Thermal aging properties of pressboard in mineral oil and natural ester

This article aims to contrastively study the thermal aging characters under different temperature between natural ester and mineral oil-pressboard insulation system. The thermal aging experiment was conducted with copper flat bars together in a sealed stainless vessel at 130 °C for 80 days, and at 100 °C for 220 days separately. Some basic physicochemical and electric characteristics of oil and cellulose varied with aging time, including moisture content, acid value, viscosity, furfural content, dielectric loss, AC breakdown voltage of oil, and the degree of polymerization were tested at each scheduled aging time. Results showed that the value of moisture content and dielectric loss in natural ester were higher than that of mineral oil, but it had a better insulation strength and service life.