On the application of High-Tc superconductors in power coils and transformers

In this study, the electro-magnetic properties of high-Tc tapes and coils are investigated. The focus is on Bi-2223/Ag tapes with non-twisted superconducting filaments as these are the only high-Tc superconductors at present available in sufficient length for practical applications. The study is confined to high-temperature superconductors and power coils operated in liquid nitrogen and intended for large-scale applications. The aim of the study is three-fold: to explore the options and the potential of increasing the critical currents and reducing the alternating current losses of practical superconductors in power coils hence aiming at improved performance; to build a model that is sufficient to describe behaviour and to calculate voltage-current characteristics of advanced Bi-2223 superconductors and coils carrying alternating current and exposed to alternating magnetic field; the application target is to develop fundamentals of high-Tc superconducting power coils and as an example to make and to study a prototype 1-MVA resonator coil both experimentally and numerically and hence to demonstrate the feasibility and predictable behaviour of high-Tc superconducting power devices. The final objective is, using the knowledge and the experience gained in the study, to evaluate the viability of a power transformer with high-Tc superconducting coils.