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MechChem Africa talks to Saien Rugdeo, SKF’s sales and business intelligence manager for Gauteng and North West Province, about specialty solutions and services developed for wind turbines and renewable energy generators.
“Globally, SKF partners with many of the wind turbine OEMs such as Nordex, Siemens and Vestas. These OEMs use either their own designed components or they incorporate gearbox and generator units from other manufacturers for installation into the Nacelles of their wind turbines,” begins SKF’s Saien Rugdeo.
“Our core focus as SKF is on the main drive shaft. Depending on the design of the turbine, this is either a direct drive with a large bearing connected directly to the generator; or a convectional bearing arrangement with a supported shaft connecting to the generator via a gearbox.
“The generator itself, which is the source of the electrical generation as well as the connecting gearbox, also requires high quality precision bearings for the rotating generator coils,” he continues, adding that SKF bearing products supplied to the wind turbine industry are vital components that keep the turbines rotating and generating safely, efficiently and reliably.
The bearings used for wind turbines tend to be large, with average shaft sizes exceeding 400 mm. “Our Nautilus hub-units for direct drive turbines, which are designed to be integrated into the Nacelles, can be in excess of 2.0 to 2.5 m in diameter. These bearings come with integrated sealing carriers to improve cleanliness and reduce the risk of bearing contamination during the mounting process. The integrated seal design also helps to reduce weight and associated costs, and it makes seal replacement easier from the top of the turbine, without having to dismount the carrier,” Rugdeo says.
“Fostering our industry partnership, we also supply a range of specialty products purpose developed for the industry, which trusts us because of our 100-year legacy of developing fit-for-purpose quality solutions and our ability to deliver at the scale and performance levels necessary and expected,” he tells MechChem Africa.
A particular innovation with respect to the bearing design for wind turbines is SKF’s black oxide coating. Black oxide is a rolling element coating developed for environments where lubrication requirements are critical, particularly in low lubrication and high moisture applications. This coating, which was originally a proprietary SKF innovation, is now widely used for offshore turbines. “Black oxide coatings enhance grease adhesion to the rolling element surfaces and are ideal for inaccessible environments where regular re-lubrication is prohibitive but critical for long term reliability. This is now standard on most main shaft and gearbox bearings,” he explains.
Because of the electrical nature of generators, SKF has also developed speciality products to overcome current leakage, which is a common cause of generator bearing failure. “An electrical path coming through the rolling elements of the bearing to the outer or inner ring can cause sparking, which causes electrical erosion on the bearing contact surfaces and damage to the lubricant. This is very common if steel bearings are used,” he says.
SKF offers two potential solutions. The first is called INSOCOAT, which is a physical surface treatment of aluminium oxide applied to the inner or outer raceway using the plasma-spray coating process. INSOCOAT coatings produce an exceptional surface finish that creates an electrically insulated barrier to prevent current leakage from occurring.
“We offer specialty SKF Hybrid bearings to solve this problem. These have rings made of steel, but instead of using steel rolling elements, Hybrid bearings use ceramic silicon nitride rolling elements as an insulating barrier between the inner and the outer rings.
“These are both SKF-developed solutions and, while obviously a little more expensive compared to standard steel bearings, they are premium products that significantly extend service life and enhance performance, particularly in the generators of wind turbines,” notes Rugdeo.
SKF also owns Lincoln Lubrication, a world leader in automated lubrication systems. These systems are ideal for use where access is difficult. “Automated multiple point lubrication systems are typically installed in the Nacelles of wind turbines for delivering the greases and lubricating oils required by the bearings of the main shaft, generator and slewing rings,” he continues. Such systems are essential because of access difficulties: the nacelle of a wind turbine is typically over 100 m above the ground and, if offshore, may only be accessible via boat or helicopter.
Also in response to the access issues, SKF has the capability to monitor the vibration data and temperature coming off installed bearings. “For wind turbine condition monitoring, we have a customised service called WindCon, which involves fitting accelerometers at strategic points that transmit output signals wirelessly to the cloud. These signals are accessed by one of our Remote Diagnostic Centres (RDCs), which are strategically placed around the world.
“Depending on customer needs, we assign analysts to remotely monitor and track the condition of each bearing – its history and fault frequencies – and we can quickly identify concerns relating to each component. This gives wind farm owners an early warning of a possible failure, enabling them to track the severity and intervene at the ideal time to minimise disruption and damage,” Rugdeo says.
“If we detect damage on the outer ring of a wind turbine bearing, for example, we will watch how that progresses, how it translates into the vibration spectrum, recording the increase in magnitude over time. Based on the expertise of our global team of analytical specialists, we can identify the point of criticality so that an ‘in-time’ replacement can be scheduled,” he explains. “Though there are many service providers able to monitor bearings on wind turbines, SKF is one of the very few, in a global sense, that can offer fault detection, replacement and maintenance services to customers,” he adds.
“In most industries, bearings don’t fail overnight or accidently. They tend to fail for an identifiable reason, such as misalignment, a lubrication failure or brinelling. From our RDCs, we can now identify which bearings are likely to fail and endeavour to act well in advance of an unexpected failure.
“With respect to development, every bearing failure report we do goes into a knowledge database, which enables us to identify common causes and devise solutions to overcome them, such as in the case of current leakage problems. We are routinely optimising geometries, developing new surface coatings, new materials or heat treatment procedures so as to constantly reduce failure rates and improve reliability,” he continues.
“An up tower bearing replacement is expensive and income loss due to downtime can be huge too, so it is vital to use premium quality bearings from authorised and accredited distributors for critical applications such as these. The intrinsic value of using SKF products is not embedded in the price paid, it lies in the peace of mind and reliability benefits that come with our products. There is a lot of knowledge and experience that comes with an SKF partnership,” assures Rugdeo.
Here in South Africa, he says the aftermarket is still relatively small since most units are still operating within their OEM warranty period. Wind Farm owners are not yet looking to manage the wind farms themselves, so they tend to take to take out service contracts with OEMs for the immediate maintenance. “This is likely to change with time, though, as more units come online and warranty periods expire,” he says.
Speaking about the raise of the embedded-generation threshold in South Africa from 1.0 MW to 100 MW, he says he was thrilled with the positive market response. “The unlocked potential for private producers to generate power is now immense. Companies and people that have the capacity, the finances and the need, can be producers as well as consumers of power.
“This is an open invitation to be self-sufficient while still contributing to the country’s wellbeing. I call this creative destruction, because it destroys our dependency on fossil fuels, while unlocking higher level and more rewarding future jobs in the new and modern renewable sector.
“This makes me very optimistic about the long-term future of the South African economy and the renewable energy sector,” Saien Rugdeo concludes.
