Wide-band modelling of tower-footing grounding systems based on the impulse response measurement

The tower footing grounding system is of major importance for analysis of the lightning overvoltages on an overhead transmission line during backflashover and shielding failure. This paper presents one approach to wide-band modelling of tower footing grounding impedance based on impulse response measurement. The model derived is implemented in the simulation software ATP/EMTP. A general methodology is presented based on the Matrix Pencil Method (MPM) for rational fitting of time domain measured signals and determining frequency domain response. The MPM is used to estimate the poles and residues of the frequency response using time domain signals. The second part of the paper describes the process of implementation of the model capable of representing grounding structures over a wide band of frequencies in EMTP type software. At the end of the paper, it is shown how the described procedure was applied to one measured impulse response of the tower-footing grounding system. The obtained results show that the simulation results of the impulse response of the tower footing grounding systems model correspond very well to the measured impulse response. It has also been shown that MPM model filters the measured signals appropriately.