Fault current limiter based on high temperature superconductors – different concepts, test results, simulations, applications

All electric equipment in a power system has to be designed to withstand the mechanical and thermal stresses of potential short-circuit currents. Any reduction of these currents can lead to significant cost savings. Among all current limiting devices, superconducting fault current limiters (SCFCL) offer ideal performance: in normal operation the SCFCL is in its superconducting state and has negligible impedance, in the event of a fault, the transition into the normal conducting state passively limits the current. Different high temperature superconductors (HTS) materials, like YBCO films, Bi2223 wires or Bi2212 bulk are under development for the use in SCFCL. Due to the brittle nature of HTS and the hot-spot problem, most HTS components for current limitation are composites comprising the HTS, a mechanical substrate or support, and an electrical bypass. The performance of the composites largely depend on the parameters: critical current density, I– V characteristics, thermal conductivity, thermal mass, and electrical bypass. Mainly two different concepts of SCFCL, namely, the “resistive” and the “shielded core” concept have been pursued in the past. In 1996 the first ever SCFCL was installed in a hydro-power plant. The device had a rated power of 1.2 MVA, it was of the “shielded core” type and was based on tubes of Bi2212-bulk material. The feasibility of the technology has been demonstrated in a one-year-endurance test. Recently more compact “resistive” SCFCLs based on the same Bi2212-bulk material have been developed. Theoretical models for the SCFCL show good agreement with experimental data. They are used to study the influence of SCFCLs in power systems in order to evaluate technical and economical advantages.