Introduction: Previous involvement with international earthing committees has resulted in the recognition and acceptance of a probabilistic risk based approach to earthing system design and assessment. The confidence gained from National Grid to support this approach was as a direct result of previous research that reviewed local fault levels and fault clearance times against site earth potential rise seen under fault conditions.

Objectives: The project addresses the issue of safety and risk assessment of earthing systems. It uses a probabilistic risk assessment approach to quantify the risk involved at large substations. The model developed in this project takes into account the detailed configuration of the earthing system and the surrounding area, and it uses historical fault data. The model can be adapted to any set of standard specification and perform the risk assessment accordingly. A friendly software routing is being developed and tested to help engineers implement the model on practical substations.