A series of continuous vibration measurements in 14 upwind wind
turbines of the same model and belonging to the same wind farm
have been conducted. The data were acquired over a period lasting
approximately half a year. The tower axial vibration acceleration
has been monitored in the frequency band from 0 to 10 Hz
with an accelerometer mounted on the gearbox casing between
the intermediate and the high-speed shafts. It has been observed
that the average frequency spectrum is dominated by the blade
passing frequency in all the wind turbines. The evolution of the
vibration magnitudes over the entire range of operating conditions
is also very similar for all the wind turbines. The root-meansquare
(rms) acceleration value has been correlated with the wind
speed, and it has been found that a linear fit with a positive slope
is a useful model for prediction purposes.