AC Dielectric Strength of Mineral Oil-Based Fe₃O₄ and Al₂O₃ Nanofluids

Abstract

This paper deals with experimental study of the influence of conductive (Fe3O4) and insulating (Al2O3) nanostructured particles at various concentrations on the dielectric strength of transformer mineral oil. The method of preparation and characterization of these nanofluids (NFs) through the measurements of zeta potential, the real and imaginary parts of dielectric constant as well as the concentration and size of nanoparticles using Scanning Electron Microscope (SEM) images of nanoparticles powders and Dispersive x-ray Spectroscopy (EDS) analysis are presented. Experimental findings reveal that these two types of nanoparticles materials significantly improve AC breakdown voltage and the magnitude of this improvement depends on the concentration, size and nature (material) of nanoparticles. For a given type of nanoparticles, the effect is more marked with the smallest nanoparticles. The conductive nanoparticles offer higher enhancement of dielectric strength compared with insulating nanoparticles based nanofluids. With Fe3O4, the breakdown voltage (BDV) can exceed twice that of mineral oil and it increases by more than 76% with Al2O3. The physicochemical mechanisms implicated in this improvement are discussed.

Statistical Investigation of AC Dielectric Strength of Natural Ester Oil-Based Fe3O4, Al2O3, and SiO2Nano-Fluids

“…It appears from the experimental results that from the point of view of dielectric strength, natural ester oil based-Fe 3 O 4 , Al 2 O 3 and SiO 2 nano-fluids are not so interesting as is the case with mineral oil and synthetic ester with the same nanoparticles. Indeed, the improvement is too weak compared with the results obtained with mineral oil or synthetic ester [21], [22]. It does not exceed 7%, with the investigated nanoparticles.…”

“…Therefore, and unlike mineral oils and synthetic esters for which the additions of some specific nanoparticles (especially Fe 3 O 4 ) improve significantly the breakdown strength, there is no unanimous conclusion about the effect of nanoparticles on natural esters. It is therefore difficult to propose a mechanism that could explain the variation (increase/ decrease) of the dielectric strength of natural esters -based nanofluids, as has been the case for mineral oils and synthetic esters -based nanofluids [21], [22] in which case a mechanism of trapping electrons by nanoparticles or of slowing the development/propagation of streamers were evoked.…”

“…Contrary to mineral oil and synthetic ester -based nanofluids where the improvement of AC breakdown voltages was very interesting when adding Fe 3 O 4 , magnetic/ conducting nanoparticles, the enhancement of natural esterbased nanofluids is less important. Indeed, for the same kinds of nanoparticles (Fe 3 O 4 , Al 2 O 3 and SiO 2 ), the best improvement of mineral oil is obtained with Fe 3 O 4 , nanoparticles at a concentration of 0.4 g/L; it can exceed twice that of pure mineral oil [21]. For synthetic ester, namely MIDEL 7131, the best improvement is of 50%; it is also obtained with the same type of nanoparticles (i.e.…”

“…Nanoparticles were supplied by Sigma-Aldrich; their purity is about 99.9%. To check the distribution of particles (homogeneity), their shape and their composition at atomic percentage, similar methods and techniques as in previous works, were used [21], [22]. This includes particle size analyzer (NanoPlus, Particulate Systems -USA), scanning electron microscope (SEM) images and energy dispersive X-ray spectroscopy (EDS) analysis.…”

“…From SEM images, one observes that these nanoparticle powders are more or less spherical and regular as shown in Figure 1; and the EDS analysis evidences the presence of each sample composition at an atomic percentage ( Figure 2). Similarly, the natural ester-nanofluid samples were prepared in the same way as described elsewhere [21], [22].…”