Short circuit test performance of inductive high T/sub c/ superconducting fault current limiters

The current limiting performance of inductive fault current limiters based on Bi-2212 high temperature superconducting tubes has been evaluated. Fault current limitation is due to the nonlinear impedance of this device when the induced current in the superconducting Bi-2212 tubes exceeds the critical current. A power load in a test circuit is first operated in nominal power conditions (<10 kVA). A fault condition is then provoked by short circuiting the load. The limiter's current and voltage characteristics are recorded prior to and during the fault. Fault currents are limited to about 5-8 times the nominal current and limitation always occurs in the first cycle. Using an approximate transformer analysis with a shorted single turn secondary, the current in the superconductor and its effective resistance are obtained. The superconductor's effective resistivity is of the order of 10 /spl mu//spl Omega/cm at the onset of a fault and increases gradually as the fault progresses. Results for the evolution of the limiting impedance with time as the nominal voltage of the circuit is increased are presented. The materials requirements for this type of fault current limiter are discussed.<
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