Effects of TiO 2 Nanoparticle Size on Dielectric Properties of Transformer Oil

A lot of efforts have been made to increase the dielectric properties of transformer oil, which is of significance to the safe operation of power system. However, there has been lack of experimental evidence that the size of nanoparticle has an effect on dielectric properties of transformer oil, which is helpful for better functional design of transformer oil-based nanofluids. Therefore, it is necessary to investigate the effects of nanoparticle size on dielectric properties of transformer oil in order to better understand the effect mechanism of nanoparticles. In this paper, an experimental study was conducted on the effects of TiO2 nanoparticle size on dielectric properties of transformer oil. Nanofluids (NFs) were prepared by dispersing three types of TiO2 nanoparticles with size of 5nm, 10nm and 15nm into the pure oil by stirring and ultrasonic treatment. Basic dielectric properties, such as permittivity, dielectric loss were tested. Moreover, breakdown strength were measured under AC stress. It is indicated that the dielectric properties of transformer oil are significantly influenced by the nanoparticle size. The permittivity of nanofluid is increased with the decrease of nanoparticle size in nanofluid. Whereas, the addition of nanoparticles dramatically increases dielectric loss. Moreover, as the decrease of nanoparticle size in nanofluid, AC breakdown voltage of nanofluid is significantly increased. In nanofluid containing the smallest nanoparticles, the AC breakdown voltage is 2.1 times as great as that of pure oil. The improvement can be contributed to the faster charge. The increased specific surface area of nanoparticles introduces more traps with the decrease of nanoparticle size in oil, resulting in a faster charge dissipate. Thus, the dielectric properties of transformer oil are improved by the decrease of nanoparticle size.