Development and Reliability Validation of J-Tubeless Installation Method for Submarine Cables in Offshore Wind Farms

In offshore wind farms developed along the southwestern coast of Korea, extensive growth of marine organisms inside pre-installed J-tubes has been observed. When cable installation is carried out several months after foundation installation, biofouling inside the J-tube significantly increases friction during cable pull-in operations, making installation increasingly difficult and raising the risk of mechanical damage to the cable. More critically, in the event of cable failure, accumulated biofouling inside the J-tube can make the removal and replacement of the cable significantly more difficult. In such cases, restoration may require the fabrication and installation of a new J-tube or additional structural modification of the jacket foundation.

These interventions involve complex offshore construction activities, prolonged recovery periods, increased operational risk, and long-term power production losses.

To address these challenges, this paper proposes a J-tubeless submarine cable installation method that eliminates the use of steel J-tubes. In the proposed approach, the cable is routed externally along the jacket structure and protected by a polymer-based Cable Protection System

(CPS), consisting of flexible protection tubes, clamps, and bend restrictors. The CPS is designed to withstand environmental loads such as waves and tidal currents while providing adequate bending control and mechanical protection to the cable throughout its service life. By removing a J-tube, the proposed method fundamentally prevents biofouling-related constraints during both installation and maintenance.

The mechanical reliability of the J-tubeless installation method is verified through a full-scale onshore fatigue test conducted in accordance with the fatigue assessment principles of CIGRE

Technical Brochure 862. The test reproduces representative cyclic mechanical loading conditions expected during offshore operation. Following the fatigue test, the cable and CPS components are dismantled and subjected to comprehensive post-test evaluations. Electrical performance is assessed through visual inspection, AC withstand voltage testing, partial discharge measurement, and conductor resistance measurement. The results confirm that the mechanical fatigue loading does not adversely affect the electrical integrity or overall condition of the cable system.

The findings demonstrate that the proposed J-tubeless installation method effectively eliminates biofouling-related risks associated with conventional J-tube installations and significantly improves accessibility for maintenance and cable replacement. As a result, the method offers a technically viable solution for reducing installation risk and enhancing lifecycle reliability of submarine cable systems in offshore wind farms.