The place of renewable energy provides a variety of different responses from Australians, but its role continues to grow, particularly when it comes to wind-generated power.
According to a count by the Clean Energy Council, five new wind farms opened last year, bringing the national total to 79. Combined capacity grew to 4,327 MW in total, provided by 2,106 turbines.
What are considered utility-scale turbines range between 100 kW and several megawatts, with local installations tending to be a couple of megawatts in size, says Ben Kang, Power Transmission and Wind Energy Sector Manager at Schaeffler Australia.
“That's a lot of power that you have to transmit through the drivetrain,” he adds regarding one aspect of the engineering challenge.
After graduating with honours in mechanical engineering from University of NSW, Kang has spent 11 years with Schaeffler, working on industrial bearings in mining, heavy industries, power transmission and wind energy.
On a wind turbine, axial loads need to be converted to radial loads through the turbine’s movement. The main rotor bearings have an especially important role in this, and - first and foremost - must maintain a high degree of axial rigidity. This is critical, as the environment will feature gusty, oscillating winds.
“The main rotor is the large shaft that travels that through the nacelle and connects the rotor hub with the blades on it through the gearbox, in some designs, to the generator,” explains Kang.
“So basically while supporting all those loads and accommodating thermal differences, the bearing location needs to actually guide that main rotor hub assembly so that doesn't actually move backwards and forwards.”
Industry designs are tending towards tapered roller assembly for their cross-section for larger turbines. A recently-released unit from his company uses a double-row tapered roller bearing unit, with inner ring flange mounted to the rotor and outer ring to the nacelle.
“We now have a much better understanding of the actual loads that the turbines see, the cycling pattern of the loads, the duration of the loads, basically the whole load spectrum,” says Kang of shifts in his industry in the last 20 years or so.
“We have a lot more information on that. The industry as a whole is in a better position to design a bearing that is more suitable or improved.”
Recent innovations range from small but significant to more obvious.
In the former category are things like design improvements for easier handling of units.
“They appear small but they can have a significant impact for installation time; things such as lifting lugs, provisions for lifting holes,” says Kang.
“These bearings can range from approximately 600 or 700 mm in diameter, to 3 or 4 m. So of course occupational health and safety and handling from a safety perspective, but also in terms of not damaging the bearing, is also crucially important.”
Other areas where recent designs have been adjusted at Kang’s company for its turbine bearings include the geometry of the rollers at the curvature interface between the roller and the raceway.
Boundary lubrication
Improvements have also been sought in terms of coatings, with raceways and rolling elements receiving improved performance in 'boundary lubrication' as well as in wear control inside the bearing.
As with any significant piece of infrastructure, maximum uptime is highly desirable, and repairs or maintenance can be especially expensive in offshore settings.
And as with many other industries, internet-based monitoring is being used to get better use out of assets through maintenance that is smart rather than reactive.
The GreaseCheck sensor and analysis system can collect parameters such as vibration, temperature, load, speed, grease condition, and this is communicated through 3G or 4G from a turbine to a cloud server and monitored elsewhere in real-time.
For monitoring grease condition, this replaces previous invasive, time-consuming and potentially hazardous 'blood test' methods. Knowing what’s going on with grease brings with it a collection of benefits.
“So you move from time-based maintenance strategy, when you inject, say, 10 kilos every year and so on, onto a condition-based maintenance, and it also has a secondary effect of being a safety measure. Lubricant is a prime cause of unreliability,” says Kang.
“With traditional methods, basically you could do a grease sample but [there was] the difficulty of being up in the turbine, safety issues, isolating the turbine, disassembling the housing, and so on. "By the time issues were picked up with older techniques, the damage was already done.”