Aurora Power Consulting was contracted by Welsh Power to carry out a detailed earthing study for a new synchronous condenser site connected to the 400kV transmission network in Scotland, UK. Auroras scope was to carry out a detailed earthing study and prepare an earthing layout to assess the Earth Potential Rise (EPR) and associated touch and step voltages for local system faults and transferred potential from the upstream grid substation in accordance with ENA 41-24 and ENA S34.

The first step in the process was to arrange for a series of soil resistivity surveys to be carried out for each area, using the Wenner method. The results of the Wenner test were then used to produce a representative soil model of the site, which allows the initial earthing layout to be carried out. A detailed simulation was then carried out to determine the fault current return split factors and transfer voltages in PSCAD, and then using CDEGS to determine the EPR and associated touch and step voltages on the system for various fault conditions, before refining the earthing system to ensure that all voltages were within tolerable limits.