Assessing electrocution risks in transmission substations using probabilistic criteria

The following work investigates the risk of electrocution from earth potential rise at transmission substations and nearby third party locations as a result of a power system earth fault. Current earthing standards use a deterministic approach where the risk assessment considers a set of worst-case conditions. However, it is recognised that most of the parameters involved in calculating the earth potential rise and associated safety voltages are probabilistic by nature. A probabilistic technique has been developed to determine the risk of electrocution of an individual under power system earth fault conditions. The so determined individual risk can be compared with accepted health & safety risk levels, employing the ALARP principle (as low as reasonably practicable). This paper presents improvements to the developed probabilistic technique by introducing defined risk zones with specific probability of presence and introducing exclusion zones where there is virtually no touch voltage risk. The improved technique is applied to a practical case study electrical installation.