DC Creepage Flashover Properties on Overlapping Structures of Pressboards in Transformer Oil

The growing use of DC transmission systems necessitates a better understanding of DC insulation characteristics in oil-filled transformers, particularly at AC/DC converter stations. This study investigates DC creepage flashover characteristics using model samples that simulate overlapping structures of oil-immersed pressboards (PBs) with oil gaps. The DC flashover voltage was measured with varying oil gap distances and PB overlapping lengths. Transient finite element analysis was performed to simulate potential distributions during flashover, enabling quantitative interpretation of the experimental results. The results suggest that the DC breakdown electric field and potential difference exhibit trends similar to AC characteristics but are approximately 40% lower in magnitude. These findings provide valuable insights for insulation design and are expected to contribute to the development of reliable and compact high-voltage oil-filled transformers for DC power transmission applications.