Operations and maintenance are critical elements and a significant amount of the costs associated with a wind farm. Having a well-planned maintenance program will ensure wind turbines are running efficiently and at their highest capacity. Overall general maintenance, up-tower repairs, and down-tower remanufacturing processes help to reduce the total cost of energy production and extend the life expectancy of a wind turbine. In general, preventative maintenance should be completed two or three times a year. However, there needs to be a balance between cost savings of completing minimal maintenance with the more significant risks of costly failures and completing a high level of maintenance that is extremely expensive with minor incremental benefits.
When developing a wind turbine maintenance plan, failures are at the center. Understanding the most common failures and identifying them before they happen minimizes the likelihood of a downtime incident. A valuable resource for information on failures is from the German Wind Energy Measurement Programme that tracked the performance of approximately 1,500 wind turbines in Germany for ten years, from 1997 to 2006. The program funded by the German government and run by the ISET accumulated 15,400 turbine years of operation and created a detailed picture of failure probabilities. Here is what they found.
The most likely component to fail is electrical equipment at a rate of 5.5 incidents for every ten machine-years with a day and half of downtime. In comparison, gearboxes and generators fail at a lower rate of approximately 1.5 incidents every ten machine-years but have a much longer outage time of over six or seven days. In a more recent analysis of 5,800 turbine years from the agricultural commission of Schleswig Holstein, Germany found similar failure rates for the various components, but significantly longer outage periods per failure. The average downtime for a gearbox increased to 14 days. The surge in downtime is likely attributed to the increased size of the larger wind turbines. In recent years, blade failure has also increased and accounts for 3,800 incidents a year.
Any unscheduled downtime of a wind turbine means lost revenue. The consequences and costs of dealing with component failures can quickly add up. For offshore wind farms, it takes time to arrange for repair vessels to visit the site while onshore wind farms could require the coordination of large cranes to complete the repairs. To alleviate unscheduled maintenance and repairs, understanding the probabilities of component failures and having condition monitoring systems (CMS) in place can indicate problems in the turbine before they become catastrophic.
Wind Turbine Maintenance Best Practices
When wind turbine components fail, it leads to unscheduled stoppages, expensive crane and repair equipment rental, and revenue loss. It is vital to develop a comprehensive maintenance plan to prevent costly and time-consuming repairs. The maintenance plan will help to control and forecast such failures.
Monitoring & Predictive Maintenance
Condition monitoring is not a new thing, but complex data analysis and interpretation are at the forefront. Utilizing monitoring systems combined with computer-based maintenance management systems enable predictive and proactive maintenance planning instead of waiting for failures to occur or planned maintenance that may not be needed.
Monitoring systems position sensors at key points in a wind turbine, and data is sent to the maintenance team for collection and analysis. Data gathered includes information on lubrication levels, vibration, temperatures, and foundation displacement. Systems can also monitor the physical movements of the rotor shaft, strain, torque, bending, and shear, as well as electrical faults.
Monitoring wind turbines is an essential part of preventing unnecessary and pricey repairs by identifying components that may have the likelihood of failing in the near future. Pinpointing the different types of maintenance to be performed can allow wind farm owners to schedule maintenance that requires leasing of cranes or other equipment for multiple turbines, which reduces costs. Additionally, scheduled preventative maintenance can be adjusted based on data collected to optimize the maintenance costs and costs associated with unscheduled fault repairs.
While completing preventive maintenance can be expensive, it reduces the chances of component failure, which leads to higher repair costs and lost revenue. Most wind turbine manufacturers do have recommended maintenance intervals, but depending on the location of the turbine and design, they may be insufficient. Following is a general list of maintenance tasks.
- Inspect electrical cabinet, gearbox, generators, yaw system, and brake
- Assess blades and blade pitching
- Survey tower foundation
- Measure oil and lubrication levels, sample, and if necessary, replacement
- Drive train alignment
- Examine and tighten bolts
- Check ventilation, air filters, and shock absorbers
- Inspect bearing and connections
- Evaluate nacelle
- Repair cracks and corrosion
The Upside of Planned Maintenance
When it comes to wind turbine maintenance and repair, it can be difficult to do so due to the remote locations of wind farms, hauling equipment and supplies over 300 feet in the air, and working in a relatively small space. However, the benefits do outweigh the challenges. Faulty components and equipment can have a devastating impact on the longevity and efficiency of a wind turbine. Failure of one component can damage or render other components inoperative, electrical malfunction due to bad or poor connections can lead to fires, and premature replacement of a gearbox requires the turbine to be offline for a significant time as well as unplanned expenditures on a crane rental. By using predictive and preventive maintenance, wind farm owners and operators can address the complexities of maintenance and increase the long-term reliability of their wind turbines.