Manufacturing and test of model double-pancake coils of HTS transformer for cryogenic insulation design

The feasibility of the development of HTS transformer has been grown and now its researches are going on actively around the world. Also the development research of 22.9 kV, 1 MVA HTS transformer is going on in Korea. To realize the development, various breakdown tests at liquid nitrogen temperature should be carried out and the breakdown mechanism should be understood. Moreover the insulation design technology that apply the basic dielectric experimental data to insulation design of it should be developed. Therefore, in this paper, breakdown tests such as ac breakdown, surface flashover and impulse breakdown in LN₂ were conducted using simulated electrodes and then the model double pancake coils were wounded on FRP former. Finally, electrical insulation tests of the model coils were performed with impulse 154 kV and ac 50 kV.