SF

6

is widely used in high voltage device because of its prefect insulation ability. However

for its greenhouse effect

it is urgently required to find an alternative matter to substitute SF

6

. Consequently

we experimentally studied the insulation characteristic of environment friendly gas c-C

4

F

8

and mix gas c-C

4

F

8

/N

2

. The DC breakdown voltages and current waveform of pure c-C

4

F

8

and c-C

4

F

8

/N

2

mixed gas were measured in different gas pressures（150

3

50 k Pa） and electrodes distance（1

6

mm） and compared with those of pure SF

6

. The results show that the breakdown voltage of pure c-C

4

F

8

is about 1.3 times that of pure SF

6

; the c-C

4

F

8

/N

2

mixed gas with a mixture ratio of 1:1 is about 0.9 times that of pure SF

6

. By calculation

the liquefaction temperature of mixed gas c-C

4

F

8

/N

2

can meet the requirements of power system. Due to the less environmental pollution of the c-C

4

F

8

/N

2

mixed gas

the c-C

4

F

8

/N

2

mixed gas can be used in gas insulated equipment for substituting SF

6

in electrical power system.