The present paper describes the work done in power quality subtask of the project ”European Wind Turbine Testing Procedure Developments” funded by the EU SMT program. The objective of the power quality subtask has been to make analyses and new recommendation(s) for the standardisation of measurement and verification of wind turbine power quality. The work has been organised in three major activities. The first activity has been to propose measurement procedures and to verify existing and new measurement procedures. This activity has also involved a comparison of the measurements and data processing of the participating partners. The second activity has been to investigate the influence of terrain, grid properties and wind farm summation on the power quality of wind turbines with constant rotor speed. The third activity has been to investigate the influence of terrain, grid properties and wind farm summation on the power quality of wind turbines with variable rotor speed . Kewords: Power Quality, Standards, Electrical System, Wind Farm.