The Analysis Of Wind Turbine Lightning Transient Overvoltage

As the size of wind farm and the rated capacity of single wind turbine continue to increase, the issue on safe and reliable operation of wind turbines is gradually concerned. Lightning is one of the main causes that make the failure of wind turbines. The lightning attachment points of wind turbine are primarily distributed on blades, nacelle and tower. When a window turbine is struck by lightning, the lightning current flows from the attachment point to the ground. At this moment, the induced voltage and current in inner circuit of window turbine and equipment will damage the equipment, or even worse, the overvoltage invades other unit equipment in wind farms via cable and ground grid, expanding the scope of lightning damage.In this paper, we study on three aspects, including the induced overvoltage of the control cable in tower when the wind turbine is struck by lightning, the rise of ground potential and the transient voltage level on both sides of box change in wind farm. Firstly, the physical models of the window turbine, control cables, tower cables and the ground grid in wind farm are established as electric system which can be calculated. After that, each electrical parameter can be calculated. Meanwhile, the transient model of the wind turbine struck by lightning can be built by utilizing the electromagnetic transient simulation software EMTP/ATP. Finally, we calculate the transient overvoltage and the ground potential in wind turbine during the lighting current flows from bade, tower and grounding device to the ground. Meanwhile, the transient voltage of other units is calculated when one unit in union is struck by lightning. We also analyze several factors for affecting the distribution of lightning transient overvoltage of wind turbine.The results show that the voltage between tower and control cable shielding layer are less affected by ground resistance. But it will grow with the increase of the gradient of wave head of lightning current and the height of tower. The voltage shows a curve with big top and small bottom. However, the voltage between control cable and wire insulation layer distributes as a shape of “U” and its value is inversely proportional to the grounding resistance and the wave head time. The tower height has no influence on distribution of the voltage but affects the value of the voltage. The higher of the tower, the larger of the voltage at the same proportion. The induced voltage of core wire distributes as a parabola going upwards and its value is proportional to the grounding resistance. The voltage decreases with the increase of wave head but leads to a flat curve. When the wave head time reaches 8?s, it has no impact on voltage. Meanwhile, the voltage of core wire will increase with the height of tower. The grounding resistance affects the amplitude of the ground potential and the wave head affects the ascend speed and the amplitude. If the wave head time exceeds 8?s, the influence on the rise of ground potential caused by wave head will be not obvious. The tower height has less impact as well. When the wind turbine is struck by lightning, the wave of voltage between the high side and low side of the box change will be varied abnormally and the voltage amplitude rises suddenly. If the set is spread as a line or cross respectively, the line shape set has little impact on transient voltage of wind farm and the rise of ground potential in comparison. The calculation results will provide a guidance in design stage for preventing the wind turbine from lightning. Wind turbine lightning strike, the cases of high and low pressure side of the voltage waveform distortion and voltage amplitude jump. Set straight lines and cross array, linear array transient voltage and ground potential rise on wind farm influence smaller. The research results can provide guidance for the design of lightning protection for wind turbine, and have important significance for reducing the economic loss caused by lightning failure.