Research On Grounding Parameter Calculation And Characteristics Of The Frequency Response For Grounding Grids

Good grounding of the substations can provide fundamental protection for safe operation of power system. Grounding grid not only provide a reference ground for various electric devices in the substation but also drains the fault current to the ground in order to ensure personal safety and equipment safety.In order to assure safe operation of the substations, it is extremely important to calculate the realistic grounding parameter. The soil is considered as semi-infinite medium in early design of grounding and Grounding resistance is estimated using simplified formula, however, Such estimates often cause great errors between calculation and experimental, So the key of numerical analysis of the grounding system is establishment of the soil layered structure model. Through long-term observation and statistics of the grounding grid of substation and power plants, it is found that lightning current flowing through the grounding is the most, however, lighting current is a unipolar pulse, which not only has very steep front but also very rich frequency components. Therefore, traditional analytical method under power frequency can't be used to analyze the discharge process of lightning current flowing through the grounding grid. So it is necessary to So it is necessary to research the time domain and frequency response of high-frequency lightning flowing through grounding grid in order to enhance the safe operation of power system.The main research topic as follows:firstly, calculation method of grounding grid parameters are studied, moment method is used to solve the parameters of grounding grid and connected with the MATLAB interface with the data post-processing. Secondly, complex image method is used to solve Green's function in order to calculate soil structure. Thirdly, using FFT transform to discrete lightning current, considering influence of spark discharge and non-linear characteristics of the soil when lightning current flows through grounding grid, frequency and time-domain response under every frequency is calculated and analyzed. Through simulation, using the oscilloscope for date acquisition, the time-domain response of the lightning current into the grounding is analyzed, which is compared with the result of theoretical analysis to verify the he program of grounding. At last, changing the wave front of lightning and the area of grounding grid, the impact of these factors are analyzed.