Siemens tests direct drive wind turbines

10 July 2008


Siemens Energy is embarking on a project to test the performance and cost of large-scale direct drive (DD) wind turbine technology.

The company is to install two 3.6 MW wind turbines equipped with DD technology at a site in west Denmark and test them over a two year period. It hopes to establish whether DD technology is competitive with geared wind turbines.

“Direct drive wind turbines are an exciting technological option, but at this stage we cannot yet state whether they will prove to be a competitive alternative to geared turbines,” said Henrik Stiesdal, CTO of the Siemens Wind Power business unit. “But with the installation of two DD test turbines Siemens is laying the foundation for such a judgment and is once more demonstrating its role as the front-runner in the development of innovative technology.”

With a rotor diameter of 107 m and a power rating of 3.6 MW, the two test turbines are similar in design to the standard Siemens SWT-3.6-107 offshore machine. They will be equipped with synchronous generators excited by permanent magnets.

Siemens says that it will continue with the development of geared turbines, and plans to release new turbines with geared technology in the coming years. The wind sector is a major contributor to the company’s environment portfolio, which in fiscal 2007 generated revenues of around EUR17 billion.

DD wind turbines have a straightforward design that negates the need for a gearbox. They therefore have the potential to reduce maintenance costs and have higher availability, but are known to be heavier and more expensive to manuacture.

A key part of the project is to establish at which turbine size the DD technology becomes competitive with geared turbines. Siemens will focus on offshore applications, where wind turbines need to be particularly robust and reliable.

The two test generators will be supplied by different companies – Converteam and Siemens Industry Sector – enabling Siemens to compare the benefits of different technical solutions with respect to generator design.

“At a nominal torque in the range of 2500 kNm the two generators are among the largest permanent magnet machines ever built anywhere in the world,” said Stiesdal.

Prior to installation of the DD test turbines, the two generators will be tested on a test bed specially built for this purpose. Inside the test bed the generators can operate up to and above nominal power and speed.

The tests on the first generator have confirmed all theoretical assumptions made in the conceptual studies, while testing of the second generator has been in progress since June, says Siemens.




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