SF

6

gas mixture can replace SF

6

gas in gas insulated electrical equipment under extremely cold conditions. In case of defect in the equipment

it will significantly reduce the breakdown voltage. It is therefore necessary to study the discharge characteristics of SF

6

gas mixture in extremely uneven electric field induced by the defect. The discharge test of SF

6

/CF

4

and SF

6

/N

2

gas mixture under needle plate electrode is performed and

compared with SF

6

gas

the variation of hump curve of breakdown voltage with the increase of gas pressure is analyzed. It is found that the hump curve of SF

6

gas mixture will shift to the right compared with SF

6

gas

and the right shift of SF

6

/N

2

gas mixture is more obvious. The breakdown and partial discharge characteristics of SF

6

gas mixtures at different pressures are compared and studied further. It is found that the breakdown voltage of SF

6

/CF

4

and SF

6

/N

2

gas mixtures has polarity reversal with the increase of gas pressure

that is

from negative polarity breakdown to positive polarity breakdown

and the gas pressure corresponding to polarity reversal is the gas pressure at the valley of hump curve. At the same time

the characteristics of partial discharge will also change with the increase of gas pressure

namely

from coexistence

of both negative and positive partial discharge to only positive partial discharge. It is found through analyzing the variation trend of initial partial discharge voltage of SF

6

gas mixture with gas pressure that

in case of exceeding the valley gas pressure

the difference between the initial partial discharge and the breakdown voltage is less

showing that SF

6

gas mixture equipment is more prone to corona free breakdown at higher gas pressure

which is consistent with the operation and maintenance experience of SF

6

gas equipment. The research results have reference significance for the operation and maintenance of SF

6

gas mixture equipment.