Modeling of Offshore Wind Turbine Under Lightning Stroke and Analysis of Impact Factors on Transient Overvoltage

In order to prevent and reduce the offshore wind farm's damage caused by lightning, it's necessary to establish an electromagnetic transient model of the actual discharge flow path, calculate and evaluate the transient overvoltage at the wind turbine's engine room caused by lightning stroke. The accuracy of grounding resistance is an important factor affecting the reliability of the lightning channel model. Considering the wide distribution of China's offshore wind farms and the great difference in sea conditions, the intertidal grounding environment is divided into three layers: seawater layer, silt layer and sandstone layer. The influence of physical depth and resistivity of each layer on grounding resistance is analyzed. Taking the 2MW wind turbine of Shanghai Electric in the intertidal wind farm in Yangkou, Rudong, Jiangsu as an example, the actual discharge flow path is divided into five parts: excitation source, blade, bearing of engine room, tower and grounding resistance. And mathematical models are established respectively. The tower is equivalent to a vertical hollow section cylinder; the bearing between the engine room and the tower is equivalent to the capacitance; the equivalent resistance of each layer is calculated by using the Green function of the soil point current, and the total impact grounding resistance is obtained by superposition. Finally, the whole model is calculated in ATP-EMTP. The relationship between impact factors and the lightning transient effect is analyzed by taking the transient overvoltage at the engine room as an example.