UHV gas-insulated transformers

As the voltages and MVA ratings of transformers increase, the weight of even single-phase transformers become so large that shipment as a unit is difficult and field assembly may be necessary. Proposed 1000 MVA single phase, 765/345 kV autotransformers using conventional designs weigh between 200 and 300 tons. This problem will get much worse at 1000 and 1500 kV where the units may have single phase MVA ratings much greater than 1000 MVA. Because of the numerous insulating barriers and the extreme care needed in drying and oil filling, conventional oil-paper units may be difficult to assemble on site. In addition, dielectric losses in oil-paper insulation can be a problem at UHV levels.¹