SHORT-CIRCUIT TEST-PERFORMANCE OF INDUCTIVE HIGH T-C SUPERCONDUCTING FAULT CURRENT LIMITERS

The current limiting performance of inductive fault current limiters b ased on Bi-2212 high temperature superconducting tubes has been evalua ted. Fault current limitation is due to the non-linear impedance of th is device when the induced current in the superconducting Bi-2212 tube s exceeds the critical current. A power load in a test circuit is firs t operated in nominal power conditions (<10kVA). 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. Fa ult currents are limited to about 5-8 times the nominal current and li mitation always occurs in the first cycle. Using an approximate transf ormer analysis with a shorted single turn secondary, the current in th e superconductor and its effective resistance are obtained. The superc onductor's effective resistivity is of the order of 10 mu Ohm cm at th e onset of a fault and increases gradually as the fault progresses. Re sults for the evolution of the limiting impedance with time as the nom inal voltage of the circuit is increased are presented. The materials requirements for this type of fault current limiter are discussed.