LEMP and ground conductivity impact on the direct lightning performance of a medium-voltage line

Abstract

• Assessment of the LEMP influence on direct lightning overvoltages of medium-voltage distribution lines of the type equipped with a shield wire and surge arresters. • Comparison between the results obtained by a 3D-FDTD method and the LIOV-EMTP code. • The LEMP contribution on the overvoltages across insulators increases with increasing values of the soil conductivity. • The appropriate modeling of the LEMP effects is important for the lightning performance assessment of the type of lines considered in this paper. In medium-voltage distribution lines equipped with a multi-grounded shield wire and with surge arresters installed along the line at relatively short intervals, lightning outages associated with indirect lightning are less frequent than those associated with direct ones. The protection for this type of distribution lines is therefore dependent on the response to direct strikes. This paper presents and analyses the response to direct lightning overvoltages of lines of such a type located over a lossy soil considering the influence of the lightning electromagnetic pulse (LEMP), which is typically disregarded in the calculation of overvoltages due to direct strikes. The calculation results, performed by means of a three-dimensional finite-difference time domain (3D-FDTD) method and of the LIOV-EMTP code, indicate that the voltage across the insulator is enhanced by LEMP effects. In addition, it is shown that the enhancement due to the LEMP increases with the increase of the soil conductivity value. The modeling of the LEMP effects is therefore important for the accurate assessment of the lightning performance of medium-voltage distribution lines of the type considered in this paper, even when direct strikes are considered.