Abstract: The invention relates to a method for monitoring yawing fault events of a yaw system of a wind turbine. The yaw system comprises one or more actuators for driving the yaw system and a holding system to resist yaw rotation. The yaw system is arranged to provide yaw rotation in response to a yaw control signal. According to the method, the monitored yaw angle is compared with the yaw control signal, and based on the comparison, a correlation between a monitored change in the yaw angle and the yaw control signal is determined. A yawing fault event is determined dependent on the determined correlation.

Abstract: The invention relates to a test tool for testing an overspeed protection system of a wind turbine. The system includes a sensor for sensing a first physical signal having a physical nature and representing a speed of rotation of a rotor of the wind turbine, and for providing a corresponding output signal; means for receiving the output signal from the sensor and for determining, based on the output signal, if the speed of rotation exceeds a threshold of speed of rotation; and means for initiating, if the speed of rotation exceeds the threshold of speed of rotation, an action reducing the speed of rotation. The test tool provides a second physical signal of the same physical nature as the first physical signal, is suitable for supplying the second physical signal to the sensor so as to simulate the rotation of the wind turbine.

Abstract: The invention relates to a test tool for testing an overspeed protection system of a wind turbine. The system includes a sensor for sensing a first physical signal having a physical nature and representing a speed of rotation of a rotor of the wind turbine, and for providing a corresponding output signal; means for receiving the output signal from the sensor and for determining, based on the output signal, if the speed of rotation exceeds a threshold of speed of rotation; and means for initiating, if the speed of rotation exceeds the threshold of speed of rotation, an action reducing the speed of rotation. The test tool provides a second physical signal of the same physical nature as the first physical signal, is suitable for supplying the second physical signal to the sensor so as to simulate the rotation of the wind turbine.