Resistive fault current limiters with YBCO films 100 kVA functional model

Within the Siemens current limiter program a 100 kVA functional model has been realized and tested successfully. According to the modular concept of the limiter the functional model is assembled of ten switching elements. YBCO-films with a thickness of 250 nm and a critical current density above 2/spl times/10/sup 6/ A/cm/sup 2/ are deposited by thermal coevaporation (TU Munich) on 4" sapphire wafers. To support homogeneous switching the superconducting film is covered with a 100 nm Au-shunt layer. Good current limiting performance is achieved: the steady limiting current is below the nominal current, the peak fault current increases up to 3 times the nominal current within an action time of one millisecond. The operational recovery time of the limiter, within which the switching elements return to the superconductive state again is about 2 s. Following our limiter program the next step will be a model device with a nominal switching power of 1 MVA.