-The grounding system plays an important part in the lightning protection system of power and communication systems. The finite-difference time-domain (FDTD) method is widely used in modeling complex electromagnetic interaction problems. However, it is difficult to model the earthing conductor using the standard FDTD method in the transient grounding resistance analysis, for the electrically small depth of the earthing conductors. In this work, nonuniform grid in the FDTD methods, which is typically used to resolve fine structures, is introduced into reduce the computational domain and therefore lead to a reduction of the computational cost. To further reduce the computational memory, the uniform grids are used in the electrode length direction while non-uniform grids are occupied in the electrode sectional directions. The efficiency of the proposed model has been approved by verifying both the electromagnetic field components near the earthing conductor and the grounding resistance.Index Terms -Non-Uniform, FDTD Modeling, Earthing Conductor.
I . IntroductionSensitive electronic components have been increasingly used lately both in power and communication systems. These components may suffer logic upset or damage at lower levels of induced electromagnetic interferences brought about by the lightning. As a result, evaluation of the transient grounding resistance of the grounding systems in the lightning protection systems has recently attracted considerable attentions [1]- [5].The finite-difference time-domain (FDTD) method [6], which provides a simple and efficient way of solving Maxwell' equations for a variety of problems, has been widely applied in solving many types of electromagnetic problems. It is good at predicting the electromagnetic characteristics of a particular structure for it provides extensive time-domain information and the frequency-domain information can be provided via a discrete Fourier transform.However, when the grounding resistance analysis of the lightning protection systems is involved, it will results in a huge memory and time usage with the uniform FDTD grids. Because the dimension of the grounding electrode and the reference electrode are so small compared with the total computational domain, and one has to refine the FDTD grid to the conductor dimension, which will result in huge memory usage.Several papers have introduced different methods to reduce the truncation error at grid boundary. In [7], two methods were introduced to maintain second-order accuracy. One method uses an appropriate mesh ratio between two regions to obtain the central finite differences. The other method uses a universal grading scheme with continuously variable lattice size; but a demonstration of the effectiveness of this method was not reported. The non-uniform grid technology in the FDTD method, which is typically used to resolve fine structures, can reduce the computational domain and therefore lead to a reduction of the computational cost [8]. Considering electrically small size of the grounding...