In china the trip faults of 10 kV power distribution lines caused by lightning account for a large percentage of distribution network faults due to low insulation level.In this paper

the reasons why the trips occur are analyzed

and the lightning protection condition of 10 kV power distribution lines is evaluated according to the characteristics of lightning activity to improve the lightning protection.The lightning parameters of Nanchuan Region in Chongqing were collected from 1999 to 2009 via the lightning location system

then a probability distribution equation of positive and negative lightning current amplitudes is derived to analyze flashover rates of 10 kV transmission lines under direct lightning and induced lightning.The results show that: the ground lightning density is 0.077 7 time/（km2.d）

of which negative lightning accounts for 94.84%;both total flashover rates of direct lightning and induced lightning close to the values of their negative lightning;and the flashover rates induced by different polarity lightning current depend on their probability distribution equations of lightning current amplitude.The calculation and evaluation of lightning protection should consider the polarity effect of lightning current.