Effect of nanoparticles on the dielectric strength of aged transformer oil

Transformer is one of the most important components of electric system. Their remaining life largely depends on what degree the insulation has been degraded as a consequence of ageing. Based on our previous investigation, a new type of transformer oil-based nanofluids with TiO₂ semiconductive nanoparticles exhibit substantially higher AC and positive impulse breakdown voltage levels than that of pure transformer oil. In this paper, we present the investigation results of aged nanofluids, which have been subjected to accelerated aging condition of 130°C for 6 days. AC and lightning impulse breakdown voltage and partial discharge (PD) characteristics of oil samples were measured according to ASTM standard methods. It is found that AC breakdown voltage and partial discharge inception voltage (PDIV) of aged nanofluids can be increased up to 1.08 and 1.12 times compared with pure aged oil, respectively. Meanwhile, it is interesting to notice that the positive impulse breakdown voltage of aged nanofluid is increased by approximately 47% and the breakdown time is prolonged by as much as 76% compared to that of the pure oil. The significant improvement in insulating performance of nanofluid is interpreted in light of electron traps theory.