The increasing demand for wind energy is driving the development of bigger turbines, which require larger gearbox components. The latest component technology – in particular, separable high-capacity cylindrical roller bearings – is supporting the development of these larger turbines, says Phil Burge, Country Communication Manager at SKF.
There is currently an on-going debate among engineers about the best options for controlling wind turbines – via a gearbox, direct drive or a hybrid of the two. Whatever the outcome, over 80 per cent of installed turbines use conventional gearboxes and this technology is likely to play an important role in the future. The challenge for designers is to develop components that can handle ever-larger turbines, with steadily growing capacity, which is increasing the strain on gearbox components, especially bearings.
Recent bearing developments have enhanced the technology and construction techniques, in particular the ways that new bearing designs can be used to reduce the weight of nacelles by eliminating main shafts, or enhance output through accurate blade pitch control.
The evolution of bearing design has moved from high capacity cylindrical roller bearings, with additional load-bearing rollers, to separable designs, with demountable inner and outer rings that are designed for use on high-speed shafts. By incorporating separable high-capacity cylindrical roller bearings to support high-speed shafts in wind turbine gearboxes, equipment manufacturers can add advanced technology and increase system reliability. For wind farm owners and operators the ability to reduce gearbox failures and turbine downtime can minimise operating and maintenance costs, helping to lower cost per kWh and increase profitability.
For example, SKF separable high-capacity cylindrical roller bearings combine the advantages of conventional cylindrical roller bearings and SKF high-capacity cylindrical roller bearings. These are sized to match standard original bearings, yet feature extra rollers for increased load-carrying capacity. In addition, they offer the ability to separate the inner ring from the rest of the bearing components, without the risk of the rollers becoming disengaged. The separable bearing design also enables easy mounting and dismounting, helping to reduce replacement and maintenance times during top-of-turbine repairs.
Quick acceleration and deceleration
Development in bearing design to meet the needs of the wind industry has also had to address the handling of minimal load conditions and quick acceleration and deceleration. These conditions can cause conventional bearings to suffer smearing due to high levels of wear, potentially leading to bearing failure. Advanced high-capacity cylindrical roller bearings are therefore optimised with the addition of an inner ring cage guidance mechanism and a lower weight brass cage, for low inertia of the roller set.
The total global wind power capacity has now moved beyond 200gigawatts and means that wind turbines now have the capacity to satisfy 2.5 per cent of the world’s demand for electricity, impressive figures for a technology that is relatively new as a mass-produced tool for the supply of energy. Now that wind power is no longer seen as an optional alternative but a vital component in the global plan to increase the provision of renewable energy, the need to support the industry with innovative and robust technology is greater than ever before. The more powerful 5MW-plus turbines are currently only provided by a limited number of suppliers, and the more common 3MW turbines may not be able to satisfy the projects in the pipeline. To meet growing demand, turbines are growing larger in size, with higher power ratings – up to 7.5MW, with 10MW turbines in the planning stages. The industry trend toward increased turbine size calls for technology advances including reduced weight, more compact and lighter nacelles, drive trains, gearboxes and generators, which facilitate safety and keep manufacturing costs in check. Meanwhile, increased offshore operations and wind farms in harsh climates and remote locations present new challenges for maintenance and repair by owners and operators.
The goal for the maintenance of wind turbines, as with any other engineering industry, is to set in place a series of procedures that will increase efficiency by preventative measures, enabling operators to minimise maintenance costs and maximise turbine availability, protecting profits for operators and providing the rest of us with a supply of renewable, reliable energy. Advances such as separable high-capacity cylindrical roller bearings and high-capacity cylindrical roller bearing versions are helping customers achieve high reliability, excellent performance and easy maintainability in their applications. For further information, please email or visit www.skf.com.