Fracture failure analysis of a lightning rod on a substation frame considering residual thermal stress

Abstract

The collapse of a typical lightning rod on a 500-kV high-voltage substation frame in central China is investigated to identify the mechanism of fracture. Comprehensive analyses are performed on the fracture morphology, metallurgical structure, chemical composition and mechanical properties of the materials at the fracture site. A finite element (FE) model of a typical lightning rod structure with an intersecting joint weld is developed and verified using experimental results. Based on the FE results and wind tunnel tests, the fatigue life is estimated for the lightning rod structure at the accident site considering residual stress. The results indicate that the fracture failure of the typical lightning rod structure is mainly caused by wind-induced fatigue damage in the weld area of the intersecting joint of the rod base and the frame beam. The welding residual stress has a severe impact on the fatigue life of the structure. Regardless of the welding residual stress, the actual fatigue life of the typical lightning rod structure under a long-term wind load is lower than the design service life. Therefore, complete analysis of the structure under complex wind-induced dynamic effects is needed in engineering design. Additionally, attention should be given to the quality control of the welding, and measures should be adopted to reduce residual stresses during manufacturing and installation.