What Could Possibly Go Wrong? Mistakes and Misadventures in Earthing

Understanding the key principles behind the operation of an earthing system and interaction with the surrounding environment is rarely taught in detail as part of an undergraduate engineering course. While there are a number of excellent commercial training courses available the gaining of experience for earthing engineers is necessarily dependent upon the business in which the engineer is employed, and the type of work undertaken by that business.

The aim of earthing system design should be that the investment is optimised to cost-effectively manage the risk profile of people, meet functional requirements, and enable the most critical aspects of the system be able to be supervised effectively and efficiently as part of an ongoing inspection and maintenance programme. This presentation will discuss examples of where an earthing system design has not managed to deliver a tolerable risk profile once installed as seen by the presenter over more than 40 years within a power utility and as a consultant. Examples include:

• How the assumptions that are made and the resultant analysis appear to accurately represent the performance of an earthing system but not identify the impact of key parameters that may vary with seasons, time of day, geographic location, or changes in power system operation. For instance, examples are given where soil resistivity testing has been inadequate and the impact on the final system performance significant.
• How identification of hazard scenarios may miss key conditions and how a staged approach to design and risk analysis may enable a designer to obtain a more robust understanding of which input parameters the performance of an earthing system is primarily dependent upon.
• How some parameters are difficult to characterise and the need for appropriate sensitivity analysis and/or different testing approaches during the design phase.
• How the application of risk quantification may misinterpret the actual situation and result in overinvestment and underinvestment in risk mitigation.
• How the installation process may not correctly implement the design as understood by the designer, or the designer require an installation that installers are not able to implement in practice.
• How a design policy may require a designer to use predefined boundary conditions regarding parameters such as fault levels, clearing times, interconnections and system configurations that result in impractical designs and significant overinvestment or poorly focused investment in managing earthing-related risk compared to other hazards for which an asset owner is responsible.
• How experienced designers may miss key considerations or opportunities due to overconfidence in the application of outdated design and installation approaches.