High voltage system on roof of EMU is the main component to obtain power reliably from the catenary.Once the roof insulator with long exposure to the atmosphere has flashover

it will cause power supply interruption or crouching of EMU. In this paper

a new type of roof silicone rubber composite insulator on EMU is taken as the object. The dry and wet flashover tests of eight insulators are carried out by the continuous voltage rising method. The test results show that the dry flashover voltage of the insulator is higher than 140 k V and the standard deviation is less than 3%;the wet flashover voltage is higher than 120 kV and the standard deviation is less than 3%;both the dry and wet flashover voltages meet the grid test value of 100 kV and 85 k V for EMU roof insulator;the higher the water conductivity of wet insulator is

the earlier the discharge arc time appears and the more obvious the arcs are which is taking by the camera. When the fitting of the low voltage side is completely coated

multiple flashover can cause obvious fusion of the protective layer edge of the coated low voltage fitting. The protective layer after fusion may be torn under the action of high-speed airflow. It is suggested that the low voltage fitting shall not be completely coated by the insulation layer in the subsequent optimization design. In order to explain the difference between dry and wet flashover voltages and discharge process

a three-dimensional model containing water droplets or water accumulation is constructed to analyze the effect of discrete water droplets or accumulated water on the electric field distribution near the surface of shed. The simulation results show that the presence of water droplets or water accumulation distorts theelectric field intensity nearby

and the electric field after the distortion can reach 100 times of the electric field whenthe surface is dry. The results of this paper can provide reference for the structural optimization design of silicone rub-ber composite insulators on the roof of EMUs.