Comparison of SF/sub 6//N/sub 2/ and SF/sub 6//CO/sub 2/ gas mixtures as alternatives to SF/sub 6/ gas

The interest in SF/sub 6/ gas mixtures has been re-ignited in recent years by the issue of the greenhouse effect of the SF/sub 6/ gas, and most research work is now focused on a SF/sub 6//N/sub 2/ gas mixture, which is suitable for application in electrical apparatus with slightly non-uniform fields. This paper presents a comparison of SF/sub 6//N/sub 2/ and SF/sub 6//CO/sub 2/ gas mixtures with a viewpoint of their possible applications to gas-insulated transformers, where both highly non-uniform field problems and partial discharges in gas/film insulation are inevitable. It is shown that in this case the dielectric strength of SF/sub 6//CO/sub 2/ is superior to that of SF/sub 6//N/sub 2/ with a minor disadvantage related to the gas decomposition in SF/sub 6//CO/sub 2/. However, this may not be a problem for the SF/sub 6//CO/sub 2/ gas mixture to be used in gas-insulated transformers, where internal breakdown is not allowed.