XEMC Darwind has ambitious plans to enter the main European onshore wind
markets with two new 4.5- and 5-MW direct drive turbines based on its
5-MW offshore XD115/5-MW model. XEMC Darwind’s CEO Hugo Groenemans
explained the new turbine’s technology specifics and benefits, which
include merging Chinese supply chain strengths with job creation and
localized industrialization.
XEMC Windpower in 2012 ranked fifth among China's largest wind
turbine manufacturers, offering XE-type 2-MW and 2.5-MW direct drive
volume-series with a Dutch technology basis origin. The wind business is
part of the state-owned XEMC Group established in 1936 as a
manufacturer of electric motors and generators. XEMC is today a
medium-sized manufacturer based in China and employs more than 11,000
staff.
Design Principle
During 2011 XEMC Darwind installed a 5-MW direct drive XD115/5-MW
prototype at an Energy Research Center of the Netherlands (ECN) test
site. This turbine is designed for International Electrochemical
Commission (IEC) wind class 1B and technologically based upon similar
design principles, but adapted to meet specific demanding offshore
conditions. Less than a year later a second similar prototype was
installed at a near-shore location in the Chinese Fujian province.
A two-year testing and optimizing programme of the Dutch prototype
has now been completed, with a Provisional Type A certificate awarded
this July. During the past six months its overall turbine technical
availability was 95 percent.
XD115/5-MW turbine technology features include a compact fully
enclosed and over-pressurized nacelle, incorporating a “classic”
inner-rotor XEMC-design permanent magnet generator measuring around six
metres in diameter, and a single rotor bearing.
Generator temperature management is enabled by a combination of
passive air-cooling, with external air flow passing over the exposed
outer stator body, and a supplementary forced-air cooling system that
incorporates a heat exchanger. Two exposed pipes clearly visible atop
the nacelle form an integral part of this cooling system loop, providing
up to 40 percent of the cumulative cooling capacity required under the
most demanding high-wind conditions.
Favourable
All failure sensitive power electronic components, including a
water-cooled converter and transformer, switchgear, and turbine controls
are located in the tower base. The turbine is further characterised by a
modest-size 115-metre rotor diameter combined with a relatively
high-rated rotor speed of 18 RPM, and for its class favourable 281-tonne
head mass (rotor + nacelle). This low-head mass positively impacts
turbine loads, tower and foundation loading, masses and costs.
The XD115/5-MW’s 108 m/s-rated rotor blade tip speed is substantially
higher compared to common values for offshore turbines that lie
typically in the 80-90 m/s range. A turbine configuration with
fast-spinning rotor in relation to a given rotor size and power rating
allows for reduced generator size, mass and cost. A resulting higher
blade tip speed inherently raises aerodynamic sound intensity level
(noise). Choice for a high rated tip speed requires additional measures
like a special protective coating applied at the blade’s leading
(rounded) edge to prevent excessive erosion-related wear and increased
risk of premature failure.
“The initial idea for entering onshore markets with new XD-platform
turbines originated from the Dutch office and was approved by our
majority shareholder,” said Groenemans. “The product-market refocusing
includes a continued offering of the XD115/5MW for European and
international offshore projects. In parallel, the XD-platform is
expanded by two 4.5-MW onshore sister models each destined to a specific
IEC wind class.”
Modified
The original XD115/5-MW product specifications indicate 115dB(A)
(calculated) maximum sound intensity. Turbine noise is not considered
important for offshore applications, but it does matter in onshore wind,
especially in noise-sensitive populated areas where it impacts product
market chances. Many suppliers under these conditions strive for a
maximum value of around 106dB(A), whereby it should be noted that
-3dB(A) represents an intensity of sound reduction by 50 percent.
The first onshore model called XD115/4.5-MW is destined for
noise-constrained IEC class 1A/1B high wind speed sites, but for
locations without such noise limitations the XD115/5-MW will be
supplied. The XD115/4.5-MW is technically largely identical to the
XD115/5-MW, and already commercially offered. Among the onshore
adaptations is a modified generator cooling system, which partly uses
clean ambient air due to less stringent demands for a completely sealed
nacelle.
Addressing the potential implications of this high 115dB(A) turbine
noise figure for XEMC Darwind’s onshore market opportunities, Groenemans
explained: “Our on-site prototype measurements showed much more
favourable at 108dB(A) sound intensity, representing a huge reduction
compared to the initial calculations. Due to our aim for further
reducing turbine noise while leaving generator dimensions and
specifications unchanged, we decided with the XD115/4.5MW for a slightly
reduced rated rotor speed. This also explains the lower rated power,
which is a function of generator torque and rotational speed, but has
here only limited yield impact for a majority of potential onshore
sites.”
Enlarged Rotor
The second onshore sister model called XD133/4.5-MW is being
developed for low and medium IEC class 3A/2B wind conditions and only
comes in a 4.5-MW version. This turbine will be equipped with a newly
developed generator and an enlarged 133-metre rotor diameter.
“Generator outer diameter and general layout remain largely
unchanged, but generator length is increased to compensate for a
substantially reduced rotational speed of the bigger rotor,” said
Groenemans.
The design team further opted for a state-of-the-art slender blade
design with carbon fibres incorporated in highly stressed structural
areas. This results in a lower mass compared to the much shorter
traditionally designed XD115/5-MW (4.5-MW) blades. Cyclic pitch control
is another design feature introduced in the XD133/4.5MW, whereby the
angle of each individual blade is continuously adjusted during each full
rotation.
“The combination of these new lightweight slender blades and advanced
control were a genuine breakthrough in the reduction of turbine loads.
This in turn resulted into an almost unchanged head mass, despite 34
percent rotor swept area increase,” he added.
The XD133/4.5-MW will feature tubular steel towers up to about
100-metre hub height, and concrete-steel hybrid towers up to 140 metres
in the latter combination adding up to a 206.5-metre total installation
height.
“Crossing the 200-metre ‘barrier’ was enabled by a combination of low
head mass and the increased availability of cost-effective high-tower
designs, together with a growing visual acceptance for such landscape
dominant objects,” said Groenemans. “Most important, for similar hub
heights and within IEC wind class boundaries, the XD133/4.5-MW will
generate about 20 percent more electricity compared to the
XD115/4.5-MW.”
Key Markets
The XD133/4.5-MW prototype is planned for Q1-2015, and commercial
market availability in 2015. Groenemans expects the initial markets for
both 4.5-MW turbine models to include the northern and eastern parts of
Germany, the Netherlands, the UK and Ireland. He pointed to the fact
that Ireland’s local grid network currently cannot absorb more wind
power, but a planned interconnector cable with the UK might open up
fresh opportunities.
Groenemans finally believes that building a European supply chain is
essential, and aims to have turbine assembly and testing close to main
markets concentrated in the Netherlands and possibly additional
locations.
For the 4.5-MW XD-series, specific main components will be procured
in China (including XEMC-made generators and finished castings), and
other components in Europe, including especially blades, towers and
rotor bearings.
“XEMC is well known for building high-quality generators, and we can
also benefit from their favourable labour costs and cheaper permanent
magnets supply. The quality of Chinese castings and their product
finishing is comparable to similar European components,” said
Groenemans. “Our main role will be in acting systems integrator, by
creating local jobs and in ensuring that our clients are served with
quality turbines offering high the highest possible return on
investment.”
http://www.renewableenergyworld.com/rea/news/article/2013/11/xemc-darwind-refocuses-on-onshore-wind-with-4-5-and-5-mw-direct-drive-turbine
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