A Study of a High-Tc Superconducting Fault Current Limiter (No. 2): Development of an Element for 100-V Class Power Systems

Abstract

The application of a high critical temperature (Tc) superconductor with a high critical current density (Jc) to a fault current limiter (FCL) was investigated to obtain a FCL which exhibits superior current limiting performance. When the superconductor changes to normal conduction, it produces a resistance that can limit fault currents. A new current limiting element consisting of a 0.4 μm — thick YBaCuO film coated with a 0.12 μm — thick protective silver film was developed. The element has a current limiting section 1 mm wide and 40 mm long. The critical current density and critical current of the superconducting film were 1.6 × 106 A/cm 2 and 7 A, respectively. For a half cycle, an alternating voltage (50 Hz) was applied to the FCL element immersed in 77K liquid nitrogen, and a typical current limiting waveform was measured. At an applied voltage of 134 Vrms, a fault current with a crest of 320 A was limited to a peak let-through current of 17 A. After the current peaked, it rapidly decreased to less than 7.5 A. By using the protective silver film, a superconducting FCL element for 100-V class power systems was developed.