Contrastive analysis of transient potential of wind turbine onshore and offshore in lightning strokes

For the lack of systematic research of lightning protection design of the wind turbine, it is necessary for further study of the transient effect caused by lightning. Essentially, the process that lightning current flows through the turbine is a wave process. In this paper, wave-process theory is adopted when effect of wave process on the transientpotential is analyzed. With the software ATP-EMTP, oscillation of transient potential throughout the wind turbine is simulated under various conditions, such as different tower body height, soil resistivity and size of the grounding device. The influence of various conditions on the frequency of oscillation is also studied. On this basis, an improved wave impedance model for the wind turbine offshore is put forward. Actually, parts of the wind turbine offshore located in different situations have different wave impedances. The multi-wave impedance model is divided into three segments. By applying this model, simulation of lightning hitting the wind turbine onshore and offshore is carried out. The transient potential at the top of the blade and the grounding device is analyzed. Through a comparative analysis, their respective characteristic is get. For the wind turbine onshore, the amplitude of transient potential oscillation is far larger, which may lead to more sever induced over-voltage. For the wind turbine offshore, the frequency of transient potential oscillation is far higher, which may cause more damage to the weak electricity system of the wind turbine. So there should be respective emphases against lightning strike for different types wind turbine, which would be a reference basis for lightning protection design of the wind turbine.