Study on Relationship between Cumulative Discharge Energy and Discharge Marks on Pressboard under High Field Strength

The insulation field strength of the UHV transformer is close to the design limit, which leads to the continuous increase of the working field strength of the oilpaper insulation structure. In order to explore the correlation between the development of PD and surface discharge marks on pressboard under high field strength, this paper used an extremely uneven electric field with a strong vertical component to study the development process of discharge marks and PD parameters under high field strength. The research found that PD under high field strength could cause serious damage to pressboard, resulted in white marks, spark discharge channels and carbonized marks. Based on the discharge repetition rate and discharge energy, the PD could be divided into three stages named initial stage, fast extension stage and near breakdown stage respectively. The development of cumulative discharge energy and the growth of carbonized mark have the same law in three stages.