A Probabilistic Approach for Human Safety Evaluation of Grounding Grids in the Transient Regime

A statistical description of safety aspects of grounding grids based on a new definition for risks of shock for human safety in the transient regime is presented in this paper. The procedure is based on a mathematical approach to evaluate the statistical distribution of lightning current followed by the Monte Carlo simulation of the grounding grid response to the probabilistic distribution of the injected current. The frequency-domain method of moments solution of the governing electric-field integral equation is used to simulate the grounding grid performance. The mapping of frequency-domain data to the corresponding transient data and vice-versa are achieved through appropriate use of the fast Fourier transform (FFT) and inverse FFT techniques, respectively. The proposed simulation methodology is used to obtain the probability by which the safety limits of a given grounding grid are violated. The safety limits are defined by comparing a severity parameter that is calculated by integration of an appropriate function of the current passing through human body over the time span of lighting current. Simulation results demonstrate the compatibility of the low-frequency safety index with that recommended in this paper for transient (high frequency) excitation of a grounding grid.