Uneven rain is a special operating condition of DC wall bushing due to the sheltering effect of the wall of valve hall

and can significantly reduce the external insulation strength of DC wall bushing;moreover

external insulation flashover caused by uneven rain is one of the main reasons influencing the safety operation of wall bushing. Consequently

we experimentally investigated the DC voltage flashover characteristics of typical SF

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insulated DC wall bushing under different external insulation wet area ratio and rain conductivity. All the tests were carried out on ±100 kV and ±400 kV SF

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insulated DC wall bushing products. By adjusting the rainwater conductivity

DC test voltages were applied to the wet bushing until flashover

and the development of arc

corona and leakage current was monitored in the flashover process. The research results show that

when the rain conductivity is 1 500 μS/cm

the lowest DC flashover voltage of ±400 kV SF

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insulated DC wall bushing occurs at 623 kV under the condition when the length ratio of dry and wet area is 1:4

which is 9.0% lower than the flashover voltage under total wet condition. When the length ratio of dry and wet area of ±400 kV DC wall bushing is 1:4

the DC flashover voltage under the rain conductivity of 1 500 μS/cm is 16.2% lower than that under the rain conductivity of 200 μS/cm. The results can provide a reference for the insulation structure design of DC wall bushing

and also provide a theoretical support for avoiding uneven rain flashover of DC wall bushing in DC power transmission projects.