Analysis of Overvoltage and Backflashover with Different Transmission Line Models

Most research on the lightning overvoltage and backflashover phenomenon caused by direct lightning strikes use EMT programs considering the J. Marti model to represent transmission lines. Additionally, Carson's equations are used to compute the earth-return impedance. However, these equations disregard ground displacement current and assume that soil electrical properties are independent of frequency. Due to these disregards, simulations can produce incorrect findings and possibly even skip backflashover into existing insulator strings. In order to carry out the study of lightning overvoltage and backflashover, a real overhead transmission line in 440 kV was analyzed, getting results that there is backflashover when using the Pettersson transmission line model, even in two phases. However, it does not occur when Carson and Nakagawa models are used in some cases of lightning. Furthermore, considering high values of electrical resistivity of the ground will increase the lightning overvoltage in the insulator string. For example, when this value increases from 1000 to 10,000 Ω.m, the lightning overvoltage increases by 249 %.