Because of the severe greenhouse effect of SF

6

it is imperative to find an environmentally friendly gas substitute of SF

6

. Consequently

we calculated the conductor and enclosure temperatures of the gas insulated transmission line（GIL） insulated by CF

3

I-N

2

and CF

3

I-CO

2

gas mixtures with different CF

3

I ratios and pressures by traditional anal

ytical methods. By comparing with the results of SF

6

gas and SF

6

-N

2

gas mixture with 20% SF

6

under the same conditions

we discussed the heat dissipation potentials of CF

3

I and its mixtures.The results show that CF

3

I-N

2

gas mixture has a better cooling ability than CF

3

I-CO

2

. The cooling ability of gas mixtures containing 30%

8

0% CF

3

I gas can be better than that of SF

6

and 20%SF

6

-80%N

2

gas mixture

and it can each up to 1.1 times better than that of 20%SF

6

-80%N

2

gas mixture as well as 1.05 times better than that of pure SF

6

. After taking the insulation strength

heat dissipation characteristics and liquefaction temperature into consideration

CF

3

I-N

2

mixtures with the CF

3

I ratio of 20%-30% can be used as the insulating medium in GIL under certain conditions.