Failure Risk of UHV AC Transmission Line Considering the Statistical Characteristics of Switching Overvoltage Waveshape

The sizes of ultra-high-voltage (UHV) towers and substations are related to the air clearances which are usually determined by switching overvoltage. Based on electromagnetic transient simulation of the first 1000-kV UHV ac transmission line in China, this paper extracted the effective wave information in accordance with the concept of the active part of the waveshape from calculated main types of switching overvoltage. Moreover, based on test results of switching impulse flashover voltages, a practical and accurate method to calculate the risk of failure was presented, which considered the variable characteristics of the insulation strength of the transmission line under different switching overvoltage waveshapes. Evaluation of the results focused on the comparison between two new methods and the traditional simplified method considering the effect of the front time.