Research On The Numerical Methods For Electromagnetic Fields Of Substations' Grounding Systems In Frequency Domain And Application

The grounding system is one of the important components of a substation, to which much attention is always paid. Supported by the National Natural Science Foundation of China (No. 50077006), in this thesis, the numerical methods for electromagnetic fields of substations' grounding systems 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:A fast approach to the Green's function in horizontally stratified multi-layer earth and its partial differentials to the earth parameters is put forward by using the complex image method. An efficient method for estimating earth structure from Wenner's four-probe test data is presented. A self-adaptation method to sample the unknown variables in the Green's function and in the generalized Sommerfeld integral in high frequency domain is proposed. Both of them provide the theoretical foundation for the analysis of the grounding systems. A method using leakage currents as unknown variables as well as neglecting the mutual inductances and a method using longitudinal currents as unknown variables as well as taking account of the mutual inductances to analyze the grounding systems in low frequency domain are presented respectively. At the same time, the former is extended to analyze the grounding systems in vertically stratified multi-layer earth, the grounding systems with cables connected to it and the 3D electric field near power towers. Calculations and experiments show that the mutual inductances can be neglected and the former method is effective enough. An effective electromagnetic approach with few unknown variables for the substations' grounding systems in high frequency domain is put forward based on the method of moment. With the help of the fast Fourier transform, the method in this thesis can be used to analyze the transient problem.A test grounding system is set up. Lots of measured data are collected by the experiments on the testing grounding system and many other substations' grounding systems, through which the validity and the practicability of the methods in this thesis are adequately testified. A software package to calculate the electromagnetic fields of substations' grounding systems in frequency domain by numerical method is developed based on the author's work. The software package has simulated many practical projects and obtained lots of valuable results that have already been accepted by correlative departments. Thus, the software package can replace other famous imported software package and provide a new method of designing grounding systems to make the work more efficient.