Improvement in electrical insulators by nonlinear fillers

The addition of a nonlinear filler in the form of particulate zinc oxide to insulating materials has been found to produce a marked nonlinear conducti vity in the resulting composite. While retaining its excellent insulating p roperties at low electric fields, this composite material acquires a measur e of conductivity at high fields. The paper investigates the influence of t his phenomenon on a number of characteristics of insulating materials, spec ifically. bulk conductivity, surface charge dissipation, electrical treeing and tracking. Models have been developed for simulation of the effects of adding the nonlinear filler to polyester resin. A. good correlation exists between the theoretical models for surface charge dissipation and treeing r esistance, modified to incorporate the nonlinear characteristic, and experi mental data derived from polyester resin containing a range of concentratio ns of zinc oxide. For tracking, a contrary result was obtained which has be en attributed to changes in the: mechanical characteristics of the filled m aterial. An improvement in the dissipation of surface charge and treeing re sistance has been demonstrated without loss of the material's insulating pr operties under normal electric fields.