Mechanically prestressed composite dielectrics and improvement of electrical tree growth resistance

Studies have been made of the retardation of electrical tree growth in epoxy resin specimens using experimental pre-stressed reinforcing fibers. These develop an initial compressive stress/strain in the resin structure, which they are reinforcing. It is shown to be feasible by this means to retard effectively the electrical tree growth of a growing tree in point-plane laboratory specimens tested at room temperature and subjected to a high alternating current voltage. The time of electrical tree growth is significantly longer than that observed in un-reinforced specimens subjected to the same voltage amplitude. The effect of fiber pre-stressing on residual mechanical stress distributions in the resin matrix is examined quantitatively. The physical mechanisms by which electrical tree growth may be retarded in prestressed systems are discussed. The main conclusion drawn from the present investigation is that the mechanically prestressed composite dielectrics, achieved by the cast-in of fibers in tension into epoxy resin, is a reliable technology for increased electrical insulation integrity.