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Monitoring and Mitigation of Low Frequency Noise from Wind Turbines to Protect Comprehensive Test Ban Seismic Monitoring Stations

Monitoring and Mitigation of Low Frequency Noise from Wind Turbines to Protect Comprehensive Test Ban Seismic Monitoring Stations Thumbnail


The first work which described the harmonic tonal nature of vibrations from windfarms was carried out at St Breock’s Down, Cornwall, UK and is described in Legerton et al (1996) and more fully in Snow, and Styles (1997). This has since raised concerns about the possible effect of wind farms on sensitive installations. Styles et al (2005) describe an extensive monitoring programme to characterise the low frequency vibration spectra produced by wind turbines of various types, both fixed and variable speed. They demonstrated that small but significant harmonic vibrations controlled by the modal vibrations of the towers and excited by blade passing, tower braking and wind loading while parked, can propagate tens of kilometres and be detected on broadband seismometers. This meant that protective measures had to be implemented to protect the International Monitoring System (IMS) seismic monitoring station located at Eskdalemuir in the Scottish Borders, the UK’s contribution to the Comprehensive Test Ban Treaty (CTBT) verification regime which must be observed by international treaty. Over 2 GW of wind turbines were planned for this region and planning restrictions were imposed to control development because of the potential effects on the IMS station. Styles et al (2005) established that vibrations of concern in the 2 to 6 Hz band, while small, were critical for this monitoring. Propagation laws and an aggregate vibration budget were derived and calculated to aid planning and permit appropriate wind farm development. With increasing pressure to reduce carbon emissions through renewable energy contributions in the UK and especially Scotland, the budget has now been reached, with at least 2.5 GW of new wind developments are still in scoping and planning. It is therefore necessary to find a method to reduce the vibrations from new and existing farms to achieve headroom for new developments. Reactec Ltd in conjunction, have developed a Seismically Quiet Tower (SQT) system which can be retro-fitted or installed during construction. This can significantly attenuate the vibrations produced and delivered to the ground in the frequency band deleterious to the discrimination capability of the Eskdalemuir station. The SQT can, and is planned to, be fitted to existing close-in wind turbines to reduce their contribution to the vibration budget and potentially release budget for new development elsewhere in the 50 km zone of concern around Eskdalemuir. Keele University have carried out a programme of modelling and seismic monitoring of this system and have confirmed that it does significantly reduce the vibration spectrum in the region of 2 to 6 Hz which has the added benefit of reducing many fatigue loads on the turbine tower itself.

Conference Name Fourth International Meeting on Wind Turbine Noise
Conference Location Rome
Start Date Apr 12, 2011
End Date Apr 14, 2011
Publication Date Apr 1, 2011
Series Title Fourth International Meeting on Wind Turbine Noise
Keywords wind turbines, noise, environmental impacts


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