| Along with the development of our cities, the power consumption is increasing rapidly, which needs building large capacity substation. But because of restrictions of the land price and city planning, the grounding grids is limited in a small area while failure current flowing into ground has increased greatly, which lead to high grounding impedance or high potential of the substation. So an effective method is needed to reduce the grounding impedance, so as to ensure safety of people and equipments.In order to decrease the grounding impedance, a good method is introduced, in which another subsidiary grounding grid is connected with main grounding grid within the distance of 1～2km.Using complex images method, the close-form Green's function of a point current source in horizontal soil is derived, which can be obtained very efficiently only by a few complex images. The Green's function is the foundation for simulation numerical calculation of substation grounding systems.Based on moment method and field-circuit coupling theory, a numerical calculation method of substation grounding grids in industry frequency is presented in this paper and Calculation program was written with MATLAB. The resistance and self-inductance of conductors as well as mutual inductance between conductors are taken into account. The results are compared with those of world popular software CDEGS and the correctness of algorithm is verified.Finally, the grounding impedance of the grounding system is computed in uniform and vertical-layered soil. To analyze the effectiveness of subsidiary grounding grid, the definition of useful length and resistance reducing efficiency is introduced. The effectiveness of some parameters such as soil conductivity, the area of grounding and the magnetic permeability of conductors is considered.
|
PDF Full Text Request