考虑多层土壤时架空线的瞬态分析

TRANSIENT ANALYSIS OF OVERHEAD LINES WITH MULTI-LAYER SOIL

基于麦克斯韦方程组,推导出土壤水平分层时电磁波在土壤中透射深度的计算公式,按照复深度法可进一步得到土壤阻抗的频域形式。为了便于时域卷积,采用矢量匹配法并结合拉普拉斯反变换将该土壤阻抗的时域形式展开为有限项指数函数之和,并验证了方法的正确性。最后,采用时域有限差分法(FDTD)对架空线的瞬态波过程进行仿真计算,结果表明:土壤阻抗对自阻抗影响较小,对互阻抗影响较大。通过与电磁暂态计算软件(EMTP)的计算结果比较,验证了所提出的FDTD算法的有效性,同时也表明了计入土壤损耗及考虑分层土壤的必要性。

Based on Maxwell抯 equations, the formulas of the complex depth are deduced when the electromagnetic wave propagates in the multi-layer soil. Thus the ground return impedance of the multi-layer soil can be obtained with the complex depth method. For the convenience of the time-domain convolution, the vector fitting method is adopted to expand the time-domain form of the ground return impedance into the sum of finite exponential functions which are easy to be treated, and tested to be valid. At last, the finite difference time-domain (FDTD) method is used to research the transient process of the overhead lines. The results indicate that the ground return impedance has less effect on the self-impedance and more effect on the mutual-impedance. For the two-layer soil, the effect of the topsoil on the voltages of the coupled lines increases when the topsoil becomes thick, and to some extent the effect of the subsoil is slight. Compared with EMTP, the method proposed is demonstrated to be effective, at the same time, the method can be used for both the overhead lines and the cables in soil.