Research On Electrical Grounding Characteristic Of Wind Turbines

In this thesis,an investigation is made on the electrical grounding characteristic of wind turbines from four aspects: grounding modeling calculation method,grounding resistance measurement method,resistance reduction measures,and lightning impulse behavior.According to the structure size and soil environment of the grounding arrangement of actual wind turbine,combined with the existing experimental conditions,a reduced-scale grounding arrangement is built for the wind turbines,and an analogue experimental system is set up for measuring its grounding resistance.In the grounding measurement,equal-distance method and three-electrode method are employed to obtain the soil resistivity and grounding resistances,respectively.By means of the professional software,the inversion of measured soil resistivity is performed to a non-uniform double-layer soil structure.Simulation calculation is carried out for the reduced-scale grounding arrangement.A comparison is made between measured and simulated results to verify the validity of the simulation procedure.In terms of the actual size data of the grounding arrangement of the wind turbines,the design calculation is performed for the grounding arrangement by the simulation method.An exploration is made for the influence of grounding arrangement size,upper soil resistivity,upper soil thickness and soil stratification on grounding resistance.Due to a high soil resistivity in mountainous areas,reduction of the grounding resistance can be realized by two the grounding resistance of the original design that meets the standard may exceed the standard value.The resistance can be reduced by using two means,i.e.extending grounding arrangement and using grounding resistance reducing agents.The contrast analysis is made on their advantages to select the measures that has low cost and high-efficiency of reducing grounding resistance.The engineering applicability of the measures is also discussed.An analysis is given to the limitation of the existing straight-line method and triangular method,and an expanded measurement method is proposed for measuring the grounding resistance.The trajectory of a circularly installing voltage pole under uniform soil was derived.The loop trajectory of the voltage pole installed under non-uniform soil is obtained from software simulation,and its feasibility was verified by actual measurement.A transient grounding model of wind turbines is established to study the impact of soil discharge and distributed parameter caused by lightning current on the impulse grounding resistance,and the correctness of the transient modeling method is verified by numerical examples.