The main features of the Growian wind energy converter are presented. Energy yield, environmental impact, and construction of the energy converter are discussed. Reliability of the windpowered system is assessed

Koerber, F.

Thiele, H. A.

English

NASA Technical Reports Server

LARGEWINDENERGYCONVERTER- GROWIAN3 MW
F. K_rber and Hans A. Thiele
M.A.N. NewTechnology
Munich, West Germany
INTRODUCTION
The large wind energy converter GROWIANhas the function of pro-
ducing electrical energy from the natural movementsof the wind. A
two-blade rotor mounted on the tower is rotated by the action of wind
and transfers its power via a gearbox to a generator. The electrical
energy thus obtained is then fed directly into the existing supply net-
work.
The plant was designed with reference to a plant site in the North
Germancoastal area. The design of the plant permits a long-term op-
timal exploitation of wind energy through the use of advanced, proven
engineering techniques.
MAINFEATURESOFTHEGROWIAN
The main features of the plant, as shownin figure i, are:
• Two-blade rotor with pendulumhub
• Leeward mounting of the rotor
• Blade construction: steel-spar design with glassfiber airfoil
, Single stayed tower
• Controlled orientation of the nacelle and rotor into the wind
SYSTEMDATA
Rated capacity
Meanannual energy output
Power-to-area ratio
Rated wind speed
Cut-in speed
Cut-out speed
Rotor diameter
Rotor speed
Hub height above ground
Massof tower head with rotor
3 MW
12 GWh
380 W/m2
11.8 m/s
6.3 m/s
24 m/s
100.4 m
18.5 rpm ± 15%
i00 m
240 t
121
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ENERGYIELD
Calculations were based on an annual meanwind velocity of 6 m/s
measured i0 m above ground. This average corresponds to the prevail-
ing wind speed at a coastal site in the North GermanPlain. The in-
stalled capacity of 3 MWyields an annual energy output of 12 GWh.
Figure 2 plots the power and the power duration curve. It can be seen
that no power is produced 23%of the operating time owing to insufficient
wind speeds. Forty-eight percent of the time the output falls below the
rated capacity, while the plant operates at rated capacity 27%of the
time. The plant is shut down 2%of the time as a result of excessive
wind speeds.
The performance characteristics of the plant are shownin figure 3.
The plant normally operates in the static control range. The extended
limits of the dynamic control range are used for controlling brief fluc-
tuations in the rotor speed. The rated capacity at nominal rotor speed
is attained at a wind speed of 11.8 m/s. At higher wind speeds the
surplus wind energy must be eliminated. To achieve this, the blade pitch
is adjusted so that even at high wind speeds no more than the rated ca-
pacity is produced (fig. 4). The power output up to the cut-out point
therefore corresponds to the output at the rated wind speed.
The efficiency of the aerodynamic conversion of a wind generator
is characterized by the power coefficient (Cp - %) chart as given for
the GROWIANin figure 5.
ENVIRONMENTALIMPACT
The GROWIANhas no detrimental effects on the environment as it
produces no noxious substances. The need for a pleasing appearance
has always received special attention.
CONSTRUCTIONFTHEGROWIAN
As shownin figure I, the wind converter comprises the main compo-
nents of tower, nacelle, rotor, and their mechanical and electrical
equipment.
Tower and Nacelle
The tower is a slender cylindrical shaft of reinforced-concrete or
alternatively of steel (fig. 6). It has an outside diameter of 3.5 m
and a height of 96.6 m. The tower contains a spiral staircase, a lift,
cable shafts, and the lifting cables for the tower head. Three pairs
of cables are attached to the stay ring in the upper third portion of
the tower and are strung to foundations in the ground.
The cylindrical nacelle is mountedatop the tower in such a way
that it can be adjusted in yawwith reference to the wind. It accom-
modates the rotor, the gearbox, the generator, and various other units.
122
The shell-type welded housing has a diameter of 6 m and a total
length of 22 m including the rotor moulted on the lee side. On the
windward side a spar approximately 20 m long extends outwards, the tip
of which contains the wind measuring instruments. Figure 7 shows a
cross-sectional view of the nacelle. The collar extending downward
houses the block and tackle system for raising the tower head, which
is completely assembled on the ground. Whenraising the tower head, the
tower shaft passes through the nacelle. The junction to the rotor is
