Non-linear fillers in electrical insulation

摘要

In unfilled polyester, and that filled with Al{sub}2O{sub}3, th( conductivity would appear to be Ohmic at low field strengths and SCL at high fields. With ZnO, however, its non-linear, semi-conducting characteristic changes the conductivity of the filled polyester at sufficiently high concentrations. At low concentrations the characteristics of the polyester dominate but for higher concentration there is a transition from SCL at low fields to tunnelling or Schottky emission across theinter-granular boundaries at high fields.The treeing tests are a practical demonstration of this phenomenon. Unlike Al{sub}2O{sub}3, which provides a barrier to tree growth due to its high adhesive bond and fracture toughness [8], ZnO provides an additional enhancement to tree resistance because of its non-linear properties and its ability to redistribute accumulated space charge.