In order to support carbon peaking and carbon neutrality goals in China

SF

6

gas-insulated equipment aren’t gradually allowed to apply in distribution grid. As perfluoroisobutanitrile (C

4

F

7

N) is one of the internationally mainstream eco-friendly alternative gases to SF

6

it is particularly necessary to develop multi-sided C

4

F

7

N eco-friendly gas-insulated ring main units (C

4

F

7

N RMUs) facing widely terminal users. In this paper

the key technologies for the design of C

4

F

7

N RMU was investigated. The key properties of C

4

F

7

N/CO

2

gas mixture

such as insulation and liquefaction

were analyzed. The control values of electric field strength for insulation design were proposed. And the liquefaction temperature values were calculated. The gas mixture configuration was set as the constant pressure with C

4

F

7

N volume ratio of 10%. The the

rmal acceleration tests of C

4

F

7

N/CO

2

gas mixture with cast steel

engineering plastics

rubber and epoxy glass fiber were carried out. The results have shown that the gas-solid material samples except rubber were with good compatibility. The gas-solid compatibility of RMU meeting the field operation requirements has been verified by the compatibility live test. The ground making test for the three-station switch was conducted with different gases of C

4

F

7

N volume ratios. The pre-breakdown time distribution

influence of switching rates and contact ablation status of the grounding switch were obtained. Referring to the results with SF

6

gas

the grounding making performance with C

4

F

7

N volume ratio of 10% was suitable for the continuous multiple making conditions required by the standard. The technical schemes of C

4

F

7

N/CO

2

gas mixture and equipment design were valid and available. C

4

F

7

N RMU has been developed and passed a full set of type tests

and the products have been demonstrated and applied in Anhui power grid. All the design key technologies of C

4

F

7

N/CO

2

gas mixture in the paper have summarized as a useful reference for the development and application of C

4

F

7

N eco-friendly gas-insulated transmission and transformation equipment.