Calculation of Lightning Outage Rate of High Voltage Transmission Line

The outage rate of high voltage power transmission lines caused by direct lighting has been analyzed and calculated, including straight lightning stroke on tower top (backstroke) and round stroke to conductor (shielding failure). Using the electrical geometry model and exposure distance, the outage rate caused by shielding failure is calculated. Based on the principles of IEEE flash program, the voltage across the insulator string and the outage rate caused by backstroke are calculated. Applying this method, the lightning outage rates of a 220kV double circuit transmission lines in Baoding, Hebei, China have been calculated. According to the calculated results the measures has been proposed which should be taken to improve the line insulation level.