Environmental Engineering Reference
In-Depth Information
years. The learning-curve effect on capital cost reduction is assumed to range from zero in a
worst case scenario to the historic level in a best-case scenario, with the most likely outcome
halfway in between. The most likely scenario is a sizeable increase in capacity factor with a
modest drop in capital cost, compared to the 2002 levels of each.
Status of Wind Turbine Design Standards
The development of a suite of international standards for wind turbines has been a major
contributor to the evolution of wind turbine technology over the past 15 years. The Interna-
tional Electrotechnical Commission (IEC) is a global organization that prepares and publish-
es international standards for electrical, electronic, and related technologies. These standards
serve as the basis for national standards and as a reference when drafting international tenders
and contracts. The IEC standards for wind turbines address certiication procedures, design
requirements, engineering integrity, measurement techniques, and test procedures. Their in-
tended purpose is to provide a uniform basis for design, quality assurance and certiication of
wind turbines and wind projects. These standards cover wind turbine systems and subsys-
tems, such as mechanical and internal electrical systems, support structures, and control and
protection systems.
In the U.S. there are no laws enforcing the IEC standards. However, many lending insti-
tutions inancing wind projects require that the turbines meet the IEC standards as a condition
of the loan agreement.
The IEC certiication document explains how the IEC suite of turbine standards should
be used to ensure a consistent design process. This design process requires an internally con-
sistent set of design conditions, design quality system, validation through prototype testing
and manufacturing quality system. The low chart of Figure 3-47 illustrates how this suite of
complementary standards should be used to design, manufacture, and install a
type certiied
wind turbine. The starting point in this process is the Wind Turbine Design Standard IEC
61400-1, which speciies minimum requirements for the design of land-based wind turbines.
The standard is intended to ensure the integrity of wind turbines and provide an appropriate
level of protection against damage from all hazards during the turbines planned lifetime. This
standard applies to wind turbines of all sizes, but there is an alternate standard, IEC 61400-2,
which may be used for wind turbines with power ratings less than 100 kW. Offshore turbine
designs are covered by a separate standard, IEC 61400-3.
Wind Turbine Design Classes
When turbines are in the design stage, designers rarely know the speciic sites where
they may be installed, but a set of site design conditions is still needed. To help solve this
problem, the IEC standards committees set up a consistent set of wind conditions or
design
classes
that are each representative of a type of potential site. Each class is deined by speci-
ied wind conditions, including a reference site wind speed, a reference turbulence intensity
level, extreme wind speeds,
etc
. Table 3-8 summarizes the wind turbine design standard
classes, with speciied wind conditions at hub elevation. The design standard speciies that
the cumulative probability distribution of the 10-minute average wind speed at hub height
shall be taken as a Rayleigh distribution (see Chs. 2 and 8).
The reference wind speeds in Table 3-8 serve to establish the severity of the wind condi-
tions used in the load cases used to design the turbine components. From the table, it is clear
that a Class IA wind turbine is designed for deployment at sites that are expected to see higher
average wind speeds, higher gust wind speeds, and higher turbulence levels. This method of
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