Transient Analysis of Grounding Systems

This paper addresses the problem of computing the ground potential rise of grounding systems during transients. Finite element analysis is employed to model the constituent parts of a grounding system. Short lengths of earth embedded electrodes are characterized as transmission lines with distributed inductance, capacitance and leakage resistance to earth. Leakage resistance to earth is accurately computed with the method of moments. The other parameters of the finite element, namely inductance and capacitance, are computed from the resistance utilizing Maxwell´s equations. This modeling enables the computation of the transient response of substation grounding systems to fast or slow waves striking the substation. The result is obtained in terms of a convolution of the step response of the system and the striking wave. In this way the impedance of substation systems to 60 cycles is accurately computed. Results demonstrate the dependence of the 60 cycle impedance on system parameters. The methodology allows to interface this model of a substation ground mat with the Electromagnetic Transient Analysis Program thus, allowing explicit representation of earth effects in electromagmatic transients computations.