ALTERNATIVE POLYETHYLENE CROSSLINKING CONCEPTS FOR POWER CABLE INSULATION

Abstract: We currently witness an accelerating shift from fossil energy sources to renewables driven by the urgent need to reduce carbon emissions. Wind, solar and hydro power is most abundant in places far away from the end user, which necessitates the efficient transport of electricity over long distances. Alternative grid designs are needed that complement high-voltage alternating current (HVAC) with high-voltage direct current (HVDC) cables. The most advanced power cable technology uses crosslinked polyethylene (XLPE) insulation, which is produced by peroxide crosslinking of low-density polyethylene (LDPE). However, peroxide crosslinking gives rise to by-products that compromise the cleanliness of LDPE and raise the electrical conductivity of the insulation material. Therefore, a by-product free curing process, which maintains the processing advantages and high electrical resistivity of LDPE, would considerably ease cable manufacturing and is therefore in high demand. This thesis introduces alternative concepts for the crosslinking of polyethylene that fulfil these requirements. In particular, the suitability of click-chemistry epoxy ring opening reactions for curing of an ethylene-glycidyl methacrylate copolymer has been explored. Three main concepts for by-products free cable insulation have been studied: (i) crosslinking of LDPE copolymers with low molecular-weight multifunctional curing agents, (ii) Lewis acid assisted crosslinking of LDPE copolymer formulations, and (iii) reactive blending of LDPE copolymers. After extensive characterization of the thermo-mechanical properties of the materials, as well as preliminary conductivity studies, it can be anticipated that the concepts introduced in this thesis are a viable, by-product free and sustainable alternative to peroxide-based crosslinking of polyethylenes.