To find a friendly alternative gas with low global warming potential（GWP） for SF

6

we investigated insulating properties of c-C

4

F

8

/N

2

and c-C

4

F

8

/CO

2

mixtures.Meanwhile

experiments in a sphere-plate electrode were done in different gap distance

pressures

and gas ratio of c-C

4

F

8

/N

2

and c-C

4

F

8

/CO

2

mixture gas under frequency AC voltage

compared with SF

6

c-C

4

F

8

N

2

and CO

2

in the same conditions.And the decomposition products were detected after breakdown.Experimental results show that the breakdown voltage of mixtures increases as the gas pressure/gap length/ratio of c-C

4

F

8

increases; there is a synergistic effect between c-C

4

F

8

and N

2

/CO

2

; In slightly nonuniform field

insulation performances of 30% c-C

4

F

8

/N

2

and c-C

4

F

8

/CO

2

mixed gas are equal to 75% and 79% of pure SF

6

in 0.1 MPa; the synergistic effect coefficients of c-C

4

F

8

/N

2

and c-C

4

F

8

/CO

2

in 5%

3

0% mixing ratio are between 0.20

0

.79 and 0.15

0

.65

respectively.From the insulating properties

liquefaction temperature standpoint and environment

c-C

4

F

8

/N

2

and c-C

4

F

8

/CO

2

gas mixture may be used as an alternative for SF

6

gas in electrical equipment.