Study on Mechanical Fatigue Loads on Insulation in a Dynamic HVDC Cable

DCDYNAMIC research project, which seeks to validate the reliability of a new dynamic

HVDC export cable and to build a fundamental understanding of combined electro‑mechanical‑thermal ageing mechanism in the insulation. As input for the material ageing tests and full‑scale tests planned within the project, it is important to establish an understanding of representative mechanical strain variations that the insulation in a dynamic cable will encounter during extreme and fatigue conditions during service.

Two scenarios were analysed; a 320 kV HVDC export cable connected to a floating HVDC substation, and a dynamic 150 kV HVDC power from shore cable connected to a floating platform. For both cases, tethered wave configurations were developed and verified as feasible with regards to extreme loads and fatigue life. Insulation strain distributions were derived from the global responses and local cross section analysis, showing that the number of cycles decreases exponentially with increasing strain range and that the maximum fatigue strain ranges were below 0.6%. Overall, the results indicate that the insulation in a dynamic HVDC dynamic cable is subjected to many cycles of relatively low strain amplitude. The established strain profiles define the operational envelope for the insulation system and provide a framework for linking the outcomes of material ageing studies to the actual mechanical conditions in the dynamic cable. They also serve as input for designing full‑scale tests so that these reflect the mechanical loading expected during real operation.