Nonlinear characteristics of filled resins under alternating fields

Previous attempts to introduce a degree of nonlinear conductivity into polymeric insulating materials, and thereby to achieve stress relief under nonuniform or impulse conditions, involved the use of zinc oxide as a filler. This technique produced a field dependent conductivity in the filled composite and was advantageous under dc and impulse conditions. Most solid insulation, under normal service conditions, is however subject to alternating voltages. Stress relief in this instance is more likely to be achieved by introducing field dependent permittivity rather than field dependent conductivity. This paper describes a successful attempt at producing a composite polymeric material that exhibits field dependent permittivity by introducing barium titanate as a filler in polyester resin. The effect of filler concentration levels on the degree of field dependent permittivity has been investigated.