Recently

fluoroket

one and fluoronitrile gases attract great attention as potential SF

6

substitutes.We studied the insulation performances of the mixtures of C

4

F

7

N and C

5

F

10

O with CO

2

.First

the Antoine constants were fitted by the reported liquefaction temperature data of C

4

F

7

N and C

5

F

10

O.The saturated vapor pressure characteristics of C

4

F

7

N-CO

2

and C5F10O-CO

2

mixtures were analyzed.Secondly

by combining the Antoine equation and the basic law of vapor liquid equilibrium

the application conditions at limits of environment temperature were discussed.Finally

the critical electric field strengths were determined from the experimental data in literatures

and the insulation performances and potentials of C

4

F

7

N-CO

2

and C5F10O-CO

2

mixtures were discussed.It is found that the electrical strengths of the C

4

F

7

N-CO

2

mixture under the limits of three environment temperatures（-5 ℃

-15 ℃

and-25 ℃） are all much higher than those of the C5F10O-CO

2

mixture

and the proper choice of mixed ratio and pressure for C

4

F

7

N-CO

2

can provide relatively high electrical strength

low GWP

and liquefaction temperature.Taking the environment temperature limit of-25 ℃ for example

the electrical strength of the 5%C

4

F

7

N-95%CO

2

mixture at 0.65 MPa can approximate pure SF

6

gas at 0.5 MPa.In addition

the GWPs of C

4

F

7

N-CO

2

mixtures are below 850 when C

4

F

7

N concentration is less than 20%.