Failure cause analysis and prevention of subsea cable failures in a joint industry project (JIP CALM)

The joint industry project for cable lifetime monitoring was initiated by the author’s companies in collaboration with international industry partners to reduce subsea power cable failures and make offshore wind energy more reliable. The project consisted of four main tasks. For the first task, a highly secure environment to safeguard all received sensitive cable system failure data was used. In total more than 100 failure cases were analysed, comprising of both power cables and accessories. Every failure case was thoroughly analysed to isolate the main failure initiating component, classify the associated failure mechanism and provide recommendations. The results were analysed, anonymised, and released to the consortium to highlight the immediate risks and their prevention for submarine power cables throughout all life cycles. These results highlight key aspects requiring attention during the cable system design, manufacturing, installation, and operation stages to prevent failures. The second task is to develop and test a Fibre-Optic (FO) based sensing technology that continuously monitors the mechanical loading of submarine power cables to prevent failures throughout the lifetime, as were identified in the first work task. Finite-Element modelling (FEM) has been applied to verify the unambiguous sensor response to critical parameters such as minimum bending radius, axial strain and twisting, as well as sensor integrity. Available FO read-out technologies have been investigated and their accuracy and response time were practically verified up till 50km distance using a dedicated test
frame. The FO-sensor unit concepts are under production and will be integrated in a submarine power cable and undergo full scale testing, in collaboration with the industrial participants. The third task focusses on the assessment of seabed and its importance for submarine cables. Sand wave dynamics is key importance for both the submarine cables. Significant advances have been made in applying a 3D morphological model for a sand wave field. It results in better understanding of the driving
forces and predictions for future seabed levels and associated uncertainties relevant for cable burial assessments. Using smart algorithms and satellite imagery, heat maps have been generated showing nearshore seabed dynamics. The long-term morphological changes can affect cable burial and its thermal dynamics, for which a model is developed. This model is tested against DTS measurements. Finally, a cable routing tool is developed, which considers expected seabed dynamics in the design of cable routes. The fourth task deals with the cost and impact assessment of the proposed innovations in this project. To make a sound assessment of the impact of the innovations proposed, the team developed a detailed model of the cable installation process and validated it with real wind farm cases. The model makes use of a discrete event approach for simulation of the transport and installation logistics planning and cost, ensuring realistic estimates and a view on the spread in results considering the operational state of art and weather conditions. The impact of the innovations, including the developed FO monitoring system, will be assessed in comparison to a reference offshore wind farm case.