Development of insulation technology for high-voltage gas-insulated transformer

Insulation technology development for 275 kV 300 MVA class SF₆ gas-insulated transformers is described. The main area of development is turn-to-turn insulation using polymer film in sheeting winding. It was experimentally demonstrated that two sheets of film, several tens of micrometer in thickness, had sufficient insulation strength for impulse and short/long-term AC voltage application. Sufficient insulation performance for coil end insulation was demonstrated by a full-scale impulse model, taking into consideration the results of three-dimensional electric field analysis. A 275 kV 50 MVA prototype with an insulation structure equivalent to that of 275 kV 300 MVA units was developed, and a three-month reliability test was conducted