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RESEARCHERS HAVE DEVELOPED active damping systems to fight ranging vibrations that constrain wind turbine operating speeds.

Spinning wind turbine rotor blades and gearbox cogwheels produce vibrations that result in a monotonal humming. This grates against local ears and leads to local authority gagging orders. It’s a common problem and one with few solutions; operators have tended to install new expensive gearboxes and passive vibration dampening systems or operate their turbines at lower speeds and generate less electricity and profit.

The problem with traditional passive dampening systems is that they only absorb noise at a specific frequency, which is now useless as modern energy converters adapt their rotational speed, and hence frequency and resulting humming noise, to the changing wind speeds in an effort to maximise electricity generation.

Fortunately, researchers at the Fraunhofer Institute for Machine Tools and Forming Technology, Germany, say they have developed a new active dampening system that can solve these problems by measuring the vibration frequency and producing the specific dampening effect to neutralise it.

“These systems react autonomously to any change in frequency and damp the noise – regardless of how fast the wind generator is turning,” says Fraunhofer research associate André Illgen. He says the key components of the system are piezo actuators that convert electric current into mechanical motion and generate ‘negative vibrations’ that precisely counteract the vibrations of the wind turbine and cancel them out. The piezo actuators are mounted on the gearbox bearings that connect the gearbox to the pylon. “We have integrated sensors into the system,” continues Illgen. “They constantly measure the vibrations arising in the gearbox, and pass on the results to the actuator control system.”

The researchers have built a working model of the active vibration dampers and hope to perform field trials soon.