The extent of generator reliability depends largely on who is asked and what equipment the particular wind farm employs, says Paul Veers from the wind division at Sandia National Laboratory in New Mexico. "We've been going to a number of operators and one of them has fits with generators and another has no problems at all," he says. The question will not be resolved, says Veers, until a comprehensive database of wind plant across turbines and owners and operating environments is built so statistically relevant data can be extracted. Veers is working with colleagues on a pilot project to create such a database.
Tales of generator failure are showing up mostly among independent third party operations and maintenance (O&M) professionals. "As an average overall, they're not having problems like the gearbox, but there are plenty of issues with the generator," says Jason McDonald, of Trico Wind. Series failures of gearboxes have been notorious in the wind industry. "On some turbines, the generators are not doing so well, on some turbines they are doing perfectly well. Sometimes you get four different manufacturers of generator in one turbine model and they all have trouble in that turbine and sometimes you have one of those manufacturers in another turbine model and they last just fine. "
Dave Luck, who leads the O&M division of Enxco, is more cautious in calling it a problem. "I don't have anything to back that up, either statistically or anecdotally. It's statistically not a big component of our downtime in our fleet. And we've got everything out there except Suzlon and Enercon. It's not been zero, but it's not big."
Opinion is divided, too, over the probable cause of generator failure. Repairing and rebuilding the units is about 70% of Trico Wind's business. According to McDonald, there is little rhyme or reason in the failures, although turbine type may play a role and random wound generators have been more symptomatic than form wound, he says, referring to how the copper coils are arranged.
Sandy Butterfield at the Department of Energy's National Renewable Energy Laboratory believes that, as with gearbox breakdowns, generator failures seem to start with bearing failure. "We're not sure why those bearings are not lasting. My goal after we've got the gearbox problem under control is to go after the generators," he says.
Daniel Laird, a staff researcher at Sandia, hesitates to call generators a major problem area, but says the problems that do occur may have something to do with units operating under conditions they were not adequately designed for. "I think where you really see the issue popping up beyond normal wear and tear is where there is some sort of mismatch between the design specifications and the application," he says. This could mean generators that do not work well with certain turbines or generators that do not cope well in certain environments, such as the extreme cold of the American upper Midwest.
Poor maintenance is a likely culprit, says Uwe Roeper at Canadian wind consultancy Ortech. Introduction of dust or moisture has proved the root cause for failure in a number of generators, he says, and some of these instances were either caused or exacerbated by sloppy oversight and maintenance of the turbine. In the simplest scenarios, loose or missing air filters or leaking nacelle housing were the cause.