Broad-Band Equivalent Circuit of Grid-Grounding System Considering Frequency Dependence of Electrical Parameters of Soil through Modified Vector Fitting Method

In this paper, wide band circuit model based on modified vector fitting method are proposed for the grid-grounding system. At first, the input impedance of the grid-grounding system in the frequency domain is computed by accurate methods such as the method of moments (MoM). The circuit models are then achieved through converting input impedance of the problem to rational functions via modified vector fitting method. These functions are formed in such a way that at first a set of starting poles in the frequency range of interest are chosen, and then the exact locations of poles are found via an iteration process by least square method. Finally, these rational functions are converted to equivalent circuits in time domain and then imported into EMTP software for modeling the ground system so that transient voltage of overhead lines subjected by lightning strikes is also efficiently evaluated.