Effect of Fe3O4 nanoparticle size on impulse breakdown strength of mineral oil-based nanofluids

Insulating oil modified by nanoparticles (NPs), which is often referred as nanofluids (NFs), has the potential to evolve into substitute of conventional transformer oil for their excellent electrical and thermal characteristics. They have attracted huge attention recently, particularly concerning the improvement of electrical breakdown. This paper develops a relationship that how sizes of NPs affect the positive and negative breakdown voltage. To be more specific, three sized monodisperse Fe3O4 nanoparticles i.e. 10nm, 20nm and 40nm were prepared and subsequently dispersed into insulating mineral oil to develop NFs with 40% W/V concentration. The lightening impulse breakdown strengths of oil samples with and without suspension of NPs were measured in accordance to IEC standard methods. The positive impulse breakdown strength manifested that breakdown strength is first increased up to a maximum value at certain size and then decreased. The results of negative impulse breakdown indicated that breakdown voltage of NFs with different sizes were less than the breakdown voltages of pure transformer oil. Possible modification mechanism of Fe3O4 nanoparticles on insulating properties of transformer oil is also discussed in this paper.