Optimized Programs for Shaped Conductive Backfill Material of Grounding Systems Based on the FDTD Simulations

A new transient grounding resistance calculation model is proposed for the finite-difference time-domain (FDTD) method. In FDTD, the perfectly matched layer is backed by the perfect electric conductor (PEC) wall. By stretching the grounding system lifting line to the PEC wall, the grounding system performance is simulated. With this model, a 2-D cylindrical coordinate domain FDTD simulation was carried out to study cylindrically shaped conductive backfill material (SCBM) performance with fine grids. From experimental results, some optimal programs have been derived for SCBM in grounding systems. It is found that a large metal rod size can reduce the SCBM resistance only when the main body conductivity is low, and the reduction effect declines as the conductivity increases. Second, the SCBM resistance is as low as the resistance of a conductor of the same size when the main body conductivity reaches 0.5 S/m. Third, enlarging the SCBM radius can reduce the grounding resistance, and resistance can also be reduced by enlarging the SCBM length when it is less than its effective length. Fourth, the grounding resistance of an SCBM, whose conductivity is linear or parabolic type varied, can be as low as that of a totally high conductivity SCBM.