Available Technology

Wind Turbine Blade Testing System Using Base Excitation: Base Excitation Test System (B.E.T.S.)

Recently, there has been a rapidly growing demand for renewable energy, including wind energy. To meet this demand, wind turbine designers are working to provide blade designs that allow a turbine connected to the wind turbine blades or to the rotor to effectively convert wind into electricity. The blades must also be designed properly to withstand inertial forces, aerodynamic forces, and structural forces so as to provide a relatively long service life and safe operation. Like all rotating machines, wind turbines are generators of fatigue, and every revolution of its components including the turbine blades produces a load or fatigue cycle, with each of these cycles causing a small, finite amount of damage that eventually may lead to fatigue cracks or other failures. Modeling may be used in some cases to determine service life of a turbine blade during normal operations. However, modeling has its limitations including variations in the as-built/manufacture blade design and the difficulty in accurately modeling operational conditions with varying and sometimes random loading. As a result, wind turbine blades are typically laboratory tested to determine that their fatigue strength or characteristics are adequate for a desired service life. Wind turbine or rotor blade testing is used to verify that laminations in the blade are safe, e.g., the layers used to fabricate a blade do not separate/delaminate and to verify that the blade will not break under repeated stress. Presently, wind turbine blades are fatigue tested in the flapwise direction (i.e., out of the rotor plane or in the direction transverse to a plane extending through the blade) and in the edgewise direction (i.e., in the plane of rotation or in a direction parallel to a plane extending through the blade). For large blades (greater than forty-meter blade lengths), these two fatigue tests are typically run sequentially, and, to simulate a typical service life of a blade, each test may involve placing a blade through one million to ten million or more load or fatigue cycles, which may take three to twelve months or more to complete for each tested direction. There is a trend for wind generator systems to become increasingly larger. Unfortunately, however, the larger blades associated with larger wind generator systems are subjected to greater static and dynamic loads and the facilities for testing these larger blades are also very large as newer generation turbine generators are being designed with blades 40 meters or more in length. It is very desirable, and often necessary, to advance test a proposed blade design to ensure that it will be capable of withstanding the expected loads with structural failure and to evaluate the fatigue resistance or the blade design, and these advanced tests may significantly delay implementation of a new blade design. The test equipment can also be relatively expensive to purchase and operate, which can drive up the costs of blades and wind energy. Hence, there is a need for blade testing techniques that are less expensive to use and take less time to complete while still providing accurate fatigue testing results.
Abstract: 
Recently, there has been a rapidly growing demand for renewable energy, including wind energy. To meet this demand, wind turbine designers are working to provide blade designs that allow a turbine connected to the wind turbine blades or to the rotor to effectively convert wind into electricity. The blades must also be designed properly to withstand inertial forces, aerodynamic forces, and structural forces so as to provide a relatively long service life and safe operation. Like all rotating...
Benefits: 
Less expensive testing technique -Faster than conventional techniques -Requires less specialized equipment -Mobile frame
applications: 
Internal Laboratory Ref #: 
NREL ROIs 07-21, 08-46 -Development -Available -03/17/2016 -03/18/2016
Lab Representatives
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