At present, transformer protection usually operates after failures. With the raise of voltage level and capacity of transformer, a fault easily becomes an accident, resulting in huge economic losses. Transformer insulation failure is the main cause of transformer accidents. In this paper, a new idea of transformer protection based on insulation critical breakdown prediction is proposed. According to the requirements of transformer protection, a prediction method of oil-paper insulation critical breakdown under DC voltage based on partial discharge analysis is proposed by studying partial discharge characteristics of oil-paper insulation defects under DC voltage and the development process. The results show that when partial discharge critical breakdown occurs in oil-paper insulation under DC voltage, the distribution of partial discharge lagging recovery time is concentrated, and dense discharge clusters are easy to form, which can be used to predict the critical breakdown of oil-paper insulation.

transformer protection,oil-paper insulation,critical breakdown,partial discharge,DC voltage