Effects of Ferromagnetic Nanoparticles and Fluorination on Breakdown of SiR/Fe₃ O₄ Nanocomposites in High Magnetic Field

High magnetic field causes premature failure of insulation. In order to improve the breakdown strength of silicone rubber (SiR), different filler contents of ferroferric oxide (Fe3O4) nanoparticles were added. Experimental results show that 1 wt% addition amount of ferromagnetic nanoparticles is beneficial to improve the AC breakdown strength of SiR by 5.40% in 12 T magnetic field due to their ability to regulate dielectric polarization and partial discharge (PD) behavior, resulting from the relative higher permittivity and permeability of Fe3O4. Magnetization of Fe3O4 nanoparticles results in 3.33% decrease of DC breakdown strength with 2 wt% filler content in 12 T magnetic field. Fluorination treatment was carried out and proved to be able to improve the DC breakdown strength of SiR/Fe3O4 nanocomposites by 8.84% in 12 T magnetic field with the treatment time being 5 minutes, resulting from the regulation of surface traps. Fluorination treatment weakened the magnetism of nanoparticles, weakening their regulation on insulation polarization and PD. Adding an appropriate amount of ferromagnetic nanoparticles before the fluorination of SiR/Fe3O4 nanocomposites can improve the AC and DC breakdown strength by 0.64% and 8.81% respectively at the same time in high magnetic field.