Method and detection assembly for the detection of changes in a building structure of a wind turbine

1. Method for detecting changes in a building structure of a wind turbine, comprising:

monitoring a reference value representing the eigenfrequency of a wind turbine over time using a monitoring unit,

providing the reference value by a reference value unit, and

using changes of the reference value as an indication of changes in a building structure of the wind turbine, wherein a change indication unit indicates the changes in the building structure of the wind turbine, and

wherein the reference value is based upon a difference between a frequency value representing a current frequency of the wind turbine and a modelled frequency behaviour value.

2. The method according to claim 1 , wherein the modelled frequency behaviour value is modelled using a temperature value representing a current temperature in an environment of the wind turbine.

3. The method according to claim 2 , wherein the modelled frequency behaviour value is calculated such that the current temperature value is multiplied with a first specific constant, and wherein a second specific constant is added to a product of the current temperature value multiplied with the first specific constant.

4. The method according to claim 3 , wherein the first specific constant represents a mean frequency of the wind turbine and/or a frequency value related to a specific type of wind turbine to which the wind turbine belongs and/or wherein the second specific constant represents a constant specific for the first wind turbine.

5. The method according to claim 3 , wherein at least one of the first specific constant and the second specific constant is a same constant as used in a context of a detection of changes in the building structure of a further wind turbine in close proximity to the wind turbine, preferably of all wind turbines assembled in a group of wind turbines which group comprises the wind turbine.

6. The method according to claim 2 , wherein the frequency value and/or the temperature value is measured by a plurality of sensors arranged inside a nacelle of the wind turbine or attached to the outside of the nacelle.

7. The method according to claim 2 , wherein the temperature value is derived from a database of representative temperature values relating to similar circumstances in time and/or weather conditions as is currently the case.

8. The method according to claim 1 , wherein the reference value comprises a classifier indicating a state of alarm and a state of normal eigenfrequency of the wind turbine.

9. The method according to claim 1 , wherein the frequency value is derived from current frequencies of a plurality of wind turbines within a wind turbine park.

10. The method according to claim 9 , wherein the frequency value is a mean value of the frequencies of the plurality of wind turbines within the wind turbine park.

11. Detection assembly for detecting changes in a building structure of a wind turbine, comprising:

a reference value unit for output of a reference value representing the eigenfrequency of a wind turbine,

a monitoring unit which monitors the reference value over time, and

a change indication unit which indicates a change in a building structure when the reference value changes,

wherein the reference value is based upon a difference between a frequency value representing a current frequency of the wind turbine and a modelled frequency behaviour value.

12. Wind turbine with a detection assembly according to claim 11 , comprising:

a frequency measurement sensor which measures the current frequency of the wind turbine,

and/or

a frequency calculation unit which derives the frequency value from current frequencies of a plurality of wind turbines within a group of wind turbines, and

a temperature measurement sensor which measures a current temperature value, or a temperature value derivation unit which derives a temperature value from a database of representative temperature values relating to similar circumstances in time and/or weather conditions.