Lightning: earthing electrodes harmonic response

The grounding behavior (resistive, capacitive, inductive) to a lightning discharge is related to the electrodes' geometrical dimensions, shapes and the soil characteristics (resistivity ρ, permittivity , permeability μ). The border between the capacitive and inductive behaviors corresponds to a frequency value (critical frequency fc), analyzed with the T line model. A practical relation (fc, ρ/1) is obtained from variable frequency tests made over different electrodes. (5 pages)