Evaluation of Underground Corrosion on Backfilled Earthing Systems

Abstract

Earthing systems connect specific parts of an electric power system with the ground, typically the Earth's conductive surface, for safety and functional purposes. For an earthing system to be effective, the earth rod should have high electrical conductivity and be less prone to corrosion. Buried earth rods must be able to allow for easy flow of current through them to ensure safety. A corroded rod loses its ability to perform these functions. This research investigated the corrosion behaviour of buried earth rods with different backfill materials. Five copper-coated cast iron rods were utilised for this investigation; one (reference) was buried without backfill material while the other four were buried with tyre ash, palm kernel cake, charred coconut husk and coconut coir as backfill materials for two years. A visual inspection along with measurement of thickness and analysis by Scanning Electron Microscopy coupled with backscattered Energy Dispersive Spectroscopy (SEM/EDS) was conducted to determine the extent of corrosion of these rods. Visual inspection revealed a colour change of the rod from reddish-brown to grey, suggesting that corrosion might have taken place. Measurement of thickness by Vernier calliper showed an increase in thickness from 1.2 mm to a maximum of about 1.9 mm, suggesting corrosion activity. A comparison of the SEM/EDS of samples of buried rods in the various backfill materials to the unburied reference material revealed an increase in oxygen content at several points of the micrographs for the buried rods, again suggesting that corrosion had taken place. Based on the results, it was concluded that all the three methods that were used for the investigation indicated some corrosion activity.