formed by the rotor bearing which is built into the hub support tube.
Rotor
The GROWIANemploys a two-blade rotor 100.4 m in diameter. It is
based on the principle of converting energy by utilizing aerodynamic
lift. The requirements of strength and stiffness within practicable di-
mensions have been met for the first version by a steel-spar rotor blade
46 m in length which is assembled in three segments (fig. 8). The steel
spar extends from the blade root to the blade tip and is given its air-
foil form by mounted glass-fiber molded segments (fig. 9). The spar and
skin of the blade were selected for their ability to withstand loads.
The airfoil section was specially designed as a laminar airfoil. A
rotor blade with a 35 m composite segmentis presently being developed.
The blades are mountedon the pendulumhub and can rotate about
their vertical axes on antifriction bearings so that their angle of
attack can be adjusted by means of a motor-driven linkage in order to
control the power output of the rotor. The pendulum hub protects com-
ponents subjected to high loads such as the rotor blades, the tower, the
tower bearing, and the nacelle from moments resulting from differential
wind loads on the two blades. Excessive rotor speeds are precluded
without resort to any extraneous power supply by means of a device ac-
tuated by centrifugal force which allows the rotor blades to turn to
their feathered position.
Mechanical Equipment
A planetary gear system with a ratio of 1:81 is used for stepping
up the rotor speed of 18.5 rpm to the generator speed of 1500 rpm. The
drive of the planetary gear is bolted to the rotor shaft. This system
consists of two planetary stages and one spur gear stage and is bolted
to the nacelle with a flange. A disk brake located at the high-speed
output end of the gearbox is able to arrest the rotor revolving at low
speeds or at full speed in an emergency, but only at the cost of its
wearing parts. A universal shaft connects the gearbox output to the
generator.
The tower head is turned into the wind by geared motors whose
pinions engage in a gear ring integral with the tower.
123
Electrical Equipment
The energy obtained from the wind converter is fed into the
local supply network with due regard to economic considerations.
Owing to the large fluctuations in the wind energy available, the
most suitable generator is one which is not restricted to a set speed
of rotation.
An asynchronous generator (3 MW),whose rotor is energized with
alternating current by meansof slip rings, lends itself well to this
purpose, the frequency of the supply current corresponding to the dif-
ference to the synchronous frequency. This unit in the supply network
behaves like a synchronous generator. By controlling the electric load-
ing in the rotor circuit, any desired reactive and active current in
the given range can be obtained.
A slipring system is provided for transferring the generated cur-
rent as well as the monitoring and control signals from the rotating
tower head to the electric cables in the tower. This system is located
at the top of the tower concentric about the tower longitudinal axis.
Servo Control
In order to makeoperation on a supply network possible, the fluc-
tuations in the speed of rotation resulting from changing wind velocity
must be reduced enough to allow the electric generator to process them.
The control system has the function of starting the plant in compliance
with a prescribed set of data, to keep it within the operating range,
and to continue operation or shut the plant down, depending on the mo-
mentary wind flow and energy requirements. Furthermore, if the plant
is operating in conjunction with the supply network, the frequency and
the stator voltage must be held constant.
Power output and speed of rotation are regulated by controlling
the blade pitch and the generator moment. The generator deviates
elastically in the subsynchronousor hypersynchronous modesof opera-
tion whenever fluctuations in the rotor speed occur until the over-
riding speed regulator has reestablished synchronous operation. A
schematic of the operating principles of the control system for power
output and speed is shownin figure i0.
Operational Control and Monitoring System
A programmablecomputer is provided for the operational control
and monitoring of the converter. In addition to continuously checking
the data, it is also responsible for registering and analyzing the
operating condition of the plant and for detecting and signaling any
malfunction.
124
