To acquire new knowledge of pollution flashover mechanism of insulators, the mechanical characteristics of local arc propagation on suspension insulators surface during AC and DC pollution flashover are analyzed in this paper. The results indicate that the propagation of local arc mainly depends on the electrostatic force and thermal buoyancy. The thermal buoyancy plays a leading role in the bigger arc current, resulting in the obvious phenomenon of arc wandering. Moreover, the effect of thermal buoyancy on AC arc is less than that on DC arc at the same arc current. DC arc wandering is more significant than that of AC. With the decrease in air pressure (the increase in altitude height), the effect of thermal buoyancy rises. As a result, it will cause severe arc‐levitating at high altitudes, making the flashover distance of insulators less than its creepage distance. Therefore, the arc‐levitating is one of the key factors for the decrease in flashover voltage of polluted insulators in high‐altitude regions.

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