| Supported by the Scientific Funds for Outstanding Young Scientists of China (No.50325723), the Teaching and Research Award Program for Outstanding Young Teachers in Higher Eduacation Institutions of MoE, China (No.[2001]182) and the Specialized Research Fund for the Doctoral Program of Higher Education (No.20020079003) in this thesis, the numerical methods for electromagnetic fields of overhead conductors and grounding systems in complex soil structure in frequency domain are researched and applied to practice.The methods presented in this thesis are verified by comparing the results with those of experiments and other famous software and by lots of applications. The main innovative achievements are as follows: 1. A theoretical model for the analysis of grounding systems with horizontally or vertical stratified multi-layer earth is presented. Exact closed-form analytical expressions for the earth potential calculations due to current sources in different regions of this soil structure have been obtained. This way has an advantage that it needn't write out the expressions of the earth potential, and it is easy to be programmed by computer. 2. Based on the method of moment and the boundary element method, an improved method to analyze the grounding system buried in multi-layer soil with finite volumes is presented. The number of unknown variables used in this method is much less than those in other methods, and the grounding system buried in multi-layer soil with arbitrary layers can be analyzed numerically. This method is verified by comparing computational results with those obtained by experiment. 3. Based on the Method of Moment, a method to analyze the electromagnetic field generated by buses, connection lines of devices and power lines on electric power stations and substations while switches are operat. The method uses currents on the metal conductors as unknown variables and can be used to analyze the electromagnetic fields in substation. In order to verify the presented method a simple model is analyzed. The results are compared with those of method of MTL (multi-conductor transmission lines), and the difference is small. A model of substation buses without load is set up, and the wave propagation of currents on the power lines and the electric field intensity are analyzed by this method and FFT. 4. To calculate the electromagnetic quickly, the electric field of horizontal line current source and vertical line current source is calculated based on the multi-direction generalize generalized pencil-of-function. Using this method the calculation speed is increased remarkable, and this is the basement of the quick method of moment. 5. A Method of Moments (MOM) solution for analyzing the electromagnetic shielding properties of rectangular metal enclosures with apertures over a lossy half space which can model the ground is presented. The objects are modeled by rectangular surface patches. The roof-top basic functions are used to expand the unknown electric and magnetic currents on the surfaces of the cavity and the apertures. An effective method based on the generalized pencil-of-function (GPOF) method is developed to calculate the generalized Sommerfeld integral (GSI). With this method, the value of Greens' function can be obtained quickly and accurately. Validation of the method is presented by comparing the calculation results with the results obtained by measurement.
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