Environmental Engineering Reference
In-Depth Information
Figure 2-7 shows a schematic diagram of the internal structure of a typical composite
wind turbine blade. The standard
x-y coordinate system
for describing the complex curved
surfaces of an airfoil has its origin at the leading edge, with the positive
x
or
chordwise
di-
mension extending aft to the trailing edge, and the positive
y
or
thickness
dimension extend-
ing toward the
low-pressure
or
upper surface
of the airfoil. Negative
y
dimensions then point
to the
high-pressure
or
lower surface
. The upper- and lower-surface designations have their
basis in airplane wing descriptions. Both the
x
and
y
dimensions are typically normalized by
the chord width
c
.
The structural arrangement in Figure 2-7 is representative of current commercial blade
designs [Grifin 2001]. The primary structural member is a
box-spar
, with
shear webs
lo-
cated approximately 15 percent and 50 percent of the chord width measured from the leading
edge, with a substantial build-up of
spar cap
material between these two webs. Exterior skins
and internal shear webs are both of sandwich construction, in which iberglass laminate skins
are separated by balsa cores.
The Power-Train Subsystem
The
power train
of a wind turbine consists of the series of mechanical and electrical
components required to convert the mechanical power received from the rotor hub to elec-
trical power. In a HAWT, this equipment is atop the tower, so low maintenance is an im-
portant design requirement. Examples of small-, medium-, and large-scale power trains are
illustrated in Figure 2-8. A typical HAWT power train consists of a
turbine shaft assembly
(also called a low-speed or primary shaft), a
speed-increasing gearbox
, a
generator drive
shaft
(also called a high-speed or secondary shaft), a
rotor brake
, and an
electrical genera-
tor
, plus auxiliary equipment for control, lubrication, and cooling functions. As illustrated in
Figure 2-8(a), some small-scale HAWTs and a few medium- and large-scale HAWTs have
a
direct-drive
from the turbine to the generator, with no gearbox.
Figures 2-8. Typical HAWT power trains.
(a) Small-scale: Bergey BWC-1500/1.5 kW
(
Courtesy of Bergey Windpower Company, Inc
.)
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