Study on thermal aging oil-paper & polymer insulation based on acid value test

Oil-immersed transformer is the main equipment of power system operation, whose insulation aging research has been a topic that deserves attention. In this paper, based on the self-developed thermal aging oven, the pure oil sample and those of 3 kinds of different oil-immersed material (paper, Polycarbonate, Polyester) were aged under three different temperature (90°C, 110°C, 130°C) for accelerated aging process. By using Metrohm 877 type automatic titrator, acid value of samples with different aging time will be tested. Results suggest that under the same aging temperature, acid value of oil sample increases along with aging time. Accordingly, the higher the aging temperature is, the larger the acid value of samples under the same aging time will be. Moreover, the increase trend becomes steep gradually as aging temperature increases. By comparison among different materials, we found that in 90°C/110°C aging process, the increasing rate of acid value of oil-paper sample is the fastest, which is followed by the PET, PC and pure one. Specifically, under the aging condition of 130 °C, the increase rate of acid value of oil-PC sample is the fastest, and that of the pure one is still the slowest.