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Close up - Avantis pins wind ambition on AV 928 turbine

Windpower Monthly technical writer Eize de Vries takes a look at German manufacturer Avantis Energy and its efforts to establish itself in the wind energy sector with its 2.5MW AV 928 turbine.

The Avantis AV 928 turbine with its distinctly-shaped nacelle
The Avantis AV 928 turbine with its distinctly-shaped nacelle

 Headquartered in Hamburg, German wind market entrant Avantis Energy has set out an ambitious global expansion strategy. The company’s key asset is its direct drive wind turbine technology developed since 2004 by both its in-house team and in close cooperation with highly experienced external specialists.

AV 928 turbine prototype operating in China (left) and a generator being hoisted as part of the construction of the nacelle.

In manufacturing, Avantis has established joint ventures with industrial groups in all main global markets and continents. The first of these was signed with a South Chinese Beihai-based firm Yinhe Avantis Wind Power Co. Ltd. Others include industrial giant Hyundai Heavy Industries (HHI) of South Korea, which signed an OEM contract to manufacture generators over a year ago.

Most recently EDRB in Brazil was brought onboard. Additional short-term manufacturing partnerships are planned for North America and Europe.

Building a track record

Avantis CTO and founder father of the Avantis technology Detlef Lange said the choice of a Chinese partner to kick-start the wind business is closely linked to the size of its wind market and its accessible project finance.

Lange added: "A presence in China offers us the opportunity for building a fast track record, and an additional benefits is that 95% of the rare earth materials applied for the generator magnets originate from this country. However, HHI has been assigned to deliver the direct drive generators for all our turbines produced worldwide."

The first turbine model is the 2.5MW AV 928. It is fitted with an Avantis water-cooled permanent magnet generator (PMG) and in-house developed A AB 92 rotor blades. It is characterised by a distinct nacelle shape designed by German industrial designer Prof. Luigi Colani

The turbine’s rotor diameter is 93.2m. Standing alongside a scale model of the turbine, Lange explained the reasoning behind this: "Our generators have been designed as a modular concept, whereby the AV 928 generator has a ‘standard’ 5 metres outer diameter and 1.2-metre depth."

This latter dimension can be adapted to different power ratings and matching rotor diameters by varying its depth. "We deliberately went for water-cooling due to its superior cooling performance compared to more common air-cooled concepts. Advantages in our view include favourable operating temperatures with only a very minor 22-degree temperature variation in the operational range including full load. That in turn reduces drive system peak loads and substantially enhances generator operational lifetime."

Key design feature

Like recent generator projects developed by competitors featuring permanent magnets in the rotor part (PMG), Avantis choose a so-called inverted generator concept. Hereby the generator outer ring, with the magnets attached inside, rotates around the stator. This enables a relatively compact design and the easy integration of the water-cooling system.

It is a clever design feature. One potential benefit is incorporation of the individual pitch fail-safe function rotor blade batteries into the generator stator, as opposed to the rotating rotor hub. The water-cooled medium-voltage transformer is located straight above the tower and the control cabinet behind it. Like the generator, these two units are water-cooled and all three are temperature controlled by a cooling unit in the nacelle rear section.

Avantis evaluated other design aspects too as part of its supply chain strategy. Lange said: "Of key importance to us is the ready option to purchase key components from multiple sources, but only those with a sound proven track record.

"That means in practice that we deliberately went for a main shaft with two rather easy available bearings instead of a single rotor bearing, despite a slight extra weight penalty. And for key power electronic components like the power converter and controllers we only work with well-established partners like ABB."

AV 928 – the bedrock of the range

The AV 928 turbine is to serve as the basis for an expanded range with various power ratings and rotor sizes. A prototype was installed Beihai in May 2009, and Avantis commenced with certification measurements this year. A first batch of 80 turbines has been sold for a project in Vietnam, with several projects in the Asian Pacific, Latin America, North America and Europe in the pipeline.

Serial production of a AV 928 Cold Weather version for use in Northern China will follow as will a 2.3MW AV 1010 (rotor diameter 100.6m) for low and medium-speed WC IEC IIIA wind conditions.

Additionally a 3.3MW ´strong wind & near shore´ version is under development and a test turbine will be installed Q2-2011. Simultaneously, Lange is exploring the possibility of developing larger power ratings both for onshore and offshore application. He thereby feels that a combination of robust mechanical design with fully enclosed PMG and climate-controlled nacelle makes the Avantis turbine concept especially well suited for offshore application.

Lange concludes: "A number of major offshore wind farm developers have already approached us in the past months with specific requests for large offshore wind turbines. This is no-doubt tempting, but we do not want to be rushed and first ensure that all our technology-related and other expectations are fully met onshore."

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