Research on impulse impedance model and protection optimization of transmission tower grounding device in mountainous area

Abstract

The impulse impedance of the tower is the core parameter to evaluate the lightning protection performance of the transmission line. The high soil resistivity and the underground rock layers in the mountainous areas will induce large impulse impedance and further lead to frequent lightning striking accidents. Therefore, this paper proposes a circuit-finite element model (CFEM) and investigates the corresponding impedance-reduction optimization method of the grounding device in mountainous areas. The model takes into account the nonlinear characteristics of the soil. Based on the parallel-plate electrode and the concentric hemispheric test device, the nonlinear curves of the soil resistivity of five typical kinds of soils with the electric field intensity are obtained. To justify the CFEM, the field experiment of a single horizontal conductor is performed, with an average relative error of 4.67%. Based on the CFEM, this paper presents an impedance-reduction optimization method for the grounding device in the mountainous areas, while proposing the best design method and the optimal layout of the grounding device in the rocky zone. The research results can provide a reference for the design transformation and protection optimization of the transmission tower grounding device in mountainous areas.