Tests of a Bi/Y transformer

In the context of a European project (READY) we designed, constructed and tested a single phase transformer. The primary winding uses a PIT-Bi-2223 tape. The secondary is wound with two lengths (2 × 8 m) of YBCO coated conductor. With these two lengths in series, the secondary characteristics are 75 V-50 A at 77 K. We designed the transformer with an integrated refrigerator. The cooler is a high cooling capacity (100 W at 80 K) single stage coaxial pulse tube cooler (PTC) developed by Air Liquide. We chose a cold magnetic circuit with low iron loss FeSi sheets. The cryostat is then very simple with metallic vessels and only one interface with the PTC, and the cooling fluid is helium in order to investigate a wide temperature range (40-80 K). About 30 hours are required to reach 70 K from 300 K using only the PTC. This paper presents the transformer layout and some electrical tests (no load and short circuit tests). The ac losses are high in the PIT coil, but in good agreement with numerical simulations. In the YBCO coil the ac losses are lower and in good agreement with the Norris formula.