| Complex AC-DC Hybrid Transmission Grid has become the trend of the development of the international power grid,which put forward higher requirements to the stable operation of UHVDC system.Dc transmission line is the highest element in the UHVDC system failure rate.As main protection of dc line,the right action of traveling wave protection is important to safeguard the UHVDC system and its stable operation.In view of the low accuracy of the present uhv dc lines traveling wave protection under the condition of lightning disturbance action,and the risk of maloperation,a correct lightning simulation model is established based on the actual operation of a UHVDC system.This article studies how lightning downward wave protection characteristics of dynamic response characteristics,and its cooperation on the temporal logic.Meanwhile the reason of traveling wave protection misoperate is found and two practical optimization strategies are put forward,which improve selectivity on sensitivity basis without sacrificing the sensitivity of traveling wave protection.This article took a real UHVDC project as the background,accurate modeling of lightning current and lightning dc lines are made in the electromagnetic transient simulation software PSCAD/EMTDC.In order to achieve the small step for a long time,long simulation requirements,the Snapshot of software technology is introduced,skillfully made an accurately depict of lightning transient process.With traveling wave protection maloperation occurs as the breakthrough point,the transient electric parameters by means of wave record chart compares the scene of the accident electric parameters established by this paper is verified the correctness of the uhv transmission lines lightning model.In order to deeply analyze how misoperation of mechanism of traveling wave protection occurs,this paper analyzes the typical uhv transmission lines and the basic principle of the traveling wave protection in detail,including three protection characteristics dU/dt??U??I algorithm,the function of line wave protection,as well as cooperation in the sequential logic.Based on analysis of traveling wave protection maloperation and the simulation results and fully considering the response of dc control system,this article puts forward a standpoint of the significant cause of non-lightening line travelling wave protection maloperation that when one pole of the uhv transmission lines being struck by lightning,the other pole being in the recovery process,the electromagnetic coupling effect between the lines causing volatility to electric parameters,and further results in the response of the protection characteristics,which exactly right meet the timing relationships.Finally,aiming at the risk that under the situation of lightning,line wave protection maloperate,this paper carries out an optimization strategy of the traveling wave protection under the condition of lightning strike.Based on characteristics of traveling wave protection misoperation accident,quickly ensuring that the correct voltage,current criterion meeting perspective,this article puts forward two kinds of optimization strategy,that in the current voltage criterion atresia logic,and improve the current criterion algorithm,without changing the original hardware devices and sacrifice protection sensitivity under the premise of greatly improving the selectivity of traveling wave protection protection,which has very important theoretical and practical significance. |
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