A gear box failure has damaged a Nordex N60 1.3 MW turbine at Canadian Hydro's Cowley North and Sinnott wind plants in southern Alberta and led to the shutdown of three sister turbines at the plant. Canadian Hydro's John Keating says all 20 turbines at the two plants were shutdown for a week in December after the damage occurred. "During that week we inspected all the machines. Sixteen were put back in service and those 16 are still in service and doing just fine," he said last month. "There were signs of wear on three other machines, so we have four machines that are sitting idle at present." The cause of the gearbox problem is not clear, says Ralf Peters of Nordex, although it is the gear rims that are affected. "Individual teeth have broken or show signs of wear," Peters says. The gear boxes are built by German Flender, one of three gear box suppliers that serve Nordex. All four damaged units will be replaced. "Then research into why the problem arose can begin," says Peters. He says there are "many possible causes" of the failure, ranging from faulty materials to a control error. He believes it unlikely that the Nordex turbine design is to blame because about 500, 1.3 MW machines are now operating worldwide, many of them with Flender gear boxes, and no signs of a serious problem have occurred. The Cowley North and Sinnott turbines have been operating since late 2001.