الفهرس 
1. INTRODUCTIONOnly 14 pages are availabe for public view
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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.