In Japan, large-capacity gas-insulated transformers (275kV, 300MVA) designed to be cooled by flowing SF6 gas have been developed and are operating in underground substations.1 They use insulating plastics with excellent heat resistance and insulation strength, in addition to cellulose materials such as insulating paper and pressboard used in conventional oil-immersed transformers. Such insulating plastics have a high surface resistance and can be electrified through contact with each other, delamination, or friction. Again, the resistivity of SF6 gas is so high that once the insulation material surface is electrified, charges are slow to leak out.

A. Inui

Papers

Static Electrification Phenomena on Dielectric Materials of SF6 Gas-Insulated Transformer