The illustration shows some of the equipment inside the Siemens 3.0 101 DD. The red mechanism at the top is a crane to assist with heavy items.
You get the impression that wind-turbine OEMs are shying away from designs that use gearboxes. Take the Siemens SWT-3.0-101 DD for instance. The company eliminated its gearbox and in the process eliminated about half the parts needed for a similarly sized gear-driven turbine. The 3-MW unit works with a 101-m dia. rotor with blades made in one piece. The nacelle is smaller and lighter than previous designs, which simplifies transportation. For those technical feats, the Siemens SWT-3.0-101 DD is our Turbine of the Month. The prototype, near the company’s wind power headquarters in Denmark, was tested and validated before the design launched for sale this year.
“Compared to a conventional gear-driven wind turbine, we managed to reduce by half the number of parts in the SWT-3.0-101,” says Siemens Wind Power CTO Henrik Stiesdal. “With fewer moving parts, the direct-drive design has potential to significantly reduce maintenance, which could result in higher turbine availability.” The machine will be targeted for onshore and offshore markets.
“This direct-drive turbine is also lighter than its geared counterparts. The nacelle of a 3.0 MW direct-drive turbine is 12 tons lighter than the nacelle of a 2.3 MW geared turbine with the same rotor diameter,” says Stiesdal. “This is important for transportation and installation.”
The turbine features a compact synchronous generator excited by permanent magnets. The advantage of PM
The recent SWT-3.0-101 uses many tested components from previous designs.
generators is a simple design that requires no excitation power, slip rings, or excitation controls. This leads to high efficiency even at low loads. The company installed the first of two 3.6-MW direct-drive turbines in 2008 to assess the drive technology’s competitiveness with geared machines. “We concluded that the concept machines are operating well and we should proceed with a commercially competitive product,” he adds.
Siemens says the generator is completely new. With fewer than half the number of moving parts of an induction generator, the new design is easy to maintain and reliable. The compact size avoids specialized transports that larger nacelles often require.
The nacelle, 6.8-m long and 4.2-m dia., weighs 73 tons. This is “light” enough to be carried on trucks available in most markets. The dimensions of the new wind turbine allow for greater flexibility in road transportation. For instance, key bridge and tunnel clearances were considered when designing the turbine. An advantage of the new nacelle size is that transporting it in one piece minimizes expensive and risky on-site assembly of critical components.
Eliminating the gearbox reduces complexity, and increases reliability. Unlike electrically excited machines (induction generators) with a gearbox, a PM excited generator expends no energy for the excitation needed to generate electrical fields. Furthermore, the SWT-3.0-101 generator uses an outer rotor that spins around the internal stator. This design leads to the smallest possible diameter, which aids in reducing nacelle dimensions. It also allows for rigid support of the stator, which allows manufacturing to narrow air-gap tolerances and thereby high generator efficiency.
Despite the smaller nacelle, the turbine gives service technicians more space for their work. The part reduction gets credit for the extra space and making key components readily accessible. The “plug and play” design for most components allows swapping them out without affecting other components.
The SWT-3.0-101 is liquid cooled. Coolant temperature is regulated with a top-mounted, passive cooling system, avoiding high-power fans and thereby improving energy efficiency.
Of the five key wind turbine components – blade, rotor hub, nacelle, tower, and controller – all but the nacelle, come from existing company designs. Using proven components lets the company eliminate many variables traditionally associated with the introduction of a new product.
Grid-stability requirements grow as more wind power is fed into it. The company says its electrical equipment (NetConverter) efficiently decouples generator and turbine dynamics from the grid. The converter is said to offer good flexibility in the turbine’s response to voltage and frequency control, fault ride-through, and output adjustments. As a result, company turbines can be configured to comply with a variety of relevant grid codes in major markets and can be readily connected to the grid. Lightning protection is based on the IEC 61400-24 Lightning Protection Level I.
The rotors of the SWT-3.0-101 are manufactured using the company’s patented process. The blades are made in one piece from fiberglass reinforced epoxy resin in a single production step. As a result, there are no glue joints, which minimizes environmental effects on the blade. WPE
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When the wires become excessively twisted it can be unplugged, untwisted and re-plugged in
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The greatest reduction in tower top weight can be achieved by installing the generator at the base of the tower. Use a right-angle gear at the top to drive a vertical shaft at medium speed, transferring the power to the generator below.
A second gearbox at the generator provides the final speed increase. This gearbox can be designed to convert variable speed to constant speed for a synchronous generator. This eliminates the power electronics and provides pure sine wave power.
Reliability of the gear train is assured. The gears no longer experience shock from the wind. These shocks will be absorbed and then gently returned by the long vertical drive shaft, which acts as a torsional spring. The problem of gearbox shaft misalignment due to heavy static and dynamic loading is eliminated, protecting the bearings. Turbine installation and maintenance is easier with the electrical equipment at ground level.