Suitability of N/sub 2/-SF/sup 6/ gas mixtures for the application at gas insulated transmission lines GIL

In gas insulated transmission lines (GIL) for insulation purposes N/sub 2/-SF/sub 6/ gas mixtures are applied because of economical and ecological reasons. With the different mixtures the same intrinsic strength for quasihomogeneous fields like pure SF/sub 6/ can be achieved by an increase of the gas pressure. However, concerning the sensitivity to defects or the surface roughness the individual mixtures have different properties. In addition the detectability of defects by PD measurements is different Therefore the range of the SF/sub 6/ content of the mixtures which are suitable for the application in GIL is limited.