Analysis of Transient Processes in a Three-Phase Single-Machine System with a High- Temperature Superconducting Transformer

The paper presents the results of a study of thermal and electromagnetic transients in an electric power system with a high-temperature superconducting transformer. A physical prototype of a three-phase high-temperature superconducting transformer with YBCO windings is developed to study the current limiting process. Liquid nitrogen is used as a dielectric medium and a coolant. A mathematical model of a three-phase single-machine system with a high-temperature superconducting transformer is developed. It allows to analytically describe the electromagnetic transient process in a three-phase grid with a superconducting transformer, to estimate the electrodynamic and thermal effects of the short-circuit current with varying load and short-circuit types. The positive effect of superconducting transformers on the operating modes of the electric power system is shown. The analysis of the current limiting function of a high-temperature superconducting transformer is carried out; its efficiency and safety for the electric power system are proved. The research of the influence of the load type and the short-circuit mode on the current limitation level is carried out. It is demonstrated that during the short-circuit current limitation, significant heat flows occur on the windings, which should not exceed the critical value above which the superconductor could not return to the superconducting state by itself.