A Mathematical Model for the Transient Lightning Response From Grounding Systems

With the Fast Fourier Transform (FFT), a mathematical model for accurately computing distribution of a lightning currents ∞owing along a high voltage a.c. substation's grounding system buried in half inflnite homogenous earth has been developed in this paper. It is a hybrid of Galerkin's method of moment (MoM) and a conventional nodal analysis method. The model can directly calculate the distribution of both branch and leakage currents along the grounding system. A dynamic state complex image method and a closed form of Green's function of a dipole or monopole in the half inflnite homogenous earth model are introduced into this model to accelerate calculations of mutual impedance and induction coe-cients. Analytical formulae for the mutual induction and impedance coe-cients have been developed to accelerate the calculation for near fleld case by using Maclaurin expansion. With the inverse FFT, the model can be used to study the transient lightning response of a grounding system.