In recent years, the accumulated research evidence in our group has demonstrated that the addition of mechanically prestressed fibers in epoxy resin will strengthen the microstructure and therefore improve the electrical insulation strength of the epoxy resin by increasing the electrical tree growth resistance. In this paper, a comparative study of the effect of some different design concepts on mechanically prestressed insulation is presented. Calculations of the effect of prestress in the resin and the optimized design for the composite insulation are based on fundamental stress analysis. The electrical treeing test results from prestressing specimens with multiple unidirectional and orthogonal fibers clearly demonstrate the beneficial effect of mechanical prestress and that enforced compressive stresses in the resin by optimized prestress design can significantly increase the electrical tree growth time to failure and therefore improve the electrical insulation.
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