深井型直流接地极散流机理研究

Study on the Mechanism of Vertical DC Grounding Electrode

准确计算直流接地装置的散流性能及接地特性是优化设计直流接地极的基础。提出了基于恒定电场理论的直流接地装置性能有限元数值计算模型,针对求解区域和接地导体截面尺寸的差异导致的剖分困难、计算量大的问题,引入"薄壳"理论,在保证计算精度的前提下大大减小了计算量;通过与文献数据对比,验证了该方法的有效性。建立典型结构的深井型接地极模型,计算深井接地极散流过程产生的地中电流密度、电场强度、接地电阻和最大跨步电压等参数;分析电流注入点个数、接地极导体长度、接地极埋深、导体并联根数以及土壤电阻率等因素对接地性能的影响。结果表明:深井型直流接地极的散流具有明显的端部效应,其接地性能基本不受电流注入点个数的影响;接地电阻和最大跨步电压随导体长度、埋深、并联根数的增加而减小,并呈现饱和趋势;在均匀土壤中,接地电阻和最大跨步电压与土壤电阻率成线性关系。

The accurate calculation of the DC flow and the grounding characteristics of DC grounding device is the basis for optimizing the design of the DC grounding electrode.In this paper,a finite element numerical model of the performance of a DC grounding device based on the constant electric field theory is proposed.In order to solve the problem of dissection and large amount of calculation caused by the difference between the section size of the region and the grounding conductor,the"thin shell"theory is introduced,and the calculation is greatly reduced under the premise of ensuring the calculation accuracy.The comparison of data shows that the method is effective.A deep well type ground electrode model of typical structure is established to calculate the parameters of the ground current density,electric field intensity,grounding resistance and Maximum step voltage,etc.;And the influence of the number of current injection points,the length of grounding electrode conductor,the buried depth of grounding electrode,the number of parallel conductors and the soil resistivity on the grounding performance is analyzed.The results show that the dispersion of deep well type DC ground electrode has obvious end effect,its grounding performance is not affected by the number of current injection points,and the grounding resistance and the maximumstep voltage decrease with the increase of the conductor length,depth and the number of parallel roots,and show the saturation trend.In homogeneous soil,the grounding resistance and maximum step voltagehave a linear relationship with soil resistivity.