Abstract: The height of the distribution network line is low, and the surrounding trees are easy to lap up with the line to form a Tree-contact Single-phase-to-ground Fault (TSF), which can lead to fire in severe cases. An important feature of TSF is the formation and development of charring channels on the surface of branches. Observing the morphology of the carbonization channel can qualitatively judge the fault process, but it still lacks a quantitative relationship corresponding to the electrical characteristic quantities of TSF. Based on this, this paper simulated TSF on a 10 kV experimental line, and studied the leakage current, combustion image and temperature distribution in the whole development process of TSF by means of electrical parameter measurement, high-speed camera and infrared temperature measurement, and established the correlation between the qualitative characteristics of carbonization channel development form and the quantitative parameters of leakage current. The results show that the TSF can be divided into five stages according to the leakage current development characteristics: the initial development stage of the carbonization channel, the horizontal development stage, the vertical development stage, the suppression stage and the ignition/stop stage. Combined with the current waveform and high-speed camera image, the development form and cause of the carbonization channel in each stage were analyzed in detail. The results show that there is a stage correlation between the change trend of the leakage current and the development process of the carbonization channel. The resistance U-shaped curve in the fault process was analyzed, and the main cause came from the time difference between the development of the carbonization channel and the water evaporation. The research results can provide theoretical reference for the identification and monitoring of TSF.

Key words: carbonization channel, equivalent resistance of tree branches, leakage current, Tree-contact Single-phase-to-ground Fault