Under humid condition

water droplets on the surface of roof insulator will lead electric filed distortion

and induce corona discharge

which is a threat to train operation. A roof insulator computational model is established based on finite element method to simulate the influence of water droplet parameters

like position

size and amount

on electric filed distribution along insulator surface. And grading ring frequently used on insulator for high voltage transmission line is applied to roof insulator

to suppress corona discharge induced by water droplet. The result shows

water droplet at the junction of shed and sheath has the greatest impact on electric field distortion.When the radius of water droplet is 2 mm

influence of water droplet on shed is most obvious. A larger distance between water droplets results in weaker maximum electric field along insulator surface. The optimal configuration scheme of grading ring is confirmed that radius is 85 mm

the section radius of grading ring is 24 mm

and the height apart from the high voltage side is 50 mm.