UHVDC垂直接地极技术经济性能分析

Grounding Performance Study and Economic Comparison on Vertical Grounding Electrodes of UHVDC

针对±800 kV直流输电工程接地极的备选极址概况,选取理论上适合采用垂直型电极的极址,设计了几种垂直接地极的不同布置形式,在子电极长度不变其它参数改变和子电极根数不变其它参数改变2种情况下进行了技术和经济性能的计算比较。结果表明,几种方案中跨步电压和接地电阻满足设计要求,但都存在接地极附近土壤温升过高的现象。几种垂直接地极布置形式中各项技术指标相对最优的方案与双圆环水平布置接地极技术经济比较的结果表明,水平双圆环接地极较垂直接地极在现场更具可行性。

The vertical electrode generally is suitable to the region where surface layer soil resistivity is higher than the lower layer＇s or the place where available region is restricted. Based on alternative electrode arrangement region of UHVDC, this paper selects a region suitable for vertical grounding electrode and designs several different arrangement scenarios of this kind of electrode, then computes their performance parameter in technology and economy. The results show that both step voltage and grounding resistance conform to the system requests in these scenarios, but soil temperature rise near ground rods cannot meet the requirement. Maximum value of temperature rise is 264.2℃ and minimum value is 148 ℃. When the sub-electrode length remains invariable while other parameters are changed or when the sub-electrode quantity remains invariable while other parameters are changed, both step voltage and grounding resistance conform to the system requests in these scenarios, but soil temperature rise near ground rods can not meet the requirement. Considering current density distribution along single sub-electrode, it can be found that the distribution is non-uniform, and a smooth ＂W＂ distribution is presented. Furthermore the distribution of temperature along sub-electrode surface is same with the current density, and end-effect is very obvious. Simultaneously, a best one of these scenarios is selected to compare with horizontal two-ring electrodes. Although both step voltage and grounding resistance in two arrangements are appropriate, but there is lower value if grounding electrode are arranged in vertical shape. Furthermore, due to non-uniform distribution of the current density along the vertical electrode surface, soil temperature rise quickly and is unacceptable. But it is not so for horizontal two-ring electrodes.