What are the chances of that? a primer on probability and poisson processes for earthing designers

Earthing design methodologies based around risk are growing in importance as they provide a better way to allocate limited resources and funding. Appropriate application of these processes requires the earthing engineer to have a sound comprehension of probability theory, upon which the processes are built. This paper reviews the basics of Poisson processes and the statistical methods and probability distributions used in their analysis. Examples and explanations are provided of how Poisson processes are used in the context of earthing, including lightning protection, to model the occurrence of power system faults and interactions with the general public. Particular attention is given to some counter-intuitive aspects that may lead a designer, ignorant of the subtleties of probability theory, to draw incorrect conclusions, potentially resulting in over-engineering or even irresponsible designs.