Search

Transformer oil-based nanofluids with TiO2 semiconductive nanoparticles exhibit substantially higher AC and positive impulse breakdown voltage levels than that of pure transformer oils. Thermally stimulated current method (TSC) and pulse electroacoustic technique (PEA) have been used to measure charge trap and transportation characteristics of pure oils and nanofluids. It is found that electron shallow trap density and charge decay rate are greatly increased in nanofluids, i.e., fast electrons may be converted to slow electrons by electron trapping and de-trapping in shallow traps of nanofluids, resulting in improved breakdown performance compared to that of pure oil. [ABSTRACT FROM AUTHOR]

Recent studies have found that the surface flashover strength of oil-impregnated insulation paper can be improved by the modification of nanoparticles. To reveal the working mechanism, this paper presents an experimental study on the effects of TiO2 nanoparticles on streamer propagation process at the surface of oil-based nanofluid-impregnated insulation paper under lightning impulse voltage. The results show that the surface flashover voltage of nanofluid-impregnated insulation paper is significantly increased by 34.6%. Streamer characteristics including shape and length at the surface of oil-impregnated insulation paper were investigated using the schlieren technique. It is indicated that streamer characteristics are dramatically changed by the addition of TiO2 nanoparticles. For nanofluid-impregnated insulation paper, streamers with more but much shorter branches tend to develop into adjacent nanofluid rather than clinging to the paper compared to that for pure oil-impregnated paper. The reason responsible for the shape dissimilarity lies in the change of electrical force due to the permittivity difference between oil and paper. Furthermore, more shallow traps introduced by nanoparticles contribute to the faster surface charge dissipation of nanofluid-impregnated paper, reducing the charge accumulation at the streamer head and suppressing the electric field distortion. Thus, it is hard for streamers to develop at the surface of nanofluid-impregnated paper, resulting in an increase of surface flashover strength. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

TiO2 nanoparticles can improve the electrical performance of oil paper insulation. In this study, 10 nm TiO2 nanoparticles were prepared and dispersed into transformer oil, and then immerse pressboards in it to obtain nanofluid impregnated pressboards (NP). Its thermal aging was accelerated together with the reference sample at 130°C for 36 days. Analyzing the acid value in the oil, polymerization degree, surface topography, AC breakdown strength, surface flashover characteristics and surface potential decay characteristics. It was observed that TiO2 nanoparticles can reduce the acid value and improve AC breakdown strength of oil. However, the degree of polymerization and surface appearance of NP and oil impregnated pressboards (OP) during thermal aging did not differ significantly. During the aging process, the energy level of pressboard surface traps shifted first towards the shallow and then gradually towards the deep. During all the aging stages, the surface flashover voltage of NP was always higher or close to that of OP. The mechanism of TiO2 nanoparticles improving the breakdown and surface flashover characteristics of oil–paper insulation during thermal aging is discussed from the perspective of water molecules and aging by‐products adsorption and introduction of shallow traps by nanoparticles. [ABSTRACT FROM AUTHOR]