EFFECT OF BARRIERS ON TREE GROWTH IN SOLID INSULATION

The effect of the inclusion of particulate barriers in point-plane sam ples of polyester resin is investigated. The increase in lifetime as t he 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 stra in can be reduced by annealing or by destroying the adhesive bond betw een particle and resin. A similar discovery had been made with the inc lusion of woven fibre barriers having a range of mesh size and thread diameter. When aluminium oxide particles are added to the fabric barri ers, the resistance of the fabric to treeing is greatly enhanced. In a ddition to the improved treeing resistance, the addition of aluminium oxide also increases the thermal conductivity of the insulation, allow ing higher equipment ratings to be achieved.