Dissolved Gas Analysis of Thermally Aged Mineral Oil and Vegetable Oil Based Nanofluids

Mineral oil (MO) is widely used as insulating liquid in transformers. However, environmental impact, reducing availability of petroleum resources and issues with disposal of used oil; vegetable ester oil (VO) is being considered as potential replacement of MO. However, with the adoption of ultra-high voltage AC and DC power transmission systems; there is a need for liquid insulator with superior electrical and thermal properties. In recent times, evolution of nanotechnology has prompted research work on MO and VO based Nano fluids (NFs) suitable as liquid insulators. Though the NFs are superior in electrical and thermal properties compared to their base fluids, further studies are needed to establish their stability to thermal and electrical stresses and applicability of existing fault diagnostic tools. In this study MO, VO, MO/VO mixture (1:1) and their NFs of 0.01% Al2O3 and 0.01% SiO2 were subjected to accelerated thermal ageing at 150°C for 168 hours in presence of Kraft paper and copper wire in sealed glass bottles with Argon blanket. Dissolved Gas Analysis (DGA) was conducted as per IEC 60567 on all the samples after ageing. The DGA result showed variation in gas concentrations in MO, VO and MO/VO mixture. Presence of nanoparticle was observed to affect the quantity of gas generated. The concentration of gases generated in MO and its NFs were relatively less compared to VO and its NFs. Gas analysis was carried out using conventional ratio techniques, Duval Triangle and Duval Pentagon for establishing suitability of diagnostic techniques applicable to various oils.