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THE WIND TURBINE
COMPONENTS AND OPERATION
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BONUS
ENERGY A/S
§
Table of contents page 4
Special Issue
BONUS
INFO
THE NEVER ENDING STORY
THE WIND TURBINE
COMPONENTS AND OPERATION
Autumn 1999
BONUS-INFO is a newsletter for
customers and business associates of
the Bonus Energy A/S. This news-
letter is published once or twice a
year.
The first number came out in 1998,
and the newsletter has now been
published in four issues.
Each number has included an
article on the components and opera-
tion of the wind turbine. We have
received many suggestions and
requests that these articles should be
reprinted and published as a special
single issue.
Bonus is pleased to have hereby
fulfilled this request with the
publication of this special issue.
Author:
Henrik Stiesdal
Responsible under the press law
Lay-out/ Production:
Claus Nybroe
Translation:
John Furze, Hugh Piggott
Autumn 1999
BONUS ENERGY A/S
Fabriksvej 4, Box 170
7330 Brande
Tel.: 97 18 11 22
Fax: 97 18 30 86
E-mail: bonus@bonus.dk
Web: www.bonus.dk
4
THE WIND TURBINE
COMPONENTS AND OPERATION
The Aerodynamics of the Wind Turbine 5
Basic Theory ¤ The aerodynamic profile ¤ The aerodynamics
of a man on a bicycle ¤ Wind turbine blades behave in the
same way ¤ Lift ¤ The change of forces along the blade ¤
What happens when the wind speed changes ¤ The stall
phenomena ¤ Summary
The Transmission System 11
The hub ¤ Main shaft ¤ Main Bearings ¤ The clamping unit ¤
The gearbox ¤ The coupling
The Generator 15
Direct current (DC) ¤ Alternating current (AC) ¤ Three
phase alternating current ¤ Induction and electromagnetism ¤
The wind turbine generator as a motor ¤ Generator operation
¤ Cut-in ¤ Closing remarks
Problem description ¤ The controller ¤ Hydraulics ¤ Tip bra-
kes ¤ The mechanical brake
5
THE AERODYNAMICS OF THE WIND TURBINE
The three bladed rotor is the most
important and most visible part of the
wind turbine. It is through the rotor
that the energy of the wind is transfor-
med into mechanical energy that turns
the main shaft of the wind turbine.
The front and rear sides of a wind
turbine rotor blade have a shape roughly
similar to that of a long rectangle,
with the edges bounded by the leading
edge, the trailing edge, the blade tip and
the blade root. The blade root is bolted to
the hub.
The radius of the blade is the distance
from the rotor shaft to the outer edge of
the blade tip. Some wind turbine blades
have moveable blade tips as air brakes,
and one can often see the distinct line
separating the blade tip component from
the blade itself.
If a blade were sawn in half, one
would see that the cross section has a
streamlined asymmetrical shape, with the
flattest side facing the oncoming air flow
or wind. This shape is called the bladeÔs
aerodynamic profile
This profile was developed during the
1930Ôs, and has good all-round proper-
ties, giving a good power curve and a
good stall. The blade is tolerant of minor
surface imperfections, such as dirt on the
blade profile surface.
The LM blades used on newer Bonus
wind turbines (from the 150 kW models)
use the NACA 63 profiles developed
during the 1940ªs. These have slightly
different properties than the NACA 44
series. The power curve is better in the
low and medium wind speed ranges, but
drops under operation at higher wind
speeds. Likewise this profile is more
sensitive with regard to surface dirt.
This is not so important in Denmark,
but in certain climate zones with little
rain, accumulated dirt, grime and insect
deposits may impair and reduce
performance for longer periods.
The LM 19 blades, specifically
developed for wind turbines, used on the
Bonus 500 kW, have completely new
aerodynamic profiles and are therefore
not found in the NACA catalogue.
These blades were developed in a joint
LM and Bonus research project some
years ago, and further developed and
wind tunnel tested by FFA (The Aero-
dynamic Research Institute of The
Swedish Ministry of Defence).
We will start by describing why the
blades are shaped the way that they are
and what really happens, when the
blades rotate.
BASIC THEORY
Aerodynamics is the science and study
of the physical laws of the behavior of
objects in an air flow and the forces that
are produced by air flows.
Blade tip
THE AERODYNAMIC PROFILE
The shape of the aerodynamic profile is
decisive for blade performance. Even
minor alterations in the shape of the
profile can greatly alter the power curve
and noise level. Therefore a blade desig-
ner does not merely sit down and outline
the shape when designing a new blade.
The shape must be chosen with great care
on the basis of past experience. For this
reason blade profiles were previously
chosen from a widely used catalogue of
airfoil profiles developed in wind tunnel
research by NACA (The United States
National Advisory Committee for Aero-
nautics) around the time of the Second
World War.
THE AERODYNAMICS
OF A MAN ON A BICYCLE
To fully describe the aerodynamics of a
wind turbine blade could appear to be
rather complicated and difficult to under-
stand. It is not easy to fully understand
how the direction of the air flow around
the blade is dependent on the rotation of
the blade. Fortunately for us, air con-
stantly flows around everyday objects
following these very same aerodynamic
laws. Therefore we can start with the
aerodynamics of an air flow that most of
us are much more familiar with: A cyclist
on a windy day.
The diagrams (next page) show a
cyclist as seen from above. The diagrams
are perhaps rather sketchy, but with a
good will one can visualize what they
NACA 44
Blade root
NACA 63
Hub
Blade profiles
The different components of a wind turbine blade
The NACA 44 series profiles were used
on older Bonus wind turbines (up to and
including the 95 kW models).
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