Research On Lightning Shielding Failure Feature And Electromagnetic Coupling Characteristics Of EHV/UHV Transmission Corridor

With the rapid development of Power Grid at Extra and Ultra High Voltage Level, the voltage level, transmission Capacity and distance are constantly increasing which lead to the lightning fault becoming more serious and corridor resource getting more shortage. According to the long-term operating experience at domestic and international shows that lightning trip-out fault of EHV is mainly caused by shielding failure, so the accurate evaluation of shielding failure performance of transmission line plays a vital role for ensuring the safety of electric power.In corridor resource shortage area, the situation of UHV AC/DC line operating in same corridor is inevitable. There are serious coupling effects between AC and DC lines at that time which result in larger induction voltage and current produced in disconnected line to serious threat to personnel and equipment safety. The shielding failure trip-out and electromagnetic coupling in same corridor has become the key issues to affect safe operation of the EHV/UHV transmission lines.In order to quantitatively analyze the numerical distribution characteristic of lightning probability and shielding failure trip-out rate in different position of transmission lines, accurately assessthe lightning shielding failure trip-out level, and avoid the uncontrollable error resulting from inequivalence replacement of lightning probability of each section, the lightning exposed width of traditional calculation method is expanded to three-dimensional exposed space alone every span of transmission lines by using catenary equation, the three-dimensional analysis method of shielding failure characteristics of transmission lines and three-dimensional calculation method of exposed width of arbitrary section in exposed space are proposed, the three-dimensional calculation formulas of lightning probability and shielding failure trip-out rate of arbitrary section are derived, and the calculation formula of total shielding failure trip-out rate is revised. Take500kV transmission lines with two overhead ground wires for example, the three-dimensional distribution of lightning exposed width as well as the two-dimensional distribution of lightning probability and shielding failure trip-out rate are calculated. The research found that the maximum of shielding failure trip-out rate in a span is9.02times the minimum, is3.20times the total shielding failure trip-out rate calculating by original formulas.By using PSCAD/EMTDC simulation program, the electromagnetic coupling models of EHV/UHV transmission lines operating in same tower or corridor are established, the influence factors of transient electromagnetic coupling when500kV in same tower, and change regularity of power frequency electromagnetic coupling when1000kV AC in same corridor with±800kV DC are studied, the impact regularity of side-phase horizontal and lower conductor vertical approach distance on induction voltage and current is analyzed under the1000kV AC conductor arrangement of triangular, horizontal, drum and inverse-triangular, finally, the optimal tower type and conductor design are discussed.These results could lay a theoretical foundation for the study of lightning shielding failure trip-out of transmission lines, and be available for reference to improve the electromagnetic couplingissue of existing and new design UHV transmission linesin same corridor.