2210 IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 15, NO. 2, JUNE 2005 Design and Operational Testing of a 5/10-MVA HTS Utility Power Transformer C. S. Weber, C. T. Reis, D. W. Hazelton, S. W. Schwenterly, M. J. Cole, J. A. Demko, E. F. Pleva, S. Mehta, T. Golner, and N. Aversa Abstract—High temperature superconducting transformers offer many economic, operational, and environmental benefits over conventional power transformers for utility applications. To establish the technical and economic feasibility and benefits of HTS transformers of medium-to-large ( 10 MVA) ratings, a team that includes Waukesha Electric Systems (transformer manufacturer), SuperPower, Inc. (HTS systems manufacturer), Oak Ridge National Lab, and Energy East has designed, built and tested a prototype 5/10 MVA superconducting transformer. The transformer’s 4.5-ton cold mass has been successfully main- tained at temperatures of 30–50 K for several months, without full-time operator attendance. The transformer has reached its full three-phase operating current, and has been tested to 1.4 times operating current (limited by available power supplies) in single-phase mode. It is now undergoing long-term tests at various current levels, high-voltage tests, and transient overcurrent tests at the Waukesha site. This paper summarizes the manufacturing, cooldown, and the test results achieved to date. Index Terms—High-temperature superconductors, supercon- ducting device testing, superconducting transformers. I. INTRODUCTION H IGH TEMPERATURE SUPERCONDUCTING (HTS) transformers offer a varied set of benefits which make them very attractive for utilities, and are now being demon- strated as prototype devices. This is the second phase of a three phase program to build increasingly larger superconducting transformers, culminating in a 30/60 MVA unit in the final phase. The benefits and fabrication choices made by this team for the 5/10 MVA transformer are described in greater detail in [1] and [2]. Assembly of the prototype 5/10-MVA transformer is complete and tests have been completed. Further details of the assembly and test can be found in [3] (Table I). II. MANUFACTURE AND TEST A. Technical Challenges In the 5/10 MVA transformer, new ground was broken in terms of handling higher voltage and heat load levels (mainly derived from ac loss considerations) than were encountered in Manuscript received October 5, 2004. This work was supported in part by the U.S. Department of Energy under Contract DE-FC36-98GO10282, and by NYSERDA under Contract 4460-IABR-IA-98. C. S. Weber, C. T. Reis, and D. W. Hazelton are with SuperPower, Inc, Sch- enectady, NY 12304, USA. S. W. Schwenterly, M. J. Cole, and J. A. Demko are with Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA. E. F. Pleva, S. Mehta, T. Golner and N. Aversa are with Waukesha Electric Systems, Waukesha, WI 53186, USA. Digital Object Identifier 10.1109/TASC.2005.849614 TABLE I SPECIFICATIONS OF THE 5/10 MVA TRANSFORMER the prior 1 MVA effort. Additional challenges were encountered in creating a three phase device where the connections between the phases were contained within the vacuum tank. Each team member was responsible for specific components of the design, development, and construction of the HTS transformer. B. Phase Set Assembly Each electrical phase consists of an assembly of multiple vacuum impregnated epoxied coil windings, with integrated cooling, encapsulated into one package. Downleads for the primary and secondary windings are included in the phase set assembly. The design and fabrication of the phase sets comprised a balance between the sometimes conflicting needs of a cryogenic system to maintain superconductivity, the high voltages present on the windings and downleads, and the use of vacuum as a thermal insulation. Voltage standoff is handled by the included insulation and the composition of the epoxy. The phase sets were then mounted on a frame (Fig. 1(a)) which also supported the thermal shields (Fig. 1(c)). C. Cooling Module The cooling module consists of the cryocoolers and heat ex- changers for the Helium gas loop to cool the phase sets. A second module consisting of a cryocooler, heat exchanger, and tank for the liquid Nitrogen system was used to cool the thermal shields. Both modules are shown in Figs. 1b & c above the phase set assembly. The cooling concepts are described in greater de- tail in [4]. D. Final Assembly The various participants in the project each were respon- sible for the manufacture of a subsection of the 5/10 MVA transformer; these were then assembled at Waukesha. With this approach to the manufacture, the transformer was very modular in design. Final assembly of the unit commenced in 1051-8223/$20.00 © 2005 IEEE