mass and aerodynamic imbalance

Wobbling giants: why is rotor imbalance an issue?

  • By saralarde
  • oct 20th, 2021
  • News

The tip of a wind turbine blade can rotate as fast as 80 m/s. That is like driving at 300 km/h. When you are going that fast, you want stability. Rotor imbalance is a concern that increases with speed. With ever longer blades, this is a key issue. Whether the cause is aerodynamic or mass, any impact on its stability can be detrimental to both productivity and wind turbine life expectancy.

Rotor imbalance affecting wind turbine lifetime


A paper published in 2015 shows the impact of rotor imbalance on the lifetime consumption of your Wind Turbine. But more immediately, Rotor Imbalance will have an impact on productivity. According to Wind Consult, just one blade misalignment can impact AEP by nearly 3,5%. With all three blades misaligned, this can go up to more than 10%!

Rotor Imbalance measurement



Rotor Imbalance has many causes and all wind turbines can be affected. When linked to weight, this may come from debris build-up or material degradation, without mentioning icing. If it is aerodynamic, then it is often a blade alignment issue, though damages can also have a strong impact on the aerodynamic flow.

This is not an isolated issue occurring rarely, on the contrary. Field experience[1] has shown that 33% of wind turbines have a meaningful aerodynamic imbalance with at least 0,5° imbalance, while 10% of wind turbines present a blade difference of a least 1°. According to its own field measurements, Det Norske Veritas has indicated that any angle discrepancy superior to 0,6° becomes an important issue which needs to be addressed quickly.

Whatever the cause, there is a simple and effective solution to address the sources of productivity loss.



How does WindEagle measure rotor imbalance?


With more than 10 years providing advanced sensors and algorithms to improve productivity, Epsiline is a key provider of turn-key solutions for the monitoring of wind turbines and their environment. Epsiline’s WindEagle is a multi-sensor unit installed on top of the nacelle to provide online and API accessible data in real-time. The WindEagle’s initial mission, of monitoring Yaw and Turbulence Intensity, to improve productivity and reduce maintenance, was expanded to encompass Rotor Imbalance surveillance and alerts. A three-axis accelerometer installed in the WindEagle provides the necessary information to differentiate between mass and aerodynamic imbalance and then to send alerts when vibration exceeds a predetermined level.

The WindEagle is easily installed on top of the Nacelle where it monitors the different types of vibration. The information concerning vibration is processed through our advanced algorithms and then sent via the cellular network to our secured servers for dispatch, either to our web portal or via an API key to your own servers. Email alerts are sent according to parameters you will have provided.

At the core of the WindEagle lies a patented LiDAR technology which measures wind characteristics 10m in front of the device, in other words, directly in front of the blades. Beyond its high wind measurement accuracy, Epsiline’s LiDAR brings this advanced technology to all by reducing cost by an order of magnitude. Where traditional LiDAR are priced around 100 000€, Epsiline’s approach makes it affordable to all asset owners and operators by reducing the cost by 10 for Wind farms.



WindEagle: an online diagnosis


Epsiline’s LiDAR technology forms the cornerstone of an advanced yet easily useable solution. Accurate measurements of wind speeds, intensity  and direction are completed by further sensors including Pressure, Temperature & Humidity (PTU), vibration and GPS. All these sensors are contained in the compact WindEagle which is installed in less than 2 hours on top of the nacelle. Data is transmitted via the cellular networks directly to Epsiline’s secure servers where the information can then be processed either through Epsiline’s advanced algorithms or through an API key for more customized analysis. Algorithm results and parameters are then accessed through Epsiline’s Web portal, giving full diagnostics to understand, monitor and improve performance.

With accurate and reliable information now readily available, fundamental performance traits are automatically analyzed, starting with Yaw , TI and Aerodynamic Imbalance.

Once an Aerodynamic Imbalance is detected and corrected, true performance improvement is measured by combining the vibration with the WindEagle’s wind data.

When the WindEagle is left permanently on the nacelle, automatic monitoring can be implemented to improve maintenance and ensure optimal productivity. Alerts are programmed to have email notifications sent whenever preset or customized thresholds have been crossed.

Epsiline’s WindEagle is uniquely positioned to support the Wind Industry in its transformation, by focusing on optimal performance through state-of-the-art sensors allowing for real-time data transmission, analysis and improvement, while improving returns for asset owners and wind farm operators.



[1] Impact of rotor blade angle misalignments,  Dipl.-Ing (FH) T. Kleinselbeck, Dipl.-Ing. (FH) R. Lieckfeldt – WIND-consult GmbH, Bargeshagen, Germany