Since the significant influence on the environment by the large use of SF

6

therefore

the study on alterna-tive gases has received extensive attention.C

4

F

7

N gas mixture has excellent insulation performance and environmen-tal protection characteristics and is expected as insulation medium to be alternative to SF

6

and used in gas insulatedequipment.For reducing harmful solid by-products generated during discharge period

a certain amount of volumefraction of O

2

needs to be added to the C

4

F

7

N/N

2

gas mixture.In this paper

the application potential of C

4

F

7

N/N

2

/O

2

gas mixture in high voltage electrical equipment is explored.The gas insulation test platform is used to perform thebreakdown test of C

4

F

7

N/N

2

/O

2

gas mixture containing different volume fractions of oxygen at 0.6 MPa.At the sametime

the gas chromatography-mass spectrometry（GC-MS）is used to analyze the decomposition products and volumefraction of the gas mixture after breakdown.It is found by the study that adding a certain amount of O

2

to C

4

F

7

N/N

2

gas mixture can improve the insulating self-recovery performance of the gas mixture at high gas pressure.The maindecomposition products of the gas mixture after multiple breakdowns are CF

4

C

2

F

6

C

3

F

6

C

3

F

8

CF

3

CN

C

2

F

5

CN

CO

COF

2

C

2

N

2

etc.The volume fraction of those products shows the trend of firstly increase and then decrease with theincrease of oxygen volume fraction.Comprehensively considering the effect of added amount of O

2

on the insulation performance of the C

4

F

7

N/N

2

gas mixture and the insulation performance as well as and toxicity of the pro

ducts afterdischarge and decomposition

it is concluded that 6%O

2

is more suitable when C

4

F

7

N/N

2

/O

2

gas mixture is used inhigh voltage electrical equipment.