Abstract: In recent years, forest fires caused by tree-line failures have occurred frequently both domestically and internationally. Forest fires have been triggered by external social factors, leading to frequent incidents of power transmission and distribution line tripping. This article focuses on the forest fire accident below a 10 kV distribution line. From the perspectives of social factors causing forest fires and tree-line failures causing forest fires, the impact of various extreme environments such as pure flames, tree line discharge, and post discharge fires on the surface traces of conductors is considered. Through a distribution network fault simulation true type test platform, the surface morphology changes of conductors under extreme environments are experimentally studied, and the fire traces, first and second traces of tree wire discharge are obtained. Based on macroscopic, microscopic, and image feature extraction methods, the characteristics of various types of traces were analyzed, and a method for identifying single discharge traces of tree lines was found. The research results indicate that the discharge marks are on the one hand, the tree line arc directly erodes the wire, and on the other hand, the arc indirectly transfers carbon slag to the surface of the wire to form carbon black marks. When the tree-line failure did not cause a forest fire in the early stage, there was only first discharge trace on the surface of the wire. Under the same conditions, the discharge from the pine tree caused the most significant change in the weight of the wire, which could increase by 0.59 g. After the forest fire caused by the last stage tree-line failures, the burn marks will cover the discharge marks and form secondary traces. After wiping the surface traces, it was found that the grayscale surfaces of the first and second traces are similar, and the difference in fractal dimensions is less than 0.03.

Key words: electrical forest fires, tree-line failures, fire traces, discharge traces, fractal dimension