Study On Calculation And Measurement Of Grounding Resistance Of Wind Farm Grounding System

Wind energy has been widely used as a clean renewable energy source.With the large-scale establishment of wind farms,the safe operation of wind turbines cannot be ignored.Wind farms are usually built in wind-enriched mountainous areas,and the possibility of lightning strikes in mountainous areas is high.There is a seasonal frozen soil phenomenon in the wind farms in northern China.The formation of the frozen soil layer makes the soil resistivity of the fan position larger.When the wind turbine is subjected to short-circuit fault,it cannot be dissipated in time,and it is easy to form a counter-attack over-voltage,which is harmful to the normal operation of the wind turbine.Therefore a good grounding system is essential for the normal operation of the wind turbine.In this thesis,the complex image method is used to derive the Green’s function expression under the horizontal two-layer soil structure.Based on the electromagnetic field theory,the unequal potential model of the fan grounding grid is established,and the grounding calculation program which consider the self-resistance mutual resistance and self-inductance mutual inductance of the grounding conductor is compiled.Verify the correctness of the grounding calculation model and program.Using the written grounding procedure to study the influence of seasonal factors on the power frequency grounding resistance of the fan,select the twelve soil resistivity reflection coefficients after the formation of the frozen soil layer and the wet soil layer,and change the soil thickness and soil resistivity reflection coefficients that affected by seasonal factors.Calculate the seasonal coefficient of grounding resistance,study the improved effect of the seasonal coefficient of grounding resistance which the vertical grounding pole and the horizontal grounding influence when considering seasonal frozen soil factors.The wind turbine grounding grid impact calculation model which considers the effect of soil spark discharge is established.The correctness of the model is verified by relevant examples.Three typical lightning current waveforms are selected to study the influence rules that the lightning impulse characteristics of wind turbine grounding which generated by the lightning current head time and the location,lightning current amplitude and soil breakdown field strength,soil resistivity,grounding conductor material.Field measurement of grounding resistance is an important basis for verifying the correct design of the grounding.According to the basic principle of grounding resistance measurement,the trajectory of the voltage pole wiring in the uniform soil structure is derived,and the influence of the relative size of the grounding body and the voltage pole position on the measurement error is analyzed.In the two-layer soil structure,studied the trajectories of the linear and angled voltage compensation points under the influence of the different soil resistivity reflectance coefficients.For the case where the grounding measurement of the fan is difficult to be long-distance wiring,the potential at the voltage pole is taken as the objective function,combined with the unequal potential model of the fan grounding grid,studied the short-distance measurement of grounding resistance and verified it by combing the examples.