The problem in the Z-750 series is partly due to quality control, says Karas, and partly because the generators have been found to have inadequate thermal capacity for the plant's projected 30 year life. The problems at Lake Benton I on Buffalo Ridge-America's flagship wind project-are all covered by warranty and are relatively minor, adds Karas. Other "relatively minor" equipment problems at Lake Benton I, says Karas, include: the replacement of gear boxes on two turbines; new yaw pads installed on 40 of the machines due to use of a lubricant unsuitable for extremely low temperatures, and flawed hydraulic power units on several units which had to be retrofitted by the component manufacturer.
As of April 24, generators on 31 of the machines at Lake Benton I had been replaced, confirms Enron Wind's Mary McCann. The remaining replacements are to be done once the icy roads in the area have thawed. Of the 143 turbines installed last year, 134 units were providing power to the grid in mid April-down from the 142 of the Z-750 kW machines that had been operating in late March. Four were awaiting high-speed pinion replacements, and five were awaiting generator replacements, says McCann.
Despite the complete retrofit, Karas says start up of the Lake Benton I project has been fairly typical. "Through our nearly two decades of project development activities, EWC's experience has been that various project start-up circumstances typically occur and are corrected during the first months of the project's life," he says. Enron Wind noticed the quality control defect in late 1998, he adds, leading the company to decide to replace the generators. "The service team found that brushes were getting hung up in holders and were not making proper contact with slip rings."
After the discovery, Zond, which is Enron Wind's turbine manufacturing arm, and the manufacturer of the "open drip-proof" generators, in Wisconsin, agreed to upgrade the generators as a preventative measure, says Karas. The procedure of removing a generator, upgrading it at the factory and reinstalling it takes a turbine off line for about a day. "The full change-out process is expected to be completed by summer 1999 and will decrease the overall annual project availability by less than one percent," Karas says.
Storm Lake finished
Meanwhile, Enron Wind has given little explanation of the status of its turbines at the other project on Buffalo Ridge, Lake Benton II. Construction had been completed in March, confirms McCann, and the project was expected to be operating fully this month. Construction is complete, however, at the 80 MW Storm Lake II wind farm using Zond 750 kW turbines near Alta in Iowa, reports Enron Wind. The first leg of the project, Storm Lake I, will be commissioned next month, bringing the total installed capacity at the site to 107 MW, says Enron.