Sustainable transformer insulating nanofluid from reclaimed waste cooking oil and MWCNTs for oil–paper aging applications

Growing demand for sustainable transformer insulating fluids has motivated the development of biodegradable alternatives to mineral oil. This study investigates reclaimed waste cooking oil (RWCO), produced through transesterification, as a transformer insulating fluid enhanced with multi-walled carbon nanotubes (MWCNTs). RWCO nanofluids containing 0.01, 0.05, and 0.1 wt% MWCNTs were evaluated for dielectric, thermal, oxidation, stability, and accelerated oil–paper aging performance. Among the formulations, 0.05 wt% MWCNT exhibited the best overall performance, with a 10.3% increase in the dielectric breakdown voltage, 16% higher thermal conductivity, and 50% improvement in the oxidation stability compared with those of RWCO, while maintaining excellent colloidal stability. Accelerated aging at 110°C and 130°C demonstrated lower moisture uptake, reduced acid formation, improved dielectric stability, and better preservation of Thermally Enhanced Kraft and Nomex 910 insulation papers. These results indicate that the optimized RWCO–MWCNT nanofluid is a promising biodegradable and sustainable transformer insulating fluid with enhanced thermal and dielectric performance, offering a viable alternative to conventional mineral transformer oil.