ALTERNATIVE POLYETHYLENE CROSSLINKING CONCEPTS FOR POWER CABLE INSULATION

Doctoral thesis, 2019

Today most of the energy consumed worldwide comes from non-renewable resources such as coal, oil and natural gas. Consequently, a vast amount of green-house gases is released into the atmosphere, contributing to global warming. Driven by the urgent need to reduce carbon emissions, we currently witness an accelerating shift from fossil energy sources to renewables. However, wind, solar and hydro power are most abundant in places far away from the end user, which necessitates the efficient transport of electricity over long distances. High voltage direct-current (HVDC) cables are a critical component of tomorrow’s power grids that seamlessly integrate green energy derived from renewable sources. HVDC cables are particularly attractive because they permit the efficient transport of power. To further reduce transmission losses the development of new insulation materials is necessary, which therefore receives considerable attention. Low density polyethylene (LDPE) is the most widely used material for high voltage power cable insulation. Typically, crosslinking of LDPE is necessary to prevent deformation of cables at elevated temperatures and under high load. Today LDPE is commonly crosslinked with peroxides, but the process releases by-products in the polymer mass which compromise the electrical properties of the cable. In order to remove volatile by-products from the insulation, cables must be degassed at elevated temperatures for several weeks, which is both time consuming and costly. Therefore, by-product free crosslinking concepts that mitigate the associated increase in electrical conductivity are in high demand. To avoid the by-products that results from peroxide curing, in my studies I explored alternative crosslinking concepts for LDPE based on click chemistry type reactions. In this thesis I demonstrate how click chemistry crosslinking of polyethylene copolymers is a promising alternative to peroxide curing, and that this technology can (1) be compatible with established cable production, (2) avoid the release of harmful volatile compounds and (3) provide the mechanical strength and low electrical conductivity required from the insulation material.