Nexans (Norway)

Floating wind energy presents a significant opportunity to harness vast wind resources that remain inaccessible with current bottom-fixed offshore wind technology. However, transmitting electricity from floating turbines to shore relies on dynamic cables, which face technological and knowledge gaps, contributing to higher costs compared to conventional static subsea cables. Although dynamic cables have a strong operational track record, their transmission capacity and voltage have been limited. To enable commercial floating wind developments, these limitations must be significantly improved—specifically, by achieving voltage levels comparable to those used in today's bottom-fixed offshore wind farms. Subsea cable costs are largely driven by material usage, particularly the conductor. Aluminum, which is significantly cheaper than copper, is widely used for static cables but has seen limited implementation in dynamic cables due to concerns about its fatigue strength and mechanical properties. Enabling the use of aluminum, alongside reducing conductor cross-sections through increased voltage, is essential for lowering the cost of floating wind electrical infrastructure. Another key opportunity lies in increasing the voltage capacity of dynamic cables. Recent advancements in dynamic dry cable designs have made 145 kV (Umax) achievable, with 245 kV (Umax) rapidly approaching qualification. Additionally, shifting to a wet 145 kV (Umax) design offers significant cost-saving potential. However, increasing voltage levels in wet designs presents challenges, particularly when combined with aluminum, as it introduces new failure modes such as stress-induced electrochemical degradation (SIED). This study explores strategies to optimize aluminum for improved conductivity and fatigue resistance while also evaluating its viability in wet cable designs. The objective is to bridge knowledge gaps related to this specific design approach, paving the way for cost-efficient electrical infrastructure solutions for floating wind.

Abstract Dynamic cables play a critical role in floating offshore energy infrastructure such as needed for floating wind and electrification of oil and gas assets. Steel alloys used for cables, umbilicals and flexibles have seen a wide range of work on their mechanical properties combined with a substantial track-record. The same cannot be said for copper conductors for which only a few studies have been undertaken accounting for a limited parameter range. One parameter that should be studied further is the effect of intermittent creep damage due to the interplay between the conductors' mean stress and loading history under displacement-controlled deformation. New and existing copper fatigue test data are used to establish a mean-stress sensitive fatigue damage model. This is used to estimate the added damage from the relaxation phase, and allows us to compare displacement- and load-controlled tests and compile the data into a unified model. The effect of this model is then assessed in light of potential loading histories.

This research topic also delves into powertrain degradation and control. In Yaw Misalignment in Powertrain Degradation Modelling for Wind Farm Control in Curtailed Conditions, Moghadam et al. examine how yaw misalignment affects powertrain components and propose a damage-aware control framework for efficient power distribution within wind farms. This study highlights the integration of degradation metrics into farm-level control, demonstrating how digital twin models can simultaneously address efficiency and durability through advanced control strategies, and allow operators to make informed decisions about the power setpoints of individual turbines within large farms. Together, these studies represent a comprehensive approach to tackling the challenges of digital twin modeling for predictive maintenance in wind energy. They collectively address the three core layers of digital twin realization-data acquisition, dynamic model processing, and decision support-each layer contributing to a robust framework for optimizing turbine performance. As digital twin technology continues to mature, these contributions highlight the technical challenges and the immense potential of predictive maintenance, steering the wind energy industry towards a more sustainable and efficient future.

The ongoing legislative push to mitigate the environmental impact of strong greenhouse gases creates a need for liquid-filled High Voltage (HV) and Extra High Voltage (EHV) terminations. The exceptionally long expected lifetime of many such components requires that on-line condition monitoring is made available to the grid operator. In this paper, we present the design methodology, prototyping and testing of a removable multi-physics sensing unit and a custom, integrated PD sensing unit for HV/EHV liquid-filled terminations. The units were successfully tested in the HV laboratory using a 245 kV oil-filled termination.

