Kai Yi

Preparation of Three Types of Transformer Oil-Based Nanofluids and Comparative Study on the Effect of Nanoparticle Concentrations on Insulating Property of Transformer Oil

Nanofluids have the potential to become the alternatives of conventional transformer oil for their exquisite electrical and thermal properties. Three kinds of nanoparticles with distinct conductivities, namely, nonconductive nanoparticle Al2O3, conductive nanoparticle Fe3O4, and semiconductive nanoparticle TiO2, with different concentrations from 5% to 40% w/v were selected and suspended into transformer oil to develop nanofluids. The lightening impulse breakdown strengths of the oil samples with and without nanoparticles were measured according to IEC standard methods. The positive impulse breakdown strength indicated that breakdown strength is first increased up to the maximum value at certain concentration and then starts decreasing. The results of negative impulse breakdown manifested that the breakdown voltages of nanofluids with different concentrations were less than the breakdown voltage of pure transformer oil. Different effect mechanisms of dielectric and conductive nanoparticles were also used to describe the difference among three prepared nanofluids.

Effect of TiO 2 nanoparticles on streamer propagation in transformer oil under lightning impulse voltage

Recent experiments have shown that some nanoparticles can influence the breakdown strength of transformer oil under lightning impulse voltage. To reveal the working mechanism, this paper presents an experimental study on the effect of TiO2 nanoparticles on the impulse breakdown strength and prebreakdown streamer propagation process in transformer oil-based nanofluid under both positive and negative lightning impulse voltage. The test results verify that the modification of nanoparticles on breakdown strength of transformer oil has a distinct polar effect: positive breakdown voltage of nanofluid is increased by up to 30.8%, whereas the negative one is decreased by 6.8%. Streamer shape, propagation length and velocity in both pure oil and nanofluid were investigated using the shadowgraph technique. It is revealed that the propagation characteristics of positive and negative streamers in nanofluid are markedly affected by the addition of TiO2 nanoparticles. The positive streamers in nanofluid form a bush-like structure with thicker and denser branches, developing much slower than tree-like streamers in pure oil. While negative streamers in nanofluid have a tree-like shape with much longer branches, propagating faster than the original bush-like streamer in pure oil. These differences in streamer propagation characteristics and breakdown strength in pure oil and nanofluid are closely related to the change of space charge distribution caused by shallow trap in nanofluid. More negative charges are formed through capturing fast electrons into slow electrons in shallow traps induced by the presence of TiO2 nanoparticles, which change the local electric field in front of the streamer tip. Thus, streamer propagation process in nanofluid is dramatically modified, leading to the change in breakdown strength.

Preparation and breakdown properties of mineral oil based alumina nanofluids

Transformer oil-based nanofluids were prepared by suspending non-conductive Al2O3 nanoparticles to enhance the insulating properties of transformer oil. Breakdown voltages under positive and negative lightening impulse voltages were measured for all the prepared samples according to IEC standards. The results indicated that the inclusion of Al2O3 nanoparticles to the base oil can modify the breakdown strength of the base oil. The results showed that addition of alumina nanoparticles improve the mean lightening impulse breakdown voltages of nanofluids and were 1.09 times as compared to base transformer oil but not the negative lightening impulse breakdown strength. A possible mechanism of insulative nanoparticles was also used to explain the difference among nanofluids and base oil.

Effect of Oleic Acid Surface Modification on Dispersion Stability and Breakdown Strength of Vegetable Oil-Based Fe3O4 Nanofluids

Well-dispersed Fe3O4 nanoparticles were prepared and modified by oleic acid at the temperature of 70°C for different reaction times. The surface modification of oleic acid could improve dispersion stability of Fe3O4 nanoparticles in vegetable oil by forming an effective chemisorbed modification layer on the surface of nanoparticles. The interaction between coordination pattern and mass faction of chemisorbed oleic acid on nanoparticles and dispersion stability of nanofluid was discussed. The optimal dispersion stability of vegetable-oil based Fe3O4 nanofluids was obtained to the nanoparticles modified for 8 hours, which has the highest AC breakdown strength of 67.78 kV.

