Feature

Narec drive train facility moves forward


David Hopwood

Steelwork is being erected on the site of a new £45m turbine drive train testing facility at the National Renewable Energy Centre (Narec) in Northumberland, UK. When complete it could be the most advanced of its type in the world.

NB: this article was first published in Renewable Energy Focus magazine. For a free subscription, click here.

As the UK's Round 3 offshore wind ambitions move from the realms of blue sky thinking into cold, hard, realism, the sheer scale of the undertaking becomes clear. As do the challenges associated with commissioning a vast number of huge wind turbines in harsh offshore terrains.

For any of this development to happen and for industrial supply chains to be empowered, investment needs to be forthcoming, and risks need to be adequately assessed.

This extends to the reliability and durability of the technology, with a new larger class of turbines under development. The challenge with offshore wind, and hence for those looking for concrete indications of how to quantify such risk, is that due to a lack of scale to this point, data is just not readily available compared to other industries. It is difficult therefore to establish how turbines respond to the harsh offshore environment, and how stresses they are put under at sea will effect them.

Companies therefore need to replicate the offshore wind regime in a testing environment, and this is one of the challenges that Narec in the North East of the UK has set itself. Narec is a research centre that is helping to accelerate grid integration of renewable energy systems, and catalyse the development and deployment of offshore wind, wave and tidal energy generation technologies.

With a 15MW drive train testing facility under construction, Narec plans to offer an independent, self contained testing hub for the offshore wind industry that OEMs and others can take advantage of to validate their technology.

Where this concept is not unique globally, what is impressive about Narec is the range of testing facilities in one location: Aside from the 15MW drive train test facility that will be commissioned in summer 2013, Narec is also home to a 3MW marine drive train test facility; two blade test facilities with testing capability for blades up to 100m; as well as a proposed 100 MW offshore demonstration site for wind turbines of novel or prototype designs (see image).

In total, a current investment of around £115 million is being made at Narec, and a further build out of the Blyth Offshore Wind Demonstration Site starting in 2013/14 will increase this figure by an additional £250 m.

The testing imperative

According to Tony Quinn, Director of Major Projects and Assets at Narec, the organisation sees its role as helping OEMs to demonstrate the reliability and capability of the technology, in advance of a developer or utility procuring that technology: “Developers are faced with a difficult procurement decision - which technology to back and which OEM to back - because they want to make their investment with a degree of confidence,” he says.

And Narec's combined test facilities will also lead to increased competition and ultimately better technology, Quinn believes: “Part of our agenda is to introduce competition to the market because the barriers to entry are high, especially with the huge investment required. So will all companies be able to build their own test facilities? – Probably not. Is there benefit of having an independent test facility independently verify this technology? – Yes, because manufacturers are cautious, so the idea of these facilities, from a political perspective, is that they reduce that barrier to entry and introduce competition – which can only be good for the industry”.

Not surprisingly, says Quinn, even with the drive train testing facility still over a year from completion, there is significant interest from the market: “It's clear that in an offshore wind world where data to this point may be scarce, test facilities become a vital way of getting investor confidence and buy in. This could extend to a utility, a developer procuring technology, a bank that is interested in financing a project, or even a company trying to buy insurance for a project.”

Failure analysis

Quinn explains that what testing facilities like Narec's offer is the ability to eliminate early life failures through robust testing. In essence there are various ways to do this without testing, he says, for example taking a “learning by doing” approach: in other words putting turbines out in the sea and observing what happens – i.e. as and when it fails you put it right.

But that clearly is a time intensive way of climbing up the learning curve.

With the case of Narec, says Quinn, “by introducing robust testing on a test rig in a controlled environment, you can go through those learning iterations much more quickly - learning the lessons much more quickly, and getting to the point of maturity more quickly.”

He adds that one of the challenges to date has been the fact that there hasn't been a test rig capable of testing the whole system on this scale. But Narec's test rig does just that, using six degrees of freedom, Quinn says:

“This allows us to get rid of any idiosyncrasies where subsystems join together, and at interface test them robustly; including the controls, the electrics; and the mechanical behaviour of the system.

“Also, we are able to replicate the real-life events of the wind. We can input a trace of an extreme wind event - where there's a large gust, an extreme gust or an extreme change of direction in the wind - or we can input small variations which are more representative of fatigue. And we can replicate this in six degrees of freedom, and this is the unique nature of this test rig. There are other test rigs that will test torque, but this test rig is capable of what's called non-torque loading, capable of replicating an over-turning moment”.

This complex testing process replicates a scenario where a blade that should be feathered, presents a large surface area to the wind, placing it and the drive train under huge stresses.

In this situation, it is difficult to assess how this affects different components - like the drive train.

“With the testing rig, we can recreate that in a controlled environment by applying an overturning moment,” Quinn says, “which is what I call the non-torque load.

“The rig that we're designing and building at the moment is capable of an overturning moment of close to 60 Meganewton metres [6,000 tonnes acting at a distance of one metre]. So a huge load”.

Bringing down procurement costs

Quinn believes that what self-contained testing facilities can really provide is a framework to ultimately reduce technology procurement costs, as well as help pull through innovation into the technology developers’ R&D labs.

“If you simply learn by doing, you observe that something has happened and then start to correct it, then that process takes a long time to evolve. You can accelerate that process by investing in innovation, and trying to pull through the technology. These test facilities have an important role in pulling through that innovation. Combining innovation with R&D, you will go through an even higher accelerated route - and that is really where we are trying to contribute to the industry moving forward, through our offshore demonstration sites – which we are developing - and investment in drive train and blade testing facilities”.

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