Nonlinear fillers in electrical insulating materials

Nonlinear composite dielectric materials can be formed through the inclusion of appropriate fillers in polymers. Depending on the type of filler used, the composite material can then possess either an electrical field-dependent conductivity (FDC) or an electrical field-dependent permittivity (FDP). These nonlinear properties can then be used for the purposes of electrical stress relief in insulation systems with divergent electric fields, reducing the intensity of highly stressed regions. FDC polymer composites are formed through the inclusion of narrow-band gap semiconductive fillers in a polymer matrix and can be used for electrical stress relief in both AC and DC applications. FDP materials on the other hand use ferroelectric fillers in polymers; however, the stress-relieving properties of these materials are only realisable under AC fields. The paper reports on the electrical characterisation of both of these stress-relieving materials, with the criteria required for them to function. The materials that have been studied in these investigations take the form of zinc oxide in epoxy resin and barium titanate in an acrylic resin, respectively. Improvements in thermal conductivity are also reported as a consequence of the introduction of these fillers