Numerical Calculation Of Lightning Electromagnetic Transient In Multi-conductor System Of Converter Station Considering Lightning Corona Discharge

The UHV converter station is the hub of the UHV DC transmission project.The lightning protection of the converter station and its characteristics are of great significance.The research on the overvoltage at the converter station caused by lightning surge on the AC side of the converter station and the transient ground potential rise caused by the lightning protection device at the converter station is very important for the lightning protection research of the converter station.Therefore,based on the finite-difference time-domain method(FDTD),this paper will study the electromagnetic transient characteristics of the converter station under the coupling of complex conductor structures from the perspective of electromagnetic fields,and the impact of factors such as impact corona on the lightning overvoltage level of the converter station.First,this paper proposes a three-dimensional subgrid algorithm and programming to realize the automatic meshing function,which improves the efficiency of FDTD simulation.In this paper,the Huygens subgrid meshing model is established based on the FDTD algorithm.First,the principle of Huygens subgrid algorithm is introduced,and the ingenious design of Huygens surface is elaborated.From the Huygens under one-dimensional conditions The layout of the surface extends to the spatial design of the Huygens surface under three-dimensional conditions.Then the system summarized the realization process of the three-dimensional subgrid and the automatic sub-grid algorithm,realized the clever modification on the basis of the existing FDTD program,and reduced the difficulty of algorithm programming to the greatest extent.Then we write a one-dimensional verification model based on the Huygens subgrid algorithm.The model reflects the electromagnetic field transfer law in the algorithm,and proves the accuracy of the FDTD-based Huygens subgrid algorithm.At the same time,we carried out the simulation verification of the sub-grid algorithm under three-dimensional conditions,and proved that the sub-grid algorithm has the same calculation accuracy as that under the uniform grid,and the simulation time is greatly shortened.Then this paper establishes the FDTD model of the wire impact corona,and studies the corona discharge characteristics and its effect on the coupling coefficient between multiple conductors.Firstly,the starting time of the thin-wire corona is determined based on the initial field strength criterion,and the radius of the corona at each time step is determined by real-time calculation of the radial discharge current and radial discharge amount,and the corona layer medium correction to dynamically simulate the evolution of the corona layer over time.At the same time,it also introduces the programming implementation method and specific process based on FDTD algorithm.Subsequently,the corona discharge characteristics of a single thin wire were studied in this paper.The radial discharge current characteristics of the thin wire were obtained by simulation,and the voltameter characteristics of the corona of the thin wire were obtained.Compared with the references,the simulation model was verified.accuracy.At the same time,this article further studies the coupling effect between two parallel thin wires under the influence of impact corona.The research shows that impact corona will increase the coupling coefficient between the thin wires.Finally,the FDTD simulation model of the converter station with complex conductor structure and the incoming line is established,the lightning transient characteristics under multiconductor coupling are studied,the impact of impact corona on the lightning overvoltage,and many other The influence of factors on the overvoltage level of the converter station.In this paper,the lightning strike response of the tower of the incoming line,the calculation of the lightning overvoltage on the AC side of the converter station,and the transient ground potential analysis of the converter station under the direct lightning strike are studied.The results of the study show that under the effect of impact corona,the arcing angle voltage of the incoming tower is reduced,and the rate of rise of overvoltage is attenuated.The shock wave amplitude and steepness that enter the line after the tower counterattacks the flashover are reduced,and the moment when the flashover occurs is delayed.Due to the impact of the lightning strike corona in the incoming line section,the amplitude of the intrusive wave at the converter station has decreased.In addition,the mutual coupling and catadioptric phenomena between the complex conductor structures of the converter station,and the overvoltage waveform oscillation caused by the intruding wave in the converter station are obvious.At the same time,we studied and calculated the transient ground potential rise phenomenon of the converter station,and analyzed the influence of complex conductor structure on the ground potential rise,as well as the effects of different lightning strike positions,soil conductivity and other factors.The above research provides a certain reference for lightning protection of converter stations.