Preparation and electrical properties of oil-based magnetic fluids

This paper describes an improvement in the preparation of magnetic fluids for electrical transformers. The samples are based on surface-coated maghemite nanoparticles dispersed in transformer insulating oil. Colloidal stability at 90 ° C was higher for oleate-grafted maghemite-based magnetic fluid, whereas decanoate and dodecanoate-grafted samples were very unstable. Electrical properties were evaluated for samples containing 0.80%-0.0040% maghemite volume fractions. Relative permittivity varied from 8.8 to 2.1 and the minimum value of the loss factor was 12% for the most diluted sample. The resistivity falls in the range of 0.7 - 2.5 × 10 10 Ω m , whereas the ac dielectric strength varied from 70 to 79 kV . These physical characteristics reveal remarkable step forward in the properties of the magnetic fluid samples and may result in better operation of electrical transformers.