考虑大地影响的直线法测量大型地网的接地阻抗

Research and Analysis on the Testing of Ground Impedance of Large Grounding Grid through Straight-Line Method Considering the Influence of Earth

在使用直线法测量大型变电站(厂)地网的接地阻抗时,由于地网敷设面积广泛导致周围土壤电阻率存在不均匀分布,使得测量时零电位点难以选取;另外由于电压、电流测量引线平行距离较长导致二者之间通过大地耦合得到的互感阻抗值较大,相对于地网本身的接地阻抗不能被忽略。这两方面的影响会导致直线法测量误差增大。提出一种考虑不均匀土壤电阻率和互感抗影响的大型地网接地阻抗测试新方法,通过电压极多点测量数据拟合找到准确的零电位点和对应的电阻分量值,通过对不同共线长度下的电感分量数据进行拟合计算,剔除测试数据中的互感抗分量。通过CDEGS软件进行仿真,验证了实测数据和仿真数据相差不超过5%,说明以上方法可有效地消除土壤不均匀分布及测试线互感对接地阻抗测量值的影响量,提高了测量的准确性。

When measuring the ground impedance of a large grounding grid of a substation(or a power plant)using the straight-line method,a measurement error will be included in the result,causing the readings higher than the actual ground impedance.The measurement error is related to two factors.One is the non-uniform distribution of soil resistivity in the vicinity of the large grounding grid,making it difficult to find the zero-potential position.The other is the mutual coupling function through earth between the parallel test leads in long distance,resulting in non-negligible reactance compared to the ground impedance.This paper presents a new method for measuring the ground impedance of a large grounding grid considering the influence of non-uniform soil resistivity and mutual inductance.In the new method,the accurate zero potential position and the corresponding resistance are obtained on the basis of fitting of the measurement curves.Besides,the influence of mutual inductance is removed by the fitting of measured data of inductance under different length of test lines.By comparing the results with CDEGS software simulation,the difference between the measured and simulated results is less than 5%.It is possible to effectively eliminate the influence of nonuniform soil resistivity distribution and mutual coupling between test lines.The new method can effectively improve the accuracy of measurement.