Wind Turbine Upkeep: In-service & End-of-Warranty Inspections

A major concern when investing in any wind farm project relates to turbine availability, which represents the risk of lower energy yields from turbines due to standstill and repair periods. The reliability of every turbine at a site is essential for a wind farm to perform effectively and profitably. Even a minor failure of a component can cause undesirable downtime and lost revenue. One solution to reducing operation and maintenance costs is to carry out In-service Inspections. In-service Inspections and End-of-Warranty Inspections can detect imminent failures of critical components at the earliest stages, thereby, minimizing the risk of costly repair periods.

In-service Inspections
Many wind farm owners and operators claim that some components, although designed to last the predicted lifetime of a turbine, fail earlier than anticipated, causing unexpected downtime and adversely affecting the overall success of a wind farm. In-service Inspections involve a series of activities, wherein various components of a wind turbine are regularly inspected and monitored throughout their entire operational lifetime. Using a system of diverse inspection and analysis methods ensures that any unexpected degradation from normal conditions is detected as early as possible to prevent unnecessary damage.

It’s worth noting, however, that In-service Inspections represent a value-added service to customers, but only when conducted by a reliable third-party supervision company. The advantages of hiring an independent inspection, verification, testing, and certification company not only result from their skill and experience, but also from their economic independence from the stakeholders. With regular In-service Inspection performed by a third-party company, wind turbine downtime is often considerably reduced, which in return facilitates the economical operation of the wind farm—providing sustainable operational costs with the anticipated return on investment.

Diversified In-service Inspections include, but are not limited to, thermographic inspection, vibration measurement of the drive train, and oil analysis. Thermographic inspection is a non-destructive testing method, developed for inspection of parts, materials, and systems of wind farms by imaging of the thermal patterns at the object’s surface. A vibration measurement of the drive train is carried out by installing sensors on the main bearing, gearbox, and generator, with the goal of detecting potential failures on bearings and teeth. This occurs while the turbine is in operation. Oil analysis enables regular monitoring of the chemical and physical changes in a lubricant, taken from the wind turbine gearbox, generator, or hydraulic system, which can provide an early warning of potential failures.

In-service inspections might further cover blade inspection, endoscope inspection, rotor imbalance, blade pitch, as well as angle measurement and industrial rope access. As monitoring of the condition of rotor blades has become increasingly important, blade inspection should be considered an indispensable part of the inspection process. Hidden defects and damage to rotor blades that cannot be detected by visual inspection can be identified by non-destructive testing techniques. Defects found in this manner include de-lamination, adhesive defects, laminate thickness variations, and resin-poor areas. Such inspections can be performed either at the place of manufacture, or on the wind farm site itself. An endoscope inspection checks the accessible gearbox teeth and bearings to determine the actual condition of the components, and validates the results of vibration measurement and/or oil analysis.

Other important features of an In-service Inspection include rotor imbalance and blade pitch angle measurement. Maintaining the correct rotor mass balance and pitch angle are vital to preventing the following: damage to important components, higher repair costs, reduced service life, poor availability, and decreased power output. A prudent inspection of the rotor balance and pitch angle is, therefore, highly recommended.

To conduct the inspection and testing of wind farm structures on hard-to-reach locations in an effective and safe manner, the implementation of industrial rope access is necessary. As a cost-effective alternative to traditional rotor blade access methods, industrial rope access is a proven method of achieving a safe working environment at heights in areas that are difficult to access. With these steps, along with regular condition monitoring, which detects failures of critical components as early as possible, undesirable downtime, consequential damages, and unexpected costs or losses of revenue are avoided.

End-of-Warranty Inspections
In addition to In-service Inspections, another method to reduce the costs of operation and maintenance of wind farms are End-of-Warranty Inspections. To ensure a wind turbine’s durability and lifetime guarantee, it’s essential to keep any potential deficiencies in check and, if necessary, repaired within the warranty period of the manufacturer. These inspections involve a series of activities in which the various components of a wind turbine are properly inspected, and a report is generated that includes a description of all deficiencies. The benefits of End-of-Warranty Inspections include: the discovery of any deficiencies, higher turbine availability (due to the prevention of damages to critical components), a detailed report with descriptions of all findings, as well as the minimization of maintenance costs due to timely warranty claims.

Conclusion
The reliability of wind farm structures has a decisive impact on the profitability of a wind farm. To minimize the risks of costly downtime and repair periods and ensure successful functioning of a wind farm, it is indispensable to conduct In-Service Inspections. Nevertheless, In-Service Inspections present a value-added service for wind farm owners when they are carried out by a reliable third-party company.


Nils Dreischerf works as a wind turbine inspector, and Olaf Robenek is the senior wind turbine inspector, onshore and offshore, both at SGS Industrial Services.

SGS is an inspection, verification, testing, and certification company, recognized as the global benchmark for quality.

SGS Industrial Services
www.sgs.com/renewables