Experimental Aging of Three-Element Mixed Oil Insulation and Pressboard for Power Transformer Applications

Mixed oils have become the focal point of research on insulating oils for transformer applications due to their superior dielectric properties. The study utilizes the compositional advantages of fatty acids (FAs) to develop a three-element mixed oil (TEMO). TEMO is created by blending methyl esters from 20% punga oil (MEpo) and 10% neem oil (MEno), along with 70% olive oil (NEoo) in its original state. In this instance, 0.1 g/L of chitosan (CN) was introduced to stabilize the resulting blend. TEMO underwent aging in accordance with IEC 62 332–2. The ultraviolet spectrophotometer (UVS) at 232 nm is used to determine the free water activity (aw) of TEMO. A consistently low aw during temperature elevation indicates TEMO’s resistance to aging. The primary oxidation byproducts (primary peaks at 232) are utilized to measure the oxidation variations in the samples. The alterations in kinematic viscosity and interfacial tension of the oil samples demonstrate an inverse correlation. The results indicate that TEMO, at its optimal ratio, exhibits Newtonian behavior and enhances the credibility of the findings. Due to fewer ester linkages, TEMO has a higher fire point than MO but generally lower pour points than other NE-based samples. The iodine index (IOI) and molecular weight (MW) are interconnected, with a decrease in MW leading to a reduction in IOI. By increasing the proportion of nondrying oil in TEMO, particularly NEoo, the degree of unsaturation causing the oil to solidify is significantly reduced. Pressboard aged in TEMO (=5508.081) shows similar hardness to MO (=5416.814) based on the texture profile analysis (TPA) test. This is attributed to the stabilization of reactive OH content in PB impregnated with TEMO while controlling H+ ions. The TEMO peak on PB samples closely aligns with the virgin PB crystalline peak and relative crystallinity (Crel) as per X-ray diffraction (XRD) analysis, indicating the integrity of PB in TEMO. Fourier infrared (FTIR) analysis is used to assess the vibrations in the OH and C = O peaks. The C = O alterations observed in PB aged in TEMO are closely linked to the ability of the methyl group present in TEMO to inhibit oxidation. A direct comparison between TEMO and MO reveals that TEMO promotes environmental sustainability by enhancing oxidation prevention.