DESIGN
The NORDEX N29/250 wind turbine is a further development of the N27 wind turbines. The
N29/250 has a rotor diameter of 29,7 m., and is equipped with an improved yaw system and a
gear design that further minimizes noise.
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GENERAL
The design of the N29/250 is based on the extensive experience gained with the N27/150 and
N27/250 wind turbines since 1987.
The N27 turbine has been, and still is, a very successfull wind turbine all over the
world, and the integrated design of this size of wind turbine has proven to be the right
choice. Therefore we chose to construct the N29/250 in the same way and only with a few
changes.
The N29/250 has a rotordiameter of 29,7 m., a new yaw system and a further noise-improved
gearbox-design.
The large rotor diameter ensures a significant increase in the annual production of the
turbine, which again makes this turbine extremely profitable.
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DESIGN
The N29/250 is made as an integrated unit with the gearbox as the main component of the
wind turbine. All other parts of the wind turbine are mounted on the gearbox, and as such
there is no machine bed. This ensures that everything is constantly in line.
Almost all parts of the wind turbine are made of ductile cast-iron.
The N29/250 is a very robust machine, in which there has been no
"just-to-the-limit" solutions during construction.
ROTOR
The NORDEX N29/250 wind turbine has a three bladed rotor, mounted upwind of the tower.
The power limitation is done by stall-regulation.
The N29/250 is supplied with 3 blades, which has many advantages if compared to turbines
with 1 or 2 blades: The efficiency is higher, fatigue loading is smoother, and complex
dynamic behaviour of a teetered hub is avoided.
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BLADES
The blades are made from fibreglass reinforced polyester.
The blade tips are pivotable and can be turned 85 degrees respectively to the main blade,
thereby acting as aerodynamic brakes. The blade tips are activated hydraulically, and
hydraulic pressure is required against a spring force to keep the tip in the operational
position. During rotation of the rotor, the sum of the centrifugal force on the tip and
the spring force will try to move the tip axially to the activation-position, and release
of the hydraulic pressure, either intentionally by the control system or unintentionally
by failure of the hydraulic system, will cause the tips to deploy and the turbine to shut
down. As such, the aerodynamic brakes of the turbine are of a truly fail-safe design.
HUB
The hub is made of ductile cast iron. The hub is flanged on the main shaft/gearbox.
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GEARBOX
The gearbox is a custom-built three-stage helical design. The gearbox is built as an
integrated unit with suspension of main shaft and generator, and as such everything is
flanged together. The gearbox is standing directly on the yawbearing. The gear wheels are
sump lubricated and the bearings are pump lubricated. As such, we are using oil for
lubrication of the two mainshaft-bearings , and not grease.The oil is filtered with
exchangeable filters.
The gear wheels are specially ground to minimize noise emmision.
The mainshaft is connected to the gearshaft through a helical gear-coupling, to avoid
bendings from the rotor to enter the gearwheel mesh.
Temperature sensors are mounted at the main shaft, on the high speed shaft bearings, and
in the oil sump. These temperature sensors will shut down the turbine in case of
temperatures increasing above acceptable limits.
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GENERATOR
The generator has dual windings (6/8 poles), and is an asynchronous 250/45 kW generator.
The large generator (6-poled, 250 kW) is used for power generation in higher windspeeds,
while the small generator (8-poled, 45 kW) is used for power generation in lower
windspeeds. The way the generator is wound gives maximum effeciency at half load. The
generator is flanged directly on the gear-unit, which excludes the need for alignment.
The cooling air for the generator is taken directly from the outside to obtain the best
possible cooling effect. An electrical fan (not a mechanical) is used for cooling of the
generator. In this way, the fan is only in operation when cooling of the generator is
needed, and the annual production of the wind turbine is increased. The air-intake is
insulated with soundabsorbing material to minimize noise emmision.
To avoid condensation water, a heating element is built into the generator.
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MECHANICAL BRAKE
The mechanical brake is fitted to the high speed shaft and has two hydraulic calibers.
In normal operation, the mechanical brake is used only as a parking-brake when the
aerodynamic brakes have decreased the rpm on the rotor-shaft.
However, in case an emergency braking of the windturbine is needed, the mechanical brake
is activated simultaneously to the aerodynamic brakes.
