flacaltenn
Diamond Member
http://www.gov.scot/Resource/0045/00454076.pdf
Measurements at distances of 25, 50 and 100 m from the St Breock’s Down wind farm, Cornwall, found discrete seismic vibrations could be detected at 0.5 Hz and multiples of 0.5 Hz, specifically 3.0, 4.5, 6.0 and 7.5 Hz (Legerton, et al. 1996, Snow and Styles 1997). Using turbine shut down sequences it was shown that the discrete vibrations were produced by the wind turbines and it was inferred that 0.5 Hz multiples were related to multiples of the blade pass frequency. It was also shown that the amplitude of seismic vibration increased with wind speed. Seismic measurements near the Stateline wind farm, Washington, USA found seismic signals that could be attributed to the wind farm up to 18 km from the closest wind turbine (Schofield 2001). The geology of the survey site is dominated by the Touchet bed of the Walla Walla Valley consisting of gravel, fine sediment and rhythmites which are up to 100 m thick (Baker 1978) which have slow ground wave propagation velocities of ~ 500 ms-1 (Schofield 2001). Schofield (2001) deployed seismometers at 10 sites ranging from 24 m to 18,270 m from the wind farm and found discrete signals at 1.47, 2.95, 4.34, 5.88 and 7.35 Hz that were attributed to multiples of the frequency at which the blade passes the turbine tower, the blade pass frequency. Stable peaks with respect to time and wind speed were found and interpreted as being due to the resonance of the tower topped by the nacelle and rotor. Schofield (2001) found that amplitude of seismic vibation reduced with the inverse of distance (1/r) and postulated that this indicated that seismic path propogated partly through air as infrasound, before being coupled with the earth to form seismic waves.
Measurements at distances of 25, 50 and 100 m from the St Breock’s Down wind farm, Cornwall, found discrete seismic vibrations could be detected at 0.5 Hz and multiples of 0.5 Hz, specifically 3.0, 4.5, 6.0 and 7.5 Hz (Legerton, et al. 1996, Snow and Styles 1997). Using turbine shut down sequences it was shown that the discrete vibrations were produced by the wind turbines and it was inferred that 0.5 Hz multiples were related to multiples of the blade pass frequency. It was also shown that the amplitude of seismic vibration increased with wind speed. Seismic measurements near the Stateline wind farm, Washington, USA found seismic signals that could be attributed to the wind farm up to 18 km from the closest wind turbine (Schofield 2001). The geology of the survey site is dominated by the Touchet bed of the Walla Walla Valley consisting of gravel, fine sediment and rhythmites which are up to 100 m thick (Baker 1978) which have slow ground wave propagation velocities of ~ 500 ms-1 (Schofield 2001). Schofield (2001) deployed seismometers at 10 sites ranging from 24 m to 18,270 m from the wind farm and found discrete signals at 1.47, 2.95, 4.34, 5.88 and 7.35 Hz that were attributed to multiples of the frequency at which the blade passes the turbine tower, the blade pass frequency. Stable peaks with respect to time and wind speed were found and interpreted as being due to the resonance of the tower topped by the nacelle and rotor. Schofield (2001) found that amplitude of seismic vibation reduced with the inverse of distance (1/r) and postulated that this indicated that seismic path propogated partly through air as infrasound, before being coupled with the earth to form seismic waves.