Predicting lifetime of dynamic cables for floating marine energy harvesting platforms

Forskningsprojekt, 2024 – 2025

It is the common vision that future energy system will be fossil-free and will be based on distributed renewable energy sources integrated into the power grid. A large share of green electricity is expected to be produced offshore by wind, wave and tidal energy. To utilize the most efficient conditions in the sea (strong ocean currents, steady unidirectional wind, etc.), electricity production facilities can be installed on mobile platforms that allow to relocate them to desired geographical locations. Such solutions become increasingly popular for wind power production. Harvesting electric energy from floating generating sites is implemented by means of networks of submarine power cables, which are used as links between platforms and for connections to the shore. In the existing installations, cables from individual generators and interconnecting cables operate at voltages up to 36 kV AC. Cable failures are among the most frequent failure modes of offshore renewable energy farms. Thus, statistics shows that ca 80% of offshore wind installations in the UK experienced cable-related incidents which have led to the downtime of the wind farms and the yearly loss from these events has been determined to be around £22.8 million/year. Electrical insulation of modern submarine cables is made of highly resistive polymers, such as ethylene propylene rubber (EPR) or cross-linked polyethylene (XLPE), which are designed to meet the requirements of static bottom-fixed wind farms, wave or tidal energy plants. However, dynamic cables for floating structures run through the water column from the generator platform to the seabed. This exposes the cables to the dynamic forces produced by marine currents and movements of waves, which cause premature fatigue resulting in a great risk of cable failure. Present knowledge about insulation ageing and degradation under such conditions and involved physico-chemical processes is pure empirical. Therefore, the overreaching goal of the research is to identify physical mechanisms of failures in dynamic high voltage cables and to develop computer models for predicting cables’ lifetime. This is crucial for preventive maintenance and thus for enhancing the reliability of the floating energy generation sites. The goal will be reached by combining experimental studies of electro-mechanical ageing of cable insulation with theoretical analysis based on computer simulations.