The mechanical brake is well capable of bringing the turbine to a complete standstill,
even if the aerodynamic brake should fail.
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| YAW SYSTEM
The yawing of the wind turbine is controlled by an electronic windvane and is secured
against cable twist by a yaw counter.
The yawing is done by two hydraulic driven worm reduction gears which engage a large and
robust ball-bearing ring. The ball-bearing ring is flanged directly on to the tower.
The yaw system is fitted with 3 hydraulic activated yaw brakes, based on a disc/positive
caliber system. When the nacelle is yawing, the yaw brakes smoothen the yawing due to
light preload of the yaw brakes. When there is no yaw operation, the yaw brakes are fixing
the nacelle securely to the tower.
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| TOWER
The N29/250 wind turbines can be supplied with either tubular or lattice-towers of 30, 40
and 50 m. heights.
The tubular tower is a conic-shape tower which dimension decreases all the way up. A
ladder and safety-wire are installed in the tower, as well as platforms. The tubular tower
is sandblasted and painted white according to ISO 12944, Class 5.
The lattice tower is made of V-iron in the 4 corners with UNP-iron as lattice. A ladder
and safety-line are also installed in the tower. The lattice tower is hot dip galvanized.
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CONTROLLER
The wind turbine is supplied with a microprocessor-based controller with a self-diagnosing
system, which secures the wind turbines unattended operation under all conditions.
In case the wind turbine is supplied with a tubular tower, the controller is placed in the
bottom of the tower. For a lattice tower, a separate house is supplied for the controller.
The controller is supplied complete with switchgear, incoming MCB (Main Circuit Breaker),
protection devices, etc., and has a keyboard for display and easy readout of more than 200
functions. The keyboard can also be used for changing the operational parameters of the
wind turbine.
Startup wind speed of the turbine is adjusted automatically from memory of earlier
operation, to maximize the production of the wind turbine to the different
weather-conditions.
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REMOTE
MONITORING
All NORDEX wind turbines are prepared for remote monitoring and control. A
telephone-connection is all that is needed for this system to be functional. Remote
communication is done via a normal IBM-compatibel computer, where more than 200 different
functions can be read from the turbine. The software is included in the delivery by
NORDEX.
In case of an error, the controller automatically reports this error, and data in the
controller is "frozen" so that it is possible to see what happened just before,
and when, the error occured.
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OPERATION AND SAFETY
LOGICS
The NORDEX wind turbines operate automatically.
When the wind increases from low values, the turbine will self-start at about 3-4 m/s
average wind speed, measured at hub height by the anemometer.
The wind turbine is motor-started by the generator, and connected to the grid via the
thyristor, shortly after to be by-passed by the main contactor.
At lower wind speeds, the wind turbine will then operate on the small generator, but will
change to the large generator when the production increases above a predetermined
setpoint. If the 2-min. average wind speed exceeds 25 m/sec., the wind turbine is shut
down through deployment of the aerodynamic brakes and application of the mechanical brake
at lower rpm. to bring the turbine to a standstill.
In case of an error, the turbine is shut down in a similar way.
However, by certain errors an emergency braking is required, and in these cases both
braking systems are activated simultaneously.
To avoid an emergency braking (which puts a lot of mechanical stress on the turbine) at
grid-drops, a UPS-system is installed as standard in all turbines. By the use of this
battery-backup function it is possible to make a normal braking of the turbine.
This UPS-function is especially valuable at locations where the grid is not always
optimal.
As the blade tips form the main braking-system, this will secure a very smooth shut down
of the wind turbine. The blade tips are hydraulically retracted and are deployed at the
release of the hydraulic pressure. This release system is fail-safe and includes more
independent systems. These include monitoring of the rotor- and generator speed and
pressure relief valve. The pressure relief valve secures that the hydraulic pressure is
released in case of overspeed on the rotor.
In case of grid-drops over a longer period of time, where the hydraulic system is not
functional due to lack of electricity to the hydraulic pumps, the pressure is kept by the
use of accumulators. These accumulators will mechanically build up hydraulic pressure
immediately as the turbine starts to rotate, whereafter the mechanical brakes and yaw
brake will be active again.
Due to continuous development and improvement of our products, Nordex Balcke-Dürr GmbH
reserves the right to change the above specifications without notice.
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