Morphological improvement of the insulation for EHV XLPE cables by an additive

In order to reduce the insulation thickness of EHV XLPE (cross-linked polyethylene) cables, a method for improving the interfacial region between the insulation and the semiconducting layer through mixing an additive into the semiconducting layer has been developed. For the purpose of improving XLPE morphology near the interface, an additive mixed into the semiconducting layer is diffused into the insulation from the semiconducting layer during the high-temperature cross-linking process. This technique is called the interfacial diffusion method. In order to analyze the morphological effects of the insulation due to the additive and its dielectric characteristics, several types of XLPE specimens directly mixed with the additive at various concentrations were prepared. AC dielectric breakdown tests were carried out on disk specimens, and the modification of the insulation was analyzed by using analytical methods. It was clarified that the density of the amorphous portion, the lamella thickness, and the spherulite radius of the insulation increase with increasing additive content and that their average breakdown strengths are improved, but the Weibull strengths at low probability are not improved. The specimens to which the interfacial diffusion method was applied showed significant improvement with regard to breakdown strength at low probability