Advanced Wind Turbine Program Next Generation Turbine ... - NREL

4 Engineering and Manufacturing Development Turbine,
EMD1.5/77
The Engineering and Manufacturing Development (EMD) turbine is an evolution from the POC
turbine incorporating the following improvements in its design:
• A larger 77-m-diameter rotor
• 37-m blades with tip curvature
• Tower-top accelerometer feedback for tower damping
• Independent blade pitch control for asymmetric load control.
These improvements were implemented in two stages. The POC configuration was converted to
the EMD configuration officially in April 2002, with the installation of the 37-m blades. Following
the power performance, loads, and noise testing of that configuration, the EMD was further
upgraded with the addition of the asymmetric load controller (ALC) and associated turbine sensor
system. The system in its final configuration was then, in June 2003, subjected to additional
loads testing.
Table 6 provides a summary of the EMD turbine configuration.
4.1 IEC Class S High Energy Capture Rotor Configuration and Loads
The development of the high energy capture 77-m rotor was motivated by two considerations.
First, earlier design efforts conducted as part of the development of the POC turbine showed that
the rotor diameter for the GE1.5 turbine could be increased to at least 77 m and possibly higher,
without a significant increase in loads if the design took advantage of the fatigue-reducing benefits
of increased rotor flexibility.
The second motivation for the 77-m rotor involved consideration of the operating conditions.
Analysis of wind speed histories from several commercial wind farms in the U.S. led to the conclusion
that one could expect 50-year gusts in level great plains areas at the 65–80 m hub heights
to be less than 52.5 m/s. The analysis also shows that both IEC Class 2A and 2B overpredict the
level of turbulence intensity at all wind speeds compared to every wind farm analyzed. The value
of k=2 for the Weibull coefficient that is typically used to define frequency distributions of wind
speed generally overpredicts the frequency of very high winds relative to what is occurring at
typical wind farms.
Since the distribution of very high winds and the turbulence intensity are factors that most define
extreme wind and fatigue, study results indicate using the IEC standard wind classes will result
in the design of a turbine that is overly conservative for the conditions typical at the sites where
wind farms are being installed in the U.S. Use of a larger Weibull factor than 2.0 and turbulence
intensities lower than IEC Class 2B would allow the use of a much larger rotor and result in the
proper projection of significantly improved energy capture and reduced COE.
Therefore, GE decided to define a special S-Class environment for purposes of designing the 77m
rotor that was felt to be typical of real operating environments:
• A 52.5 m/s 50-year 3-second-average extreme gust
• 9 m/s annual average wind speed
• A Weibull distribution of wind speeds with coefficient k=2.3
• IEC Class B turbulence intensity
• 1.2 kg/m 3 annual average air density.
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