Engineering calculations may say the design will work, but experience has proven that conditions in the real world cannot be fully anticipated. This fact was expressed in early Department of Energy writings about the promotion of wind power in the United States. In order for wind power technology to become successful, design validation and testing capabilities needed to be created. Unfortunately, mechanical test equipment above 2 megawatts with flexural misalignment simply didn’t exist at the time of the DoE’s publication.
This has created a significant challenge in the test community. Even though the top end of transportation applications can be 2 megawatts, wind turbines are being demonstrated at 7 to 8 megawatts. The prevailing philosophy in the industry is that building them bigger will make them more efficient and improve return on investment. So this trend is expected to continue.
Testing of cars, heavy duty trucks, tanks, helicopters, even locomotive engines, has been the forte’ of Renk Systems for many years. Having the experience of building dynamometers in the 2 megawatt range put the company in a unique position to support the emerging wind industry systems, which five years ago were frequently 1.5 and 2 kilowatt. But extensive experience provides a platform to extend the reach needed to achieve the power level of the 15MW system at Clemson.
The most difficult thing to contemplate is applying forces to intentionally mis-align the rotor. In the real world the wind does not blow symmetrically on the three propeller blades. This is known to create bending forces in all directions that stress the critical coordination needed at the root of the blades which are mounted perpendicular to the hub and drivetrain. These components are undergoing many tons of force and testing is crucial to either drive out weaknesses in the design work, or prove that new equipment is suitable for field installations. To solve this problem, Renk designed an interposing flywheel mass with flexibility built in, s0 that wind power drive trains can be exercised more fully.
By designing the flywheel with 36 high force hydraulic actuators (as shown in the illustration), Renk created a way to introduce large forces radially and axially to produce deflections that are consistent with the what the machine under test will see in the real world. In addition, the company provided full closed loop controls to operate the hydraulic system in any combination of actuators desired at frequencies up to 2 Hertz. At 150 tons of flywheel mass, this is quite an accomplishment.
Cooperation between Clemson, Renk, Teco Westinghouse and National Instruments have made possible a facility that is without equal in the world and positions the US to fulfill a leadership role in the wind industry.