The effect of composition and processing on electric characteristics of XLPE for use in HVDC cable applications

Polyethylene exhibits many key characteristics including low dielectric loss, high breakdown strength and good processability. Most modern extruded high voltage cables employ cross-linked polyethylene (XLPE) as the insulation material. The main advantage of XLPE is its excellent thermo-mechanical properties; it is relatively cheap and has low dielectric loss and low conductivity making it an ideal material for this application. Crosslinking enhances a number of thermo-mechanical properties such as deformation resistance at higher temperatures, tensile strength and creep properties. In comparison with low density polyethylene (LDPE), the heat deformation characteristics of XLPE are superior and, for this reason, XLPE is currently the most common insulation material for power cables ranging from low to high voltages. This paper reports on an investigation into the development of a new XLPE formulation for use in high voltage direct current (HVDC) cable applications. Specifically, the electrical performance of two novel LDPE resins are compared with an industrial standard (reference) LDPE material. For crosslinking, dicumyl peroxide (DCP) was selected, as the decomposition temperature is high enough to prevent pre-curing during processing and to allow an efficient and rapid crosslinking at moderate temperatures. Moreover, the behavior of various systems is compared in terms of electrical breakdown performance and the influence of material composition and processing on these parameters is described.