AbstractA 3000/6000V, 1000 kVA class superconducting transformer (SC‐Tr) was developed for aProspective Power TransmissionModel SystemIntegrated underSuperconductingEnvironment (PROMISE). In this transformer, the core and superconducting windings are immersed in liquid helium and the major insulation is provided by the liquid helium. This paper describes both the design features and measured characteristics of the SC‐Tr. Fundamental characteristics of the SC‐Tr are obtained through no‐load, short‐circuit tests and quench experiments. The results of the no‐load test have verified that the SC‐Tr has the capability to withstand ac voltage of 3000/6000 V of 60 Hz without any partial discharge. The short‐circuit tests have proved that the SC‐Tr is capable of carrying ac current of 170 Arms without quench in the superconducting windings. Furthermore, in a real‐load experiment with the PROMISE, electric power of 3800 V‐460 kVA of 50 Hz in high‐voltage side is transmi