| Under the situation that energy problem is becoming more and more severe, wind power has become the fastest-growing and the most widely used renewable energy in the world today. Since wind turbine acts as a carrier invert wind energy into available energy, with the continuous increase of its capacity and the tendency of the large-scale and oceanic wind farm, it’s extremely important to keep the safe and stable operation of the wind turbine and the whole wind farm for the development of wind energy resources.Due to its strong energy, high voltage, high current, high frequency, lightning is a great threat for the effective development and safe utilization of wind power. Especially total height of the wind turbine increases with its increasing capacity, making it much more vulnerable to lightning strike; on the other hand, humid and rainy atmospheric environment with more frequent thunderstorm phenomenon on the sea makes the operation condition of offshore wind turbine more and more adverse, increasing the probability of a lightning strike. When lightning hits wind turbines, lightning current which carried huge energy usually strikes the arrester at the tip of the blade or the lightning rod. It flows along the conductor inside the blade or the cabin, and then it goes from the tower body into the grounding device, eventually drains into the earth. During the transient process that lightning current flows downwards along the wind turbine, on one hand, the transient potential along the current-flow path would rise which would do damage to the electrical equipment insulation; on the other hand, electromagnetic field inside the tower body caused by the lightning current is likely to result in electromagnetic interference within the power or signal lines and electrical control systems, which threatens the safe operation of wind turbines.Considering the layered characteristics of oceanic grounding environment, this paper established the grounding resistance model of the offshore wind turbine, and proposed a numerical calculation method of the grounding resistance. Wave impedance model of the blade was established according to the rotation characteristics of blades. By the theory of conical antenna, wave impedance numerical calculation formula the tower body was derived. Based on the above, lightning transient integration model of offshore wind turbines was put forward. Based on the research of the characteristics of the lightning, proper lightning model was selected for the simulation analysis. With the electromagnetic transient analysis software ATP-EMTP, the transient integration model above was established to simulate the lightning transient wave process on the wind turbine. Various factors, such as the lightning strike point, rotation position of blade, blade length, height of tower body and lightning current parameters, were changed to discuss their influence on the lightning transient process. Furtherly, electromagnetic field inside the tower body was calculated by using the Ansoft Maxwell software based on finite element method (fem). By contrastive analysis, we can conclude that the space distribution of the magnetic field inside the tower is symmetry in horizontal direction, and the maximum value decreases with the distance from the tower wall; In the vertical direction, the magnetic field distribution gradually tends to be more uniform from the top to the bottom of the tower. |
PDF Full Text Request