In recent years

fluoronitriles have been widely studied to replace SF

6

in the gas insulated equipment. In order to fully reveal the power-frequency breakdown characteristics of fluoronitriles/CO

2

mixed gas under different electric field dis

tributions

pressures

and mixing proportions

and to select a scheme for engineering application configuration

we calculated the liquefaction temperature of fluoronitriles/CO

2

mixed gases at different proportions of fluoronitriles and pressure

and tested the breakdown voltage of fluoronitriles/CO

2

gas mixtures and SF

6

with different electric field nonuniformity

pressures

ratios in power frequency electric field. In order to obtain the breakdown characteristics under different conditions

the power frequency breakdown tests of the gas were carried out in different electrode forms. As nonuniformity of electric field grows

the N-curve characteristic of breakdown voltage appears in fluoronitriles/CO

2

and a similar phenomenon occurs in SF

6

. Further increase of electric field nonuniformity still presents an N-curve. In addition

according to the fluoronitriles/CO

2

gas mixture liquefaction temperature limit for –10 ℃

when the pressure range is 0.3 MPa and above and the electric field nonuniformity is 1.05

1.58

9.6

13.8 and 22.5

the fluoronitriles ratios must reach 9%

5%

7%

5% and 5%

respectively

so that the insulation strength of fluoronitriles/CO

2

can reach 0.8 times that of SF

6

. If the insulation strength of fluoronitriles/CO

2

is 0.9 times that of SF

6

the mixing ratio of fluoronitriles must be increased to 13% and above.