Computations of soil temperature rise due to HVDC ground return

The purpose of this paper is to present an application which historically, did not make use of computing methodology in the solution of design problems. The design of High Voltage Direct Current (HVDC) ground electrodes involves the careful selection of several parameters in order to meet strict operating constraints. In particular, the operation of HVDC ground electrodes, results in a rise of the surrounding soil temperature which must be reasonably computed so as to permit safe operation of the grounding network. The classical approach to this design issue was to make several simplifying assumptions and thereby obtain a closed form solution which approximated the situation. Unfortunately, this technique is extremely limited in its scope and the accuracy of solution is dependent on the simplifications made in order to obtain a solution. The technique presented in this paper uses a numerical model to represent the system to be studied. This approach provides extreme flexibility, thus a minimal of assumptions are needed in order to accurately obtain realistic solutions to the problem. The complexity of the numerical model however, requires substantial computing capabilities. Symbols g = heat generated, W/m3 p = soil electrical resistivity, - mJ = current density, A/m2T = temperature of the medium, °C k = thermal conductivity, W/°Cm α = thermal diffusitivity, m2/sCp = specific heat, J/kg°Cd = mass density, kg/m3V = electrical potential, V λ = over relaxation factor