Preparation of a vegetable oil-based nanofluid and investigation of its breakdown and dielectric properties

Investigations during the last decade have shown that conductive nanoparticles can be dispersed in transformer oils to form nanofluids. Well-dispersed nanoparticles are capable of increasing the breakdown voltage of the oil under power frequency and lightning impulses. They also increase the inception voltages for partial discharge [1]. With increasing moisture content, reduction of the breakdown voltage of the nanofluid at power frequency is significantly smaller than that in the corresponding transformer oil [1]. The electrical and thermal properties of four types of nanofluid, prepared by dispersing Al2O3, Fe3O4, SiO2, and SiC nanoparticles in transformer oils, were described in [2]. It has also been reported that the thermal conductivity of such oil was enhanced by 8% when aluminum nitride nanoparticles were dispersed in it at a loading of 0.5% by weight, and its cooling capability was improved by about 20% [3]. An electrodynamic model has been developed describing streamer formation in transformer oil-based nanofluids, which presents generation, recombination, and transport equations for each charge carrier type [4]. Vegetable insulation oils are based on natural ester oils, which are environmentally friendly and fire resistant [4]–[9]. At the moment, little is known about the preparation of nanofluids using natural ester oils and their dielectric, breakdown, and aging properties. Surface modification of nanoparticles is a very effective procedure to avoid nanoparticle agglomeration in insulating nanofluids [10]–[14]. However, the surface modification procedures used for mineral oils cannot be applied to vegetable oils because of their very different molecular structures. We therefore investigated new approaches to the preparation of vegetable oil-based nanofluids. This paper presents some of the results of a study of the breakdown voltages and dielectric properties of a vegetable oil-based nanofluid. The nanofluid was prepared by dispersing Fe3O4 nanoparticles in a vegetable insulation oil obtained from a laboratory at Chongqing University. Oleic acid was used for surface modification of the nanoparticles.