Analysis of overload induced arc formation and beads characteristics in a residential electrical cable

The process and mechanism of breakdown induced cable insulation exposed to conductor heating caused by overload were investigated. The time from the beginning of the overload to the occurrence of an electrical arcing event was measured. A mathematical equation between the average time of the initial breakdown and current was established for 220 VAC distribution systems. The phenomena in these experiments were captured with a high-speed camera. The times and durations of arcing events occurring repeatedly were documented throughout the whole process, which could present some information associated with the possibility of this fault to ignite combustibles. The formation process of breakdown was evaluated theoretically. The established mathematical equation to calculate the average time of the initial breakdown could be employed to predict the interval between overload occurrence and breakdown arcing. The formation process of arc beads was affected by the hot environment created by breakdown and insulation combustion. Kinds of metallographic microstructure of arc beads might be found during a test, such as dendritic segregation structure, equiaxed recrystallized grains, and cylindrical crystals. This work could provide basic data for determining the breakdown occurrence attributed to overload.