Research on impulse property of pin-type grounding device in mountainous area based on thin-shell theory

Reduction of impulse resistance for grounding systems in mountainous soil structures is the basic work to improve the lightning resistance of transmission lines. In this paper, firstly, the spatial finite element and time-domain finite difference method are combined to calculate the impulse property of the tower grounding system, in order to simulate the time-varying and spatial distribution of the soil resistivity in the process of lightning current discharge, the soil resistivity is set as a function of the spatial electric field strength. Then the large size difference between the cross-section of the grounding conductor and the soil discharged area will lead to division difficulty and calculation surge, so thin-layer grounding conductor is equivalent to a two-dimensional plane with a certain virtual thickness. Finally, the influence of pin-type grounding devices geometry on impulse properties was analyzed. The results showed that soil structures (hillside slopes and vegetation layer thicknesses) will influence optimal pinning geometry. The pin length achieves its optimal value when maximized provided that it remains within the vegetation layer thickness. Under different hillside slopes, the optimal pinning spacing is 1.5 times the length, and the optimal pinning angle increases with the slope. Under different vegetation layer thicknesses, the optimal pinning spacing is 1.5~2.0 times the length, and the optimal pinning angle of pin-type grounding device in hillside and ridge is about 60° and 75° respectively when the vegetation layer thicknesses are 4, 5, and 6 m.