Modern wind parks usually consist of multiple individual turbines, which are connected to the grid using power electronic interfaces. Depending on their topology, they could be a source of distortion in the frequency range below 2 kHz (harmonics, interharmonics) and above 2 kHz (supraharmonics). Consequently, the assessment of the impact of wind parks on the voltage distortion in the network is an important issue. This paper explains some of these issues based on extensive field measurements at a recently commissioned 12 MW wind park consisting of 6 turbines with full inverter (type 4) and a rated power of 2 MW each. While the first part discusses the distortion characteristic of an individual turbine, the second part is dedicated to the wind park as a whole and its impact on the voltage distortion at the connection point. Based on the experiences from the project some recommendations for field measurements at wind parks are summarized.