水电站接地网暂态特性及其评估技术研究

发布时间：2018-02-21 22:12

本文关键词： 接地网暂态特性冲击接地电阻异质土壤 CDEGS　出处：《西南交通大学》2017年硕士论文　论文类型：学位论文

【摘要】：水电站受水能资源分布影响,大多位于高山峡谷地区,相对普通变电站而言,其土壤环境更为复杂,且水电站接地网由站内多个接地网组成,分布范围广、结构多样。对于接地系统而言,其冲击接地电阻、暂态地电位升等接地参数都与其所处的土壤环境、拓扑结构以及导体电气性能参数密不可分。本文针对水电站土壤结构复杂、接地网结构多样的特点,首先基于水平双层土壤模型、垂直双层土壤模型和局部异质土壤模型,分别研究了接地网暂态特性参数随各土壤特征参数的变化规律,根据仿真结果得出:水平双层土壤下,接地网冲击接地电阻随上层土壤电阻率的增大呈非线性增加,受底层土壤电阻率影响较小;垂直双层土壤下,接地网冲击接地电阻随雷电流注入一侧土壤电阻率的增大呈非线性增大,受另一侧土壤电阻率的影响较小;局部异质土壤下,当外围土壤电阻率一定时,随着异质土壤电阻率的增加接地网冲击接地电阻不断增加,异质土壤横截面越大,接地网的冲.击接地电阻越大,且其对接地网冲击接地电阻的影响越显著。然后针对水电站典型地网结构,仿真计算了存在垂直接地极的接地网和双层接地网的雷击暂态特性,发现在距离雷电流注入点一定范围内,随着接地极数量的增多,接地网冲击接地电阻下降越明显,采用外疏内密的方式敷设增加的垂直接地极来降低冲击接地电阻的效果最好;对于双层地网结构,上层接地网的雷电流注入点与连接导体越近,越有助于降低上层接地网导体的暂态电位,但会导致下层接地网导体的暂态电位升高,所以在布置接地引下线时应当充分考虑与上、下层接地网连接的一次、二次设备的绝缘性能。最后,针对某水电站220kV开关二次设备故障,搭建了接地网等比例模型,仿真计算了接地网故障区域导体的暂态电位分布以及雷击点附近接地网导体的暂态电位差,发现避雷针附近的接地网导体电位升高对一次设备绝缘的威胁不是很大,但雷电流注入点附近导体段的暂态电位差很大,超过了二次设备的绝缘耐受水平,建议在避雷针接地引下线处1m的范围内至少增加3根垂直接地极,或者将原避雷针的位置进行调整,建议将避雷针安装在距离变压器电缆就地端子箱大于15m的位置。
[Abstract]:Most hydropower stations are located in high mountains and canyons, the soil environment is more complex than ordinary substations, and the grounding grid of hydropower stations is composed of many grounding grids in the station, and the distribution range is wide. The grounding parameters such as impulse grounding resistance, transient ground potential rise and so on are closely related to the soil environment, topology and electrical properties of conductors. In this paper, the soil structure of hydropower stations is complex. Firstly, based on horizontal double-layer soil model, vertical double-layer soil model and local heterogeneous soil model, the variation of transient parameters of grounding grid with each soil characteristic parameter is studied respectively. According to the simulation results, the impact grounding resistance of grounding grid increases nonlinearly with the increase of the resistivity of the upper layer of soil, and is less affected by the resistivity of the bottom layer under the vertical double-layer soil. The impact grounding resistance of grounding grid increases nonlinearly with the increase of lightning current injection into one side of the soil, and is less affected by the other side of the soil resistivity, while in the local heterogeneous soil, when the peripheral soil resistivity is fixed, With the increase of the resistivity of the heterogeneous soil, the impact grounding resistance of the grounding grid increases continuously. The larger the cross section of the heterogeneous soil, the more the impact of the grounding grid. The impact of grounding resistance on ground grid is more significant. Then, the transient characteristics of lightning strike of grounding grid with vertical grounding pole and double-layer grounding grid are simulated and calculated for typical ground grid structure of hydropower station. It is found that within a certain range of distance from the lightning current injection point, with the increase of the number of grounding poles, the impact grounding resistance of the grounding grid decreases more obviously, and the increase of vertical grounding pole is the best way to reduce the impact grounding resistance. For the double-layer ground grid structure, the closer the lightning current injection point of the upper grounding grid is to the connecting conductor, the more helpful it is to reduce the transient potential of the upper grounding grid conductor, but it will lead to the increase of the transient potential of the lower grounding grid conductor. Therefore, the insulation performance of the primary and secondary equipment connected with the upper and lower grounding grids should be fully considered in the arrangement of grounding lead down lines. Finally, for the 220 kV secondary switchgear fault of a hydropower station, a proportional model such as grounding grid is built. The transient potential distribution of the conductors in the fault area of the grounding grid and the transient potential difference of the grounding grid conductors near the lightning strike point are simulated and calculated. It is found that the increase of the potential of the grounding grid conductors near the lightning rod is not a great threat to the insulation of the primary equipment. However, the transient potential difference in the conductor section near the lightning current injection point is very large, which exceeds the insulation tolerance level of the secondary equipment. It is suggested that at least three vertical earth poles should be added within 1 m below the lightning rod grounding lead. Or the location of the original lightning rod should be adjusted and the lightning rod should be installed in the position where the terminal box of the distance transformer cable is more than 15m.
【学位授予单位】：西南交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TV734;TM862

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