Research On Impulse Resistance Reduction Method Of Grounding Device In Consideration Of Spark Effect And Shield Effect

Reducing the impulse grounding resistance of grounding device can effectively improve the lightning protection effect in power system. For a long time, grounding design of the substation and tower mainly relied on empirical formula, and it cannot acquire ideal effect of impulse resistance reduction, likely to cause power system lightning accident, finally, it would seriously affect the safety and stable operation of power system. Therefore, it is important for improving the stability of the power system by conducting a comprehensive analysis of the impulse characteristics of grounding device and studying the method of reducing grounding resistance.In this paper, via executing a comprehensive analysis of impulse diffusion mechanism of the grounding device, a method of reducing impulse resistance is proposed from the perspective of enhancing spark effect and suppressing shielding effect. By adding diffusion ends on typical grounding devices to enhance spark effect, it can achieve the purpose of reducing the impulse grounding resistance. In consideration of dynamic ionization property of the soil, the finite element algorithm which combined space finite element and time finite difference is established to analyze the impulse characteristics of grounding device, by utilizing this model,the analysis and calculation of the impulse diffusion principles of a simple grounding device was accomplished. By analyzing the spark effect region after adding diffusion ends on typical grounding device, the influence of sparks effect and shielding effect on impulse characteristics was studied.Based on similar principle, the simulation experiment of impulse characteristics was carried out to verify the method of reducing the impulse resistance which was proposed in this paper. Under conditions of adding the diffusion ends with different location and spacing, a reasonable layout scheme of diffusion ends was obtained by studying the influence of the shielding effect on the result of grounding resistance reduction.The results show that adding diffuser ends can be utilized to reduce the impulse resistance, which can effectively improve the diffusion ability of grounding device; considering the shield effect, when adding a single set of diffusion ends, the horizontal grounding device with adding the diffusion ends in middle region could gain a more pronounced reduction in impulse grounding resistance, the suggestion which controlled adding location at 1/3 and 2/3 of the grounding electrode length is more reasonable; while adding two or more sets of diffusion ends, the desired resistance reduction results are achieved by maintaining appropriate spacing between the diffusion ends,the spacing of diffusion ends with length L is controlled at over 2L, it can significantly reduce impulse grounding resistance by suppressing shielding effect.