Modeling the Electro-Quasistatic Field of Ground Electrodes Under the Influence of Electro-Osmosis

High voltage direct current (HVDC) systems are commonly structured as monopole or bipole type system. Ground electrodes are installed to use the earth for carrying the return current. With an applied electric field, the soil in the vicinity of the electrode dries out, resulting from the effect of electro-osmosis. With a humidity dependent electric conductivity of the soil, a time varying electro-quasistatic field is seen. For the computation of the resulting electric field, the electric and thermal conductivity and the electro-osmotic conductivity are modeled using measurements from literature. The resulting electric field stress is computed within a coupled simulation. Simulation results of a cylindrical electrode lead to an electric field that exceeds the electric field without electro-osmosis by 10-40 %. Due to low values of the electro-osmotic conductivity, the process is slow and needs to be considered only in the close vicinity of the electrode. Results indicate that for operation times of a few days, electro-osmosis has only a minimal effect and can be neglected for the computation of the surface step voltage.