The difficulty of insulation structure design of high-voltage DC apparatus increases significantly with the increase of voltage level

and it cannot be simply handled by increasing the size of AC insulation part. Otherwise

it will not only increase the size and cost of the product

but also accumulate a large amount of charge on the surface of the insulation part with temperature gradient during operation

causing severe distortion of the electric field distribution. In recent years

numerous studies have attempted to improve the electric field distribution of DC insulation part by adjusting the quality of insulation part or applying surface coatings. Although some research results have been obtained

yet they cannot be used in product design. It is emphasized in this paper that the opinion of improving charge accumulation and electric field distribution by adjusting the shape of insulation part

new design of DC insulation part with small structural dimensions and good electric field distribution called ‘disc/cone’ is proposed. Its structure and electric field are optimized and calculated. The design of the support part in the busbar of basic busbar unit of GIS is analyzed and verified. In addition

the corresponding prevention measures on the design idea of prevention of metal particle of insulation inside the product

with prevention rather than the control

is proposed. The research scheme of permissible value of various filed strength which must be used in the design of HVDC product is proposed. It is proposed in this paper that conical disc/cone spacer insulating parts is also applicable the selection and application of other EHV/UHV DC gas insulated apparatus