C1 Connections, a Dutch company from The Hague, has introduced the C1 Wedge Connection™ – a new connection technology that takes a completely different approach to connecting the tower sections in wind turbines.
The offshore wind industry is one of the backbones of the energy transition around the globe, which has led to offshore wind turbines growing massively in size over recent years. Through this development the next generation of wind turbines is expected to reach 20 megawatt of power. These large machines, with rotor diameters of over 250 metres, require tall towers to support the generator above the sea. Due to the large rotor and the tall tower, the loads exerted by these turbines have now reached a point where the traditional bolted L-flange connection simply cannot deal with the load anymore. Overturning moments at the base of these tall towers can be as high as 1GNm. To put this into perspective, this is the same load as lifting a Tesla with a 50km long stick.
Over the recent years, OEMs and wind farm developers have scaled up stud sizes at a rapid pace from M64 to M80 and M90. Even M100 studs are being considered for some wind farms. As a result, the tools required to tension these large studs become extremely heavy with weights of more than 100kg. Often workers are also required to work below suspended loads.
The C1 Wedge Connection™, developed by C1 Connections, plans to solve these challenges. The new connection technology takes a completely different approach to connect the tower sections in a wind turbine.
Working principle
The C1 Wedge Connection™ is a symmetric flange connection to connect tubular sections. The connection consists of a cylindrical shaft shaped lower flange and a fork shaped upper flange. During installation the upper flange slides over the lower flange until the top of the lower flange is in contact with the upper flange. Both flanges have radially elongated holes evenly distributed along the circumference that are aligned via a guide system during installation. C1 fasteners are placed in these holes to pull the two flanges together.
The fastener of the C1 Wedge Connection™ uses a small, horizontally placed bolt. The bolt pulls two wedges together. This pushes an upper block upwards in the lower flange and a lower block downwards in the upper flange. This creates a preload at the interface between the flanges. Upon applying the preload, the nut holds the wedges in place.
The wedges magnify the horizontal bolt force into a much larger preload (typically more than five times) at the interface between the flanges. This allows a small bolt to be used to generate a high interface preload. Due to the perpendicular orientation of the bolt between the flanges, relative to the externally applied load, it is isolated from external load fluctuations on the connection.
The C1 Wedge Connection™ uses a preload in the interface similar to traditional bolted flange connections. When an external tensile load is applied, the preload between the two flanges is reduced and the tensile load is transferred to the lower flange.
Benefits of the C1 Wedge Connection™
The C1 Wedge Connection™ presents several benefits over conventional connections. Firstly, it has a high ultimate and a high fatigue capacity, which enables future generation wind turbines to be connected to the foundations – where current L-flange connections cannot deliver sufficient capacity anymore.
In addition, offshore installation work with wind turbines requires the connection of a lot of flanges. With the growth in turbines, the tools and fasteners for conventional connections have reached a point where they cannot be handled safely by workers anymore. When installing the C1 Wedge Connection™ no fasteners need to be lifted since these components are pre-installed. Plus, the tools are lightweight since small studs are used to tighten the fasteners. Furthermore, installing conventional flange connections in offshore wind turbines is unsafe with technicians working below suspended towers. The C1 Wedge Connection™ addresses this issue by making a temporarily safe connection upon the landing of the tower onto the foundation without the involvement of personnel. This allows people to safely enter the tower once the connection is secured.
To add to this, the C1 Wedge Connection™ is typically 50% lighter than a conventional L-flange connection. As a result, the price for the total connection (flanges and fasteners) allows significant financial savings compared to traditional connections.
“Following years of development, the technology has been fully certified by DNV for use in wind turbines in dry and splash zone applications,” reports Jasper Winkes, director of C1 Connection. “The connection has already been implemented several times, including a two year successful implementation in a 14MW wind turbine. We see that the industry is embracing our solution and we have the biggest players in this field on board to introduce the technology on a large-scale to the market.”
Having spent a decade in the fastener industry experiencing every facet – from steel mills, fastener manufacturers, wholesalers, distributors, as well as machinery builders and plating + coating companies, Claire has developed an in-depth knowledge of all things fasteners.
Alongside visiting numerous companies, exhibitions and conferences around the world, Claire has also interviewed high profile figures – focusing on key topics impacting the sector and making sure readers stay up to date with the latest developments within the industry.
