Comparative Research on DC Dielectric Properties of Crosslinked Polyethylene and Polypropylene Laminated Paper

As an important part of the DC Electric power transmission, high-voltage DC (HVDC) cables have been widely applied in long-distance transmission across the sea, wind power grid connection and island power supply. Compared to AC cables, DC cables have stricter requirements for insulation materials due to the strong dependence of conductivity on temperature and the space charge accumulation. Crosslinked polyethylene (XLPE) and polypropylene laminated paper (PPLP) are both polymer insulation materials, which have been applied to plastic HVDC cables and oil-paper HVDC cables, respectively. In the paper, the DC dielectric properties of XLPE and PPLP are tested and compared. Results demonstrate that the conductivity of XLPE exhibits stronger temperature sensitivity than that of PPLP at lower field strengths, while the temperature dependence of them has no obvious difference at higher field strengths. In addition, XLPE shows a higher DC breakdown strength than that of PPLP at room temperature, but the DC breakdown strength of XLPE displays a faster decay rate than that of PPLP with the increase of temperature. PPLP has superior DC breakdown characteristics than XLPE at high temperature. Furthermore, the space charge accumulation characteristics of PPLP are more severe than those of XLPE, which is attributed to the multilayer interface structure of PPLP. The paper can provide some guidance for the application of XLPE and PPLP in DC cables with higher voltage level.