A New Identification Method for Bolt Looseness in Wind Turbine Towers

Table 3

Vibration test conditions of the wind turbine towers.

Experiment ID	Content of working condition	Test environment condition	Tightening condition of flange plate
1	Vibration test when tower is in an inactive state	Wind speed is less than 5 m/s	Before tightening
2	Vibration test when tower is in an inactive state	Wind speed is 18∼2 m/s	Before tightening
3	Vibration test when tower is in an active state	Wind speed is 7∼10 m/s	Before tightening
4	Vibration test when tower is in an active state	Wind speed is 18∼24 m/s	Before tightening
5	Vibration test when tower is in an inactive state	Wind speed is 18∼22 m/s	After tightening
6	Vibration test when tower is in an active state	Wind speed is 18∼24 m/s	After tightening

Note. Flange tightening refers to only retightening of each bolt on the flange by the torque method.