AC and DC Dielectric Breakdown Characteristics of Fluorinert Liquid and Fluorinert-Paper Composites

Oil-paper composite insulation is widely used in power transformers; however, the flammability and explosiveness of its insulation oil, along with its environmental unfriendliness and maintenance difficulties, pose significant technical challenges today. This paper selected an environmentally friendly liquid with excellent insulation performance, fluorinert liquid (FC-40), and investigated its fundamental physicochemical properties and AC/DC breakdown characteristics. Based on this, a new composite insulating material of fluorinert-paper composites (Nomex) was prepared by vacuum impregnation for 48 hours, and the AC and DC breakdown properties of composites insulation materials were investigated, and the breakdown characteristics of insulation liquid and composite insulation were statistically analyzed using the Weibull distribution. The research results indicate that the AC and DC breakdown field strength of the fluorinert-paper (Nomex) composites insulation material is significantly higher than that of the fluorinert liquid. The DC breakdown field strength of the composite insulation is higher than the AC breakdown field strength. The breakdown field strengths of the fluorinert-paper (Nomex) composites insulation material and the oil-paper composites insulation are similar under both AC and DC conditions. Additionally,the breakdown dispersion of the fluorinert-paper composites insulation is smaller than that of the oil-paper composites insulation. The analysis suggests that fluorinert-paper composites insulation exhibits lower dielectric constant and loss, along with excellent breakdown performance (similar to oil-paper composites insulation), making it a promising candidate for application in transformers.