Study On Calculation And Measurement Of Grounding Resistance Of Wind Turbine

In recent years, with the continuous development of power system and the progress of the society, people have a great interest on wind power which is a kind of clean energy and begin to promote it. The installed capacity of wind turbines has also increased from a few hundred kW to a few MW. As a result of the expansion of installed capacity of wind farms, the grounding short circuit current increases accordingly, which leads to stricter requirements for the design of the grounding system of wind turbines. In this paper the grounding resistance of wind turbines is studied including the following aspects:the calculation and research of grounding resistance in different soil structure, research of the measuring methods of grounding resistance and the impact characteristics of grounding device of wind turbines.A basic structure model of the grounding device of wind turbines is proposed in this paper. In the proposed model the grounding conductor is discretized and the spatial position relationships between conductors are discussed. By setting image conductors and using average potential method the grounding resistance coefficient matrix is calculated. Using MATLAB software programming, the calculated values of grounding resistance of wind turbines are obtained. Thereafter, an experimental model is set up and the field measurement is carried out. The measured results have verified the correctness of the proposed model. With the proposed model the deficiency of simply using empirical formula in calculation of grounding resistance of large wind turbines is solved. At the same time factors that influence the grounding resistance values are analyzed with experience values.On account of the different structural of the soil, it is necessary to discuss the calculation of grounding resistance in non-homogeneous soil. For this reason, an algorithm that calculates the grounding resistance coefficient matrix in double layer soil is proposed. The calculation is made by programming a MATLAB program. And then the investigations are also carried out into the factors which influence the value of grounding resistance, including the soil resistivity, the upper layer soil depth, and soil reflection coefficient.In the operation of power system, the grounding resistance requires periodic measurement. The commonly used measuring method of grounding resistance—three electrode method (including straight line method and the triangular method) is described and the disadvantages of this method are also pointed out. In order to overcome the disadvantages of the previous measuring method a new measuring method is proposed and programmed in MATLAB. A comparison is made between calculated and measured values of grounding resistances to verify the proposed measuring method. And the influence factors of trajectory of voltage pole layout point are discussed under the condition of different soil structure.In the end the impact characteristics of the grounding resistance are studied. A transient model of grounding systems is proposed by taking the distribution parameters effect of grounding device and ionization effect of soil into account. Afterward the influence factors of impact grounding resistance are analyzed. By some numerical examples the influence of lightning current on the impact grounding devices are discussed.