AC Creeping Flashover Characteristics of Oil-Paper Interface Caused by Floating Discharge Under Parallel Component

Floating discharge was a typical fault in oil-immersed power transformers. Test models used in previous research were primarily simple vertical components, mainly simulating the barrier area. However, in the actual operation of transformers, areas with parallel components (such as the angle ring region) were equally critical. While the creeping flash-over characteristics of parallel components had been relatively well understood, studies on creeping flashover of the oil-paper interface caused by floating discharge under parallel components were limited. To investigate the flashover characteristics and processes, this study designed a test model featuring multi-ring electrodes and copper sheet floating electrodes. AC flashover tests were conducted on insulating pressboard subjected to floating discharge. The results showed that, for creepage distances of 60- 80 mm, the flashover voltage increased linearly with the creepage distance, while the average failure field strength fluctuated slightly around 3.54 kV/mm. Using a combination of macroscopic and microscopic analysis, the distinct asymmetry of damage on both sides of the suspended electrode was characterized. Additionally, high-speed imaging recorded the flashover process, including streamer discharge, from both perpendicular and parallel perspectives of the pressboard. This study clarified the entire flashover process, which included the stream-er discharge stage, the through discharge stage, and the complete flashover stage. Through finite element modeling of the corresponding stages and analysis of the carrier generation mechanism during streamer discharge, the intrinsic relationship between pressboard trace characteristics and the flashover process was elucidated. Overall, these findings are helpful for understanding the development of floating discharge and creeping discharge process under parallel component