ECN publication
Conditiebewaking rotor bladen
Published by: Publication date:
ECN Wind Energy 10-5-2007
ECN report number: Document type:
ECN-E--07-025 ECN publication
Number of pages: Full text:
43 Download PDF  

Condition monitoring of wind turbine components is of growing importance. For bearings, gearboxes and other rotating equipment, techniques are available from other applications. For condition monitoring of rotor blades, no suitable techniques are available up to now. However the interest for it is increasing in order to get more insight in the occurring loads and to reduce these loads by applying other control techniques. Within this project, a blade condition monitoring system has been designed, integrated and installed in a large wind turbine. Three activities have been executed in parallel: • Development of a read-out unit and data acquisition system • Further development of Bragg sensors • Development of diagnostic software. The read-out unit and the data acquisition system including a rotor part and a turbine part have been designed, built and tested by FOS and ECN. The design is based upon a set of requirements as defined by ECN. Based on the requirement specification, a test program was defined and executed in the laboratory as well on a large turbine. Apart from the activities with respect to the measurement system, further development of the sensors is essential. During this project, a retrofit type has been applied. This enables to install sensors after production of the blades and to replace them in case of failure. Bragg sensors are sensitive for temperature variation. For this project, active temperature compensation has been chosen. The temperature sensors, based upon the same technology, have been modified in order to prevent for strain modulation. These sensors have been tested together with the other sensors and the instrumentation in the laboratory as well as on a turbine. The diagnostic software should provide information to the user which can be used for planning of maintenance. The modules providing most information for that, being load counting, frequency analysis and fatigue damage calculation have been worked out during the project. An initial version of the diagnostic software was implemented in the blade condition monitoring system. Because the system was not operational for large periods of time, the modules have been tested offline based on available load data from another turbine of the same farm. After execution of the tests has been concluded that: • The delivered hardware was not suitable to operate in this environment and further development focused on this application will be necessary. • The strain sensors gave problems with respect to accuracy and reproducibility. Apart from that, the temperature sensors also show stain modulation. Further developments for sensors and methods for temperature compensation will be necessary. • The diagnostic software shows very good results with respect to the interactive method for processing of measurement data and the calculation of the load spectra. Via frequency analysis small shifts in the eigen frequency can be detected. On line tests are necceassary as further follow up in order to demonstrate the usefulness in practice.

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