Development of large capacity low-noise gas-insulated transformer

In order to handle increasing demand for electric power and protection against fires in large cities, larger-capacity and higher voltage SF₆ gas-insulated transformers have been developed and are in practical use. They use high pressure gas to enhance cooling and insulating performance. However, they have some drawbacks such as higher noise and heavier tank. We carried out developments to enlarge the ranges of capacity and voltage to which low pressure gas can be applied. Firstly, its interior structures and cooling system were designed using thermo-fluid and gas flow analyses. Secondly, electric field stresses in the transformer were kept under control by the adjustment of relative permittivities and position of insulators. Thirdly, a low-noise type gas blower was developed after careful tests. As a result, 100 MVA 154 kV SF₆ gas-insulated transformer of 65 dB class using low pressure SF₆ gas (0.24 MPa at 20°C) has been developed.