Blowing in the wind: GE’s new workhorse gets off to a flying start

PEi recently visited GE’s upgraded ‘centre of excellence’ for wind turbines in Salzbergen, northwestern Germany, to examine the US giant’s new 2.5xl MW turbine, poised to become the company’s new workhouse for the European wind sector.

Tim Probert, Deputy Editor

Credit crunch? What credit crunch? seems to sum it up. Despite the tough financial conditions, there are still some booming markets left. Wind power is one of them. The European wind power industry alone is expected to grow by 1-2 GW a year to total around 15 GW of new installations by 2012, an annual average growth rate of 11 per cent.

The current financial crisis apparently holds little fear for GE’s wind turbine business, which is now worth some $6 billion a year. Mete Maltepe, global wind sales leader for GE, believes the wind power sector will sail through the choppy waters.

GE’s 2.5xl wind turbine supercedes the successful 1.5 MW machine to become its new European workhorse
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“Our view of what is going on in the markets is that in the short term there is turmoil and projects will be delayed, but the fundamentals are that people need energy and governments support renewable projects,” he said. “Wind energy projects are quality projects and when credit is tight money usually goes to quality projects. We think that in a few months when the credit markets are back to normal, wind projects will benefit so we are not worried at all.”

At Salzbergen, northwest Germany, at its so-called ‘centre for excellence’ for wind energy, GE is gearing up to meet this expected demand. The US giant has unveiled its new 2.5xl MW wind turbine, which incorporates GE’s most advanced technology in terms of efficiency, reliability and grid connection capabilities, and is designed to yield the highest annual energy production in its class.

The 2.5xl MW wind turbine is designed to be a direct replacement for the 1.5 MW wind turbine, which has been nothing short of a triumph for GE. Operating in 19 countries, with more than 125 million operating hours and generating over 75 000 GWh of power, the 1.5 MW machine is claimed to be the most widely deployed wind turbine in the world. Vic Abate, GE’s vice-president for renewables, said: “The 1.5 MW is an industry leader. The 2.5 MW machine is built off the same strategy: a workhorse that fits broad applications and helps the European region achieve its renewable energy goals.”

The 1.5 MW was inherited from Enron, GE having acquired its wind power business in a bankruptcy sale following the collapse of the fallen giant in 2002. Maltepe said: “We took the design we acquired and applied GE technology to places such as the legs and gear boxes and improved the design, the efficiency and the reliability, and significantly improved the diagnostic capabilities. By the end of this year we will have about 10 000 of these units operating around the world and more than 2000 in Europe.”

The 2.5xl machine is specifically designed for the European onshore (class II and III) wind turbine market. The turbine can be equipped with various towers resulting in hub heights of 100 m, 85 m and 75 m, meeting potential tip height constraints and maximizing energy yield.

GE claims the 2.5xl wind turbine also excels on sites that are constrained by environmental regulations. For example, the optional noise reduced power operation modes accommodate noise restriction, while maintaining a high energy yield.

Higher efficiency

The 2.5xl wind turbine is equipped with a permanent magnet generator, ensuring high efficiency even at low wind speeds.

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Compared with a conventional doubly-fed system, the efficiency in the partial load range is remarkably higher, resulting in increased revenues for wind power producers. Employing magnets instead of copper coils in the generator rotor reduces electrical losses in the generator and current flow through the rotating parts of the generator. The brushless system also simplifies maintenance activities.

The interior of the nacelle is designed to optimize maintainability and ergonomics for the maintenance crew. It provides an environment that facilitates safe and efficient maintenance and inspection work.

Automatic lubrication systems for the grease-lubricated bearings are used to accommodate a 12-month maintenance interval under normal operating conditions. Not only does this minimize turbine down-time and provide the opportunity to avoid maintenance in the windiest seasons, it also provides the operator of remote sites with the opportunity to plan for maintenance in the season that the turbine is most accessible.

The optional elevator and climb-assist facilitate ergonomically optimal operations and maintenance of the turbine, enabling people to visit more wind turbines per day. This improves availability and reduces the size of the labour force required to operate a wind plant.

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A double-bearing main shaft minimizes gearbox thrust and bending loads by transmitting loads through the bedplate to the tower. The gearbox is only subjected to torque loading, which is controlled by the wind turbine through the converter, resulting in less severe and better predictable loads than in conventional drivetrain designs.

The double-bearing main shaft also improves overall drive train reliability and improves gearbox lifetime predictability. Additionally, a full power converter separates the generator and gearbox from the grid, allowing them to remain essentially unaffected by transient grid loads. This system design results in robust and reliable power conversion.

GE claims the main bearings remain well lubricated even under severe conditions due to grease lubrication, which unlike oil, requires no heating at low ambient temperatures to keep its lubricating properties.

The hub design contains an integrally cast web in the blade root opening, providing high stiffness to the hub assembly. Higher stiffness results in less deflection of the hub, and therefore less loads on the components mounted to the hub. Consequently, stresses on the pitch bearing and pitch drive are reduced significantly when compared with conventional designs.

The 2.5xl MW wind turbine is designed according to GE’s Design for Reliability (DFR) methodology. DFR starts with the definition of reliability goals and the environmental conditions in which the wind turbine components must operate. The reliability targets are then broken down to component level models that are developed to predict reliability.

A key step in the DFR process is validating design assumptions on both component levels and system levels. Different types of testing are used for validation, including climate chamber testing, compliance testing and Highly Accelerated Life Testing (HALT). HALT testing is a tool to flush-out design flaws rapidly. In the test, components are subjected to loads of the entire design life, but in a very short time frame.

The next step is field validation. The 2.5xl design was validated with more than four years and 500 000 hours of operating experience. After extensive field validation, one turbine was decommissioned so that GE’s engineers could tear it down and inspect all of the major components.

The last step of the DFR methodolgy is production auditing, where validation is focused on ensuring that the 2.5xl design is free of flaws. The production audit is focused on ensuring that each unit is delivered with consistent quality by understanding the impact of manufacturing variability.

Electrical system design

The electrical system design of the 2.5xl wind turbine consists of a permanent magnet generator and full power conversion. In the lower tower section, the power module efficiently converts the energy from the permanent magnet generator into power that provides the necessary frequency and voltage control required by transmission system operators.

GE’s new 2.5xl MW wind turbine being manufactured at its ‘centre for excellence’ in Salzbergen, northwest Germany
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The integration of the converter and transformer into the downtower, rather than the nacelle, ensures that vibration loads do not affect the reliability of the power electronics. The converter cooling system has been designed to minimize moving parts for reliability and features passive coolers that use the same wind that powers the turbine.

Seamless grid integration

Wind turbine performance is a critical issue in light of increasingly stringent grid requirements. By providing a sophisticated set of grid-friendly benefits similar to conventional power plants, GE says its integrated suite of controls and electronics offers “seamless grid integration”.

The full-size power converter concept is an important technical advantage to reduce grid constraints and to maximize the connectable MW capacity at the network. GE technology can support the grid through reactive power supply, and with the WindCONTROL system, it can be operated in a similar way to a conventional power plant.

The training centre at Salzbergen allows 2.5xl turbine owners and operators, as well as GE’s own service technicians, to get to grips with the new machine
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With the WindFREE Reactive Power feature, the 2.5xl wind turbine can generate reactive power even when the wind is not blowing. Consequently, it reduces the need for additional VAR-generating equipment, thus minimizing investments in electrical infrastructure.

Maltepe said: “We are definitely a leader in this industry at working with the grid companies to understand the requirements they might have. If you have more and more renewable energy on the grid à‚— intermittent energy à‚— there are more issues to deal with and we are working to provide reactive power. So I think you will see from GE a new feature every year to help support the grid.”

With demand for the 2.5xl expected to be strong, GE has invested more than $100 million and added 160 jobs to enhance the facility, not just in manufacturing but also services, and a world-class training centre, allowing owners and operators to get to grips with the new 2.5xl machine.

The Salzbergen plant expansion includes the addition of 28 000 m2 of property, revamping of the production hall to prepare for the ramped up production of the 2.5xl wind turbine turbines, and adoption of LEAN six sigma manufacturing processes.

The site has a moving line production system based on Toyota’s methods of simplifying the manufacturing process and shortening lead times, where the turbines are assembled on a constantly moving platform carrying the turbine from one numbered workstation to another.

The Salzbergen facility is capable of producing about a turbine every 30 hours in a three nine-hour shift system including a three-hour parts ‘take time’. To shorten lead times, GE’s philosophy is to avoid variances, such as modifications to the downtower electronics, until the final stages of the manufacturing process.

The upgraded site also features a training facility that includes a 2.5xl test turbine, which uses a generator to drive its shaft rather than wind power and means the roof of the building does not have to be removed to make way for the 100m blades.

A 10m-high mock-up of part of a turbine tower is also used to teach rescue methods in case maintenance staff are injured accessing the 50m-plus turbines. During 2007, 1110 students were trained in the facility and that tally was surpassed by the third quarter of 2008.

GE has already received more than 1000 MW of orders in Italy, Spain, Belgium, Poland, Turkey, Germany, Romania and France for the 2.5xl product, which equates to enough wind-generated electricity to meet the demands of more than one million German households. With support from carbon credits, cap-and-trade, government subsidies and emissions targets, it is hard to disagree with GE when it says it expects the 2.5xl to help the European region achieve its renewable energy goals.

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