Influence of two typical mountainous terrains on impulse impedance of grounding device

It´s important to study the influence of two typical mountainous terrains on impulse impedance of grounding device for lighting protection. According to the local terrains of transmission towers, three dimensional impulse impedance computation models for tower grounding device, considering two typical terrains, are established based on the finite element method(FEM). The open boundary field is transformed into finite field by the way of space coordinates transformation. Moreover, the changing of soil resistivity against local electric field strength is also taken into consideration. The impact of soil structures upon impulse impedance of grounding device which is buried at top of the mountain as well as ridge is analyzed. Calculated impulse impedance results show that with the slope of mountain or ridge growing, impulse impedance of grounding device increases non-linearly under the precondition of the same superface area; Similarly, impulse impedance of grounding device decrease when the top area increases, furthermore, the decreasing trend is obvious only under the case of the slope is large.