Current endurance testing of termination earth connections for offshore wind farm array cables

Power generation from offshore wind grew vastly in the last 20 years, whilst remaining a relatively young industry without installed technology reaching the end of its design life before advancements are made. Most of the technology of MV (medium voltage) array cable accessories are based on the more experienced land power distribution industry, which faces very different operating conditions and yet are still bound by the same design and test standards. Recently the industry has seen failures related to some “T-connector” terminations on array cables operating offshore at 33 kV, over multiple wind farms and differing cable and termination suppliers. Root cause analysis has been performed by the Authors on one of these windfarms where the main cause of failure was identified as the screen earthing connection within the terminations. As no test methods exist in the relevant international standards, a new current endurance test has been developed to determine the suitability of the installed T-connector earthing methodology, as well as alternative designs. It was found during analysis of the test results that the installed earthing design, although having passed the required short circuit testing to the relevant standards, was not suitable for the design life of the larger cable cross sections used in the project. Two alternative designs, although improved were also not deemed suitable. Two newly designed connections, based on established technology utilising a soldered connection and a mechanical connection, have however, been approved for use.