Abstract: A first aspect of the invention provides a method of testing a yaw system (200) of a wind turbine, the wind turbine comprising a rotor; the yaw system (200) comprising a yaw gear (202) coupled to the rotor so that rotation of the yaw gear (202) causes yaw rotation of the rotor, and first and second sub-systems (204a, 204b), the first sub-system (204a) comprising a first pinion gear (206a) and a first drive motor (208a) coupled to the yaw gear (202) by the first pinion gear (206a), the second sub-system (204b) comprising a second pinion gear (206b) and a second drive motor (208b) coupled to the yaw gear (202) by the second pinion gear (206b).

Abstract: A first aspect of the invention provides a method of monitoring the condition of a yaw system of a wind turbine, the wind turbine comprising a rotor, the yaw system arranged to control a yaw rotation of the rotor, the method comprising: providing design data 5 representing an expected relationship between yaw moment and yaw rotation speed; measuring a pair of parameters, the pair of parameters comprising a yaw moment parameter indicative of a yaw moment applied to the yaw system, and a yaw rotation speed parameter indicative of a yaw rotation speed caused by the yaw moment; using the design data to evaluate whether the pair of parameters deviates from the expected 10 relationship; and determining a condition of the yaw system on the basis of the evaluation.

Abstract: A first aspect of the invention provides a method of testing a yaw system (200) of a wind turbine, the wind turbine comprising a rotor; the yaw system (200) comprising a yaw gear (202) coupled to the rotor so that rotation of the yaw gear (202) causes yaw rotation of the rotor, and first and second sub-systems (204a, 204b), the first sub-system (204a) comprising a first pinion gear (206a) and a first drive motor (208a) coupled to the yaw gear (202) by the first pinion gear (206a), the second sub-system (204b) comprising a second pinion gear (206b) and a second drive motor (208b) coupled to the yaw gear (202) by the second pinion gear (206b).

Abstract: A first aspect of the invention provides a method of monitoring the condition of a yaw system of a wind turbine, the wind turbine comprising a rotor, the yaw system arranged to control a yaw rotation of the rotor, the method comprising: providing design data 5 representing an expected relationship between yaw moment and yaw rotation speed; measuring a pair of parameters, the pair of parameters comprising a yaw moment parameter indicative of a yaw moment applied to the yaw system, and a yaw rotation speed parameter indicative of a yaw rotation speed caused by the yaw moment; using the design data to evaluate whether the pair of parameters deviates from the expected 10 relationship; and determining a condition of the yaw system on the basis of the evaluation.