Low cost acceleration measurement system as a retro-fit solution for vibration monitoring of wind turbines in operation

Kurzfassung

Wind turbines are subjected to a combination of various loads during operation and must also withstand extreme weather conditions. In some conditions wind turbines exhibit vibrational problems due to unknown circumstances. In these cases, it would be helpful to have an easy installable measurement system to monitor the vibrational behavior of the rotor blades or even the whole wind turbine. The standard measurement technology using rugged measurement hardware including a measurement system and acceleration sensors is quite expensive. It is usually only applied for prototype testing but not for long term monitoring of vibration and operational conditions. Therefore, a development of low-cost and low-power measurement hardware has been initiated at the German Aerospace Center (DLR) institute of aeroelasticity based on MEMS acceleration sensors, such as those used in millions of smartphones or other mobile devices. But not only the cost for sensors has to be reduced. Also, a low-cost solution has to be found for data acquisition hardware and signal processing hardware. Based on the MEMS sensor concept, a measurement system has been developed that also relies on low-cost electronics for all other components. In its current state it is capable of measuring up to 25 sensors of the type ADXL362 without phase shift at a sampling rate of 200 Hz. Currently the German research wind farm WiValdi in Krummendeich is built up by the DLR. Within the DFWind research project supporting WiValdi a rotor blade has undergone a modal test on a test rig at Fraunhofer IWES in Bremerhaven with heavy external and internal instrumentation of accelerometers. During this test, the MEMS based measurement system were extensively tested and benchmarked against high cost prototype testing equipment. MEMS sensors has been added to 14 of 16 internal measurement positions so that a direct comparison of the standard system, an imc Chronos Flex with IEPE accelerometers and the DLR low-cost MEMS system has been accomplished. In total, data from 13 different measurement runs and three excitation points have been recorded with the MEMS system. These are then examined in the frequency domain and with operational modal analysis. The resulting modal parameters, such as the eigenfrequencies, damping ratios and mode shapes are used for the comparison between the standard and the low-cost MEMS system.