Insulation go-ordination procedure for 420 kV gas insulated lines (GIL)

After stating the reasons leading to EDF´s interest in 420 kV GIL and the technical and economic imperatives to be considered, the principles adopted for the insulation co-ordination of 420 kV GIL up to a few tens of kilometers long are described. The insulation coordination approach is based on the global failure rate requested for GIL taking into account: the gap in terms of reliability between the actual technology of GIS and the one needed for reliable GIL, the dielectric characteristics of the N₂/SF₆ mixtures selected, the specific features of GIL with regard to insulation co-ordination (many insulations in parallel, on-site dielectric tests at reduced levels, etc.) compared to substation equipment, the “withstand voltage” guaranteed for the whole GIL by the type tests, and on site tests