Study On Lightning Strike Selectivity And Influencing Factors Of Transmission Lines

At present, the ways of evaluating shielding failure performance of transmission lines include three different methods: the standard method, LPM and EGM. As a kind of shielding failure calculation method, EGM is base on the lightning discharging characteristic and introduces the concept of strike distance, which connecting attractive power to lightning with structure and size of transmission lines.In this thesis, every kinds of engineering applied transmission lines models are t-otoly compared and analyzed firstly. Then using the conception of strike distance and basic idea of EGM, determining the IEEE recommended formulas to judge the shielding failure situation of towers .On the relationship among different lightning current, critical flashover lightning current and max shielding failure current are both determined. Moreover, the shielding failure situation of tower can be judged. This method was applied in two high voltage transmission lines whose name are Dong-tie line of 220kV and Neng-bo line of 500kV in Huizhou city, which located in Guangdong province. By calculating the max shielding failure current of towers in those lines, the curve diagrams of its influencing factors such as slop angle, angle of protection, tower height and strike distance factor are drawn. The result fit the fact. At the same time, according to the special and forms of groove/valley crossing span and considering the effect of sag and span length to shielding failure performance of transmission lines, the calculation method based on the EGM was given out. The analysis show that: at the central part of groove/valley crossing span, the shielding failure rate of lightning wasn't lower, sometimes even higher than that of tower Also, the strike distance factor was applied to describe the difference of electric field intensity between shielding wires and conductors when the lightning leader is approaching to them, the shielding failure performance of the towers with negative angle of protection is also discussed.The simulation experiments were applied in this thesis too, the experiment was based on the similarity of spark and lightning, influence factors of spark hit point is researched. Basing on lots of analysis and statistics, the results shows that the trend of strike distance factor is opposite to the height of lines, which is coincident with empirical statistics.