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When it comes to choosing the right drive train technology for a wind power plant, high yield is only one aspect that has to be considered. Reliability and costs – which include transportation and logistics as well as service after the turbine is installed – play an equally important role. Siemens offers two different turbine types for different application: geared and direct drive wind turbines.
The first wind turbine installed by Siemens was a geared one. So clearly, with an over 30-year track record of reliable operation, our geared turbines are proven technology that stand for high availability, low investment risk, and a long lifetime.
Their drive train marks the result of a long evolution. The gearboxes convert the massive torque of the main shaft into rotation speed. The fully enclosed asynchronous generator features a squirrel-cage rotor without slip rings, which helps to extract the maximum energy yield. This proven combination of gearbox and generator is an evolutionary design for high-energy yield – even at less than full loads – because the generator rotor construction and the stator winding are specifically designed for high efficiency at partial loads.
Drawing on our extensive experience, we have improved the efficiency and resilience of all components over the years. For maximum protection of the internals, a square steel canopy encloses the nacelle. Furthermore, to lower service costs and reduce work time, the nacelles are specifically designed to make the moving parts easier to access.
In wind turbine design, it’s crucial to take a holistic view that incorporates the design and construction, materials, processes, manufacturing, and installation. Since the first prototypes were installed in 2009, our gearless direct drive solutions have carefully balanced all these factors in a compact system. Service personnel are directly involved in the development process, to ensure optimal working conditions and serviceability.
Notwithstanding the reliable track record of gearboxes over the years, they remain the most complex components in wind turbines. It follows that eliminating the gearbox reduces complexity and can further increase reliability. Replacing the gearbox, the coupling, and the high-speed generator with a low-speed generator eliminates two-thirds of the conventional drive-train arrangement. As a result, the number of rotating and wear-prone parts is greatly reduced compared to a geared machine, and therefore maintenance is a lot easier.
For optimum efficiency, we chose a permanent magnet generator. The main advantage of permanent magnet generators is their simple and robust design that requires no excitation power, slip rings, or excitation control systems. This leads to high efficiency even at low loads. The generator is positioned between the tower and the hub, producing a comfortably lean arrangement of the internals in the nacelle. This leaner nacelle, the removal of the gearbox, and other design simplifications result in lighter weight and smaller dimensions – which means lower costs for transportation and installation.