Thermal Conductivity and Dielectric Characteristics of Transformer Oil Filled with BN and Fe3O4 Nanoparticles

The purpose of this paper is to investigate the influence of different types of nanoparticles on thermal and dielectric properties along with the relation between them. Boron nitride (BN) nanoparticles with high thermal conductivity and ferriferrous oxide (Fe3O4) nanoparticles as a typical magnetic oxide were dispersed into transformer oil to form different types of nanooil. Thermal and dielectric properties of the nanooil with different mass fractions were measured. Thermal conductivity and thermal diffusivity under different temperature were measured for each type of the nanooil in order to investigate the effect of nanoparticles on thermal property. Dielectric property experiments were performed in accordance with IEC standard. Relative permittivity, dissipation factor and electrical resistivity tests for the nanooil were conducted along with ac and dc breakdown strength in a range of temperature. It is found that both types of the nanooil showed improved thermal property compared with non-modified oil. The nanooil exhibits different performance in dielectric property due to the different properties of the nanoparticles. The obtained results show significant improvement in heat transfer process with increasing the mass fraction of BN nanoparticles while the oil modified by Fe3O4 nanoparticles shows considerable enhancement in dielectric breakdown strength. Through further comparison between the two types of nanooil, it is proposed that the improved thermal property contributes to the enhancement of the breakdown strength.