Semi-Submersible Floating Offshore Substation Wave Basin Model Test

Abstract Today there is an emerging trend where more offshore wind farms are moving further offshore into deeper waters, the bottom fixed offshore substations are less feasible technically, logistically, and economically. There are quite a few pilot floating wind turbine projects in the world while there are no floating offshore substations except for one small Fukushima floating substation (66kV, 16MW) in Japan. For large commercial size floating wind farm projects in deep water areas, such as USA west coast, large size floating offshore substation (FOSS) is necessary to make the project viable. A semi-submersible floating offshore substation solution (810MW, HVAC) has been developed for USA west coast. This concept design is based on the metocean data in Morro Bay Area, California. The selected floating offshore sites water depth is about 1100 meters. The 1100-meter water depth and swell metocean (long period wave) give rise to extra technical challenges for floating OSS design, especially for the dynamic cable design. In addition to HV substation equipment qualification tests, the design of the entire floating offshore substation solution needs to be confirmed by a system level qualification test that includes a wave basin model test. The numerical simulations can be verified and validated by the wave basin model test results. Certain behaviour or phenomena, which may not be able to be simulated by the software, can also be observed by the wave basin model tests. The whole concept design process was approached in two phases: numerical concept design and analysis, and wave basin model test confirmation and validation. Physical wave basin model tests have been performed at one wave basin in 2023. This paper gives details of the scaled floating platform, the model test set-up configuration and instrumentation, and test procedure for the semi-submersible floating offshore substation (FOSS) solution (810MW, HVAC). System Identification Test results and overall model test conclusion summary are presented in this paper. The model test results confirmed the design prediction values including motion, acceleration and airgap. No slamming on lower deck nor green water on top of the column has been observed during the model test, even with 1000-year event considered.