Research On Transient Characteristics Of Lightning Of Grounding System Of Wind Power Generation Plant

With the increase of wind turbine capacity and wind farm dimension，thesecurity of wind turbine operation is more and more important. Lightning isbecoming one of the main factors to affect the security of wind turbine operation.During the lightning stroke process the induced overvoltage may appear on thecommunication line and even the power line which are configured within the towerwhen lightning current passes through them, In addition, the ground potential will beraised for the existence of grounding resistance which may cause backlash to thedevices installed inside the tower. Therefore, in this paper the model of wind turbinesis established and the transient overvoltage caused by lightning stroke is calculatedand analyzed.A theoretical model for the analysis of grounding systems with horizontal ormulti-layer earth is presented. This way has an advantage that it doesn’t need to writeout the expressions of earth potential, and it is easy to be programmed by computer.The target function and soil structure inversion model is established with themathematical relationship between pole-to-pole distances and the apparent groundingresistance measured with the4-polemethod and the depth of measuring electrode. Thecomplexity issues of the calculation of uneven ground soil parameter is solved.The nonlinear characteristic of soil ionization is taken into account and theinfluence of soil ionization is equivalent to the dimension increase of groundingelectrodes. The grounding parameters are amended to the situation of soil ionizationand the transient grounding responses are solved dynamically. Combining circuittheory with electric-magnetic theory to propose new method to analyze thefrequency-domain property of grounding grid when considering the non-linerproperty of the spark domain. Combining this method with FFT method, a theoreticalmodel for the research of impulse characteristics of grounding grid is built up.Analyzing the influence of dimension of grounding grid, soil resistivity and structureto the characteristics of the grid by quantity of calculation using this method.An integrative transient circuit model of wind turbine established according tothe lightning flowing path and the lightning stroke is considered to be the currentsource injected to the network. The induced voltages and currents on the cable sheath are calculated by EMTP.