Characterisation of earth electrodes subjected to impulse and variable frequency currents

The evaluation of the lightning response of earthing systems is important for the design of overvoltage protection of power systems and for ensuring electrical safety of personnel. The response is affected by many factors including the impulse shape and magnitude, the geometry and extent of the earthing system as well as the physical properties of the soil medium. In this work, controlled field tests of a 1.2m vertical ground rod has been carried out with both low voltage impulse and variable frequency energisations using a concentric ring current return arrangement to encourage uniform current distribution around the test electrode. The electrode potential is measured with respect to a remote earth reference. The frequency responses of the tested electrodes are determined from measured…