Ac loss properties of a 1MVA single-phase HTS power transformer

We designed and built a single-phase 1 MVA-22/6.9 kV HTS transformer with the multi-layered cylindrical windings composed of Bi2223 parallel conductors. In advance of the design, the ac loss induced in the windings was estimated on the basis of the observed results in a strand. A subcooled liquid nitrogen cryogenic system with the corresponding cooling capacity was developed and attached to the transformer. The actual ac loss was measured by an electrical method. It was a great part of the total heat load and dominated the temperature rise of subcooled liquid nitrogen. We discussed the validity of the present estimation procedure of the ac loss in the windings as compared with the observed results.