Method and arrangement to detect an oil leakage between sections of a hydraulic cylinder

A wind turbine comprising:

• a plurality of rotor blades;
• a hydraulic pitch drive system for aligning a rotor blade of the plurality of rotor blades into incoming wind;
• and
• an arrangement for detecting an oil leakage between a first section and a second section of a hydraulic cylinder of the hydraulic pitch drive system, the arrangement comprising:
• a movable piston of the hydraulic cylinder that interacts, via a position of the movable piston, with the rotor blade to turn the rotor blade to specific pitch angles, wherein the movable piston is arranged between the first section and the second section in a way that the movable piston changes the position between the first section and the second section dependent on a difference between a first force, which acts at the first section on a first cross sectional area of the movable piston, and a second force, which acts at the second section on a second cross sectional area of the movable piston;
• wherein the first section comprises hydraulic oil with a predefined first pressure, while the first force is calculated based on the predefined first pressure and based on the first cross-sectional area, and the second section comprises hydraulic oil with a predefined second pressure, while the second force is calculated based on the predefined second pressure and based on the second cross-sectional area;
• wherein the first section is connected with a remote controlled first valve, which is closed for the leakage detection;
• wherein a sensor is coupled with the movable piston in a way that any change in position is detected, while a change of the position results from the difference of the first force and the second force resulting from closing the remote controlled first valve and from an alignment of the first pressure to the second pressure due to the leakage between the first section of the hydraulic cylinder the second section of the hydraulic cylinder;
• wherein the sensor is coupled with a control unit, which is prepared and arranged to detect the leakage of oil based on the change of the position;
• wherein detecting the oil leakage is initiated in response to the wind turbine reporting a sequence of errors including:
• (i) a pumping time becomes prolonged, (ii) a temperature of the hydraulic oil starts to increase, and (iii) an unwanted pitch tracking occurs during operation of the wind turbine.