COSS – Compact Offshore SubStation
Grid integration is being discussed in this edition as one of the possible key elements to achieving the sorely needed cost reduction to make offshore wind development in Europe viable. It therefore seemed to us a right time and place to highlight a current development of a substation design that is claiming to do just that! Dutch engineering and consultancy company Liandon is working together with Dutch engineering company KCI and Japanese Toshiba in developing COSS, the Compact Offshore Substation.
Liandon told Offshore WIND that the use of onshore proven technologies has resulted in heavy topsides leading to high project costs and installation costs. With the wind farms at sea getting larger and larger it also means that the substations need to accommodate for this growing energy flow and have therefore grown even larger and heavier. Liandon and partners decided to look for alternatives to reduce the weight of the substations and thus aiming to reducing costs.
The result is the COSS, the Compact Offshore Substation, design. The partners found a way to reduce the weight and the size of current substation designs. By replacing the heavy oil based transformers and auxiliary systems by alternatives, a massive weight reduction and compacter size could be achieved. They found the solution in Gas Insulated Transformers (GIT), a technology already used and proven viable for 40 years in the Far East, mainly for its capability of being almost explosion free and taking up minimal space.
The COSS is a flexible modular design, based on two (SF6) GITs with a total power of 360 MVA and can be used both near and far offshore. For the incoming cable connections, it uses 33kV switchgear while 170kV Gas Insulated Switchgear is applied for the outgoing and transformer connections.
Replacing the usage of oil makes the substation a lot less vulnerable for explosions and therefore guarantees a higher availability and power handling. With substations becoming more and more working and storage platforms, this is definitely of importance, especially in projects further offshore and in harsh environments. Liandon is responsible for the design, KCI for the engineering and Toshiba for the transformer.
This concept might not seem much different in the sense that it uses onshore proven technologies but Victor Krijt, Business Developer at Liandon, is very firm when stating that this would not do the design justice at all.
“The uniqueness of the design lies in the use of redundant GIT’s. This contributes to a lower weight and gravity point of the topside construction. At the moment, a patent is pending on our design,” adds Mr Krijt. Altogether the COSS-platform offers an optimal balance between weight and power, leading to more reliable outputs, compared to existing platforms. “Several parties have already expressed interest in COSS. Furthermore we take part in the Green Deal Offshore Wind initiated by the Dutch wind energy association, NWEA.”
In the end it comes back to the most important factor; reducing costs in installation and output without compromising safety. Implementing the GIT in the offshore substations would bring down the weight and size of it. This means that transportation and installation would no longer be exclusively a job for the large and expensive installation vessels. Instead, smaller and therefore cheaper vessels can take on the task.
Other cost savings can be made in the foundations of the offshore substation. Because the topside is so much lighter, a jacket foundation required for a heavy topside could easily be replaced by a monopile.