الفهرس | Only 14 pages are availabe for public view |
Abstract of power transformers with small size and high voltage level is one of the challenge points in transmission and distribution networks. To achieve this point, transformer oil with high dielectric strength should be introduced. Therefore, it is important to enhance dielectric properties of transformer oil. Nanotechnologies have potential to be used in transformer industry in enhancing material properties which may lead to a compact design of transformer and a reduced manufacturing cost. This thesis is divided into two phases. In the first phase, a breakdown mechanism of nanofilled transformer oil is suggested. The suggested breakdown mechanism is based on nanoparticles motion through oil when exposed to an electric field. This motion comes due to the exerted forces on nanoparticles due to the attraction and repelling forces generated as a result of surface charges formation on nanoparticles surfaces when exposed to an electric field. The charge formation process comes due to polarization effect of nanoparticle atoms when an electric field is applied to the nanofilled oil. In our opinion, motion of nanoparticles through oil has a vital role in its breakdown phenomenon. To validate this point, a simplified theoretical model is adopted to show nanoparticles motion through oil when an electric field is applied. Considering this model, different parameters of nanoparticle materials are studied. These parameters are nanoparticle relative permittivity, nanoparticle size, applied electric field nature (DC or AC) and the frequency of the applied electric field. The theoretical findings are validated using experimental work. Hence, three nanomaterials (SiO2, TiO2 and CO) with different relative permittivities are added to mineral oil. Different concentrations are studied. Breakdown strength considering different filler loadings of the three materials is measured. The breakdown voltage of the base and nanofluids is measured according to ASTM D1816 standard. The results show that the theoretical findings can be used efficiently to discuss the effect of nanofillers on breakdown strength of nanofilled oil. In second phase, the effect of D.C. magnetic field on breakdown strength of nanofilled transformer oil is carried out. The evaluation is carried out with and without D.C. field. Two different nanoparticle types are evaluated considering magnetic (Fe2NiO4) and non-magnetic (ZrO2) nanoparticles. The adopted nanoparticle types have the same size of 50 nm. The evaluation of breakdown strength is carried out considering different nanofiller concentration levels. The results show significant improvements in breakdown strength of the nanofluids in comparison to the base transformer oil. Finally, the magnetic field is significantly affecting the breakdown strength of nanofluids considering the magnetic nanoparticles. |