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IEC Shines Spotlight
Popularity of Wind Power Puts Greater Emphasis on Wind Turbine Gearbox Standards |
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Popularity of Wind Power Puts Greater Emphasis on Wind Turbine Gearbox Standards
Brent Reardon, principal engineer with Garrad Hassan, an international wind power consulting firm, is chairman of the Wind Turbine Drives Committee for the American Gear Manufacturers Association (AGMA). He is also one of the U.S. delegates to the ISO/IEC joint working group that is currently developing the next generation of international standards for wind turbine gear drives. He explains the significance of gearbox standards and how they affect the growing wind energy industry. Q: Why is ANSI/AGMA/AWEA 6006, Design and Specification of Gearboxes for Wind Turbines, so important? There wasn’t a specification for wind turbine gearboxes before this. So throughout the history of the wind industry, gear boxes have been one of the main failure issues with wind turbines. This specification provides guidelines on how to make a better gearbox. And it also puts out minimum standards for how to approach the design of wind turbine gearboxes. Q: Has it helped cut back on failures associated with gearboxes? We believe it has. I think what we’ve seen since the specifications came out that there are very few failures due to design issues with gears. And right now the failures are mostly in the area concerning bearings. Q: So the big problem now is bearings? Yes, and there are reasons for that. The wind industry is a very dynamic industry, it’s growing very quickly, and the sizes of gearboxes have doubled every two or three years until just recently. The industry has kind of leveled out making turbines between the 1.5 megawatt and 3 megawatt range over the last couple of years. So we’re starting to see a little more maturing of the industry with the design of gearboxes and bearings. Some of the issues have been that gearboxes for wind turbines are highly loaded components and so there are lots of new innovative designs and things being tried in the industry. And some of those don’t work. Q: In terms of the turbines themselves or the gearboxes? Both. Most wind turbines today are a three-blade upwind wind turbine. But there are different designs. Some have multiple generators, some don’t have gearboxes at all and are direct drive, and some are a combination of medium-speed generators and medium-speed gearboxes. There’s not one particular optimum design for wind turbines as we speak. In exploring how to build the best wind turbine out there, people will try different things. The bearing companies recommend new products and sometimes they don’t work well. A lot of that has to do with the environment that wind turbines work in. And in the rush to get a new product on the market, sometimes you don’t get the level of testing that you’d like to see as opposed to the automotive market or the aircraft market, where significant amounts of testing are done before the product ever becomes commercially available. In the wind industry, the cycle time for a product to make it to market is very quick. So in a lot of cases, you don’t get the years of experience that you would see in other industries. Q: What’s the typical cycle time for a new wind turbine design? To design and build a turbine, maybe three to five years. Or less. And that’s complete design and manufacture. Q: How does that affect standards such as AGMA 6006? Q: Wind turbines are based on the amount of power they generate? Yes, when I refer to size I refer to the amount of power that a wind turbine generates. But there are different wind regimes out there… There are very high wind sites that are turbulent and they would be class 1 sites, then there are other sites that are class 2 sites that have moderate wind and moderate turbulence and there are class 3 sites that have low wind and low turbulence. So you can take a turbine that is rated at 1.5 megawatts and put a smaller rotor on it, say a 72-meter rotor, and you can put that in a high wind site. Now, if you have a medium to low-wind site, you can put a 77-meter rotor on it, a bigger rotor that captures more wind, and it’ll perform basically the same in a different wind regime. So when people refer to sizes of wind turbines, it’s usually based on those two elements. How big the rotor is and what the capacity in megawatts or kilowatts of the machine. Q: Since the standard was written for 1.5 megawatt wind turbines, is your committee looking at updating it? There is an international committee that’s a joint committee between the IEC and the ISO, and they’re writing the next generation of gearbox standards. In the interim, what happened is the international committee accepted AGMA as the international standard, and it’s now been issued as ISO 81400. Q: Have there been international standards in the past? No, but when we wrote AGMA 6006 it was a very international effort. It was the largest AGMA committee ever put together. Toward the end of it, we were having upwards of 50 people show up to the meetings with representatives from multiple industries and seven different countries. Q: Will the next generation of standards take into consideration the needs of larger turbines? There are a couple unique features in the new one. One is trying to better define the loads that affect the design of a wind turbine gearbox. Another is focused on improving communications between the designers of wind turbines and the designers of gearboxes so that they can better understand the interfaces between those two items. That’s a critical component. Obviously, the more that you understand about how the equipment in the field works, the better job you can do about designing to fit those needs. Q: When is the new international standard expected to be released? It could be a year or two. Q: In the meantime, what do companies dealing with these larger wind turbines do? They use the current standard and the current methods and apply those as best they can to the larger units. A lot of things are very applicable to just basic design. Q: Overall, would you say that wind turbines are more dependable than they used to be? I’ve been in the wind industry a little over 20 years. Yes, they’ve become a lot larger, a lot more complex and in general, a lot more reliable. |
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Wind is creating big business opportunities around the world, and in particular in the United States. According to a report released in May by the American Wind Energy Association (AWEA), the U.S. wind energy industry is expected to install more than 3,000 megawatts of wind power generating capacity by the end of the year. This means more wind turbines are going up than ever before—putting even greater emphasis on turbine reliability and performance.