Analysis of Thermal Stability and Breakdown Characteristics of Cellulose Insulating Pressboard Modified by Nano-TiO2

The composite insulation system of oil-immersed pressboard is used as internal insulation for converter transformer. However, the thermal aging of insulating pressboard leads to the deterioration of its thermal stability during long-term transformer operation, which shortens transformer service life. In order to improve the breakdown characteristics of the cellulose insulating pressboard, the pressboards modified by 5wt% nano-TiO2 with 10 nm diameter were prepared. The accelerated thermal aging test under 130°C for conventional oil paper and nano-TiO2 composite oil paper were performed. Thermogravimetric analysis method was adopted to analyze the pyrolysis of oil pressboard under different temperatures. Weibull distribution model was used to calculate the breakdown voltage of the pressboards modified by nanoparticles. The results indicate that oil-immersed pressboard modified by nanoparticles has better thermal stability than the unmodified one, and the thermal stability of modified pressboard is gradually reduced with the increasing of thermal aging degree. Furthermore, the breakdown characteristic of pressboard modified by nano-TiO2 has been greatly improved. The research in this paper provides some guidance for the suppression method of oil-paper insulation during the thermal aging.