Transmission-Lines Shielding Failure-Rate Calculation by Means of 3-D Leader Progression Models

In this paper, by creating a 3-D model of power-line equipment and lightning leader progression models, an alternate procedure for calculating the shielding failure rate (SFR) of transmission lines is presented. The stepping nature of lightning downward leader is modeled according to field observations with the use of discrete line charges approaching the earth. A simplified self-consistent model for an upward connecting leader is also adopted to find the position of lightning incidence to the transmission line. The required electric field in an environment is computed by using the charge simulation method. A comparison has been made between the SFR calculated by proposed method and the values calculated by conventional electrogeometrical model. In addition, different previously proposed incidence criteria are implemented and compared. Some comparisons are also made between the calculated SFR and available field data for selected overhead lines.