Improved flashover prediction for overhead lines: Considering ground stratification and insulation volt-time characteristics

Abstract

This paper presents an approach to accurately forecast the yearly occurrence of flashovers caused by lightning-induced voltage in overhead power lines in the presence of layered ground. The aim is to improve the accuracy of flashover rate estimation by using the insulator volt-time model. In particular, two-layer horizontal ground structures are considered. A 3D finite element method is used to calculate induced voltages and a Monte Carlo simulation is applied to determine the annual flashover rate. Volt-time insulator characteristics are used to identify the flashover condition. The results are compared with those obtained by using the standard 1.5 times the critical flashover (CFO) threshold criterion. The results indicate that the conventional 1.5 times the CFO criterion may underestimate the rate of flashovers, particularly in regions with horizontally stratified soil, as the volt-time method offers a more accurate presentation of the flashover process. Furthermore, the effect of upper soil depth, upper soil conductivity, pole spacing, and different flashover distance calculation techniques on flashover rates are analysed. This paper presents a new mathematical formula for estimating yearly flashovers based on the results obtained by the volt-time method in the presence of stratified ground. The derived analytical formula provides an insightful tool for power system engineers to evaluate the lightning performance of overhead lines and implement efficient mitigation strategies.