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United States

Working harder to run turbines for longer

UNITED STATES: As an increasing number of US turbines move out of warranty,we look at the developments to maximise turbine efficiency, minimise unscheduled maintenance and extend turbine lives.

Eighties models… Maintenance has become more sophisticated as the industry strives to make newer turbines last as long as some of the older ones
Eighties models… Maintenance has become more sophisticated as the industry strives to make newer turbines last as long as some of the older ones

Big data is key in operations and maintenance (O&M) in order to progress from an out-of-breath sprint to a well-managed marathon. It may take terabytes of information daily, analysed via remote diagnostics using a custom management system with models and overlays, but owners and operators can keep tabs on what is happening now and plan the next steps to maximise profitability and success.

This was one of the conclusions from a session on turbine maintenance at the American Wind Energy Association's annual conference in Florida in May. "Data is how you go from a sprint to a marathon," announced session chair Michelle Arenson, regional director of wind generation at Alliant Energy, a Wisconsin-based public utility holding company.

Steve Scott, general manager for renewables at Duke Energy Renewables, agreed. "Data is king. You make decisions based on good data." Of the data gathered, the weekly vibration report by site is the single most important, he added. "Is there a trend? Is there an issue out there, and can we take action?"

Duke Energy, the largest utility in North America, has about 2GW of wind turbines in operation and is the third-party O&M contractor on another 1GW. A challenge, however, is screening out the "noise" from one machine, said David Harwood, director of renewable energy at Michigan based-utility DTE Energy, which has about 850MW of wind turbines, many of them GE's 1.5MW machines.

Mix and match

Operators may oversee turbines made by several different manufacturers, and not always the best turbine out there - owners must be opportunistic in the marketplace. Having a diverse fleet can present logistical challenges. "I would sleep better if we used one turbine," said Duke's Scott. "You need a good supply chain." Managing the supply chain is the biggest challenge in effective O&M, after managing data. Duke provides O&M services for turbines by eight different original equipment manufacturers (OEMs).

On the other hand, owning and operating turbines by several OEMs can allow you to avoid one fatal flaw, said DTE's Harwood. About half of his turbines have come out of warranty in the past year or so, and DTE uses a third-party O&M provider. The utility is currently taking bids for the next provider, and it may even decide to operate some turbines itself.

When might an operator choose not to renew an OEM service agreement? Justin Johnson, director of performance management for EDP Renewables North America, noted that his company has become self-performing at some sites, and also has some third-party servicing. "It's a question of seeing what the market is offering," he said. Duke Energy Renewables, with its broad experience, tends to self-perform. It's an economic decision made on a case-by-case basis, said the utility's Scott. An available workforce can be developed with the right training. "We (also) look at the stability of the OEM. Will they be around?" he said.

Core strengths

Harwood admitted that it can be hard for a utility to keep its hands off the servicing of turbines. "(But) if you want least cost, you need to assess what you're good at or not. If it's not a core strength, it's easy to go third-party," he said. With a third to one half of DTE's turbines transitioning out of warranty, the utility is leaning towards a full-wrap service agreement with its own strong oversight of each site. It has used third-party service providers after warranty expiration, and has found that model successful.

William Watts, director of wind service Americas at Siemens Energy Inc, said his company is moving towards doing more "health checks" on turbines, creating a dynamic check list. That is, Siemens is moving towards more condition-based monitoring rather than relying upon time-based data.

Collaboration between owner and the OEM providing service has always been an issue, specifically with sharing of information. "We're all in this together," EDPR's Johnson said, but sometimes when there's dollars involved, there's a tendency not to share the data with the owner, he said. A problem encountered during warranty may not necessarily be disclosed by an OEM. Yet OEM service providers, with greater access to data on the turbines, can also alert you to a problem sooner than if you used another provider.

Keeping the door open to cross-sharing of information, EDPR makes it a priority to collaborate with the OEM during the warranty period, so we find out less "after the fact", said Johnson. But a note of caution was added by Duke's Scott, who said that if the owner shares too much data back with an OEM, it can help competitors. And the information received can vary, as not all OEM warranties are of the same quality, he added. "Some are much more sophisticated than others."

Siemens always pushes for a warranty extension, said Watts. Unsurprisingly, his company starts a collaborative discussion before the expiry date.

Slow down, live longer

The issue of de-rating turbines - reducing loads to help extend their lives - is a hot one. Johnson told the session that at one 10MW project, generators and gearboxes were failing so frequently that the company decided to try de-rating the turbines. The project was de-rated by 25%, but the overall loss of annual energy production has been just 3%, he said. In the US, EDPR operates a 4.5GW fleet of turbines from six different OEMs. The projected life of its wind farms is 25 years.

For life extension, Watts said Siemens is experimenting with different greases, oils and electrical components: "It's to see how far we can push it," he said. Some major owners, such as utilities, are trying not to change oil but instead to filter it throughout the life of the turbine.

Duke Energy's new assets are all being built with a special storage place for oil and grease, separate from other O&M equipment, so that, for example, the temperature can be controlled, said Scott. In his experience, most OEMs are now offering different packages to extend life.

Maintenance is an increasingly attractive business for OEMs. Christian Venderby, group senior vice president and head of service at Vestas, said: "There's a general interest in extending turbine life by another five or ten years." This is on top of a 20-year design life, he added. Vestas is in fact the largest provider of servicing in the industry globally.

Vestas expects its service business, which has been a separate unit for almost a year, to grow by 30% over the next three to five years, he said. Last year, the unit increased in size by 7% and posted EUR1 billion in revenue. It now has a EUR7.5 billion backlog of long-term service agreements.

Overall, Vestas services more than 47GW of turbines with long-term agreements, including other manufacturers' machines. As many as 85% of Vestas turbines out of warranty are still serviced by the company, which also intends to service more non-Vestas turbines in future, he says.

Cost control

Is there a tipping point after which a turbine is no longer worth servicing? "No, we constantly monitor them," says Venderby. "We use predictive failure analysis. We do a lot to control the event and control the cost. We work hard to reduce the cost per event." And indeed, in the Altamont Pass in California, for example, there are some 1980s turbines made by Vestas - and other OEMs - still operating well beyond their design life.

In mature markets such as the US, more turbines are reaching the stage when the warranty has run out, after something between two to five years old, leaving owners and operators vulnerable to unpredictable maintenance costs. Operators typically keep some $5 million of capital on their balance sheet for unscheduled maintenance costs, says Fraser McLachlan, CEO of GCube Insurance Services.

But all-risks insurance policies typically exclude serial loss and limit coverage to perhaps four or five events. Design defect was the cause of 11.5% of its US claims in 2012, says GCube.

Gearboxes, blades, yaw and pitch bearings as well as foundations are components that often prompt insurance claims. GCube found that an average claim for foundations was $1.3 million.

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