考虑潮间带接地环境的海上风机一体化电磁暂态模型

The Integrated Electromagnetic Transient Model of Wind Turbine in Intertidal Zone Considering the Grounding Environment

为了预防和减少海上风电的雷害,对由雷击引发的风机机舱暂态过电压进行计算和评估非常必要,前提是建立可靠的风机雷电泄流通道模型。接地电阻的准确性是影响雷击通道模型可靠性的重要因素。考虑到我国海上风机场分布广,海况差别大的特点,将潮间带接地环境分为3层:海水层、淤泥层和砂石层,分析各层的物理深度和电阻率等因素对接地电阻的影响。以江苏如东洋口港潮间带风电场上海电气2 MW风机为例,将雷电通道划分为激励源、桨叶、机舱轴承、塔筒、接地电阻5个部分,分别进行数学建模。其中:塔筒等效成垂直中空分段圆柱体;机舱与塔筒间的轴承等效为电容;应用土壤点电流格林函数计算各层的等效电阻,通过叠加得到总的冲击接地电阻。结果表明,由潮汐引起的海水深度变化是影响接地电阻的主导因素,海水越深接地电阻越小,对应的暂态过电压也越小;淤泥层和砂石层的电阻率均与接地电阻正相关,但当海水达到足够深度时,它们的影响趋于稳定。

In order to prevent and reduce the offshore wind farm’s damage caused by lightning,it’s necessary to calculate and evaluate the transient overvoltage at the wind turbine’s engine room caused by lightning stroke.The premise is to establish a reliable electromagnetic transient model of the actual discharge flow path.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 ground 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 2 MW 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.The results show that the variation of sea water depth caused by tides is the main factor affecting the grounding resistance.The deeper the sea is,the lower the grounding resistance and the corresponding transient overvoltage is.The resistivity of silt layer and sandstone layer is positively correlated with grounding resistance.But its effect stabilizes when the sea water depth is deep enough.