Conceptual Design of an HVDC Tension Leg Platform (TLP) Floating Offshore Substation Solution

Semi-submersible), a Tension Leg Platform (TLP) floating HVDC offshore substation solution

(1320 MW, VSC monopole) has been developed. Floating Offshore HVDC Substations will be the next frontier to harvest deeper offshore wind power. 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. California has typically swell metocean (long period wave). The 1100meter water depth and swell metocean give rise to extra technical challenges for floating OSS design, especially for that of the dynamic cable.

This paper presents the complete conceptual design of TLP Floating Offshore Substation. This

TLP concept developed for the USA West Coast floating offshore sites, is one optimised solution for the topside HVDC substation equipment, floater, and dynamic cables. Special technical challenges for the Floating HVDC offshore substation will be explained. Design difference between the HVDC and HVAC FOSS will be introduced. Floater technology selection will be described. This Concept Design can be modified or updated for FOSS projects in other oceans based on the project specific metocean conditions, so the concept design is not limited to US West Coast only.

The Finite Element Analysis (FEA) for HVDC equipment (i.e., valve, valve reactor) and AC equipment (transformer, GIS, harmonic damping device) will be performed. Design enhancement and mitigation will be proposed to make such HVDC and HVAC equipment suitable for the offshore floating environment. Certain qualification tests will be proposed and explained.

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 1 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 has gone through two phases: numerical concept design and analysis, and wave basin model test confirmation and validation. Physical wave basin model tests were performed.