Testing
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See Also:
Type Testing
Type Characteristics

CONTENTS

 
NWTC Certification Test Capabilities

The National Renewable Energy Laboratory now offers certification evaluation and testing services at the National Wind Technology Center (NWTC) that lead to wind turbine certification. This page describes the basic testing capabilities employed to provide quantitative data required to certify wind turbine equipment, including the activities required for Type Testing and Type Characteristics Measurements.

In addition, NWTC Evaluation Services provide manufacturers and developers with an objective source for reports on design process verification and wind turbine facility assessment.

Performance Tests
Power performance tests quantify the relationship between power output and wind speed, commonly known as a power curve. The power curve is used to estimate annual energy production from a wind turbine, as well as other characteristics. Annual energy production is often used as a basis for revenues, taxes, and, in some cases, subsidies. Thus, accuracy in power curve measurement can have a strong impact on business decisions. The power curve also provides technical information important to selecting a wind turbine for a specific application.

During power performance testing, instrumentation measures wind speed and direction, air temperature and pressure, and turbine power output and operating status. At least 180 hours of performance data are gathered when winds are between low-wind cut-in speeds and high-wind cut-out speeds. Wind speed is measured by precision anemometers on a meteorological tower placed 2.5 rotor diameters upwind of the turbine.

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Noise Emissions Tests
NWTC Noise emissions tests use
equipment configurations and
procedures specified by IEC
standards.		 Acoustic & Noise Emission Tests
Wind Turbine noise is often a key factor in siting negotiations, especially in Europe where wind turbines are commonly located close to homes and businesses. A-weighted decibel (or dBA) sound-power level, octave, and tones are three acoustic measurements required for certification. These measurements are made with four microphones placed around the turbine on hard plywood "sound boards." Microphone signals are recorded by an instrument-quality, digital tape recorder and are analyzed using a dynamic signal analyzer. Other measurements include wind speed and direction and turbine power level.

All instrumentation used at the NWTC meets IEC standards and all measurement, analysis, and reporting procedures follow the IEC 61400-11 standard for wind turbine acoustic testing. These procedures call for determination of source sound power levels as functions of wind speed and microphone direction relative to wind speed.

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This innovative hub required a
special blade test mount.		 Blade and Structural Tests
Blade structural tests are now required for certification. They address key concerns about wind turbines of interest to certification organizations, such as whether the blades meet design load specifications.

NREL recommends two tests: an ultimate-load test and a fatigue test. An ultimate-load test simulates extreme wind loading and indicates the blade's strength safety margin over the worst winds specified for the turbine design class.

A fatigue test applies cyclic bending loads to the blade. The fatigue test simulates repetitive high-wind conditions that the turbine might undergo during a 20- to 30-year exposure to the environment.

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A new 1.5MW dynamometer will
augment present test capabilities
in 1999.		 Dynamometer Tests
Drive-train testing can be used to verify the life and performance of gearboxes, generators, power electronics, and yaw drive systems. NREL is developing a 1.5 MW dynamometer facility to augment existing smaller test systems. When completed and made operational at the NWTC, this new dynamometer will be able to test the largest wind turbine drive trains envisioned for use for the next decade.

Dynamometer testing is not required for certification.

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Other Tests
In addition to the four tests presently offered, the NWTC is developing additional testing services that will soon be required for certification:
  • Loads testing seeks to ensure that the turbine assembly will withstand the wind conditions it might encounter during its lifetime. Typical measurements will include blade edgewise and flapwise bending, mainshaft bending and torsion loads, tower bending, yaw and rotor positions, and environmental conditions.
  • Safety system verification tests verify the performance of the key safety features of the turbine, especially the turbine braking systems.
  • Power quality testing measures the effects that wind turbines have on the grid's voltage and current characteristics. These effects are important when wind turbines comprise a significant addition to power from conventional generators. Tests include power variation, reactive power demand, voltage and current fluctuations, start-up and shut-down transients, and harmonics.

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Prepared by
National Wind Technology Center
National Renewable Energy Laboratory
Operated for the
U.S. DEPARTMENT OF ENERGY
by the Midwest Research Institute

Updated: November 21, 2002