| According to the condition that the lightning accidents are taken frequently for 500kV Yafu transmission line, the paper studied on the lightning protection performance deeply. Used regulations method calculating, analyzing and comparing the lightning protection performance with field data for the line firstly,. Then Put forward more reasonable model (distributing parameter model) to calculate the surge impedance of tower combining the existing model and validate by EMTP, furthermore studied the striking distance factor based on electromagnetism. Conclusion are drought as follow by studying the lightning protection performance for 500kV Yafu transmission line: the outage rates is in 0.32 flashes/year by regulations method. Using distributing parameter analyzing the surge impedance of tower, the simulation value of tower surge impedance is close to the test value and the relative error between is in ten percent. The value of the outage rate with distributing parameter model is larger twenty five percent than with regulations method. The striking distance factor is not equal to but smaller than 1 for higher tower, the value of lightning current is not influence in the striking distance factor. The different between the result by traditional EGM with the field data is large. The outage rates is 0.884265 flashes/100km/year by improved EGM and tallies with the field data. The main factor that influence the lightning protection performance are grounding resistance, the strength of insulators, the height of tower, ground obliquity, terrain along the line and so on. By combining with the field data, this paper also bring forward some more reasonable methods of lightning protection. The results of this paper will provide gist to the protection of YaFu 500kV transmission line and the same type transmission lines.
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