Continuous rotor blade monitoring
Wind turbines, and particularly rotor blades, are exposed to a wide range of environmental influences. These can cause blade damage that is not visible from the ground. Typical damages include blade tip damage caused by lightning strikes, trailing edge cracks, web separation and blade bearing damage.
Abnormalities and damage to rotor blades can build up, particularly as they age. In addition, systems that are already over 20 years old are expected to remain in operation for another five to ten years. Continuous data recording by the monitoring systems serves as the basis for making reliable predictions about the ongoing operation of the systems.
Targeted rotor blade monitoring with necessary sensors continuously records the condition of each individual rotor blade and detects even minor changes. 24 hours a day, 365 days a year, regardless of the location of the wind turbine. In contrast to visual inspections, in some cases initial damage not visible from the outside can be identified up to twelve months earlier. The risk of expensive repairs is reduced, and the economic efficiency of the entire installation increases.
"Blade monitoring systems allow a more detailed and faster recognition of damage at rotor blades. Therefore, they can increase turbine availability, reduces downtimes, and ensures better efficiency."
Daniel Brenner, Head of Monitoring, Weidmüller Monitoring Systems GmbH
Blade monitoring is not only useful for older systems. Often, structural damage can occur even in new turbine classes. "With a 3.x turbine type, we saw one specific critical damage on over ten percent of the equipped systems. With a five MW class turbine type, there were deviations from normal behaviour in over 40 percent of the turbines equipped with condition monitoring systems" explains Daniel Brenner, Head of Monitoring at Weidmüller Monitoring Systems GmbH.
This shows how important continuous rotor blade monitoring is. If the damage is severe, some systems can send a signal to the turbine control system, which can then immediately stop the turbine and prevent blade lost.
Continuous monitoring ensures gentle operation
Acceleration sensors in the single rotor blades allow accurate and compact measurement in a single module. Data from the rotor blades can be combined by monitoring systems in the hub and transmitted to the gondola. An evaluation unit (ECU) installed in the tower base, for instance, analyses and documents the data on a continual basis. Damage is detected, classified in relation to its severity, and then the information gathered is forwarded on for further analysis. Experts in the monitoring centre evaluate the data and prepare concrete action recommendations for the operator.
Especially in offshore turbines, operators can lose out on high earnings when their multi-megawatt turbines are at a standstill. Due to strong winds, high waves, fog, or currents, the turbines can only be reached a few days a year. In addition, the repair costs are much higher than onshore, due to the complicated logistics involved. Continuous monitoring makes it possible to plan service work on a predictive basis, and significantly reduce costs.
Example of a digital overview of a rotor blade condition monitoring system with status of blades, ice detection and performance data © Weidmüller
In addition to damage to the rotor blades themselves, some monitoring systems can also detect aerodynamic imbalances as well as loose parts in the blade and hub. This allows an optimal planning of necessary repair work whilst avoiding high follow-up costs. Continuous monitoring ensures gentle operation and serves as the basis for improving earnings and extending the service life of the turbine.
Via online visualisation users and operation managers can check the rotor blade and turbine status. Some systems have a traffic light system, that shows the status of each rotor blade: green for normal function, yellow for minor damage and red for serious damage. The same system is used by some systems to detect ice: green for ice-free, yellow for ice accretion and red for ice coverage, stopping the turbine.
Ice detection sensors
Rotor blade monitoring means not only detecting damages early on, but also ensuring operation in every season. State-of-the-art ice detection sensors allow measurements to be conducted on the rotor blade itself. Thanks to the highly sensitive sensor system and special algorithms, modern systems can achieve a measurement resolution for the thickness of the ice in the millimetre range. This guarantees the environment is safe. Ice detectors with high-quality technology not only detect when rotor blades reach a critical level of ice accretion, but also when the danger has passed. This means the turbines can be restarted automatically at any time.