Gearless wind turbines more often picked for the job

Siemens Energy has been awarded another order from Minnesota Power for 35, 3-MW SWT-3.0-101 direct drive wind turbines for its Bison 2 wind energy center near Center, North Dakota. The scope of supply for the wind-power plant includes transportation, erection, and commissioning of the 35 wind turbines, as well as a three-year service and maintenance agreement. Deliveries of the wind turbines will commence in August 2012, and the wind power plant is scheduled for commissioning by the end of 2012.

This order is the third for Siemens direct drive wind turbines in the U.S., including Minnesota Power’s Bison 1 North Dakota and Oklahoma Gas & Electric’s Crossroads Oklahoma wind power plants. “Our direct drive turbines have only half the parts required for a conventional geared wind turbine and a significantly smaller number of moving parts, allowing for increased output and improved maintainability,” says Jan Kjaersgaard, VP and general manager of Siemens’ Americas Wind Power business.

 The SWT-3.0-101 direct-drive wind turbine has a rated power output of 3 MW, a rotor diameter of 101 m, and an innovative permanent magnet generator. The first prototypes of the SWT-3.0-101 have been running for more than a year and are meeting all expectations in terms of reliability and performance, according to the company.

Siemens
http://www.siemens.com/energy

2.3 MW direct-drive turbine manufactured in Saginaw

The Northern Power 2.3 MW wind turbine is based on the company’s 100 kW unit and has, says the company, more than 50 years of cumulative field operating experience. Northern Power adds that the permanent-magnet generator and power electronics technology are state of the art. The company has installed and commissioned its first prototype Northern Power 2.3-MW wind turbine. The prototype is owned by Heritage Sustainable Energy and installed at the Stoney Corners wind farm in McBain, Michigan. This prototype turbine, shipped from the new Northern Power factory in Saginaw, Michigan, is the largest direct drive wind turbine in commercial operation in North America.

Using advances in permanent magnet (PM) generators and power electronics, the 2.3-MW unit  is said to represent the next generation in wind turbine technology. Its drivetrain eliminates need for a high-torque gearbox, thereby greatly simplifying the design while removing a frequent area of failure in competing wind turbines. The turbine rotor connect directly to a slow-speed PM generator rotor, without a separate gearbox, main shaft, bearing set, or couplings. This simple design transmits operating loads more directly to the tower, with a minimum number of parts in the load path.

The PM generator eliminates also need for rotor field windings, a field excitation system, and field-circuit slip rings. Eliminating field-circuit losses results in higher overall turbine efficiency, especially when operating at partial load. The proprietary low-speed PM generator is optimized for efficient energy capture with a higher power curve. Other advantage include 20% less weight of magnet materials, 75% fewer stator-coil assemblies, higher power density, and it’s easier to fabricate and assemble

The company adds that the FlexPhase power converter’s design offers high efficiency, high output-power quality, low generator stress, and advanced grid support and ride-through capabilities. The power converter, matched, and optimized for operation with the low speed generator, uses rack-out modules for fast and easy service.

The power converter, in combination with the PM generator, optimizes overall power train performance. This system results in more power delivered onto the grid than from competing designs. The software-enabled advanced topology has 40% fewer IGBTs, 50% fewer capacitors, and a higher power curve than similarly sized turbines.

In addition, the power converter and main transformer are located up-tower. Electricity is converted to medium voltage closer to the point of generation, minimizing long power cable losses between components. This layout results in increased efficiency and lower electrical losses, yielding more revenue-generating power.

Northern Power Systems

northernpower.com

Direct-drive generators find more followers

No gearbox will ever fail in our turbines, says Northern Power Systems VP James Stover. The reason for that is there are no gearboxes in the company’s turbines. Stover says his company’s Northwind 100 can still match the power needs of many local applications, whether municipalities, schools, farms, or business campuses. The turbine’s physical size is said to fit within constraints common to highly populated areas. The Barre, Vermont company says the unit was developed with a NASA grant, and designed for remote and isolated sites.

The company adds that its turbine works well in low winds, so users need not live in a high-wind area to benefit from wind power. The turbines can begin making power at wind speeds as low as 3 m/s. The gearless direct drive is said to maximize energy capture and it outperforms conventional gearbox designs. The turbine’s power converter provides smooth, clean power to local grids which simplifies grid interconnect. The company says its advanced fiberglass reinforced blades use an aerodynamic design shaped by its engineers.

The firm adds that one to three of the 100 kW units can meet all the energy needs for most municipalities, schools, and small industrial sites. Furthermore, the company says the turbine is without complicated approvals or expensive interconnection requirements.

The Northwind 100: By the numbers

Direct drive turbine needs no gearbox

Most utility-sized wind turbines use a costly speed increaser to drive a generator. Netherlands-based Emergya Wind Technologies (EWT) however, builds wind turbines based on a direct-drive (gearbox free) design. The company says its turbine offers improved performance and reliability over conventional wind turbines.

The company’s main product is a 900 kW, pitch controlled variable speed wind turbine. The unit builds on over ten years of operational experience with the company’s 750-kW turbine, of which over 200 units have been installed. A future challenge, says the company, is to develop large wind turbines in the multi-MW range for onshore and offshore cites.

EWT’s 900-kW design uses a multi-pole ring generator that rotates slower than conventional designs, for long life. An autotransformer, which sits between the generator and a power converter, reduces the voltage to 690V. This is standard in the wind industry.

The generator operates at a varying frequency, directly proportional to the rotor speed. The converter modifies this variable frequency output to a fixed frequency corresponding to the grid frequency, 50 or 60Hz. This arrangement, according to one consulting firm, is now finding favor with many manufacturers of multi-megawatt turbines.

This design replaces a complex high-speed geared drive train common in most conventional wind turbines. To further reduce the number of rotating components, a large single main bearing (three row, cylindrical-roller unit) carries the rotor assembly and generator rotor, to reduce the number of rotating components. A monocoque main chassis gives easy service access to essential rotor hub internals, such as rotor-blade-pitch drives and back-up batteries.

The turbine feeds generator power into the grid by means of a ‘back-to-back’ (ac to dc to ac) type full-converter equipment. This converter has several programmable functions such as a capability to limit output during night hours and a noise reduction feature. Built-in grid-fault-ride-through technology is available on demand. The company says the features make the design well suited to solitary applications, weak grids, and high-turbulence sites. EWT says it operates in compliance with ISO 9001:2000 and is VCA** certified, one that tests safety control systems of servicing companies in an objective and structured way. It is comparable to OHSAS18001. The table lists a few specs.