Thermal Class of Natural Ester/Thermally Upgraded Kraft Paper Insulation System

Arrhenius life curves and the thermal class of the liquid-immersed transformer insulation systems was determined using sealed tube testing per IEEE Std C57.100 Rev. 2011. The insulation system evaluated in the present study is natural ester (MIDEL 1215) and thermally upgraded kraft paper (TUK). The method determines the thermal class of a new insulation system by comparison to a known reference system. It was found to be practical and efficient and resulted in thermal class of 137°C for the system under study. The Degree of Polymerization (DP) was determined after sealed tube testing at various temperatures and timelines. After these tests, the oil was analyzed for various parameters which are important for health assessment of transformer oil and are indicative of the rate of aging of oil. The acid number, moisture, viscosity, and dissipation factor of the oil increased and the Interfacial Tension (IFT) and Dielectric Breakdown decreased after sealed tube test exposure due to various aging processes such as oxidation and polymerization.