Effect of Mechanical Strain on Water Treeing Mechanism of Dynamic Cable for Floating Offshore Wind Applications

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Offshore wind energy is central to UK's ambition of transitioning to a sustainable future electricity grid. The growth in power generation from floating wind turbines are increasingly further away from shore and utilising the floating wind turbine support structures. This increases the mechanical strain the cable is subjected to, which is enhanced further by in-service oscillatory movement caused by tidal and wave motion. It is unknown whether low frequency physical oscillations in cable structures pose an intrinsic reliability risk since conventional land cables are typically installed in relatively benign environments. Typically, cable assets contribute to 5-10% of the total investment costs for an offshore wind farm. However, cable failures cause the majority of the offshore power outages and account for approximately 80% of insurance claims in this industry. This project will investigate the effect of varying mechanical strain on the water treeing mechanism in dynamic cable and model the ageing of such design under representative test conditions. A bespoke water treeing test rig with varying mechanical strain will be developed and to be tested under different parameters. A series of small-scale experiments will be initially carried out to investigate the impact of steady state and low frequency mechanical oscillations on the characteristic change in water tree growth. This is to determine whether cycling of mechanical strain accelerates water tree initiation and growth processes. Thereby, potentially increasing the risk of failure for dynamic cables.