The Analysis On Lightning Protection Performance Of ± 800kV/500kV UHV AC/DC Transmission Lines On The Same Tower

UHV transmission project has its unique advantages like large transport capacity;high power supply;long conveying distance as it can solve the problem of optimize the allocation of resources.since the continuous development of UHV project like the long line corridor.There is a high risk of the UHV lines suffered by lightning when the circuit goes through a complex landform and the lightning climate is changeable.With the development of UHV transmission,UHV power grids are expected to set up mixed-voltage transmission lines on the same tower in areas with relatively scarce land resources such as the eastern part of the country.Therefore,research on lightning protection of UHV transmission lines on the same tower is imminent.Firstly,the paper discusses the principle of lightning overvoltage formation and lightning protection calculation methods.It takes the ±800kV/500kV UHV AC/DC multi-circuit line on the same tower as the research object,sets up a simulation model in ATP-EMTP,according to the simulation results,the back striking level of UHV AC/DC transmission lines on the same tower is obtained,The results shows:In the UHV AC/DC transmission lines on the same tower,the back striking level is related to the transmission lines tower height and the resistance value of the grounding resistance.The tower height and grounding resistance are negatively related to the back striking resistance level,that is,the higher the tower height,or the greater the resistance value of the grounding resistance,the lower the lightning current that causes the line to counterattack and trip,that is,the lower the counterattack lightning resistance level;In the UHV AC/DC tower circuit,the level of back striking resistance is mainly determined by the 500kV AC line;Compared with the separately erected lines,the back striking resistance level of the ±800kV DC line is greatly improved,and the back striking resistance level of the 500kV AC line is almost no change.In view of the characteristics of the lightning resistance of the ±800kV/500kV UHV AC/DC transmission lines on the same tower,based on the improved electrical geometrical model method,considering the variation of the exposure distance under different lightning intrusion angles and the effect of mutual shielding of the conductor,the shielding failure trip-out rate was calculated.The result shows:The change of the ground inclination angle will lead to the lines shielding failure trip-out rate change,and the shielding failure trip-out rate will change significantly during the gradual increase of the local plane inclination from zero,among which the change rate of the shielding failure trip-out rate of the outer conductor of the upper layer of the AC line.The fastest,indicating that in areas with large changes in the inclination of the ground such as mountains,attention should be paid to distinguishing it from lightning protection design in plain areas.The length of the tower crossarm has an effect on the protection angle of the lightning conductor.When the length of the crossarm of the tower increases,the protection angle of the lightning conductor is smaller,which helps the shielding failure trip-out rate of the smaller circuit;increasing the tower height will increase the shielding failure trip-out rate of the conductor.Rate,the higher the height of the tower,the stronger the ability to attract lightning,is not conducive to lightning protection design.Considering the above factors,the shielding failure trip-out rate of the outer conductor of the upper layer of the 500 kV AC line is the highest,and the lightning protection design of the line should be emphasized.