Improvements in the electrical and mechanical strength of pre-stressed insulation

The mechanical pre-stressing of electrical insulation has been achieved by the inclusion of aromatic polyamide fibres under tension in polyester and epoxy resins, in a manner akin to that employed in the prestressing of concrete. On completion of the owing process and subsequent removal of the external tensile stress, the fibres are found by Raman spectroscopy to retain their tensile stress and impart a balancing compressive stress to the surrounding resin. Previous work has demonstrated that electrical treeing is accelerated by tensile stress and retarded by compressive stress. The compressive stress in our prestressed samples follows this earlier work and the resistance to electrical treeing is found to increase as mechanical pre-stress is introduced. As an additional benefit, it has been found that the tensile strength of the samples is enhanced by the introduction of the fibres. This is of great importance where the electrical insulation is a structural component of a system and is required to sustain mechanical loading