Study of the Thermal Degradation of Different Insulating Papers Impregnated with a Natural Ester

Insulating materials used in power transformers are being improved to meet the new requirements. It is necessary to study the performance of these new materials. In this work, three insulating papers, a thermally upgraded paper (TUK), a Diamond Dotted Paper (DDP), and a mixture of wood pulp and cotton paper (Grade 3), have been analyzed. Materials were impregnated with a dielectric sunflower oil and subjected to an accelerated thermal aging at 150 °C for a maximum of 5232 hours. Degradation of both the liquid and papers was analyzed through the measurement of the dielectric properties of oil, including dielectric dissipation factor (tan
$\delta$
), permittivity (
$\varepsilon$
) and resistivity, chemical properties of oil, as moisture content and acidity, and properties of paper, as the tan
$\Delta$
and the degree of polymerization (DP). Results showed that the TUK and DDP papers suffered a similar degradation, whereas the Grade 3 insulation was the most damaged. Also, the liquid insulation was more deteriorated when aged with the Grade 3 paper than with the other materials.