Effect of barriers on tree growth in solid insulation

The effect of the inclusion of particulate barriers in point-plane samples of polyester resin is investigated. The increase in lifetime as the particle size was increased is found to be only indirectly related to the particle size. The increase in lifetime is found to be due to a layer of compressive strain at the resin/barrier interface. This strain can be reduced by annealing or by destroying the adhesive bond between particle and resin. A similar discovery had been made with the inclusion of woven fibre barriers having a range of mesh size and thread diameter. When aluminium oxide particles are added to the fabric barriers, the resistance of the fabric to treeing is greatly enhanced. In addition to the improved treeing resistance, the addition of aluminium oxide also increases the thermal conductivity of the insulation, allowing higher equipment ratings to be achieved