AC Creeping Flashover Characteristics with Floating Discharge Over Long Distance (>75 mm) of Oil / Pressboard Interface

Floating discharge is a typical fault type of oil-immersed power transformers. Current research mainly simulates the floating discharge fault in the barrier board where the normal electric field component is dominant, and has mastered its partial discharge characteristics. For the angle ring with creep stress, its creeping flashover characteristics with floating discharge are unclear. Therefore, this paper designs an test model based on the multi-grading ring electrode structure, carries out the AC creeping flashover test with floating discharge, and records the flashover process. For the AC creeping flashover test with floating discharge of insulating pressboard with a creepage distance of 100 mm and a floating electrode width of 25 mm, the failure electric field strength is 3.13 kV/mm, which is much smaller than the flashover failure field strength of defect-free insulating pressboard under a slightly uneven field. The carbonized tracking of the pressboard and the high-speed photography images both confirm that the streamer discharge starts from the floating electrode and then develops towards the two side electrodes. The reason is that the electric stress at the “triple junction“ of the floating electrode-pressboard-oil is as high as 5.66 kV/mm, which far exceeds the allowable surface field strength, inducing the start of the streamer discharge. In general, this paper initially reveals the AC creeping flashover characteristics with floating discharge, and provides new insights into the whole process of floating discharge causing creeping flashover of insulating pressboard.