| The ±800kV UHVDC transmission line has the advantages of long transmission distance,large transmission capacity,narrow transmission corridor and low line loss,which is an important way to solve the problem of energy optimal allocation in China.However,due to the long transmission distance and complex transmission environment,lightning threatens the safe and stable operation of UHVDC transmission lines.The installation of line arrester is one of the effective means to improve the performance of line lightning protection,which is applied in AC / DC transmission lines of various voltage levels.According to the installation mode of±800kV line arrester in use at present,the line arrester and the protected insulator are not directly connected in parallel.In order to ensure the reliability of overvoltage protection of arrester,it is necessary to study the insulation coordination relationship between arrester and insulator when they are struck by lightning.Firstly,based on the traveling wave theory,the propagation process of lightning on the line is regarded as the propagation process of wave,and the formation principle of lightning overvoltage is discussed.The electromagnetic transient calculation program atp-emtp based on traveling wave method is used to build the simulation calculation model of ±800kV line struck by lightning.The overvoltage distribution characteristics of ±800kV line struck by lightning are studied and analyzed,The results show that: Under the action of direct lightning,the potential amplitude of the node on the tower is related to the height of the node on the tower.The higher the node is on the tower,the greater the potential amplitude is;Under the same lightning current,the lightning overvoltage of insulator string is quite different between lightning shielding failure and lightning counterattack,and the lightning shielding failure is several times of lightning counterattack,which indicates that lightning shielding failure is a greater threat to ±800kV line.Based on the lightning overvoltage distribution characteristics of ±800kV transmission line and the overvoltage protection principle of ±800kV transmission line arrester,a concept of protection margin coefficient is proposed to evaluate the protection performance of transmission line arrester under different installation modes.In this paper,the protection margin of ±800kV transmission line arrester is calculated according to the two kinds of installation methods of tower body supporting type and cable-stayed type,and the influence of tower height and grounding resistance on the protection margin of arrester is considered.The calculation results shows: The results show that the protection margin of the two lightning arrester installation schemes are different in counterattack and shielding.When counterattacking,the protection margin of cable-stayed type is larger than that of tower supported type,In case of shielding failure,the protection margin of tower supported type is larger than that of cable-stayed type;The protection margin of arrester is related to the grounding resistance.When lightning strikes back,the protection margin of arrester increases with the increase of grounding resistance,while when lightning strikes around,the protection margin decreases with the increase of grounding resistance;According to the simulation results,it is found that the tower height has little influence on the protection margin of arrester.As the lightning arrester of UHVDC line is mainly based on shielding failure protection,the installation strategy of lightning arrester of UHVDC line should mainly consider the protection margin analysis results in the case of shielding failure.Therefore,in order to improve the lightning protection performance of ±800kV line arrester,the size of grounding resistance should be reduced as far as possible.As far as the protection margin of arrester is concerned,the tower supporting type is preferred as the installation method of ±800kV line arrester. |
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