Nordic Windpower (Nordic) is a Berkeley, California company that designs, manufactures and sells utility-scale wind turbines.
Earlier this month Nordic announced that it had received a $16 million loan guarantee offer from the U.S. Department of Energy. Nordic said it will use the government funds to expand its Idaho assembly plant.
Nordic’s turbines have a two-blade design rather than the more traditional three-blade rotor common in utility-scale wind.
A two-blade design reduces the cost associated with providing blades and simplifies assembly but also requires a different hub design because a two-blade turbine is less balanced and more prone to fatigue from that unbalance than the conventional three-blade turbine.
Teeter hubs, which are hinged to the turbine shaft, were developed for two-blade turbines, but they don’t hold up well in extreme wind conditions.
Nordic has developed flexible teeter hub technology so the rotor blades can flex at the hub to dissipate high winds before they can reach or damage the turbine drive train. International Pub. No. WO 02/079647 (‘647 Application) describes and claims Nordic’s flexible teeter hub assembly.
The ‘647 Application is directed to a teeter hub (2) that allows some flexing while also better absorbing extreme torque. Blades (1) are connected to the hub (2), and the hub is connected to the turbine shaft (3).
The reaction arm (15) extends all they way through the hub (2) from the periphery adjacent the turbine shaft (3) to the opposite side of the hub. The length of the reaction arm (15) allows the hub assembly to better absorb extreme torque caused by high winds.
The bearing (12), the reaction arm (15) and the spring elements (13) together form a hinge assembly. When high winds blow, the hinge assembly allows the hub (2) to pivot slightly while the springs (13) counteract the teeter movement.
The torque is absorbed with an even distribution on the bearing (12) and the springs (13) thus minimizing damage to the turbine.