電氣映像技法을 利用한 大地抵抗率과 接地抵抗 分析에 관한 硏究

Abstract

The grounding system of the subsurface should ensure the safe and reliable operation of power systems, and guarantee a human being's safety in the situation of grounding fault in the power system. The safety of power apparatus in the subsurface can be reached by decreasing grounding resistance and grounding potential rise of subsurface. The optimal design of grounding systems for subsurface can ensure the equalization of the potential distribution of the ground surface above the grounding system, and can obviously improve the safety of the grounding system. This thesis deals with the 2-dimensional reconstruction of the earth's resistivity distribution based on DC resistivity data. This task represents a nonlinear and ill-posed minimization problem with many degrees of freedom. In this work, techniques for regularization and controlling of this problem are described and classified. The system of equations as resulting from the application of the Gauss-Newton minimization can be solved efficiently. The characteristics of the four reconstruction algorithms such as Gauss-Newton, TSVD(truncated singular value decomposition), SIRT(simultaneous iterative reconstruction algorithm), and TLS(truncated least squares) algorithm are compared and analyzed. Furthermore, a modified FEM scheme is used to test several widely-used resistivity arrays, namely Wenner, Schlumberger and dipole-dipole. The electrode arrangement of the arrays is described and the characteristics of above three array types are compared and analyzed. The proposed methodology has been proposed according to which, after carrying out a set of soil resistivity measurements, one can compute the parameters of the multi-layer earth structure using a genetic algorithm(GA). The results provided by the GA constitute the indispensable data that can be used in circuital or field simulations of grounding systems. The methodology allows to proceed toward a very efficient simulation of the grounding system and an accurate calculation of potential on the ground surface. Methods of error estimation, forward modeling and the calculation of the Jacobian matrix for DC resistivity data are developed. Procedures for appropriate parameterization and inversion control are pointed out by studies of synthetic models. Different inversion and regularization methods are examined in detail. A linearized study is used to compare different data sets considering their efficiency. Finally the inversion methods are applied to field data. The described optimization strategies are realized in practice, which increases the economic relevance of two dimensional data acquisition. The structure of the subsurface is imaged in detail for several applications in the fields of cavity detection, archaeology and the investigation of ground falls. The resolution analysis is successfully established to appraise the obtained results.