毕业设计[论文]题目：雷电对变电站二次设备的电磁干扰分析

毕业设计[论文]题目：雷电对变电站二次设备的电磁干扰分析 Computation of Electromagnetic Interference on the Control Equipment by lightning in Substation abstract The paper discussed the influence of lightning on control systems in substation. Based on electromagnetic coupling, the interference on the secondary equipment, especially the control devices of protection will be computed. The interference appears because the shielding sheath of cable is connected with the grounding grid of substation, it will affect the controlling part of the protection, make the protection act improperly, if the value of the electromagnetic influence is too big, it will make the protection equipment breakdown . The following conclusions were obtained from calculation results, the more the distance between the point of lightning strike and the cable is, the less the influence appear. So the lightning preventation system is placed at the corner of the substation; increasing the length of the cable can decrease the potential of the cable and the voltage between the sheath and the core; the magnitude of the lightning current also affects the electromagnetic influence, the potential of the secondary cable is at direct ratio to the magnitude of the lightning current; the shape of the lightning will affect the result, when the time duration of wave head is changed from 1.2 microsecond to 2.6 microsecond, the potential and the voltage both rise; for the same structure of the grounding grid, adding grounding resistivity will decrease the influence of the lightning by about 50%; high soil resistivity will bring high electromagnetic influence, when the soil resistivity is 100 to 300 and 500 , the results are 240V, 1000V and 2000V respectively, so in the area of high soil resistivity, we should pay attention to the secondary system protection more. Key words: electromagnetic influence, secondary equipment, soil resistivity, grounding grid 雷电对变电站二次设备的电磁干扰分析 中文摘要本论文主要讨论雷电对变电站二次设备的干扰。通过电磁耦合的计算，计算出雷电对二次电子设备，尤其是继电保护控制端的干扰。其干扰的原因是由于二次电缆外皮与电网相连引起的，由此产生的电磁干扰轻则影响继电保护的控制端，导致其误动作，严重时还会使继电保护设备受到损坏。计算结果表明，二次电缆距离雷击点越远，其所受的影响越小，并且衰减很快，电缆端部的电位差从240伏衰减至2伏，所以一般变电站的避雷系统都放置在四个角；增大电缆长度能够减小雷电造成的电位和二次电缆端部的电位差；雷电幅值的不同也会产生不同的影响，从进行的三次计算可以看出，二次系统的电位与雷电流的幅值基本上成正比；雷电波形的不同也会产生不同的影响，当雷电的波头时间由1.2微秒增至2.6微秒后，计算结果显示，电缆电位和电位差均有上升，但这是在某一种地网结构和电缆参数的情况下得出的结论。对不同的情况，其结果不一定相同；同样的地网结构，增加匹配电阻能使导芯端部和表皮端部的电位差减小大约50%左右，但是选择不同的电阻和不同的接地点区别不大；高土壤电阻率地区比低土壤电阻率地区更加危险，土壤电阻率从100 到300 到500 的计算结果分别为240伏、1000伏和2000伏，所以更应该重视二次系统的保护工作。 关键字: 电磁干扰，二次设备，土壤电阻率，地网指导教师: 何金良 PRACTICAL SHIELDING AND GROUNDING TECHNIQUES BASED ON ELECTROMAGNETIC TOPOLOGY The fundamental problem of interference control is the separation of a source of interference from a potential victim. The source could be the pulse power experiment and the victim could be the diagnostics electromagnetically. Because the experiments of interest involve fast transients, the separation must be broadband. Furthermore, because most of the experiments also involve high power levels, the separation must be large. Ad hoc solutions to interfacing problems abound in the literature, and almost all these approaches are narrowband remedies. Such remedies are usually insufficient for an effective electromagnetic separation in a transient environment. Interference control problems are basically electromagnetic problems, but they must be solved by circuit designers who are knowledgeable about circuit elements. Hence, these problems are often addressed as equivalent circuits with lumped parameters. If the equivalent circuit is a good model of reality, and if the lumped parameters can be well defined, such an approach is efficient and equivalent circuit, which does not lend itself to a good understanding of the underlying physics. This problem was recognized when protection of military systems against external transients became important. Power line transients, the effects of a high-altitude electromagnetic pulse (HEMP), and lightning, are examples of such transients. These broad-spectrum, high-amplit