How the observed declining strength of Distribution Earthing Networks will impact the risk exposure of power utilities

Abstract

The ‘strength’ of a distribution earthing network is dependent on the size and density of that network, the local soil resistivity and a host of other factors. The ultimate outcome is that in the majority of cases the power utility earthing network is strong enough to ensure customer’s premises remain sufficiently safe under all reasonably foreseeable circumstances. In those circumstances where the strength is insufficient, the power utility is responsible for adverse outcomes, regardless of their understanding or appreciation of the situation.The ‘strength’ of an earthing system or network is best described by ascertaining the level of hazard created by an imposed earth fault and where those hazards will occur. To definitively establish the ‘strength’ measurement always beats estimation!Based on over 50 years of experience field testing earthing systems, the authors examine the pitfalls of earth testing through a number of case studies. The testing skills that have been developed have been employed on 3 continents, across installations as large as power stations, to as small and sensitive as the instrumentation earthing system for a nuclear laboratory, and as obscure as interference to an undersea, intercontinental optical fibre cable.The paper explores by application of the fundamental physics and dynamics which describe earthing system performance how that performance will change. In particular the paper explores how asset managers may need to respond as the risk profile of future assets change compared to existing ones.