S100A4 is a DAMP protein. S100A4 is overexpressed in patients with systemic sclerosis (SSc), and levels correlate with organ involvement and disease activity. S100A4-/- mice are protected from fibrosis. The aim of this study was to assess the antifibrotic effects of anti-S100A4 monoclonal antibody (mAb) in murine models of SSc and in precision cut skin slices of patients with SSc. The effects of anti-S100A4 mAbs were evaluated in a bleomycin-induced skin fibrosis model and in Tsk-1 mice with a therapeutic dosing regimen. In addition, the effects of anti-S100A4 mAbs on precision cut SSc skin slices were analyzed by RNA sequencing. Inhibition of S100A4 was effective in the treatment of pre-established bleomycin-induced skin fibrosis and in regression of pre-established fibrosis with reduced dermal thickening, myofibroblast counts, and collagen accumulation. Transcriptional profiling demonstrated targeting of multiple profibrotic and proinflammatory processes relevant to the pathogenesis of SSc on targeted S100A4 inhibition in a bleomycin-induced skin fibrosis model. Moreover, targeted S100A4 inhibition also modulated inflammation- and fibrosis-relevant gene sets in precision cut SSc skin slices in an ex vivo trial approach. Selected downstream targets of S100A4, such as AMP-activated protein kinase, calsequestrin-1, and phosphorylated STAT3, were validated on the protein level, and STAT3 inhibition was shown to prevent the profibrotic effects of S100A4 on fibroblasts in human skin. Inhibition of S100A4 confers dual targeting of inflammatory and fibrotic pathways in complementary mouse models of fibrosis and in SSc skin. These effects support the further development of anti-S100A4 mAbs as disease-modifying targeted therapies for SSc.

Scanning electron Microscopy (SEM) coupled with energy dispersive X-ray analysis (EDX) were used for qualitative and quantitative trace element analysis of inception sites of vented water-trees in a modern HV XLPE cable aged in salt water. The aim of this paper is to examine different methodologies based on SEM/EDX to identify localized high concentrations of ions responsible for the initiation and growth of vented water trees. Long vented water trees were observed initiated at the insulation and conductor screens with lengths larger than $600 \mu\mathrm{m}$ after 4 months of ageing at 500 Hz. The initial results presented in this paper indicate that measurements at the sample sub-surface only, are likely not sufficient to reliably detect the ions causing vented water treeing. The FIB - milling technique showed to be a promising technique.

A fundamental component of subsea power cables is the thin galvanized steel tape winded around the dielectric and sheathing layer in order to prevent permanent thermal cycling induced deformation. The pressure state induced by the resistance offered by such tapes against radial reformation reduces the triaxiality ratio of the stress state of the lead sheathing layer. It is known that a reduced triaxiality has a beneficial effect on ductility and fatigue life of metals. In the present work a series of finite element simulations are performed in presence of galvanized steel tapes at three different winding angles and without such reinforcement at all, obtaining a qualitative indication of its effect on the stress state induced in the sheathing layer. Loading conditions as internal pressure related to thermal dielectric expansion and cable bending are modelled. The numerical qualitative results are discussed in connection to a series of full-scale fatigue tests performed on subsea power cables with and without the support of steel tapes.

One of the challenges with cables in deep waters is the high topside tension caused by the weight of the cable and the risk of overloading the conductor. Keeping the cable weight as low as possible is therefore a key parameter to reach deep waters. One way to reduce the cable weight is to replace the copper conductor in the cable with an aluminium conductor. When using aluminium conductor in a wet design XLPE cable (no water barrier) there is a risk of local corrosion of aluminium that forms porous structures in the inner semiconductor, leading to accelerated ageing of the XLPE insulation. This phenomenon is known as Stress-Induced Electrochemical Degradation (SIED). SIED has so far only been seen in service-aged cables, which had been exposed to external mechanical damage causing water penetration in the conductor. It has also been found that the deterioration of the inner semicon is more severe when the cable is mechanically stressed. In order to learn more about the risk of SIED in a wet XLPE cable an extensive ageing test program has been carried out. This paper summarizes the results from this testing.

One issue with the use of crosslinked polyethylene (XLPE) insulation in high voltage power cables is the presence of oxidized particles. Oxidation may occur during production of polyethylene, during the extrusion and curing process used to produce XLPE cables, or in subsequent processes/operation of the cables. Oxidized particles are here referred to as organic contaminants. In the present study artificial organic contaminants were introduced in XLPE samples made for electrical treeing measurements. Instead of using the common needle-needle or needle-plane configuration, a wire-plane configuration was used. Organic contaminants have an increasing conductivity and permittivity as function of increasing degree of oxidation. These properties most probably give rise to local electric field enhancements in the material. The morphology of organic contaminants also differs from virgin XLPE, which probably cause bad adhesion between the XLPE matrix and the contaminants. A combination of these factors was found to affect the electrical performance of the insulation. Several different parameters, such as dry and wet ageing, as well as AC voltage and DC voltage stress, were included in the study.

StatoilHydro, Weatherford, FMC Technologies and Nexans Norway are cooperating in a project called Integrated Fibre Optic Subsea System (IFOSS), where multiple aspects of utilizing optical fibre subsea for enhancing bandwidth and reach are addressed, when compared to conventional control systems. The project scope includes utilizing techniques and components from the telecom industry. A holistic approach is taken to include digital communication and transport of analogue signals from fibre based sensors.