Influence on the Mechanical Characteristics of Dynamic Power Cable From Internal Temperature Fluctuations Caused by Power Transmission

This study emphasises dynamic power cables, i.e. cables with low bending stiffness, designed for floating offshore structures in motion. The study’s objective was to investigate how the temperature fluctuations inside the cable, caused by the power transmission, affect the stress-based fatigue life of the copper conductors and the fatigue-critical location along its length. A methodology that used the COMSOL software to simulate and calculate the temperature gradient in the cable’s components for various examples of power transmissions is presented. The COMSOL results were used in an in-house code that calculated the cable’s axial, bending and torsion stiffnesses. These results were transferred to a simulation model, built in the DNV SESAM software, of a heaving-point absorber wave energy converter and its power cable that transmits power from the WEC to a hub station. The study’s results show that the temperature fluctuations inside the cable lowered the mechanical stiffness properties of the cable with increased power transmission. This effect, combined with the temperature dependence of the fatigue strength coefficient in the Basquin equation, resulted in shorter fatigue life than a power cable at room temperature (i.e., no power is transmitted through the cable). The most fatigue-critical location along the cable’s length was relatively unaffected by the effect of different power transmission levels.