Environmental Engineering Reference
In-Depth Information
Table 3-8. Basic wind parameters deining wind turbine design classes
[IEC 61400-1]
Wind conditions apply at rotor hub elevation
Wind Turbine
Design Class
Reference Wind Speed over
10 min,
V
Ref
(m/s)
Reference Turbulence
Intensity at
V
= 15 m/s,
I
Ref
IA
50
0.16
IB
0.14
IC
0.12
IIA
42.5
0.16
IIB
0.14
IIC
0.12
IIIA
37.5
0.16
IIIB
0.14
IIIC
0.12
S
Speciied by Designer
classifying turbines seeks to insure that a wind turbine selected for installation at a speciic
site will perform reliability over its intended lifetime.
It is dificult to over-emphasize how important the IEC standards have been in estab-
lishing a basis for comparing the cost effectiveness and long-term performance of different
turbine designs. These standards have facilitated the development of large markets for com-
mercial wind generation by deining a common set of transparent design requirements and
common design processes. Type certiication is generally a required by the lender and banks
as a requirement for project inance, which shows the conidence placed on the standards by
the inancial community.
Standard Design Load Cases
A wind turbine must be designed to a set of relevant load cases that represent the fa-
tigue and extreme loading situations the turbine will see over its lifetime. These load cases
are representative of the operational modes combined with the appropriate wind conditions
from Table 3-8. Other situations must be addressed in the design process, such as assembly,
erection, maintenance, and external conditions. The design load cases used to verify the
structural integrity of a wind turbine shall be calculated by combining:
-
normal design situations and appropriate normal or extreme conditions, in-
cluding wind loading combined with other events.
-
fault design situations and appropriate external conditions.
-
transportation, installation, and maintenance design situations, combined with
appropriate external conditions.
It is also required that when a correlation exists between an extreme external event and a fault
event, the combination of these events must be considered as a design load case.
A brief summary and description of the IEC load cases is presented in Table 3-9. The
IEC 61400-1 wind turbine design requirements document speciies a matrix of eight basic
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