A step in safety, installation speed and cost reduction
Offshore wind energy is developing at a rapid pace. The turbines and monopiles are getting bigger and offshore wind turbines produce more energy than people could imagine 5 years ago. All technology grows, while people remain the same size, leading to installation challenges. Loads on towers and foundations are growing rapidly due to higher hub heights and larger rotors. “The limit of current connection technology requires alternative solutions”, explains Jasper Winkes managing director of C1 Connections BV.
The C1 Wedge Connection is a new innovative connection that can be used for bottom fixed and floating wind turbines. The increasing size of wind turbines in combination with harsher conditions have pushed the limits of existing connections. The C1 Wedge Connection can easily be scaled to deliver the required higher capacity and fatigue resistance. The connection is robust and maintenance-free, requires less steel usage and reduces the installation time to half an hour while ensuring a Health and Safety (HSE) friendly installation.
A C1 Wedge Connection uses a fork-shaped upper part and a lower part with elongated holes. A fastener is placed in these holes. The fastener has an upper and lower block which expands when two wedges are pulled together creating a pre-stressed interface between the upper and lower part of the connection.
Jasper Winkes: “We see that both the rotor size as the hub height grows which results in a large increase in bending moment. The C1 Wedge Connection can deliver high line-loads and also has a high fatigue capacity. The connection is also not relying heavily on the exact amount of preload making the connection maintenance free. Personnel free installation, low weight equipment and components make this connection a big improvement from an HSE perspective.”
Health and safety
At present, the L-flange connection is often used as the most cost-effective solution. The turbine section is lifted above the monopile foundation and manoeuvred into position by the technicians to get the holes right above each other. Then, massive bolts are put through the flange and tightened to make the connection. As the size of the turbines is getting bigger, the force on the connection between monopile foundation and turbines is growing.
Bolts that are currently used to secure traditional L-flange connections are reaching their limits. On one hand, because of the load capacity, on the other hand, because of the size and weight of these bolts.
Safety is a very important advantage of the C1 Wedge Connection. No personnel is required to be under a suspended (or hooked-on) load during construction. The whole alignment and quick-connection are done with a personnel free alignment and quick-connection system. The parts and tools are light and easy to handle by a technician. Jasper Winkes states: “Our connection is also cost-effective: Full installation is possible in less than 0,5 hour and the connection allows large savings in primary and secondary steel. Further savings can be made in the operational phase since no maintenance is expected to be needed since the C1 Wedge Connection does not rely heavily on an exact preload level at the interface”.
The C1 Wedge Connection has received the component certificate by DNV. In order to get the connection certified, there were 3 essential phases. At first extensive modelling of the connection showed that it can deliver a high ultimate and fatigue resistance. This was confirmed in the second phase, the testing phase whereby over 20 segments were subjected to tens of millions of load cycles. In the third phase the fabrication of the connection was shown demonstrating that the connection can be fabricated within the required tolerances.
These types of innovations require multi-stakeholder input, from smaller companies, but also from university and industry. That is the key to success. Jasper Winkes: “The project is a good example of how small companies can successfully work together with industry and the scientific world”.