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1、8.4 接地的原理 8.4 The basic concepts and principles of grounding,8.4.1 接地概念及分类 8.4.1 Concept and classification of grounding 8.4.2 接地电阻，接触电压和跨步电压 8.4.2 Grounding resistance, contact voltage and step voltage 8.4.3 接地和接零保护 8.4.3 Grounding and TN protection,8.4.1 接地概念及分类 8.4.1 Concept and classification of
2、 grounding,接地就是指将电力系统中电气装置和设施的某些导电部分，经接地线连接至接地极。埋入地中并直接与大地接触的金属导体称为接地极。电气装置、设施的接地端子与接地极连接用的金属导电部分称为接地线。接地极和接地线合称接地装置。 Grounding refers to the connection between conductive parts of electrical installations and facilities and the ground by the grounding wire pole through wires in power system. The me
3、tal conductor buried in the earth directly is called grounding pole. The wire connecting electrical installations, facilities and grounding terminal in the earth is called grounding wire. They are totally referred to grounding devices.,接地按用途可分为： Grounding can be divided into four categories 工作接地 Wor
4、king grounding 保护接地 Protection grounding 防雷接地 Lightning grounding 静电接地 Electrostatic grounding,8.4.2 接地电阻，接触电压和跨步电压 8.4.2 Grounding resistance, contact voltage and step voltage,大地具有一定的电阻率，如果有电流经过接地极注入，电流以电流场的形式向大地作半球形扩散，则大地就不再保持等电位，将沿大地产生电压降。 The earth has a certain resistance. If a current flows in
5、to the grounding, the current spreads to the earth in the form of current field in hemispherical-proliferation shape. Then the earth will be no longer the equal potential object. There will be the voltage drop along the earth.,电位分布曲线如图8-42所示。 Potential distribution curve is shown in Figure 8-42.,图8-
6、42 接地装置的电位分布 Fig.8-42 Potential distribution of grounding device Ut接触电压Contact voltage Us跨步电压Step voltage,接地装置对地电位 与通过接地极流入地中电流 的比值称为接地电阻。 The ratio between grounding device-to-ground potential and current through the ground into the land is defined as the grounding resistance. 人处于分布电位区域内，可能有两种方式触及不
7、同电位点而受到电压的作用。当人触及漏电外壳，加于人手脚之间的电压，称为接触电压。 People are in in the region of the distribution of potential. There may be two ways to hit a potential point of difference being the role of voltage. When people touch leakage shell, the voltage between the other hands and feet is called contact voltage.,当人在分
8、布电位区域内跨开一步，两脚间的电位差，称为跨步电位差，即跨步电压。 When people walk in the region to the distributed potential , the potential between the feet is known as step voltage.,8.4.3 接地和接零保护 8.4.3 Grounding and TN protection,发电厂、变电所的接地保护 The protection of power plants and substations,发电厂、变电所中的接地网是集工作接地、保护接地和防雷接地为一体的良好接地装置。
9、,Power plants and substations grounding grid is a good grounding device integrity by grounding, protective grounding and lightning protection grounding.,一般的作法是：除利用自然接地极以外，根据保护接地和工作接地要求敷设一个统一的接地网，然后再在避雷针和避雷器安装处增加35根集中接地极以满足防雷接地的要求。 The general practice is laying a unified ground network in addition o
10、f natural grounding . Then the lightning and surge arrester are installed at an increase of 3 5 focusing on grounding pole in order to satisfy the requirements of lightning protection grounding.,按照工作接地要求，发电厂、变电所电气装置保护接地的接地电阻应满足： According to grounding requirements of power plants, electrical substat
11、ions, protective grounding devices resistance should be calculated by the formula:,(8-77),2. 输电线路的接地保护 Transmission line grounding protection,高压线路每一杆塔都有混凝土基础，它也起着接地极的作用，其接地装置通过引线与避雷线相连，目的是使击中避雷线的雷电流通过较低的接地电阻而进入大地。 High voltage line has a concrete foundation for each tower. It also plays a role in gr
12、ounding. The grounding device connects with the lightning protection lines through the wires, with purpose of inducing lightning current hit by lightning through the line of low-resistance grounding to flowing into the earth.,高压线路杆塔的自然接地极的工频接地电阻简易计算式为 ,k为各种型式接地装置简易计算式系数， 为土壤电阻率。 The calculation form
13、ula of grounding resistance of high-voltage line tower grounding poles in working frequency is ,k is the coefficient of various types simple calculation formula of grounding device, is soil resistance.,3. 计算用土壤电阻率 The calculation of soil resistace,接地电阻除与接地极的形状、尺寸大小有关外，还跟土壤电阻率 密切相关。土壤电阻率 主要取决于其化学成分及湿
14、度大小，计算防雷接地装置所采用的土壤电阻率应取雷季中最大可能的数值，一般按下式计算：,Grounding resistance is not only related to the shape of grounding, size, but also effected by the soil resistance greatly. Soil resistance depends largely on its chemical composition and humidity. To calculate soil resistance of lightning protection, groun
15、ding devices should take the maximum possible value in summer which is generally determined by the formula:,土壤电阻率 soil resistivity (m ),考虑土壤干燥所取的季节系数 The season coefficient,雷季中无雨时所测得的土壤电阻率 Soil resistivity measured when no rain in the summer (m),(8-78),接地按用途可分为：工作接地、保护接地、防雷接地、静电接地 Grounding can be d
16、ivided into : working grounding, protection grounding, lightning grounding, electrostatic grounding. 大地具有一定的电阻率，电流以电流场的形式向大地作半球形扩散，将沿大地产生电压降。 The earth has a certain resistivity. the current spreads to the earth in the form of current field in hemispherical-proliferation shape. There will be the voltage drop along the earth.,小 结 Summary,发电厂、变电所中的接地网是集工作接地、保护接地和防雷接地为一体的良好接地装置,Power plants and substations grounding grid is good grounding device of grounding
