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Denmark

Denmark

Tough utility gear box demands

A Danish electric utility developing offshore wind farms is demanding that the wind industry get its act together to solve gear box problems. Flemming Vagn Jensen of SEAS -- the utility developing, among others, a 150 MW offshore wind farm at Rødsand in Denmark -- points out that onshore it is relatively easy to access wind turbines and arrange for the necessary crane equipment if a gear box failed. The new focus of large wind farms at sea complicates the issue, says Jensen, particularly in the light of extensive gear box failures that have emerged in the past year (Windpower Monthly, May 2000). "These problems, which have been hidden in the background, are getting pulled out into the spotlight now," he says.

"It's SEAS opinion that a broad front must be formed to improve gear box reliability. It is unacceptable just to specify a lifetime of 20 years when the guarantee only covers a fourth of this."

Gear designers must assume that the machinery will be operating at sea, where replacement of one small part can require an enormous amount of planning. "It must be reasonable to demand that -- all the way back to the first blueprints of the gear box -- the designers have considered how the bearings can be replaced on-site in a simple and efficient way, without taking the whole gear box down," Jensen says. In addition, designers must account for new monitoring and other maintenance solutions for gear boxes in the tough operating environment.

Internal design must be improved as well -- particularly to enable optimum lubrication. Only conditioned oil must reach critical components and any metal particles must be filtered immediately. Quality demands in manufacturing must also be intensified, and gear box quality must be far better documented. "It is unacceptable that gear boxes are already being contaminated with damaging particles at the factory," Jensen says. Noise, vibration, temperature, oil purity and quality and other specifications must also be documented and standards should be tightened. From commissioning, the gear box's condition must be monitored, so that defects can be caught and repaired before they damage other components -- and before the guarantee runs out.

"It can often be impossible to find the single cause of a gear box failure, since failure is often the result of several influencing factors," says Jensen. "It's therefore necessary that so many of these factors are eliminated as possible. The more of these damaging factors we can eliminate, the closer we'll come to a problem-free wind turbine gear box."

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