After Alsthom designed an LTS 220 kVA transformer and operated it successfully under a 70 kW load, many small-scale LTS units ranging from 10 kVA to 100 kVA were manufactured in Japan in order to confirm various aspects of basic operating behavior. Subsequently, larger units were built and tested by Nagoya University in conjunction with Takaoka (100 kVA), Kansai Electric in conjunction with Mitsubishi (2,000 kVA using Nb3Sn), Osaka University in conjunction with Toshiba (40 kVA), and Kyushu University in conjunction with Toshiba (1,000 kVA). In addition to acquiring better understanding of the sensitivity of performance to changes in the critical design parameters, one of the more important results from these trials was acquiring better understanding of the stability of the ac conductor and the quench protection afforded by the particular design. Low ac losses were achieved in the LTS conductor through the use of twisted and transposed conductors having fine filaments and high resistivity matrices. The HTS conductors available for use in transformers at the time of this study neither have fine (submicron) filaments nor are readily twisted and transposed, due to the somewhat brittle nature of the ceramic filaments. Moreover, the stabilizing material surrounding the filaments is composed of silver or silver alloy, which do not exhibit high resistivities. However, ability to operate at elevated temperatures makes it possible for the HTS conductors to tolerate higher ac losses than are tolerable in LTS systems, due to the large reduction in refrigeration costs. When LTS design parameters were used to estimate bounds of performance for HTS wires, Iwakuma et al. (1996b) concluded that an Ag-10%Au alloy sheath suffices for resistivity reduction, and that the filament diameter/thickness must be smaller than 25 microns and 10 microns for the case of round wires and flat tapes, respectively. They also determined that the ac losses of transposed Bi-2223 tapes are less than those of nontransposed tapes and about equivalent to the losses measured in single wires (Fig. 3.5).