Effect of Fe 3 O 4 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.

Preparation and study of breakdown features of transformer oil based magnetic nanofluids

Nanofluids were developed by suspending conductive nanoparticles (Fe3O4) to improve the dielectric properties of transformer oil. The AC and lightening impulse breakdown voltages were measured for prepared samples in accordance to IEC standards. The results menifested that the addition of conductive nanoparticles (NPs) to the mineral oil can improve the mean AC breakdown performance 1.16 times of that for carrier oil approximately. Additionally, for nanofluids, the mean lightning impulse breakdown voltages were also enhanced than that of base transformer oil and were 1.36 times in comparison to host oil. A possible mechanism of conductive nanoparticles was also used to describe the difference among the performance of nanofluids and base oil.

Fabrication, characterization, and insulating property of Fe3O4 nanofluids

ABSTRACT Monodisperse Fe3O4 nanoparticles modified by oleic acid were synthesized by a solvothermal method and dispersed into mineral transformer oil to prepare Fe3O4 nanofluids. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis indicated that the obtained nanoparticles are single crystals with an average diameter of 15 nm. The test results indicate that the nanoparticles exhibited good dispersibility in the nanofluids at a wide range of concentrations. Moreover, the positive impulse breakdown strength of nanofluids was greatly improved by 36.6% at the optimum concentration of nanoparticles.

Breakdown characteristics of transformer oil based silica nanofluids

A fluid consisting of nano-sized particles is known as nanofluid. It manifests better cooling abilities compared to the host fluid. The aim of this study is to analyze the AC and impulse breakdown strength of mineral oil based SiO2 nanofluids (NFs). The volume fractions used was 20%. The influence of moisture on AC breakdown strength was investigated. Moreover, the positive and negative impulse breakdown strength was measured and compared with pure oil. The positive lighting impulse breakdown voltages indicated an enhancement as compared to pure oil where the measured negative impulse breakdown voltages of nanofluids were lower than the host oil. The modification mechanisms of nanoparticles on breakdown properties of mineral oil were also discussed.

Effect of Fe 3 O 4 nanoparticle concentrations on dielectric property of transformer oil

Nanoparticles have the potential to enhance the insulation conduct of transformer oil. The concentration of nanoparticles influences the breakdown vitality of mineral oil. In this investigation, mineral oil based nanofluids were prepared by scattering magnetic nanoparticles into transformer oil with different concentrations from 5% to 80% w/v. The AC and lightning impulse breakdown strengths of the oil samples with and without nanoparticles were investigated in accordance with IEC standard methods. The test outcomes indicate that addition of magnetic nanoparticles can enhance the insulation strength of transformer oil. With the increase of nanoparticle concentrations, the AC and positive impulse breakdown strength of transformer oil are first increased and up to the maximum value at the concentration of 40%. After which the breakdown strength start decreasing. The result of negative impulse breakdown showed that the breakdown voltage of nanofluids with multiple concentrations were lower than the breakdown strength of pure transformer oil. The probable modification mechanisms of Fe3O4 nanoparticles on dielectric features of transformer oil were also reviewed.

Effect of SiO 2 nanoparticle on insulating breakdown properties of transformer oil

Nanoparticles have manifested the potential to enhance the breakdown performance of transformer oil. The AC and positive lightening impulse breakdown strengths of the oil samples with and without nanoparticles were measured according to IEC standard methods. The test results indicate that addition of silica nanoparticles can enhance the ac breakdown strength of transformer oil. Additionally, the mean lightening impulse breakdown voltages of prepared nanofluids were also enhanced than that of base transformer oil. Possible modification mechanisms of SiO2 nanoparticles on breakdown properties of transformer oil were also discussed.