FDTD and laboratory modelling of earth electrodes including the effect of soil ionisation

This video presents the modelling of a driven rod earth electrode under lightning current impulse using the Finite Difference Time Domain (FDTD) method including the effects of soil ionisation. This paper investigates the effects of relative permittivity, resistivity and soil ionisation gradient on the step voltage using the Darweniza and Liew variable - resistivity model. A 10 kA Terespolsky lightning current impulse is applied and the relative permittivity, resistivity and soil ionisation gradient are varied. A thin wire model is used to model the electrode which involves the application of a permittivity and permeability correction factor and the Liao second order absorbing boundary condition is used to terminate the grid. It is found that effect of the soil ionisation effect is to decrease the step voltage which as expected. It is also shown that the reduction percentage is proportional to the relative permittivity, and resistivity. It is highlighted that nothing to the same extent can be said about the critical field from the results other than the critical field does have an influence on the step voltage. The electric field distribution is shown to be like that of the electric around a cylindrical conductor which is a 1/r^2 relationship. It is mentioned that the results of the experimental procedures could not be compared to those obtained from the FDTD computation due to difficulties in determining the relative permittivity and soil ionisation gradient. Finally, it is recommended that the required physical soil sample parameters be determined to validate the work presented.
Student names:
Aphelele Mlomzale and Nico Muka
Supervisor name:
Prof Ken Nixon