Under the influences of global warming and increasing extreme weather

the rain flashover faults of insulator strings happen with high frequency. Enhanced electrical performance of insulators or insulator strings in extreme weather is important for grid disaster prevention and mitigation

and is also a powerful support for the strong and smart grids in China. However

flashover accidents of insulator strings in heavy rainstorms happen with high frequency

and there is little study on the flashover mechanism and performance of insulator strings in heavy rainstorms. This paper deals with the AC flashover performance of insulator strings in heavy rainstorms. Two types of insulators

XP-160 porcelain insulator and LXY4-160 glass insulator

were tested. The results show that: 1)the rain flashover voltage of the insulator strings is independent on the contamination on lower surface of the insulators

and changes almost linearly with string length;2)the rain flashover voltage decreases with the increase in flux and conductivity of rain

satisfying negative power function relation;and 3)different angles between rain curtain and conductor affect the flashover voltage. It is concluded that preventing formation of rain curtain and increasing surface resistance of insulator can facilitate prevention of rain flashover on insulator strings in rainstorm.