C

4

F

7

N/CO

2

gas mixture

the eco-friendly gas for the alternative gas to SF

6

in the electrical equipment ispresently the focus both at home and abroad.The purpose for the development of the work in this paper is to explorethe breaking characteristi

cs of C

4

F

7

N/CO

2

gas mixture in 12 kV ring main unit.Saturated vapor pressure characteris-tics is used to study the selection range of mixing ratio of C

4

F

7

N/CO

2

gas mixtures for the engineering application inmedium voltage ring main unit.The splitter arc extinction structure used in ring main unit is selected to study break-ing characteristics of C

4

F

7

N/CO

2

gas mixture with different mixing ratio between the small current at 100 A and ratedcurrent at 630 A at compartment pressure of 0.15 MPa.The ring main unit after the breaking test is subject to gascomposition and proportion detection and power frequency withstand voltage test.It is found by the study that thebreaking capacity of the gas mixture increases with the increase of C

4

F

7

N volume fraction.The pressure in the gascompartment after the breaking test increases by 0.16 bar（1 bar=100 k Pa）.It is due to C

4

F

7

N decomposition throughgas composition detection.And it will not recover after being placed for a long time.The composite characteristicsof gas decomposition products are weak.The ring main unit passed the power frequency withstand voltage test be-tween phases

to earth at 42 kV/1 min and across open contacts at 48 kV/1 min and proved that that the decomposi-tion products have strong insulating properties.