Abstract:In this paper, a comparison of positive streamer diffusion propagation is carried out in three configurations of oil transformers: mineral transformer oil, mineral oil with solid dielectric barriers, and a nanofluid. The results have been solved using a finite-element method with a two-dimensional (2D) axi-symmetric space dimension selected. Additionally, previous results from other research has been reviewed to compare the results obtained. As expected, it is confirmed that the nanoparticles improve the dielectric properties of the mineral oil. In addition, it is observed that the dielectric solid blocks the propagation of the streamer when it is submerged with a horizontal orientation, thus perpendicular to the applied electric field. The computer used, with four cores (each 3.4 GHz) and 16 GB of RAM, was not sufficient for performing the simulations of the models with great precision. However, with these first models, the tendency of the dielectric behavior of the oil was obtained for the three cases in which the streamer was acting through the transformer oil. The simulation of these models, in the future, in a supercomputer with a high performance in terms of RAM memory may allow us to predict, as an example, the best concentration of nanoparticles to retard the streamer inception. Finally, other dielectric issues will be predicted using these models, such as to analyze the advantages and drawbacks of the presence of dielectrics inside the oil transformer.

Nano-based dielectric fluids (NDF) seem to be a good alternative for improving dielectric and thermal characteristics of conventional liquid dielectric systems used in power transformers. Fe3Q4 (magnetite) nanoparticles (NP) is one of the most investigated type of NP. Sorne experiments have shown that with its addition to mineral oil (MO) and ester, increases in breakdown voltage (BV) can be achieved applying both AC and DC voltages. This kind of NP have the advantage that can be handled and synthesized safely and easily using a two-steps method. Resides, streamer propagation can be reduced or avoided introducing Fe3Q4 NP in dielectric fluids. These NP act as electronic traps and behave like slow-moving charged particles in the NDF. This behaviour as well as other dielectric characteristics such as resistivity, permittivity and loss tangent, depend on the type, size and concentration of NP. In this work, comparisons and analyses of thermal and dielectric performance ofNDF with different Fe3Q4 NP concentration are made taking into account the evolution and behaviour of streamers. It has been found that temperature in streamer tip, its length and speed depend on the Fe3Q4 NP concentration and the BV is affected because of changes in streamer speed. The most adequate concentration for controlling the streamer has been obtained through simulations and comparisons with experimental results showing good agreement.

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