考虑土壤频变特性的接地装置频域矢量有限元模型

Vector Finite Element Model of Grounding Devices in Frequency Domain Considering Soil Frequency-dependence

发、变电站及输电线路的接地装置是保障电力系统供电可靠性的重要基础设施,准确计算接地装置的频域特性可为合理设计接地系统提供理论依据。为此,通过引入Visacro-Alipio土壤参数频变公式,采用麦克斯韦全波方程建立了计及土壤频变特性的接地装置频域矢量有限元模型,并采用空间坐标变换法处理了模型中无穷散流空间与有限计算资源之间的矛盾;基于提出的模型和方法,对接地网进行了仿真计算,并将计算结果与现场试验及国际公认软件包CDEGS的计算结果进行了对比,验证了该模型在低频及高频注入电流作用下计算的准确性。结果表明:空间坐标变换算法的引入,使得该模型在保障计算精度的基础上降低了计算量;考虑土壤参数频变性时,接地参数明显低于不考虑时的情况;当注入电流频率低于2 MHz时,"电感效应"起到主导作用,接地电阻随着注入电流频率增加而增大;当注入电流频率高于2 MHz时,接地参数随频率增加而基本稳定,土壤电参数的频变特性使得"电感效应"导致的接地电阻随频率增加而近似线性增加的现象有所缓和。

The grounding devices of power station, substation and transmission lines are important facilities to guarantee the supply reliability of power system. Accurate analysis of grounding device frequency characteristics can provide reasonable theoretical basis for the design of grounding engineering. By introducing the Visacro-Alipio soil frequency-dependence formula, a vector finite element model in frequency domain of grounding device considering the soil frequency-dependence was presented based on the full wave Maxwell equation is built. In the presented method, the open boundaries of earth are processed by introducing spatial transformation which translates the semi-infinite space into the finite space. Based on the presented model and method, the grounding grid was calculated, and the calculation results were compared with the measured results and simulation results by CDEGS from literature, then the accuracy of pre- sented model for low frequency and high frequency fault current were validated. The results show that, the introducing of spatial transformation can induce the amount of calculation, while the accuracy has been improved; the grounding parameter is significantly reduced when considering the soil-frequency dependence. When the frequency of fault current is less than 2 MHz, ＂inductive effect＂ plays leading role in the current dispersal process, and the resistance of grounding grid increases along with the increasing of current frequency. If the frequency of fault current is greater than 2 MHz, the grounding resistance keeps steady with the increasing of current frequency. The soil frequency-dependence can ease the grounding resistance increasing along with the fault current frequency caused by ＂inductive effect＂.