Vector Fitting-Based Models of Vertical and Horizontal Electrodes under Lightning Strikes to Interface with EMTP

In this paper, wide band circuit models based on vector fitting method are proposed for the grounded vertical and horizontal electrodes. At first, the input impedance of the electrodes 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 electrodes to rational functions via 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 locations of poles are reformed via an iteration process. Finally, these rational functions are converted to equivalent circuits in time domain and then imported into EMTP software for modeling the ground systems so that transient voltage is efficiently evaluated.