Surface insulation of insulator is the weak link of DC GIS/GIL insulation system. Since the conventional design criteria of AC insulators is not applicable to DC condition any longer

the development of new type of GIS/GIL insulating spacer is of great significance to improve reliability of DC gas insulated apparatus. In this research

the influence of dangerous motion behavior of metal particles in GIS/GIL is included in the filed strength control of GIL surface electrode

and the control criterion of the surface field strength of the insulating spacer under the initial state and DC imposed lightning impulse composite voltage is clearly defined and the test model of field strength of the insulating spacer along the surface under the action of surface charge accumulation and the composite voltage coupling is set up. The design method of DC insulating spacer based on the surface contour curve is proposed further. The reconstruction of surface contour curve of insulating spacer is developed based on Berstein equation

the concept and definition of the contour curve geometrical control coefficient is set up and the optimization design of the insulating spacer is supported. The minimum of normal field strength (

E

n

) and tangential field strength (

E

t

) of the insulating spacer is taken as the target. The particle swarm optimization is used for geometrical control coefficient optimization analysis and the design of DC insulating spacer is developed. Compared with the AC insulting spacer

the structure of the new type of insulating spacer can keep the

E

n

on the convex side and concave side to be reduced by 45.4% and 53.0% respectively

Et of those two sides to be reduced by 1.4% and 7.5% respectively. The

E

t

on both sides of the under composite voltage is 7.34 kV/mm and 8.33 kV/mm respectively

which can meet the insulation requirements. This study can provide guidance and reference

for the design and development of DC GIS/GIL insulating spacer.