In recent years

the environmentally friendly insulating medium C

4

F

7

N/CO

2

mixed gas has attracted wide attention due to its excellent electrical performance and environmental protection advantages

which has the potential to replace SF6 gas. In this paper

the decomposition experiments of C

4

F

7

N/CO

2

mixture under partial discharge

partial over

heating and spark discharge were carried out according to the fault conditions that may be encountered in actual operation. The decomposition products under different working conditions were qualitatively analyzed by gas chromatography-mass spectrometry（GC-MS）

and the characteristic decomposition products under different working conditions were proposed. The results show that the decomposition products under three different conditions are mainly composed of saturated fluorocarbons（CF

4

C

2

F

6

C

3

F

8

C

4

F10）

unsaturated fluorocarbons（C

2

F

4

C

3

F

6

C

4

F

8

i-C4 F8） and nitrogenous compounds（C

2

F

3

N

C

3

F

5

N

C

2

N

2

HCN）. According to the difference of decomposition products under different working conditions

HCN and peak area（C3 F8）/peak area（C2 F3 N）>1 can be used as the characteristic decomposition products under partial discharge condition.C4 F8 and its isomer i-C4 F8 are used as characteristic decomposition products under partial overheating condition. Under the condition of spark discharge

CF4 and peak area（C3 F8）/peak area（C2 F3 N）

<

1 are taken as the characteristic decomposition products of spark discharge. Characteristic decomposition products of power frequency breakdown are C4 F6 and C3 F3 N.