software of CDEGS, the grounding characteristics for long VGR and short VGR are analyzed in this chapter. Long VGR presents sound effect on resistance reduction, by inhibiting the spread of fault current through grounding conductors. Meanwhile, short VGR proves to be not effective on resistance reduction. Moreover, with the increase of long VGR, most fault current flow into the earth rather than spread in grounding conductors, thecurrent density decreases in the direction of horizon and the electric-fieldstrength is reduced, as a result the step and touch voltage is limited. Formulas for grounding trunk computation with long VGR are described; the design of long VGR is discussed in details, including the selection, location, quantity and depth, as well as the construction method.In Chapter 4, the chemical preparation used for resistance reduction are discussed, including the characteristic, classification and operating principles, as well as the related computation. In view of the present situation of disordered market, this chapter centers on the selection of chemical preparation. Its characteristics, corrosiveness and stability are put forward. The construction method is also described.In Chapter 5, other methods for resistance reduction are discussed, including outward extension and underwater grounding conductor etc. Related computation formulas are briefed.Finally, the selection of grounding method is much important to the safe operation of electric power systems, willful use of resistance-reduction methods proves to be harmful. Based on the study and analysis of each method, this thesis sums up its respective characteristics and scope of application, and clarifies some common mistakes in practice. Results of this thesis provide the help for further study and takes notable effect in electric power engineering.更多还原