Research On Lightning Overvoltage Performance And Its Influence Factors Of EHV AC Transmission Lines

With the rapid development of Power Grid at Extra and Ultra High Voltage Level, the height of transmission lines, transmission Capacity and distance are constantly increasing. Transmission lines often suffer the invasion of various lightning overvoltage leading to blackout accident, thus lightning fault has become the first factor to affect safety operation of transmission lines. In order to draw up more economical and rational lightning protection measures to prevent lightning fault, it is extremely important to further research the lightning properties and accurate evaluate the lightning overvoltage performance of transmission lines. Through simulating propagation process of lightning overvoltage along EHVAC transmission lines, to find its influence factors and explore its characteristic regularity will be of great theoretical significance and value for engineering application.In this paper, according to the occurrence mechanism of lightning overvoltage and the actual situation of500kV EHV AC transmission lines, the lightning models of transmission lines including lightning current model, transmission line tower model, insulator flashover model and the transmission line model etc. are established by using Electromagnetic transient simulation program PSCAD/EMTDC. The impact of impulse corona and power frequency voltage has been taken into account in these models, thus the lightning overvoltage of transmission lines could be more realistically simulated. Based on the established simulation models, the lightning overvoltage transit features of transmission lines are analyzed on the situation of back striking, shielding failure and lightning without fault respectively, the main physical characteristics of overvoltage waveform at both ends of the insulator and the overvoltage feature of the tower top, three-phase conductors, ground wires are found, the propagation range of lightning overvoltage along the transmission lines are determined, the lightning overvoltage change considering the impact of corona or not is contrasted.By using PSCAD/EMTDC simulation program, the characteristic of lightning overvoltage and the relationship of parameters on tower top or conductors are studied when the lightning current waveform, amplitude, arrangement mode of ground wires, tower type, conductor configuration including arrangement mode and split number as well as grounding resistance are changed, and the key factors which affect back striking and shielding failure overvoltage of EHV AC transmission lines are found. The results show that the back striking overvoltage of transmission lines is affected by lightning current waveform, amplitude, tower type and grounding resistance, while the shielding failure overvoltage is influenced by lightning current waveform, amplitude, arrangement mode of ground wires and split number of conductors. These results could lay a theoretical foundation for the study of lightning overvoltage of transmission lines, and be available for reference to increase the lightning protection level of existing transmission lines and design lightning protection of new lines.