| Summary: | Dielectric liquids are widely used as electrical insulation industry area. Currently the insulating liquids which are typically employed in high-voltage (HV) systems are naphthenic mineral oils. However, stringent environmental protection regulations encourage operators of HV equipment to use more environmentally friendly liquids. There is also a strong demand for the development of industry which requires insulating liquids provide advanced dielectric properties. Natural and synthetic esters are considered as potential substitutes for traditional mineral oils due to their environmental friendly properties. Meanwhile a new approach to the modification of dielectric properties of insulating liquids has been introduced which is based on the addition of ultra-fine particles (with sub-micrometre dimensions) to insulating liquids (nanofluids). There are a number of published papers reported that nanfluids provide better thermal and breakdown properties than those of base liquids. However the full understanding of the breakdown properties of nanofluids is not completed. The comprehensive study of breakdown properties of nanofluids is required. In this thesis, the breakdown properties of mineral oil, ester, and nanofluids based on these liquids, developed using titanium dioxide (TiO₂) and boron nitride (BN) nanoparticles have been investigated. Nanofluids were prepared with various concentrations. The experiments have been designed and preformed: AC breakdown voltage, lightning impulse breakdown voltage, lightning impulse pre-breakdown time, and DC pre-breakdown current. The experimental results show that nanofluids with low concentration provide higher breakdown voltage as compare with those of base liquids. There is an ‘optimal’ concentration, nanofluids provide the highest AC, impulse breakdown voltage, and longest impulse pre-breakdown time as compare with those of other tested liquids. The measurement of DC pre-breakdown current in base liquids allowed calculation of the field distribution in liquids. As the pavement for further investigations, several potential mechanisms of nanoparticle influence on breakdown properties of nanofluid have been compared and discussed.
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