The fault current limiting feature of the SC transformer with the HTS 2G windings provide protection and significantly reduce wear and tear for circuit breakers and other substation power equipment. A comparison of the short circuit currents of the 64 MVA transformer wound with copper and YBCO 2G HTS tapes is made in this paper. The results of the analysis show that the YBCO 2G tapes enable to built the superconducting transformer with the ability to limit the short-circuit currents. The superconducting windings require special considerations for the induced electromagnetic forces in order to limit them below the allowable tensile stresses. Strongly anisotropic Y-123 tape used in the winding of the transformer will be exposed to different orientations and amplitudes of the local magnetic field. If the transformer is going to act also as a fault current limiter, the uniformity of the transition of the transformer winding is crucial to avoid sectional responses of the transformer. Therefore it is essential to conduct systematic current-magnetic field measurements to define `constant current domain' for the conductor at a given operating temperature.

Superconducting fault current limiters (SFCL) are designed to protect the electrical grid from faults that result from lightning strikes, downed power lines and other system interruptions. The rapid increase of impedance of the SFCL reduces the short current in the circuit. Several coreless constructions of inductive SFCLs have been tested. The space between the windings is the thick of the polyimide film kapton insulation to increase the coupling and reduces the leakage reactance. Both primary and secondary windings have been immersed in liquid nitrogen. The presented solutions reduce the size and the weight of the device. A few limiters based on HTS 1G and HTS 2G tapes has been described, tested and compared.

The inductive type SFCLs and the transformer type SFCLs need the iron cores. In both, the fault current is transformed from the primary winding to the secondary winding. The difference is in the secondary windings. The superconducting materials for every kind of SFCL should have both high value of resistivity in the resistive state,rho_tau , and high critical current density . The paper shows, that the transformer SFCL can be made using every type of commercial HTS elements. The inductive SFCLs need the HTS materials with very large value of the rho_tauJ_c parameter.

The high-T/sub c/ superconducting fault current limiter (SFCL) can be classified into resistive, inductive and hybrid types. The inductive type HTSFCL seems to show most prospect due to the simple design (construction) of the secondary superconducting winding in the form of ceramic type BSCCO and for the reduction of current leads. In an inductive type SFCL, ferromagnetic cores for magnetic flux are applied, however open cores are also taken into consideration in order to simplify the construction. The results of experimental and computational investigations of inductive SFCL parameters are presented in this paper.

Transformers represent one of the oldest and most mature elements in a power transmission and distribution network. The new superconducting transformers are smaller and lighter than conventional ones and they have lower power losses. Also, the new 2G superconducting tapes with high resistivity in the normal state allow to build transformers with high short-circuit strength. The short-circuit current limiting feature of the superconducting transformer, which is the most important benefit of replacing conventional windings by superconducting ones, provides protection and significantly reduces the wear and tear of circuit breakers and other substation power equipment. This paper describes the design and test results of a model of a 1-phase, 8.8 kVA superconducting transformer with windings made of 2G HTS tape. The authors also present the results of a numerical analysis of the design. A special regard is given to the ability of the device's superconducting winding to limit the short-circuit current, in particular its resistivity in normal state at a temperature of 77 K.