Environmental Engineering Reference
In-Depth Information
Table 2: Basic parameters for SWT classes (IEC 61400-2).
SWT class
I
II
III
IV
S
Reference wind speed,
V
ref
(m/s)
50
42.5
37.5
30
Values to be specifi ed
by the designer
Annual averaged wind
speed,
V
ave
(m/s)
10
8.5
7.5
6
Turbulence intensity at
V
= 15 m/s
0.18
its scope is mostly limited within the design safety parameters of SWTs. The pri-
mary goal of the new task is to give incentives to this industrial sector to improve
the technical reliability of SWTs and therefore their performance.
4 Wind conditions
4.1 External conditions
SWTs are subjected to external conditions, which are divided into wind condi-
tions, other environmental conditions and electrical conditions [1].
4.1.1 Wind turbine class
Wind conditions are the primary external conditions and SWT classifi cation is
given in IEC standard IEC 61400-2 depending on wind conditions as shown in
Table 2 .
Reference wind speed is a basic parameter which is defi ned as an extreme
10 min averaged wind speed with a recurrence period of 50 years. For standard
SWT classes I-IV, annual average wind speed is given by the formula:
V
=
0.2
V
(5 )
ave
ref
4.1.2 S class
Offshore conditions and conditions experienced in tropical storms (hurricanes,
cyclones and typhoons) are excluded from Standard classes I-IV.
The SWTs that will be driven by the winds whose characteristics exceed those
of standard classes in Table 2 is classifi ed to special S classes.
Both for designers and owners of SWTs, site selection will be quite important,
although mini- or micro-WTs are easily installed at any place or on a building. It
is because wind conditions considerably vary depending on the site. For large
WTs, the sites are mostly open free fl ow fi elds, while for SWTs the sites may often
gardens, parks, roofs or rooftops of urban houses/high buildings, etc. At these
sites, fl ow characteristics are often quite turbulent and those SWTs installed there
should be also classifi ed into S.
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