Renewable energies

Rotor imbalance inevitably leads to damage of wind turbine components, downtimes, loss of efficiency and higher noise emissions. Causes of aerodynamic influences are for example deviations in the rotor blade angle or twisting of the rotor blades themselves. Mass eccentricity can also be caused by blade erosion or damage, or asymmetrical ice formation.

Aerodynamic and mass-related imbalances result in unfavorable forces and vibrations in the wind turbine. The low rotational frequency of the rotors necessitates the use of sensors for structural health monitoring (SHM) that operate in a frequency range below 0.5 Hz and also feature excellent amplitude resolutions below 20 µg.

The triaxial accelerometers ASC 5511LN (aluminum housing) or ASC 5515LN (stainless steel housing) are ideally suited for this application.

Wind turbines are subjected to vibrations due to operating conditions and environmental influences. Damage to wind turbines results primarily from such vibrations. Early detection of vibrations requires continuous monitoring of the systems.

Due to the harsh ambient conditions, however, wind turbine manufacturers have very challenging requirements for condition monitoring systems. For example, they must be able to reliably and continuously detect vibrations in the gearbox and rotor blade as well as the rotor and generator bearings in a broad frequency response range from 0.1 Hz to 10 kHz.

Ideal sensors for such condition monitoring applications are the piezoelectric accelerometers ASC P311K-A15 (side-connector)  and ASC P311K-A25 (top-connector) as well as the triaxial ASC P313P-A15 – compact, very robust and designed for flexible configuration.

Offshore wind turbines are subjected to many different types of loads. However, low-frequency aerodynamic tower tilting, wave induced influences, hydrodynamic forces and seismic movement of the sea bed can be measured optimally with capacitive tilt sensors of the ASC TS series. The stainless steel version with IP68 protection is ideal for offshore applications.

These sensors also feature a low frequency response range (DC up to 100 Hz), which allows precise detection of static and quasi-static tower movements, while suppressing disturbing signals from higher-frequency vibrations.

Test systems are used for detailed analyses of the dynamic behavior of wind turbines. In these tests, wind turbines are caused to vibrate with defined forces. Accelerometers detect reactions exactly, which makes it possible to measure the entire frequency and amplitude behavior by means of modal and structural analysis.

The measurements obtained are the basis for simulations, which can be used to model a digital twin of a wind turbine. Design variations and other actions enable a substantial increase in the durability and efficiency of wind turbines, as well as reduction of vibrations and noise emission.

Continuous monitoring of wind turbines by means of condition monitoring and structural health monitoring ensures early detection of critical changes in their components. The complex applications and parallel measurements require ever more compact and more intelligent sensor solutions. Smart sensor systems ASC AiSys® VibroTherm provide the answer to these challenges. Not only critical vibrations, but also the oil temperatures on bearings and gears are acquired and analyzed synchronously.

Self-learning algorithms, for example, make it possible to predict the further progress of imbalances or material fatigue. This in turn serves as the basis for defining threshold values at which maintenance becomes necessary. Predictive maintenance is especially necessary in difficult-to-access offshore wind parks, to enable more effective maintenance and inspection intervals.