Analysis of transformer insulation systems with dielectric nanofluids

Résumé

A number of authors have reported that the dispersion of small concentrations of nanoparticles may improve the dielectric and thermal properties of insulating oils. Extensive experimental work has been published reporting large improvements in the dielectric strength of these fluids compared with the properties of the base liquids. However, even if those materials enhance the dielectric properties of conventional liquids, there are serious concerns about their applicability to real transformers in the future. The main difficulty is related with the long-term stability of the liquids at transformer service temperatures. This factor would only be improved if multidisciplinary research teams cooperate in the development of nanofluids which remains stable in the long term. Another critical aspect is related with the interaction of nanofluids with other elements of the transformer, and the impact that they might have on the properties of these materials. In this field, the study of the interaction between nanofluids and transformer solid insulation is specially relevant. However only a small number of works have studied the topic up to date. This PhD. Thesis carries out a research to get insight on the interaction between dielectric nanofluids and transformer’s solid -insulation. An analysis on the morphological characteristics of nanofluid-impregnated paper was conducted that confirms the penetration of nanoparticles in the cellulose structure. Then several dielectric properties were investigated, including the dielectric strength and the polarization processes in nanofluid-impregnated solid insulation. Finally, the impact of the nanoparticles on the transformer ageing process was studied, to understand how the chemical reactions that lead to the degradation of solid materials on the transformer changes when the impregnation liquid is a nanofluid. Research on nanodielectric fluids for transformer insulation is still a new field of study and these materials are still far from being of application to real transformers. The development of comprehensive studies, as the one presented in this Thesis, may contribute to the advance of this technology and to the promotion of new applications for these materials in the future.