| The grounding resistance of most transmission line towers in China has met the requirements of the regulations,and many lines are equipped with lightning protection devices,but line faults caused by lightning strikes are still a big problem that troubles the power sector.With the rapid development of China’s power industry,the scale and grade of lines are increasing year by year,and the problem of line lightning protection is becoming increasingly serious.Therefore,the simulation calculation and field test on the lightning power transmission line can help to obtain the transient response of the tower,lightning protection line and phase line under the action of lightning current,and provide key lightning protection parameters for the lightning protection project of the line.Firstly,this paper combines the electromagnetic field theory and the finite element method to build a tower surge impedance calculation model that can consider complex tower structures.In this model,the electric field energy and magnetic field energy around the tower are calculated respectively,and then the surge impedance of the tower is calculated according to the electromagnetic field energy,and verified by scale tower experiment,the error is within15%.Based on this model,the boundaries of the electric field and magnetic field modules are divided into blocks,and the electromagnetic field energy corresponding to different positions of the tower is obtained respectively,then calculate the surge impedance at different positions.Therefore,the multi-surge impedance model of power transmission tower based on the finite element method is proposed,scale experiment is also used to verify,the error is within 15%,which proves the effectiveness of the model.This model has been applied in the subsequent research on the transient characteristics of scale towers and real scale towers.Then the field test scheme of lightning overvoltage characteristics of power transmission lines based on scale tower is studied.According to the reduction ratio of 11.5:1,a scale model of a typical 110 k V umbrella-type iron tower was built.A large number of impact tests are carried out to investigate the influence of grounding resistance,number of lightning protection line,insulator flashover and other factors on the lightning overvoltage characteristics of the scale tower.A simulation model of scale towers was built for comparative analysis.Finally,the lightning transient model of the tower was built in the EMTP software,and the influence of the current waveform,crossarm structure and layout on the transient characteristics of the tower lightning strike was analyzed.Considering the main body structural factors of tower such as the size of the upper and lower openings of the tower body,height,the type of the bracings and the density degree,a large number of geometric models of the main body of the tower are drawn,the simulation calculation is carried out in the surge impedance and multi-surge impedance models of the tower based on the finite element method.The influence of the main body structure of tower on the surge impedance and the transient voltage of the tower is analyzed,and provides some suggestions about lightning protection,type selection and design of the tower.A typical lightning transient model of 110 k V doublecircuit transmission line was built,and the variation rule of transient current distribution under the influence of current waveform,tower distance,grounding resistance and other factors was analyzed. |
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