UHVDC圆环接地极接地性能分析

Analysis on Performance of UHVDC Cirque Grounding-electrode

为研究UHVDC圆环接地极接地性能,用三维有限元法计算了考虑钢体自身电阻率时其性能参数,在相同电极长度下计算比较了单圆环、双圆环和三圆环3种不同电极型式的接地特性,结果表明引流电缆注入点处的电极电位和温升略高于电极其它部位,且单圆环电极的最高电位升、接地电阻和最高温升最小,双圆环次之,三圆环最大;还分析了双层土壤上下层电阻率、电极埋深等参数对接地性能的影响。结果表明,电极埋深越大,最高电位升和接地电阻越小,但随着埋深的增加,温度却难以扩散,导致电极最高温升变大。此外土壤电阻率是影响接地性能的重要因素,随着土壤电阻率的增大,最高电位升和接地电阻等指标均有不同程度的上升,电极埋设层土壤电阻率对接地性能的影响较下层土壤电阻率的影响更大。

The performance parameters of UHVDC cirque grounding electrode are computed by 3D finite element method when self-resistance of grounding electrodes was involved in. The work is carried that compare grounding performance of single-cirque, two-cirques and three-cirques grounding electrode on condition of same electrode length by calculation. The results show that there have the minimum value, intermediate value, maximum value of maximum potential, grounding resistance and maximum temperaturerise when grounding electrode is arranged in single-cirque, two-cirques and three-cirques respectively. These indicate shielding effects intensify that influence current to diffuse when augment number of cirque. So it can be considered that select single-cirque as grounding electrode if suitable grounding field can be imposed on condition of maintain electrode length and dofft increase engineering investment. At the same time, because most of uneven soil can be modeled approximatively by double-layer soil, so a series of influencing factor of grounding performance such as electrode＇s depth of burial, top-layer soil resistivity and bottom-layer soil resistivity are analyzed when considered double-layer soil model. The results show the more depth of burial is, the lower maximum potential and earthing resistance are. However, the temperature is difficult to spread, which will result in the maximum temperaturerise grow as depth of burial increase. Furthermore, it can be affirmed that soil resistivity play a important role on performance of grounding electrode. With soil resistivity increase, the maximum potential and earthing resistance, etc were heightened in a certain extent. But the influence of top-layer soil resistivity to grounding electrode performance is more than bottom-layer soil resistivity.