In order to study the pollution flashover performances of DC wall bushing under different pollution conditions

the influences of different composite umbrella structures on the flashover characteristics of DC wall bushing

and the influences of the internal conductor and shielding structure of the wall bushing on pollution flashover characteristics of composite coat

we carried out artificial pollution tests of ±400 kV SF

6

insulated DC wall bushing with composite insulator as its coat in the large artificial climate laboratory

and obtained the negative power index relation between the 50%withstand voltage(U

50

) and salt deposit density（SDD） of different composite umbrella structures of wall bushing. The research demonstrates that the fla

shover voltage value of unit creepage distance of the wall bushing composite insulator with one big/one small umbrella structure is higher than that with one big/two small umbrella structure. The results are also obtained when the SDD is 0.08

0.15

and 0.20 mg/cm

2

the 50% withstand voltage(U

50

) of the DC wall bushing with internal conductor and shielding structure is improved by 5.3%

4.2%

and 5.3% than the DC hollow composite insulator without internal conductor and shielding structure. According to the research results

we suggest that the umbrella structure with a higher utilization ratio of creepage distance can be employed in the appropriate external umbrella structure design of ±1 100 kV UHV DC wall bushing

and the creepage distance is not less than 48 mm/kV.