Effects of cost optimised grid configuration on earthing system performance: a comparative assessment

Abstract

This study presents the comparative analysis of earthing grid configurations to determine the optimum design in terms of safety parameters and cost for 66/11 kV substation. For different grid configurations, a fixed earthing area of 9000 m2 was considered. Rectangular, triangular, L-shaped and T-shaped grids buried in two-layer soil model were considered for this study. Three methods, i.e. ANSI/IEEE standard 80-2000, finite element method and genetic algorithm, were used to design the grids. All safety constraints as mentioned in the IEEE standard were followed for designing the earthing grid. A new mathematical cost function (CF) was proposed for designing an effective and economic L-shaped, T-shaped and triangular earthing systems. The CFs used in this study include grid depth, dimensions of earthing rod and horizontal conductor, number of rods and conductors, revetment and excavation area. The economic earthing grid obtained through the proposed method reduces the total cost related to grid materials, installation and excavation. Analysis also showed that the rectangular grid showed preferred results in terms of safety parameters while the triangular grid showed optimum cost design for the earthing system under study. Good agreements were found with the rectangular earthing grid in comparison with triangular, T-shape and L-shape configurations.