Conductivity and space charge dynamics of XLPE samples during temperature cycling

Compression or press molding method has been widely used to create plates of polymeric material and characterize them. The method is based on melting granulates of polymer between two layers of protective film at high pressure and temperatures. Polyethylene terephthalate (PET) film has been utilized in many studies. In this paper space charge and conductivity have been simultaneously measured on press-molded samples. Two different XLPE samples were used; one prepared by PET and the other by aluminum (Al) as the press molding films. A pulsed electroacoustic (PEA) method was utilized to perform space charge measurements. To resemble the temperature conditions during type testing and qualifying DC cables, the measurements were done during temperature cycling. Based on the results, it was observed that the conductivity and electric field enhancement within the PET-pressed insulation was stronger than that of the Al-pressed one. In addition, the conductivity and space charge dynamics were also different. Such dynamics came to be visible by temperature cycling. Furthermore, there is a serious impact from the press molding film. This indicates that the choice of press film can lead to misrepresentation of the material properties.