Improvement of functionality and reliability by inductive HTS fault current limiter units

The inductive type high temperature superconducting fault current limiter (HTS FCL) is one of the prospective and developing applications of HTS materials. A transformer type FCL build up of YBCO rings using a magnetic core with an adjustable air gap has been built and studied. For the practical applications of HTS FCLs in industrial environments we have investigated various connections of individual FCL units, viz. series, parallel and matrix (combination of series and parallel) arrangements of FCL groups to increase the fault power capacity as well as the reliability of HTS FCLs. A modeling method and a respective simulation have been developed, which include the hysteresis and heating of the HTS and the nonlinear characteristics of the magnetic core. Simulation results were verified by tests. We propose an important application viz. a self-limiting transformer using HTS YBCO rings, which is a combination of a transformer and a fault current limiter in one unit. The theory and the build-up of such a transformer is described, test results with respect to the operation of the self-limiting transformer are presented.