半岛地质条件下计算高压直流输电地中直流分布的扩展镜像法

Extended Image Method to Determine the Underground DC Current Distribution of HVDC Transmission Systems Under Peninsula Geological Conditions

明晰地中直流分布是研究直流偏磁效应及其抑制技术的基础。为此,利用保角变换中的正幂函数变换,将三维空间转化为二维空间,提出扩展镜像法的概念,据此推导出半岛地质环境下地表电位分布的函数表达式。分析表明,半岛地质分层土壤的表层土壤电阻率对地表电位具有显著影响,且海岸线夹角愈小,半岛地表电位梯度愈大;再者,接地极距海岸线越近,地表电位下降越迅速。结合山东半岛的具体电网结构,针对我国在建的±660kV宁东-山东直流输电工程进行了具体计算,验证了上述方法的有效性,同时表明,半岛地质对该地区某些变电站的地中直流影响较大,须采取必要的直流偏磁抑制措施。

Using the positive power function transformation,three-dimensional space was turned into two-dimensional space,and the concept of extended image method was put forward.Thereby,mathematical expressions for surface potential calculation under peninsula geological conditions were deduced.Subsequent analyses indicate that,the surface resistivity of the upper layer soil significantly affects the surface potentials,and the surface potential gradient increases as the coastline inclination angle reduces.In addition,the closer the earthing pole is to the coastline,the quicker the surface potentials will descend.Computations for ±660 kV Ningdong-Shandong HVDC project verify the effectiveness of the proposed method,and the results show that the peninsula geology results in evident impacts on the underground DC currents in some substations nearby,and necessary measures should be taken to suppress the DC bias effects.