Thermal evaluation of high-temperature insulation system for liquid-immersed transformer

High-temperature oil-paper insulation system offers an opportunity to improve the overloading capability of distribution transformer facing seasonal load variation. This paper describes the thermal evaluation of such system. The insulation systems evaluated comprised combinations of cellulose, TUK(thermal upgraded kraft paper), DMD (Dacron and PET laminates) and T910 (cellulose and aramid blended paper) with mineral oil and natural ester oil. The systems were evaluated for compatibility and aging tests at 130□, 150□ and 180□. The DMD aging shows quick degradation and delamination in mineral oil as compared to both TUK and the 910 paper. DMD aging in natural ester fluid is reduced vs. the mineral oil, but is quite variable depending on the source of laminate. The comparative results of the different insulation systems will help inform the development of a high-temperature system to meet Class B insulation system required for fluid filled transformer.