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Gear change

Gearless technology promises to save money by improving wind turbine reliability and efficiency. RET looks at some of the market’s latest products

Developments in gearless technology are cutting costs and improving reliability and efficiency for wind power

The move towards gearless units in the wind sector has been propelled by the growth of offshore wind and a conviction amongst leading turbine makers that it offers the best solution for improved reliability and reduced operational and maintenance costs. The need to focus on cost has also been sharpened by the effects of the economic downturn in Europe and the States.

So what gearless technology is out there and what exactly are their benefits when compared with gearbox systems?

Improving the yield

Italian group Leitwind is one of the world’s leading manufacturers of gearless wind turbines. To date it has installed 200 units worldwide with a particular focus on its home market in Italy and India.

According to the company, its gearless product range meets all “thinkable climate and grid demands” and includes the LTW70 2.000 KW turbine, with a rotor diameter of 70.1m and the LTW101 3.000 KW turbine, with a rotor diameter of 100.9m. The range is buoyed by an annual EUR 5.8m R&D budget.

Leitwind says the turbines are equipped with a direct-drive multi-pole synchronous generator using permanent magnets attached to the rotor thus “improving the yield by eliminating the need for electrical excitation of the generator coils” through a gearbox.

In essence this is the heart of direct drive technology - replacing traditional turbine design which sees the gearbox and the rotor connected to a generator to get a flow of current.

Leitwind says the benefits of its technology include reducing the number of rotating parts, which means less friction and more efficiency with fewer mechanical and electrical losses. As the technology produces slower rotor speeds there is also the advantage of reduced downtime and maintenance activities through less wear and tear. Leitwind is also able to change coils in the stator part of the generator and magnets; a task it claims only a few turbine manufacturers can do.
 
“Our design is based on a modular concept that lowers installation costs,” the company says. “The generator is part of the load-bearing structure which contributes to an economical weight management. This allows a speedy replacement of generator parts without having to dismantle the whole generator and without having to involve crane operations.”

Due to the modular concept Leitwind is able to use standardised truck transport, reducing logistics costs and environmental impact. The company also claims that its turbines are less noisy than those containing gearboxes.

As a result of its quieter and more reliable technology the company says new wind markets such as Alpine forests can now be opened up. It also sees further development in the offshore wind sector for gearless units.

“It has huge future potential,” says Leitwind.

Increasing lifespan

German turbine manufacturing Enercon says its direct drive technology is based on a basic principle.

“Fewer rotating parts reduce mechanical stress and increases a machine’s lifespan,” the company says. “Wind turbine maintenance and service costs are reduced because of fewer wearing parts and no gear oil changes.”

Its rotor hub and the rotor of its annular generator are directly interconnected to form one consolidated unit. The rotor unit is mounted on a fixed axis, called the axle pin. The annular generator, a low speed synchronous generator with no direct grid coupling, has separate excitation.

“Unlike conventional geared systems with a large number of bearing points in a moving drive train, our drive system only requires two slow moving rolling-element bearings,” Enercon says. “The reason being its low direct drive speed.”

Lightest in class

German giant Siemens is also making serious inroads into direct drive technology. It recently launched its third turbine with a direct drive system, a 6 MW model with rotor diameters of 120m and 154m and specifically for use offshore.

It says its model has 50 per cent fewer parts than comparable geared wind turbines and helps it become the “the lightest machine in its class”, easing installation out at sea. It builds on the direct drive technology installed in its 2.3 MW class turbine using a compact permanent magnet generator to maximise production at sites with low to moderate wind speeds. This type of generator requires no excitation power, slip rings or excitation control systems. The company says this results in “high efficiency even at low loads”.

Henrik Stiesdal, chief technical officer of the Siemens Wind Power Business Unit, says: “Gearless technology is low maintenance. It maximises our customers’ returns.”

That in essence is the main driver behind the growth of direct drive. As the downturn in Europe and the US continues it will become of increased importance for operators in those regions. But those in emerging wind markets should also be interested in the potential of gearless turbines to help them boost profitability and aid investment as they begin their wind journeys.