Study On Lightning Performance Calculation Of Transmission Lines And Accurate Modeling Of Grounding Device

There are a total of120000km220kV AC overhead transmission lines,7500km330kVlines,20000km500kV line across China currently, and the1000kV UHV lines are underconstruction too. The lines which are over tens of thousands of kilometers in geometricscale and long-term exposure to a complex atmospheric environment have a high risk ofbeing struck by lightning. Lightning may cause single phase or multi-phase earth faultdetection and protection devices tripping on the one hand. On the other hand, the lightninginvasion wave may invade into the substation along the transmission line and damage theinsulation of electrical equipments in it. The weak ability of lightning protection of thetransmission lines which are of high voltage level and great capacity would seriouslythreaten the safe operation of the whole power grid.Currently, a lot of lightning protection measures are taken in the EHV lines, but theprotection performance is not good enough. Lightning protection design and analysis areoften over-reliance on experience or lack of a mature theoretical guidance, so that thedesigners still use the regulation method which are behind the times, or rush to use a newalgorithm which is not mature when designing. So the lightning protection measuresproposed by the designers are not scientific enough. Therefore, proposing a comprehensiveassessment to evaluate the lightning performance of transmission lines is a serious problemin design of power transmission lines.Operating experience shows that the direct lightning strokes cause the most damage tothe power system, while, the inductive lightning is a threat to only35kV lines and below.Therefore, the shielding failure flashover and the back-flashover caused by direct lightningstroke are the main reason for the line trip-out. The traditional model which was proposedby foreign scholars based on electric geometry method (EGM) is used widely inengineering now. However, this model cannot explain the phenomenon of shielding failurewhen the protect angle is below zero. The paper proposes a more reasonable shieldingfailure calculation method based on EGM which successfully explain the phenomenon ofshielding failure when the protect angle is below zero. Based on the ATP/EMTP program,the paper has made a comprehensive study of the key models for back-flash calculation in ATP. Also, the accurate circuit model in ATP of the grounding device is first put forward inthe paper and calculation results indicate that the lightning back-flashover performance issignificant positive when using the impulse resistance model which is common used now.So using a resistor as the grounding device’ model in back-flash calculation is not rigorousenough. Based on the proposed method of shielding and back-flash calculation, the paperfurther proposes a complete lightning performance evaluation solution for transmissionlines, which are important theory reference for lightning protection design or algorithmprogramming on lightning performance analysis.