Editor’s note: The XD115 onshore 4.5MW turbine is derived from the offshore’s dedicated 5MW. This turbine benefits from its offshore predecessor. The company says it still focuses on fast installation and low maintenance and now provides some detail.
The company produces two models now, one for onshore and another for off. The main difference with the offshore turbine is that the air treatment system is simplified to meet the onshore demands. The onshore unit operates under IEC class IC conditions.
Darwind uses the philosophy of horizontal integration what means all manufacturing is outsourced and it only assembles and tests before sending the turbine to site. All design work however is done in house and with strategic suppliers for components such as blades, bearings, hydraulic systems, towers, and pitch system. In this sense the company is a system integrator although most components are of exclusive design.
All intellectual property rights of the XD115 turbine are vested in XEMC Darwind B.V. (Netherlands). To date no license rights have been granted to third parties. To protect XEMC Darwind’s unique position over 20 patents are pending. XEMC turbines are based upon the single bearing, direct drive, and permanent magnet principle.
Use is made of a single multiple row roller bearing on which the hub is mounted on one side and generator carrier and –rotor on the other side. The stator is mounted on the opposite side of the carrier which in turn is mounted on a compact casted nacelle frame. The advantage of this design is the relative large diameter the load path follows, contrary to the traditional designs with a main shaft. Hence the design allows considerable weight reduction In addition, innovative design and new materials have resulted in an easy to install, large, lightweight turbines.
The product platform is based on the direct-drive principle, thereby dispensing with the need for gearboxes. Gearboxes pose a significant problem for offshore wind turbines because the enormous torque of multi-megawatt wind turbines. In contrast, gearless turbines require less maintenance, are more reliable and therefore boast higher operating availability.
The rotor speed is allowed to vary during power production. Matching the available aerodynamic torque and the electromechanical torque of the generator determines the rotor speed. The torque-speed curve is programmed in the frequency converter controller and the inverter adapts the generator stator current in response to the measured generator power frequency.
Coil driven generators make use of electrical excited magnets. XEMC’s Permanent Magnetic systems are lighter and more compact, more efficient, and require less copper than coil driven generators. Because no additional electricity is required to magnetize the rotor coils, there is no need for generator `brushes` to transfer this electricity. This increases both efficiency and reliability because the rotating part of the generator contains no electrical systems.
Combined single main bearing and generator
The XEMC Darwind XD and XE platform is based on the single main bearing concept. The large diameter bearing lets it bear the enormous load of the rotor: there is no central shaft. The bearing component integrates into the generator thanks to the direct-drive design. This innovative design creates a compact and lightweight permanent magnet direct-drive generator, and results in significant savings in logistics, foundation and support structure costs.
The tower and nacelle of the offshore turbine are fully sealed to keep out the salty and moist sea air. This protects our valuable components, increases operational availability and saves a great deal of maintenance.
Full power conversion
The ac-dc-ac converter, mounted at the bottom tower section, lets the generator operate with a variable speed while the power is fed into the grid with a constant frequency of 50 Hz (or 60 Hz for the countries where this applies). It furthermore assures an average constant power output for wind speeds above rated. The power factor at the grid side is controllable at standstill as well as in operating mode. Above rated wind speed, the blade pitch control maintains a more or less constant rotor speed between admitted boundaries.
Grid code flexibility and compliance
XEMC wind turbines have a pitch-controlled variable speed rotor and a full power converter, capable of meeting the requirements of the most demanding grid codes, e.g. with respect to reactive power.
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