Leader propagation models of ultrahigh-voltage insulator strings based on voltage/time curves under negative lightning impulses at high altitude

Abstract

Lightning protection analysis is the foundation of estimating the lightning protection behaviors of transmission lines. The lightning flashover criteria of insulators/gaps are an important part of such analysis. One lightning flashover criterion of an insulator/gap is the leader propagation model recommended by CIGRE; however, this model does not consider altitude or longer gaps/insulators (>5 m). In this paper, the 50% disruptive-discharge voltage U50% and 50% voltage/time curve for an air gap of 7.1 m configured by a composite V-string and composite I-string of 7.1 m were measured under negative lightning impulses at the National Engineering Laboratory for Ultrahigh-Voltage Engineering Technology (Kunming), at an altitude of about 2100 m. The insulator types and configurations are similar to those used in the +800kV Ultrahigh-voltage Direct Current (UHVDC) power transmission project. The experimental result shows that the 50% disruptive voltage U50% of the V-string is 7% higher than that of the I-string, and the best-fitting constants of the new leader propagation model of the V-string are different from those of the I-string. The two 50% voltage/time curves were compared with the voltage/time curves predicted by the leader propagation model recommended by CIGRE. The best-fitting constants in leader propagation models are proposed to be used for long air gaps of the V-string insulator and longer I-string composite insulator at high altitude. The new models are verified for a 1.9 m air gap in parallel with a 2.04 m composite insulator and 2.04 m I-string composite insulator.