| The medium voltage distribution line is directly connected with the transmission network and power consumers.Its safe and stable operation is an important guarantee for the safety and reliability of power supply.However,the voltage level of medium voltage distribution lines is low,the insulation level of lines is low,and the total length of lines is huge.In the actual operation process,it is easy to cause the line insulation flashover,trip or even breaking due to lightning induced overvoltage.In addition,the forest,industrial park and other ground protuberance near the medium voltage distribution line corridor have certain ability to attract lightning.In the natural thunderstorm weather,the actual situation of trees and buildings near the medium voltage distribution line is very likely to be struck by lightning.If the distance between the medium voltage distribution line and the surrounding object is small,the struck object will flashover back to the medium voltage distribution line under the action of high amplitude lightning current.For this reason,this paper evaluates and analyzes the distribution characteristics of lightning overvoltage and the influence of different factors on the medium voltage distribution line in three cases: the ground near the line is struck,a tree near the line is struck and a building near the line is struck by lightning.In this paper,the lightning overvoltage characteristics of medium voltage distribution lines under the indirect lightning are analyzed comprehensively.The conclusions can provide some reference for the lightning protection of medium voltage distribution lines.The main research work is as follows:For the situation that the ground near the line is struck by lightning,according to the formation mechanism of line lightning induced overvoltage,the simulation model of medium voltage distribution line lightning induced overvoltage is established,and the distribution characteristics of lightning induced overvoltage on medium voltage distribution line and the influence of six different factors are evaluated and analyzed.TL model is used as lightning return stroke model,Agrawal model is used as field to line coupling model,and a simulation model of lightning induced lightning overvoltage on 10 k V distribution line is built in ATP-EMTP.The simulation results show that the lightning induced overvoltage amplitude increases with the increase of the lightning current amplitude,increases with the increase of the lightning return stroke speed,decreases with the increase of the distance between the lightning point and the line,decreases with the increase of the lightning current front time,increases with the increase of the line height,and decreases with the increase of soil conductivity.For the situation that a tree near the line is struck by lightning,the simulation model of lightning overvoltage of 10 k V distribution line is built based on the dynamic and static arc model.The characteristics of induced lightning overvoltage and back flashover arc overvoltage are evaluated and analyzed.The influence of four different factors is simulated.The simulation results show that the induced lightning overvoltage amplitude increases with the increase of lightning current amplitude,decreases with the increase of lightning current wave front time,does not change with the change of tree height,and decreases with the increase of tree line spacing.The arc overvoltage amplitude increases with the increase of the lightning current amplitude,the wave front time of the lightning current,the height of the trees,and the distance between the lightning point and the line,until the air gap between lightning point and the nearest position on the line to the tree will not be broken down and the arc overvoltage will not be generated.For the situation that a building near the line is struck by lightning,the lightning overvoltage simulation model of 10 k V distribution line considering the wave propagation characteristics of buildings is built.The characteristics of induced lightning overvoltage and back flashover arc overvoltage on the distribution line are evaluated and analyzed,and the influence of three different factors is analyzed.The simulation results show that for the lightning induced overvoltage,the smaller the grounding impedance of the building corresponding to the lightning point,the lower the lightning induced overvoltage amplitude on the line;the lightning induced overvoltage amplitude basically does not change with the height of the building;the lightning induced overvoltage amplitude decreases with the increase of the distance between the building and the line.For the back flashover arc overvoltage,the smaller the grounding impedance of the building corresponding to the lightning point,the lower the arc overvoltage amplitude;the arc overvoltage amplitude increases with the increase of the height of the building and increases with the increase of the distance between the building and the line,until the air gap between the lightning point and the line will not be broken down and the arc overvoltage will not be generated.The effect of protection gap and arrester on lightning protection performance of 10 k V distribution line is compared and analyzed in the cases of the nearby ground struck and a nearby tree struck by lightning.The protective effects of five installation density cases are compared,which are the whole line installation,the installing every two towers with the closest part of line to lightning point installed or not and the installing every three towers with the closest part of line to lightning point installed or not.The simulation results show that the protection gap's and the arrester's voltage limiting effect are not obvious in two cases that the equipment is not installed on the part of line closest to lightning point;the protection gap's and the arrester's voltage limiting effect are obvious in three cases that the equipment is installed on the part of line closest to lightning point and the distribution line meets the insulation requirements. |
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