ASSEMBLYANDERECTION
The steel tower as well as the reinforced-concrete tower are
erected on a concrete foundation, which is laid at the site. The 9 m
sections of the steel tower are set on top of one another with a crane,
are bolted together, and then welded (fig. ii). The concrete of the
reinforced-steel-concrete tower is formed with the aid of sliding molds.
At the same time the plant building is erected.
Whenthe tower has reached a height of i0 to 15 m, the shell com-
ponents of the nacelle are placed over the tower shaft and are welded
in place. The rotor shaft and the pendulum frame are positioned in
their bearings with the aid of suitable lifting gear. The rotor is
assembled in a horizontal position. The three blade segments are bolted
and welded together in the steel sector. After the tower and the nacelle
with rotor have been completed, the tower head is raised with the aid
of the built-in hoist. The tower shaft passes through the nacelle.
PLANTRELIABILITY
Special emphasiswas placed on operational reliability in both the
designing of the plant and the dimensioning of its components. The
measures taken ensure that the CROWIANis not endangered in its oper-
ation and does not constitute an environmental hazard even under the
most inclement atmospheric conditions. Its stability complies with the
specifications usually prescribed for high-rise structures. In the
calculations of the static and dynamic loads arising from the action
of the wind, gusts with a wind speed of up to approximately 60 m/s
were taken into account.
DISCUSSION
Q.
A.
Q.
AI
When will the GROWIAN be in operation?
We expect to have it in operation in, roughly, two-and-a-half years.
Could you explain the emergency pitching apparatus in the event the electri-
cal pitch control were to fail?
As shown on that slide, there is a quick release bolt arrangement in the
linkage connecting the pitch control actuator to the blade. Incase of an
emergency, it is activated and the blade becomem free. The blade then
pitches itself to the feathered posit:ion by aerodynamic forces. The
machine uses full span pitch control, as was specified by the government.
Q. What is the weight of the machine and the blades?
A. The weight of the machine is about 240 tons. The weight of the reinforced
concrete is 750 tons, and each blade weighs 23 tons.
125
Figure i. - Large wind energy converter GROWIAN 3 _
_o
Insufficient wind
2
1
/
0
0 20 40 60
A % time
wind s_ed 6.3 m/s 11,B r_
AnnuaL EaerQy
12 GWh
I
I
8O
Figure 2. - Power duration curve.
_xces sive w_-nd
100
i
24m/,
126
o1,5 -
2.0
1,5
4.1
t.j
t_
e_
o 1,0
4J
e_
0
0
_'ind power curve
[or wind speeds
13
mls
12
11-
i
0,7
I
/
, i , ,,Ii i i
0,8 i 0,9 110 1,1 : 1.2
I
Speed/rated speed i
18.5
i i i i i • _ i 1 , i
14 15 16 17 18 19 20 21 22 23
Rotor speed, rpm
P_wer characteri-_tic of
generator
Figure 3. - Performance characteristics.
5
4
3
i .,_,
/,
I
 S,,i
.4/! ,I"-,,,
-8
25 20 15 10 5
Blade pitch, '_.7 dee
0 -5 -10 °
Figure 4. - Rotor performance.
127
o61Cp0.5
o,4.
g
_ 0,3-
o
_ 0,2,
03,
Wind speed, m/s
T T T T T T T T T T
56453630 24 20 16 12 10 %5
f l
5 4,61
-3"
2 _
32_ -__
2 4 6 8 10 12
2"
5 •
Blade pitcil
'2
14. 16 18 20
Speed ratio
22X
Figure 5. - Power coefficient chart.
Stay ring
Maintenance platform
Rotor blade support
Figure 6. - Tower.
128
NACELLE
1 Rotor blade
2 Rotor bearing
3 Teei.ered hub
4 Rotor pitch adjustment
S Step up gearbox
6 Brake
14
17
7 Generator
8 SllDring body
9 Yaw bearing
I0 Yaw drive
II Lift
12 Telescoping slewing crane
13 Auxiliary lift
14 Spar for wind measuring instruments
and mountin 9 ballast
15 Lifting device
16 Main control room
17 Ballast room
Figure 7. - Machine housing.
/
GROWIAN rotor blade.
129
Figure 9. - Cross section of the rotor blade.
I
I
vl
T
__i _ ! Speed
_- regulator
ns = nN 1
.3
Ps_e.._
co
z
<
_- 'GS,I 0
_-_-" ni
Pi I ni
I
I
MGS -- (Ps/ns)
.,,_+
i
IControl *
L_ _d___ __J
Pitch
regulator
i iiii ii•
Me
| M El =' Mel
L_p__J
I
',Pi
I
T
Indices :
i = actual value
M = moment A = drive
n : speed of rotation el = electric N = rated value
opt = optimum
p = power G = generator
V = wind speed S = nominal value
_" = rotor blade pitch
Figure I0. - Effective output-rotational speed control.
130
I Crane
2 Cable equipment
3 Stay rinQ
4 Nacelle
5 Scaffolding
6 Mobile platform
? Spar
8 Rotor
9 Mounting ballast
I0 Hoist
II Stay
12 Foundation for stay
13 Winch
/
/
6
7
#
I II III IV V
S
<13
/
11
k'kk !2
13
Vl
Figure ii. - Tower and machine housing assembly.
131


Large wind energy converter: Growian 3 MW

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