Epoxy based high permittivity nanodielectrics for electric stress mitigation

In this work, we investigate the possibility of using nano-sized fillers in conventional polymeric insulating materials to obtain a high permittivity nanodielectric in order to mitigate field stress. In this work, Barium titanate (BT) fillers are used in an epoxy (Bisphenol A) polymer matrix. The average BaTiO₃ nanoparticle diameter is 90 nm. Specimens with various filler contents up to 5% by volume are studied. The nanoparticles used are either unmodified or surface treated with 3-glycidoxypropyltrimethoxysilane (GPS). The preparation of nanocomposite has a marked effect on their eventual properties, so it is important to ensure that there is a proper dispersion of the nanophase material. The specimens are thoroughly examined under FESEM (Field Emission Scanning Electron Microscopy) in order to verify homogeneity of particle dispersion. Dielectric breakdown strength, permittivity and conductivity are measured. Dielectric permittivity measurements are performed using an LCR meter. An electrometer, with a built in voltage source, is used to measure dc conductivities of the specimens, from polarization and depolarisation current measurements. Analysis of the measured data indicates a small increase in breakdown strength of nanodielectrics with silane-coated nanoparticles compared to those with the as-received nanoparticles. Preliminary results indicate improvement in permittivity at the higher volume fractions. Conductivity is seen to increase with increasing field for all specimens.