Eco-friendly mixed gas C

4

F

7

N/CO

2

has the most potential for replacing SF6. Based on dealing with theproblem of C

4

F

7

N/CO

2

gas mixing and its engineering application

an insulation test

platform for investigations is builtin this paper

a experimental prototype with typical disconnecting contact structures of 72.5kV GIS is adopted. Gasinsulation characteristics influencing by different filling pressures and different contact distances under lightningimpulse voltage are studied. The insulation characteristics of 20%C4 F7 N+80%CO2 are analyzed and compared withthat of pure SF6 and pure CO2 under the same testing conditions. Analysis and results show that C

4

F

7

N/CO

2

gas needsa certain time for recovering

the breakdown performances of pure SF6

CO2 and C

4

F

7

N/CO

2

are all approximatelylinear increasing with the contact distances and filling pressures

but the rising slope of C

4

F

7

N/CO

2

is the largest.C

4

F

7

N/CO

2

50% breakdown voltage increases from 65.75kV to 179.88kV when contact distance changes from 5 mmto 15 mm under filling pressure 0.2 MPa

and it is 35.45kV higher than that of pure SF6 under contact distance15 mm and filling pressure 0.15 MPa.