Verification Testing for a 1 MVA 3-Phase Demonstration Transformer Using 2G-HTS Roebel Cable

We present results from testing to verify the performance of major subsystem components for a 1-MVA three-phase transformer demonstration project. The transformer utilizes a 15-strand Roebel cable for the low-voltage windings and a 4-mm-wide superconductor for the high-voltage windings. Both windings use a YBCO conductor. The winding assemblies will be housed in three individual vacuum insulated glass-fiber composite cryostats and will be cooled by circulated liquid nitrogen and subcooled to a target operating temperature of 70 K. Results from thermal insulation performance tests on a sample composite cryostat are presented. AC loss test results of a low-voltage winding assembly are also presented. The Roebel cable is proven to exhibit low AC loss operation at high current. We conclude that AC loss is not a fundamental obstacle to HTS transformer commercialization.