Low-maintenance steel connection
The Dutch private company C1 Connections BV has developed a low-maintenance connection that can be used for connecting tubular steel foundations to the Transition Pieces or directly to the tower sections. The connection, the C1 Wedge Connection, serves as a cheaper, faster and safer alternative to the usual bolt connections.
According to Jasper Winkes, director of C1 Connections, the conventional bolt connections, the L-flange connections, are reaching their limits in terms of the load that this connection can bear. The increase in load is due to the ever-increasing size of the turbines and the growth of the turbines in countries with increasingly higher extreme wind speeds. The company therefore developed a prestressed symmetrical connection that can not only bear a higher load, but is also faster, safer and cheaper to use.
The C1 Wedge Connection consists of a fork section at the bottom of an upper tube section where the lower tube slides into. In both the fork and the lower tube there are large oval-shaped holes where a fastener slides in that pulls both tube parts together by means of two wedges and thus creates a symmetrical prestressed connection. The connection is immediately confirmed relatively well via a quick connection. This is in contrast to the installation with traditional bolt connections where the parts are still loosely stacked before the bolts are placed and tightened. This immediately creates a safer working environment.
In addition, the relatively smaller bolts of the C1 Wedge Connection ensure that less heavy tools are required to bring the bolts to the correct tension. The necessary tools are very handy and weigh less than 10 kilos, Winkes explains. This is a significant difference from the conventional connections where the bolts can weigh well over 20 kilos each and the tool weighs more than 50 to 60 kilos. The connection can be completed very quickly. “With three people at a time, it only takes a few minutes to temporarily secure it and the connection is completely ready in less than half an hour.”
Another great additional advantage is the service life of the connection. The connection shows minimal fatigue phenomena. In theory, the connection can last the life of the turbine without any maintenance. Winkes: “The unique thing about this connection is that even if theoretically there were only 10% bias that the connection would still reach its lifespan.”
Collaboration with Siemens Gamesa and TU Delft
The C1 Wedge Connection was recently tested in full size in Delft, with a diameter of 4.5 meters. Parallel to this, C1 Connections tested the connection using computer simulations for the impact of forces that occur with this connection during the driving of foundations.
Test pieces were also dynamically loaded with TU Delft for thousands of hours. The tests confirmed the aforementioned benefits of the compound. All these advantages provide an advantage in both CAPEX and OPEX.
C1 Connection works for the further development for application in wind turbines in close collaboration with Siemens Gamesa and TU Delft. The emphasis here is mainly on the connections above water. This development was funded by the Netherlands Enterprise Agency (RVO).
The three parties are also jointly continuing the development towards market readiness. Winkes: “Together with Siemens, we look at what it takes to produce in large numbers, the specific transport requirements, installation challenges, et cetera.” The C1 Wedge Connection is currently undergoing a certification process at DNV GL. Several patents have been obtained on the technique and several patent applications have been filed.
This article appeared in the December 2020 edition of Wind Energy Magazine