High voltage traction transformer of electric train demands reliable transformer oil with good heat transfer properties. Anyhow thermal stress due to high temperature initiates premature thermal ageing that deteriorates the properties of transformer oil even after multiple purification process. Influence of silicon dioxide (SiO 2), aluminium oxide (Al 2O 3) and titanium oxide (TiO 2) nanoparticles on treating purified aged transformer oil (PATO) has been addressed in this study. Oil samples were collected after validation process using colour condition standards. Each nanoparticle was suspended in the aged oil using magnetic stirrer and ultrasonic bath at 0.1% volume concentration. Stability analysis was conducted using photo capturing and zeta potential analyser method. Thermal conductivity and viscosity were investigated from temperature range of 30°C to 70°C. Based on the experimental results, PATO-based SiO 2 nanofluid was chosen as no sedimentation detected even after 144 hours with zeta potential value of 71.83mV. Thermal conductivity of PATO was enhanced up to 20.83%. Besides that, the suggested nanofluid obeys Newtonian fluid law with the viscosity enhancement up to 6.7%. On the other hand, it was found that the properties of PATO were improved with the suspension of SiO 2 nanoparticles, thus helps railway industry to optimize the life span of transformer oil.

Presence of water content or moisture promotes premature thermal aging which hampers the properties of inhibited, isoparaffinic transformer oil used in electric multiple unit (EMU) train. Unpurified aged oil with high water presence is collected from the traction transformer and contaminants is removed using Double-Stage Vacuum Insulation Oil Regeneration Filtration Machine to produce purified aged oil. New transformer oil is selected as a control sample. The objective of this study is to investigate the effect of oil purification process on the thermal conductivity and breakdown voltage of the oil samples. Thermal conductivity measurement was done from temperatures of 30°C to 70°C. Dielectric characteristics are shown by analyzing breakdown voltage. Unpurified oil shows an increment from 1.54% to 3.13% as compared to new oil in response to temperature variation whereas purified oil has the lowest thermal conductivity value. However, breakdown voltage of purified oil is higher than unpurified oil and slightly lower than new oil. From this, it can be inferred that presence of water gives positive impact towards thermal properties and vice versa to dielectric properties. A relationship between thermal conductivity, breakdown voltage and presence of water has been deduced at the end of the study.