Research On Impedance Characteristics And Lightning Protection Methods Of Grounding Wire-Tower-Grounding System

The power transmission line undertakes the key task of transportation and distribution of electric energy in a large area,so its safe and reliable operation is essential to the entire power system.A blackout of the power transmission line will cause huge economic losses.Nowadays,with the development and innovation of equipment and technology in the field of power transmission in China,there are very few accidents caused by human factors in the transmission line’s trip and blackout.Thunderstorms occur frequently in China,and there is a high probability of lightning striking high-voltage transmission lines.Lightning strike has become the main cause of transmission line’ blackout.Although most of China’s high-voltage transmission lines are equipped with lightning protection equipments,lightning trip accidents still occur frequently in China’s plateau and mountainous areas.One of the reasons is that the grounding resistance in the mountain and rock area is generally high,which leads to the high potential at the top of the tower.Another reason is that when the lightning wave propagates to the parts of the tower body,the junction of the tower and the grounding device,and the junction of the tower and the grounding wire,the refraction and reflection phenomenon will occur due to the sudden change of wave impedance,which will greatly change the potential at the top of the tower.Thus,it is of great importance to study the influence of the wave impedance of grounding wires,towers and grounding devices on the overvoltage of lightning strikes and propose corresponding lightning protection measures.This thesis first carried out an impulse test to obtain the relationship functions between the resistivity and the electric field strength of typical soils.Based on electromagnetic field theory and circuit theory,an impulse grounding electromagnetic field-electric circuit coupling model was established,and the error between the model calculation result and the high-voltage experiment result is within 9%,which verifies the correctness of the impulse grounding model.Based on the model,the integrated model of grounding wire-tower-grounding system was established,and the error between calculation and experiment result is within 10% compared with the scale tower experiment,which verifies the correctness of the model.The models can provide key methods for grounding reconstruction,tower optimization,and reasonable configuration of grounding wire.Based on the models,the effect of the wave impedance of the grounding wire-towergrounding system on the lightning performance of the transmission line was studied,and the effects of different types and sizes of the towers,different lengths and structures of the grounding wires,and different grounding resistances on the lightning overvoltage and overcurrent were studied.Research results provide reference and basis for further lightning protection and optimization design.Furthermore,the lightning protection optimization measures based on the optimization of the tower structure and the reasonable configuration of the lightning protection line,as well as the optimization schemes of the impulse resistance reduction of the grounding system in different working conditions were studied.The effects of erection of insulating crossarms on tower and the location and number of grounding wires on power transmission line’s lightning performance were studied.Lightning protection optimization recommendations for optimizing tower’s structure and rationally configuring grounding wires were given.For the grounding device,the impulse resistance reduction characteristics and the best match form of external grounding electrodes with vertical grounding electrodes and external grounding electrodes with short conductors were studied,and when using less grounding materials,corresponding resistance reduction optimization schemes were proposed for three typical working conditions.Finally,a typical tower grounding device was selected to complete the field trial application of the optimization schemes,and the application results proved the effectiveness of the optimization schemes.The research in this thesis enriches the lightning protection methods of high-voltage power transmission line,and has certain reference value for the improvement of tower’s lightning protection performance in mountainous areas.