Study On Corona Discharge Characteristics Of UHV Transmission Line Ground Wire Surface Under Thundercloud Electric Field

In response to the national strategic goal of carbon peak and carbon neutrality,China has accelerated the construction of ultra-high voltage long-distance transmission lines to promote the formation of China’s power supply pattern of west-east power transmission and south-north power supply.Due to the wide span of ultra-high voltage transmission lines,tripping faults are prone to occur.In thunderstorm weather,the charge generated by corona discharge on the ground wire surface causes the distortion of the spatial background electric field.Therefore,it is necessary to consider the influence of space charge generated by corona discharge on the lightning protection characteristics of transmission lines.In this paper,the UHV DC transmission line is taken as the research object,and the establishment of the lightning protection performance calculation model for the space charge on the ground surface is studied in detail.The main research work of this paper is as follows:（1）Based on the Kaptzov hypothesis theory of corona discharge boundary,a two-dimensional numerical calculation model of corona discharge on ground wire surface under thundercloud electric field is established and tested.The simulation results show that with the increase of thundercloud electric field,the positive ion concentration on the ground surface increases,and the corona current increases.The maximum current is 11.96μA/m,and the distribution of positive ions in space is elliptical.By comparing the corona discharge on the surface of single and double ground wires,it is concluded that the discharge of single ground wire is more intense.In order to verify the correctness of the simulation,the high voltage corona discharge test is carried out to measure the corona current amplitude of the ground wire surface when the voltage increases,which is similar to the simulation results.（2）A 3m×3m×3m small climate simulation room was built to measure the photon number and corona current of the ground wire surface corona discharge at different absolute humidity in the space,and the simulation calculation was carried out to study the ground wire surface corona discharge at different humidity.The experimental results show that the corona discharge intensity decreases and the corona current decreases by 0.0231m A when the absolute humidity in the space increases.The simulation results show that when the absolute humidity in the space increases,the positive ion concentration of the corona discharge on the ground wire surface decreases by 2.48×10¹⁰m^-3,and the corona current decreases by 1.48μA/m,resulting in the increase of the electric field intensity above the ground wire,which is beneficial to the initiation of the uplink leader.（3）The corona discharge test simulation platform of ground wire surface under natural wind is built.Combined with the simulation data,the influence of wind speed and wind direction on the corona discharge process of ground wire surface is analyzed.In the experiment,the photon number and corona current on the ground surface were measured when different natural wind speeds were set.The test results show that when the wind speed increases,the corona discharge of the ground wire intensifies,the current increases by 0.5m A,and the number of photons increases by 3000.The simulation results show that the corona discharge on the ground wire surface increases with the increase of wind speed in space.Moreover,with the increase of wind direction angle,the corona discharge degree on the surface of the ground wire intensifies,and the positive ions above the ground wire increase with the increase of wind direction angle,and the probability of electron recombination increases,which inhibits the formation of electron avalanche and the development of streamer,and inhibits the formation of upward leader above the ground wire.（4）Considering the development process of lightning downward leader,a corona discharge model of±1100k V UHV DC transmission line under thundercloud background electric field is established.When the current leader develops,the leader voltage,line operating voltage and thundercloud voltage work together,and the corona discharge on the surface of the conductor and ground wire of the transmission line increases rapidly.When considering the environmental factors and the development of the downward leader at the same time,the degree of corona discharge on the surface of the ground wire is weakened when the humidity in the space increases,but the overall value of the corona current is much higher than that only under the action of the thundercloud electric field.When the wind speed increases,the degree of corona discharge on the surface of the ground wire is aggravated,which is not conducive to the initiation of the upward leader above the ground wire and increases the probability of lightning striking the wire.