Coiled power cables on a ship next to offshore wind turbines.

Optimised power cable installation for coupled tension-torque behaviour

For offshore wind turbine installations, the grid of subsea power cables represents a critical infrastructure for transporting the electric energy to the market. This includes both dynamic cables connecting the bottom-fixed/floating wind turbines to the seabed and sections of static cables linking each turbine to the grid and each wind farm to the market.

During installation, the power cable is exposed to vessel motions and forces from local wave kinematics. The cable motion and structural response is influenced by several other factors such as water depth, vessel heading, cable-soil interaction, tension-torque coupling and internal friction of the power cables.

According to current design practice, the weather window in terms of acceptable sea state parameters allowing cable installation is established before the operation takes place and is based on simplified global dynamic models. It is noted that vessel availability is a cost driver. To reduce installation cost, it is necessary to explore non-linear cable behaviour in more detail.

Through the work at NorthWind, we plan to develop the methodology from TRL 1 to TRL 3.

Outcomes from NorthWind

  • Improved FE-models for simulating cable behaviour during installation. The model has been developed and shall be implemented in general FE-software suitable for dynamic simulation of offshore power cable installation.
  • Improved evaluation criteria for combined cable loads, i.e. combinations of tensions (compression), torque and bending moment by use of suggested interaction formulas. These interaction formulas are suitable to judge load severity in a typical power cable subjected to combined tension (compression), bending and torque loading. These are in a format suitable to evaluate and make explicit the combined loads experienced and seen in dynamic simulation of installation operations.