HMZ WindMaster and Aerpac are discussing who is to bear the burden of repair costs for blade failures in a wind farm operated by the Public Power Corporation of Greece. Blades were damaged by lightning and longitudinal root cracks have appeared as well. Repairs will consist of an entire root replacement with a re-modelled version.

A fix for the blade root problem on all 34 WindMaster 300 kW turbines in Greece -- stopped since the beginning of the year -- was proposed to the owner of the machines, the Public Power Corporation (PPC), in mid October. The Greek utility, furious about the failures, is now deciding whether it finds the fix acceptable or not.

The turbines, supplied by Belgian company HMZ WindMaster to PPC in late 1992 and early 1993, operated well until longitudinal cracks appeared after two or three months at the roots of the blades on the 25 metre rotor, says WindMaster's general manager, Peter van Heukelom. Subsequent examination by WindMaster and the blade supplier, Aerpac of the Netherlands, revealed, however, that the cracks did not affect the strength of the blade and it was decided the turbines could remain in operation while a repair was devised.

The decision to stop the machines was taken in January this year when PPC's problem with the WindMaster machines was exacerbated after a number were struck by lightning, causing severe blade damage, says WindMaster's unit manager in Belgium, Luc De Groot. "At the time it was not clear that lightning was the cause of the damage. We did not know what was going on so we decided to stop all the turbines," he says. Since then Aerpac, together with classification society Germanischer Lloyd and WindMaster, has been working on the best repair or retrofit for the root problem, says Van Heukelom.

"We think we have a good solution which we have made known to PPC and we are waiting to hear from them," he adds. The fix, to be carried out on site in Greece to minimise transport costs, involves replacement of the entire root with a re-modelled version. It has been designed by Aerpac under the close scrutiny of both Germanischer Lloyd and WindMaster. "Everybody has problems at some time. But problems are to be solved and we will solve this one," says Van Heukelom. Sales manager Michel Ardoullie concurs: "It is a technical question and can be solved. The question is paying for it." Van Heukelom assures that WindMaster and Aerpac have not yet come to blows over the issue. "We are still talking," he says. "We are talking until we find a solution."

In the meantime PPC is almost beside itself with rage. "Out of 25 MW now running, 10 MW has been a disaster. As much as 40% of the installed capacity in Greece is not working," storms Nicolas Yiparkas, a wind engineer with PPC. "It has been raining left and right with wind turbine blades." He continues: "The wind parks are considered to be public safety hazards. They never got beyond commissioning. We have never accepted them." Yiparkas claims that WindMaster has dragged its feet over finding a solution. "We have seen blades which look like pine trees because the skin has peeled off," he says.

Strength unaffected

Van Heukelom and Ardoullie deny that WindMaster has been slow to tackle the problem. "If it is to be done properly these things take time," says Ardoullie. De Groot also points out that not one blade has dropped off a turbine in Greece because of a root crack. "The crack does not cut a critical fibre. The strength of the blade is the same," he says. "It is a question of lifetime, not of safety." According to De Groot the crack rapidly expands in the first two or three months and then gets worse very slowly.

The severe lightning problems in Greece seem to have caught all involved in the development unawares. "The lightning in Greece seems to have a lot worse effect than elsewhere," says De Groot who adds that technically the problem can only be alleviated and not solveds. "One of the important factors is terrain. In Holland lightning strikes on wind turbines are almost unknown," he says.

A total of 62 WindMaster machines are now running with the troubled Aerpac blades, but so far no serious problems have shown up on either the Dutch Lelystad wind farm or at Blyth Harbour in England. These sites are less turbulent than those in Greece. David Still from Border Wind in England, developer of the Blyth Harbour wind farm, says: "We have seen a little surface crack but we are getting excellent back-up from WindMaster. We are not concerned about the problem." Van Heukelom says it may be necessary to also retrofit blades other than those in Greece.

In the meantime ten of WindMaster's re-designed 300 kW turbine are going up at Caton Moor in England for New World Power of the US. The new 300 kW has a 28 metre rotor with larger blades supplied by Dutch Polymarin and a gear box on rubber chocks. Van Heukelom says the machine is more efficient and quieter than the older 300 kW. A prototype is being installed at the testfield of ECN, the Netherlands' national laboratory, and it is being certified by Germanischer Lloyd, says Van Heukelom. WindMaster is also supplying ten 300 kW wind turbines to a site at Dunkirk in France. A new blade, of carbon fibre, is being built for this project by French company Atout Vent.

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