Evaluation of solid insulating paper properties aged in natural ester and mineral insulating oil

Abstract

This study was carried out in order to evaluate properties of new insulating paper (Hybrid paper or HP, aramid/cellulose composite) and thermally upgraded kraft paper (TUK) during ageing at 165 and $185 ^{\circ}\text{C}$ in natural ester (NE, corn-based oil) and mineral insulating oil (MIO). Results will be complementary to a detailed and critical study to determine Arrhenius life curve for the liquid immersed transformer insulation system composed of NE and MIO in combination with TUK and HP. Accelerated ageing tests were carried out in laboratory for the HP, according to IEEE C57.100 standard, revised in 2011. Tests were conducted with MIO and with NE. A commercially available TUK paper was used as a reference, which was subjected to the same test condition. In this study, preliminary paper properties observed in TUK/NE, TUK/ MIO, HP/NE, HP/MIO insulation systems at temperatures of 165 and $185 ^{\circ}\text{C}$ are described. Degree of polymerization (DP), tensile testing and infrared analysis were performed on aged papers. HP presented a better performance in relation to TUK, in both oils. Furthermore, in NE slower degradation was observed for both papers at 165 and $185 ^{\circ}\text{C}$. Infrared spectroscopy analysis of aged papers showed that there was no transesterification reaction in both papers aged in insulating liquids (NE or MIO).