DP and dielectric characteristic research of polymer materials under high temperature in mineral oil

Power transformer is one of the most important power transmission equipments in the power system. The reliability and operational efficiency of power system is directly related to its performance and quality. The insulation paper used in oil-immersed transformer cannot resist high temperature, and the significant difference of dielectric constant between the insulation paper and the transformer oil will lead to the unevenness of electric field. These two shortcomings limit the capacity and lifetime of transformer. So, it is very significant to explore new polymer materials that can replace insulating paper to improve electric field distribution and insulation structure. In this paper, two kinds of high-temperature resistance polymer materials-Polycarbonate (PC) and Polyester (PET) are chosen as the candidates to comparison with paper. They are put in the transformer oil with electrical-thermal aging for 300 days under 90°C, 110°C and 130°C respectively. The tests of the dielectric constant and degree of polymerization (DP) are studied to estimate whether they can be used in oil-immersed transformer.