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Investigating the root cause of rotor induced vibrations in wind turbine drivetrains

It is critically important to monitor wind turbine rotor balance, given that vibrations resulting from imbalance will fatigue all components in the load path – from the blades down to the foundation.

At our 2019 North American Wind Turbine Technical Symposium, 16th-18th September 2019, ONYX InSight‘s Wind Drivetrain Engineering Consultant Mike Hornemann will be presenting on Rotor Balance Seeded Fault Results. In this blog, Mike previews his Symposium presentation by exploring the investigation of the root cause of rotor induced vibrations in wind turbine drivetrains.

Most turbines have a basic piezoelectric accelerometer mounted in the nacelle to provide a warning via the SCADA system if the tower acceleration alarm threshold is reached.  From a safety perspective, these devices protect owners as they provide an automatic shutdown command in the event of a gross rotor imbalance. Unfortunately, these sensors are too simplistic for predictive maintenance since they do not facilitate trending, neighbour comparison or outlier analysis.

In designing ecoCMS – ONYX InSight’s online turbine vibration monitoring hardware, we incorporated triaxial MEMS sensor that can measure vibration down to 0 Hz with a very fine frequency resolution. As such we are able to monitor and trend for rotor imbalance comprehensively. Rotor imbalance can affect site OPEX by reducing a wind turbines aerodynamic efficiency and increasing structural fatigue of critical components. Early detection of rotor imbalance allows turbine owners to take corrective action before the imbalance causes component damage or money is lost through aerodynamic efficiency.

A case study from a recent ecoCMS retrofit, on 63 wind turbines, demonstrated just how useful this is. ONYX vibration analysts performed an individual turbine vs. farm comparative analysis to look for machines exhibiting abnormal imbalance behavior. The heat map view in Figure 1 clearly shows 3 outlier turbines with ongoing imbalance issues.


Figure 1: The fleetMONITOR heatmap allows for easy identification of outlier turbines for any trended parameter.  In this example, three turbines with imbalance worthy of investigation and corrective action are flagged.

With fleetMONITOR we can examine the trend plot and compare the problem turbine with a set of neighbor turbines, giving a refined view on the magnitude of the imbalance error.

Figure 2: The fleetMONITOR trendview shows the problem turbine vs. several neighbor turbines.  The imbalance magnitude is more than 2 standard deviations above typical values.  This provides the confidence to wind turbine engineers to schedule further investigation. 

There are various possible sources for imbalance. An aging blade with moisture ingress could cause mass imbalance. An improperly adjusted pitch position could cause aerodynamic imbalance. Damage or incorrect control settings in the pitching system is another possibility.  In this case we scheduled a rotor hub inspection and what we found was exciting and required corrective action to be quickly organized before the problem became serious!

Interested to hear more?  We invite you to join us for our 2019 NA Wind Turbine Technical Symposium where our Wind Turbine Reliability Engineer, Mike Hornemann, will be presenting an in-depth case study.


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