Wind energy is clean energy but not without its usual baggage. Their noise disturbs those who reside in the close proximity with a wind farm. Many a time wind turbines are forced to operate under partial load so that residents and wind farms can exist in peaceful co-existence. But operating under partial load means lower energy production. Even high winds go unutilized in residential areas. The sources of the noises are many. First is the motion of the rotor blades and another is the cogwheels. Cogwheels generate noise in the gearboxes. These are transported to the tower of the wind turbine, where they are emitted across a wide area — and what the residents hear is a humming noise. This noise comes out as if mosquitoes are buzzing constantly.
If an active damping system is employed at wind farms they make this noise somewhat ineffective by producing counter vibrations. To neutralize this humming operators have to install additional damping systems or even substitute the gearbox. And these things are certainly not cost effective. If we examine closely the efficiency of the existing passive damping systems, we will find its success is limited. They operate only at certain frequencies. And it is their greatest drawback because modern wind energy converters rotate and keep changing their rotational speed according to the wind velocity to generate maximum energy. But all this leads to variations in humming sounds too and this limits the usefulness of the modern damping system. Despite noise decreasing measures, humming noises permeate the surrounding areas.
A team of researchers from Schirmer GmbH, ESM Energie - and Schwingungstechnik Mitsch GmbH and the Dr. Ziegler engineering office, IWU are developing an active damping system for wind turbines. The project is financed by the Deutsche Bundesstiftung Umwelt.
This active damping system is obviously an improvement over its predecessors. It senses the change in frequency and neutralizes the noise without affecting the speed of the wind generator. Piezo actuators are the key constituents of this system. These units transform the electric currents into mechanical motion and create “negative vibrations.” These anti-noises offset the vibrations from wind turbines. How do these piezo actuators fine-tune to the changing noise frequencies? Here the research team has devised some sensors that constantly calculate the vibrations coming out from the gearbox. These measurements of frequencies are transferred to the actuator control system. The researchers have already developed a working model of the active vibration dampers, and their next step will be to perform field trials.
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