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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.Index Terms-Fault current limiter, high-temperature superconductors, inductive-type, superconducting devices. I. INCREASING POWER RATING AND RELIABILITY OF THE FAULT CURRENT LIMITERT HE inductive type high-temperature superconducting (HTS) fault current limiter (FCL) is one of the prospective and developing applications of HTS, which can make electric power networks more reliable [1]. In our case a transformer type FCL built up of YBCO rings [2] using a magnetic core with an adjustable air gap is being investigated. The basic design is one with a closed magnetic core. This design allows fast activation and recovery processes both within 5 ms. We developed and applied a special design to significantly reduce the impedance in normal operation mode, and to properly adjust the impedance in limitation mode. The FCL can be designed with predictable parameters, and can withstand thousands of activation and recovery cycles [3], [4].For practical applications of HTS FCLs in industrial environments we investigated the possibilities to increase power rating and reliability. For the mentioned purposes we investigated various FCL topologies. In our terms topology means the type of connections of individual units. Units can be arranged in series, parallel and combined (matrix) connections. Tests were performed for series and parallel connections of FCLs to investigate the fault processes in the individual units and the resultant effects of the whole FCL group [5]. Fig. 1 shows the interrelations of the two parallel connected FCLs. Increasing the current, it achieves the activation value of FCL#1, its main field impedance appears and it limits the current of its own branch. The current decreases along this branch and, at the same moment, the current of FCL#2 increases. When the current exceeds the activation value of FCL#2, it is also activated. In this state the whole FCL group is in the limitation mode.When decreas...

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