PO100

Offshore Substation Jacket Substructure Design Development - Challenge the Norms and achieve More Efficient Design

Trevor Hodgson, David Fielder, Chris Cowland, Kate Rudman
Atkins Ltd, UK

Abstract

Offshore substations are important components of the offshore wind farm.  The design of offshore substations substructures (for both AC and HVDC power) needs to fulfil whole life cycle requirements by considering all design phases (including fabrication, installation, operation and decommissioning). 

New projects in the offshore wind industry are moving further from shore into deeper waters.  This will lead to an inevitable cost increase due to more complex fabrication and installation.  To offset the costs involved in developing such challenging projects, there is a clear need and emphasis towards reducing the cost of substructures, through improved reliability, structural efficiency and challenging the norms.  This initiative applies to offshore substations as it does to offshore wind turbines.

In this presentation, the authors will provide an overview of current trends in offshore substation substructure design around the world, highlighting the different options being considered.  The presentation is primarily focusing on fixed structure, but an overview of and floating substation will be discussed.

The presentation will then describe hands-on experience of designing fixed offshore substation substructures of various types with the aim of achieving simpler solutions in harsher offshore environments.  Based on such experience, a holistic approach taking account of fabrication, installation, operation and decommissioning requirements is ultimately important for successful delivery of the design.  The presentation identifies some of the key aspects driving the offshore substation substructure design philosophy.

Method

Extensive market research has been carried out on the current AC / HVDC markets.  This has identified historic trends in substation design around the world, observing key design drivers and characteristics.  Based on Atkins extensive experience in the substation substructure design, in-depth in house knowledge has been used for the prediction of future trends.

Since there is potential synergy between offshore wind turbine substructure and substation substructure, a comparison between these two type substructures have been made, and the key differences between both structures have been identified and listed.  This is supplemented by carrying out an in-depth review of DNVGL-ST-0126 (Support structures for wind turbines) and DNVGL-ST-0145 (Offshore substations).  Any opportunities of standardisation of design across the wind farm are also discussed and highlighted.

Results

The work has challenged current design practice.  Recent design experience has shown that savings of jacket weights of up to 15% can be achieved.  This saving resulted from reviews of the requirements for cable pulling, corrosion allowance and the methodology for local jacket joint design.  However, further future weight savings are also considered possible. The presentation concludes by providing recommendations as to areas of potential future developments and weight saving for the offshore substation.  This will be applicable to both AC and HVDC platforms.

Conclusions

With the importance of achieving lower cost of energy, appropriate design decisions are critical to project decisions.  The drivers of design decisions for offshore substation can be quite different from wind turbines.  To achieve efficient (or lighter) design, it is important for the industry to challenge current design philosophy and to integrate further with wind turbine substructure design, so that efficiencies in installation may be obtained by standardisation.   

Objectives

The learning objectives of this presentation are as follow: