New technology improves the reliability of wind turbines

The world's first commercial Brushless Doubly-Fed Generator (BDFG) is to be installed on a 20kW turbine at or close to the University of Cambridge Engineering Department's Electrical Engineering Division Building on the West Cambridge site by early 2008. This will help the University meet its obligations under new legislation, which requires a new building to obtain ten percent of its electricity from renewable sources.

The research team, led by Dr Richard McMahon, have developed a new generator technology for the wind turbine industry to the point of commercial exploitation. This type of generator can be used in a wide spectrum of wind turbines ranging from multi-megawatt systems for wind farms down to micro turbines used for domestic power generation

Research in Cambridge on this type of generator was started by Professor Williamson in the 1990s and, since 1999, is now being undertaken by Richard and his team. The team are collaborating with Durham's Head of Engineering, Professor Peter Tavner. The research has recently matured, enabling practical and complete designs to be made with confidence. Wind Technologies Ltd has recently been founded to exploit the technology.

"We are very excited about the new installation. This will be the first time BDFG is to be used commercially. The benefits to the wind power industry are clear: higher reliability, lower maintenance and lower production costs" recalls co-researcher and Managing Director of Wind Technologies, Dr Ehsan Abdi. "The West Cambridge medium size turbine should successfully demonstrate the applicability of the new generator, and we hope it will encourage the developers of other new construction projects to consider local wind-powered electricity generation to meet their obligations", adds Ehsan.

On a larger scale, a 600kW generator built by Wind Technologies is to be tested on a DeWind turbine in Germany, starting next spring. Its planned one-year test should demonstrate the improved performance of the BDFG technology to the key players in this industry. "This will put Wind Technologies in a position of strength in pursuant discussions on technology trade sale, licensing or partnering with large generator manufacturers, which is the strategy of choice for tackling this concentrated marketplace", says Ehsan.

A contemporary Brushless Doubly-Fed Machine (BDFM) is a single frame induction machine with two 3-phase stator windings of different pole numbers, and a special rotor design. Typically one stator winding is connected to the mains or grid, and hence has a fixed frequency, and the other is supplied with variable voltage at variable frequency from a converter.

In the majority (more than 90%) of newly-installed wind turbines in the world, generation is from a slip-ring generator. There are drawbacks to the use of slip-ring generators, particularly the additional cost and bulk of a machine which incorporates slip-rings and the need to maintain brush-gears including replacement of the brushes on a regular basis. Studies have shown that problems with brush-gear are a significant issue in wind turbine operation and reliability, and that the problem will be more severe in machines deployed offshore where there are stronger winds and accessibility is impaired.

The project received the Scientific Instrument Makers Award and the Cambridge University Entrepreneurs Business Idea Award in 2004. In 2005, the Institution of Electrical Engineers, now the Institution of Engineering and Technology, added its Innovation in Engineering Award. The company has recently received grants from Cambridge University Challenge Fund and East of England Development Agency to carry out market assessment, file patents and complete the pre-production prototype.

Harnessing wind power for electricity generation is becoming ever more common, both by large-scale wind farms, and increasingly by small domestic installations, with the UK the world's leading market for micro wind generation. "We hope that our generator, through offering high reliability and low maintenance, will significantly contribute to the wider adoption of wind power generation, particularly in offshore developments. This will lead to significant reductions in CO2 emission and further reduce our dependency on fossil fuels" says Ehsan.

Technorati : improves, reliability, technology, turbines, wind

String Theory's Next Top Mode

Ernest Rutherford used to tell his physics students that if they couldn't explain a concept to a barmaid, they didn't really understand the concept. With regard to the cosmological implications of string theory, the barmaids and physicists are both struggling-a predicament that SLAC string theorist Shamit Kachru hopes to soon resolve.
String theory is currently the most popular candidate for a unified theory of the fundamental forces, but it is not completely understood-and experimental evidence is notoriously elusive. Physicists can, however, gain crucial insight into the theory by evaluating how accurately its models can predict the observed universe.

Using this indirect approach, Kachru, in collaboration with theorists at Rutgers University and the Massachusetts Institute of Technology, sought models that could reproduce inflation-the prevailing cosmological paradigm in which the nascent universe experienced a fleeting period of exponential expansion.

Although there is already a substantial body of literature presenting such models-spawned in part by publications of Kachru and his Stanford and SLAC colleagues Renata Kallosh, Andrei Linde and Eva Silverstein in 2003-the complexity of the models leaves room for doubt.

"They incorporate inflation, and they're the most realistic models of string theory," Kachru said, "but they're complicated. They're fancy. They have a lot of 'moving parts,' and we need to fine-tune all of them, so we can't verify anything to a high degree of accuracy. It forces us to ask-are we confident that we really understand what's going on?"

To achieve a comprehensive understanding of how inflation can be embedded in string theory, Kachru and his collaborators employed a pedagogical tactic. "What we wanted was an explicit 'toy' model," Kachru explained. "The goal wasn't to have something realistic, but to allow us to understand everything to every detail."
"There are deep conceptual questions about how inflation is supposed to work," Kachru continued. "In order to understand these issues, it's best to have a simple model. There's so much clutter in the complicated examples, you can't disentangle the conceptual issues from the clutter."

The group investigated three versions of the simplest formulation of string theory, and found that they were incompatible with inflation. "This means we're going to have to consider slightly more complicated scenarios," said Kachru. "There are a lot of levels between this and the fancier working models, so we'll find one eventually."
"There are deep conceptual questions about how inflation is supposed to work," Kachru continued. "In order to understand these issues, it's best to have a simple model. There's so much clutter in the complicated examples, you can't disentangle the conceptual issues from the clutter."

The group investigated three versions of the simplest formulation of string theory, and found that they were incompatible with inflation. "This means we're going to have to consider slightly more complicated scenarios," said Kachru. "There are a lot of levels between this and the fancier working models, so we'll find one eventually."

Kachru and his colleagues published their work in Physical Review Letters D, providing a framework for others in search of simple inflationary models of string theory. "There are so many successful models out there that incorporate string theory and inflation, so we'll undoubtedly find a simpler version.

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