Proper vibration control and structural adhesives can keep a wind farm from shaking its turbines into early retirement.
Andrew B. Swoyer Jr., Manager, Marketing and Sales
Carlos Cruz, Market Manager Product Assembly Adhesives and Coatings, Americas Region
Lord Corp., Cary, N.C., www.lord.com
The components around the nacelle show a few mounting and vibration control devices from Lord Corp..
Ground-based power generation equipment has the advantage of mounting to foundations with large masses that dissipate vibration so it is not passed to nearby equipment. Wind turbines have no such advantage. Their equipment is bolted to a large frame but vibration control is minimal. The good news for turbine OEMs and O&M crews is that there are a range of devices for controlling vibration.
Mounting devices
Untamed vibration shortens major component life, loosens bolts, causes weld failures, and contributes to gear and bearing failures. Because nacelles are perched 200 to 300-ft up and at the end of a swaying tower, equipment mounts, often vibration isolators for the equipment in a nacelle, must work reliably for long periods to minimize maintenance. Noise and vibration attenuation are key considerations driving a need for isolation systems that are easy to install, provide a long service life, and reduce the transmission of noise and vibration.
Gearboxes and generators inside the nacelle are often mounted on vibration isolators. These should reduce vibration amplitude, lower structure-borne noise levels, and extend equipment life – all important to the wind industry.
Meshing gears, rotating components, and generators on the turbines also produce excess vibration and noise signatures in large, small, new, and old wind turbines. Several manufacturers are focusing on ways to improve the operation of 1.5-MW versions, a size frequently found on today’s wind farms.
Large isolators provide a ‘soft’ attachment between the gearbox, nacelle, and tower structures to interrupt the noise path, reducing stress on large, expensive components, and eliminating critical vibration modes that could cause structural damage. Torque-restraining mounts that react to torque and provide isolation have also been considered.
Isolating torsional vibration
Rotating components in turbine drivetrains also present challenging reliability issues. One solution to drivetrain component-life issues in similar equipment is to apply torsionally soft couplings to reduce variable torque and tune away harmful resonances. Side benefits to this solution include reduced drive-train noise and improved life of rotating component
Structural adhesives and passive motion control devices from Lord Corp. can be used in a variety of applications in the wind-power industry.
Noise and vibration in smaller turbines are equally troublesome, but solutions differ. For instance, isolators for small turbines are readily available, cost-effective, durable, and maintenance-free. Center-bonded mounts have been used in turbines with generating capacities of 100 kW and smaller to isolate most equipment. One application used standard company products and a center-bonded mount.
The isolation mounts were field-tested and installed in a particular 100-kW unit, resulting in a unit that ran quieter and lasted longer. Peripheral equipment in the nacelle, such as electrical cabinets, enclosures, and wire harnesses can also benefit from vibration isolation. Wiring-connector failures are just one example of common failures due to excessive vibration.
Standard, readily available isolation devices are commercially available for these components. Center-bonded mounts, platforms, grommets, and bushings are just a few of the possible isolation solutions. All have been field-proven in a wide variety of similar industrial and aerospace applications.
Selecting isolators
Generally, selecting a vibration isolator requires collecting structural information and parameters about the system or unit to be isolated. Key information includes:
1.) Dimensions of the unit
2.) Static weight, center-of-gravity location, and maximum torque reaction forces
3.) Mounting locations
4.) Vibration excitation characteristics
5.) Environmental resistance requirements such as ozone, chemical, or temperatures
Rubber-to-metal mounts are widely used on helicopters, aircraft, locomotives, and large construction equipment to support equipment and isolate intermittent or continuous vibration. Easy-to-install anti-vibration mounts are resistant to oils and weather-related stresses making them appropriate for work in turbine nacelles. Furthermore, the devices are rugged, offer long service life, and require no maintenance – especially important for structures that are located up to 300-ft high.
Most companies that design vibration isolators also provide assistance selecting them. For that purpose, most vibration control company’s like ours maintain a staff of applications engineers and a comprehensive database of available components, ready to analyze needs and recommend isolators.
The company also provides design testing and validation services to help demonstrate that the mounting device meets the customer’s exact requirements. And where conventional, passive rubber-to-metal isolation solutions are limited in performance, semi-active devices may be useful. Semi-active devices react in real-time to mitigate displacement, velocity, and acceleration events that can cause damage to mounted equipment or discomfort to equipment operators. Although these devices have not been applied thus far to wind turbines, they serve as an example of possible next-generation isolators for the wind market.
Structural adhesives
Structural adhesives in wind-power applications are used to join the two halves of a turbine blade after they are removed from their molds. Such adhesives can also affix smaller items. Modern structural adhesives offer the benefits of design flexibility, high performance, corrosion resistance, and durability, along with an ability to join dissimilar materials. The adhesives, designed to replace traditional mechanical fastening methods, are available in three chemistries: acrylics, epoxies, and urethanes.
Recent structural adhesives are applicable to a variety of turbine structure components including:
- Blade assembly (blade bonding and component bonding, void filling, along with bolt, stud, and metal-insert fixing)
- Nacelle assembly (panel and stringer structural bonding)
- Hub, bearing, and gearbox assembly (bearing-to-hub assembly)
- Electrical components
- Tower assembly (component bonding)
- Installation and maintenance, such as blade repair.
Engineering assistance is available for joint design, fixturing recommendations, adhesive selection, and MMD (bulk dispensing) equipment guidance. Engineers looking to tame vibrations can pick-and-choose what they need, such as design assistance, fixturing help, adhesive selection, and joint design – most any advice a vibration engineer would need.
Curing times are a crucial aspect of bonding. Some applications require adhesives that cure quickly, such as repair operations, while other applications need a slower cure time, as in manufacturing.
Large wind blades, for one, need a slower cure time. When bonding the two blade halves and laying down beads of adhesives, it’s good to have a curing process begin at the same time. An adhesive should not start curing before all of it is applied to the entire blade. When the dispensing finishes, the two halves are placed together, and the curing can commence. Curing at room temperature lets the adhesives provide crack resistance for a variety of composite, metal, and plastic assemblies.
As global demand for energy increases, wind power and its advantages are garnering interest as an economical source of energy. The Global Wind Energy Assn says demand “will require significant investment in new power generation capacity and grid infrastructure.” Wind-turbine manufacturers are ready to make investments, so they are looking for methods to increase production, decrease costs, and provide reliable solutions on the production line and in the field.
Filed Under: News, O&M
