Keywords: grounding, multilayer soils, boundary element method, acceleration convergence.

Designing safe grounding systems for large electrical installations has been a challenging problem since the early days of the industrial use of electricity. The main objectives of grounding systems are to carry and dissipate electrical currents produced during fault conditions into the ground, in order to ensure the safety of the persons in the vicinity of a grounded installation and to guarantee the power supply and the integrity of the equipment. To attain these goals, fault electrical currents should dissipate into the soil mainly through the grounded electrode, while potential values between close points on the earth surface must be kept under certain maximum safe limits (step, touch and mesh voltages), established in most of the guides and legal procedures for grounding system design. In practice, most of grounding grids of electrical substations consist of a mesh of interconnected cylindrical conductors, horizontally buried, and supplemented by vertically thrusted ground rods in certain places of the substation site.

Equations governing the electrical current dissipation into the soil through a grounded electrode are well-stated from Maxwell's electromagnetic theory. In recent years the authors have developed a numerical formulation based on the boundary element method for the analysis of grounding systems embedded in uniform soils. This approach has been implemented in a computer aided design system that currently enables the analysis of real grounding grids in real-time on personal computers. The extension of this approach for the grounding analysis in layered soils is straightforward. However the analysis of real earthing grids in multilayer soils requires an out of range computational cost due to the poor rate of convergence of the series that appears when the method of images is applied to represent the different layers of soil.

In this paper we present a computer aided design system based on this boundary element method numerical formulation for grounding analysis in multilayer soils that includes an efficient extrapollation technique in order to accelerate the rate of convergence of the involved series expansions. Finally, we show some examples by using the geometry of real grounding systems.

purchase the full-text of this paper (price £20)

go to the previous paper
go to the next paper
return to the table of contents
return to the book description
purchase this book (price £140 +P&P)