A review on the return stroke engineering models attenuation function: Proposed expressions, validation and identification methods

One of the most important and studied topics in lightning research is the development of suitable models for the return stroke current and electromagnetic fields. In particular, when dealing with the so-called engineering models, the definition of a function that expresses the attenuation of the current while flowing in the discharge channel (from now on, the attenuation function) is of crucial importance for a reliable computation of the lightning discharge electromagnetic fields and the resulting over voltages induced in a power distribution electric system. The paper contributes to such topic in two ways: first of all, a review of all the well-known engineering models is presented, highlighting the definition of each attenuation function and comparing the models in terms of the resulting overvoltage induced on a typical distribution line. Secondly, an innovative idea based on the possibility of reconstructing the attenuation function starting from the measured electromagnetic fields is presented. The state of the art in this research line is outlined and the issues that are still open are presented. In particular the possibility of adopting the so-called regularization techniques to solve ill posed inverse problems to evaluate the current starting from electromagnetic fields is addressed analysing the available results and highlighting that, to the best of the authors knowledge, these techniques have never been applied with experimental data.